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Visual attention in psychopathic criminals Harpur, Timothy John 1991

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VISUAL ATTENTION IN PSYCHOPATHIC CRIMINALS By TIMOTHY JOHN HARPUR B.A., Oxford University, 1982 M.A., University of B r i t i s h Columbia, 1985 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES (Department of Psychology) We accept t h i s thesis as conforming to the required standard. UNIVERSITY OF BRITISH COLUMBIA January 1991 © Timothy John Harpur, 1991 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia Vancouver, Canada Date 12* \°l°lt DE-6 (2/88) - i i -Abstract This study was designed to examine the hypothesis that criminal psychopaths di f f e r from criminal nonpsychopaths in their a b i l i t y to over-focus attention on certain kinds of stimuli. For the purposes of this study, the concept of over-focussing was operationalized to mean the a b i l i t y to process stimuli more quickly or ef f i c i e n t l y by making use of one or more attentional mechanisms for selecting among locations or stimuli. A second aim of the study was to identify the component processes contributing to this more effici e n t selection. Five experiments were run to assess several different components of attention contributing to selection of stimuli in a variety of paradigms. Experiments 1 and 2 assessed covert orienting of attention across the visual f i e l d using both peripherally presented physical cues and centrally presented symbolic cues to prime locations in visual space. Three dissociable components of attention were assessed in this paradigm. Experiments 3-5 were designed to assess the efficiency of processing a target item in the presence of a distractor item. Four additional dissociable components of selective attention were measured in these three studies. The results supported the hypothesis that psychopaths can over-focus attention, but the groups were differentiated by only one of the component processes measured. In Experiments 1 and 2 endogenous orienting of attention was greater for - i i i -psychopaths than f o r nonpsychopaths. In thes e paradigms endogenous f a c i l i t a t i o n c o n t r o l l e d the a l l o c a t i o n o f a t t e n t i o n t o cued l o c a t i o n s , and the subsequent speeding o f r e a c t i o n time t o t a r g e t s p r e s e n t e d a t those l o c a t i o n s , when t h e cue was symbolic o r p r e d i c t i v e , but not when i t i n v o l v e d a p h y s i c a l change of energy a t the cued l o c a t i o n . T h i s s t r a t e g i c a l l o c a t i o n of a t t e n t i o n p r o b a b l y r e s u l t e d from the p r e d i c t i v e v a l i d i t y (approximately 68% v a l i d ) o f the cue i n r e l a t i o n t o the t a r g e t . Other component pro c e s s e s f a i l e d t o d i f f e r e n t i a t e the groups. These i n c l u d e d measures of exogenous o r i e n t i n g and i n h i b i t i o n o f r e t u r n i n experiments 1 and 2 , and measures of i n t e r f e r e n c e due t o a d i s t r a c t i n g s t i m u l u s , h a b i t u a t i o n o f i n t e r f e r e n c e , a t t e n u a t i o n o f i n t e r f e r e n c e due t o s p a t i a l d isplacement of the d i s t r a c t o r , and n e g a t i v e p r i m i n g i n exp er iment s 3 - 5 . The d i f f e r e n c e i n c o v e r t o r i e n t i n g was r e p l i c a t e d i n experiments 1 and 2 i n two groups of c r i m i n a l s who a l s o f a i l e d t o demonstrate any a b n o r m a l i t i e s i n a v a r i e t y o f o t h e r p r o c e s s e s i n v o l v e d i n a t t e n t i o n . I t was concluded t h a t psychopaths d i f f e r from nonpsychopaths s p e c i f i c a l l y i n t h e i r s t r a t e g i c a l l o c a t i o n of a t t e n t i o n i n s i t u a t i o n s of moderate u n c e r t a i n t y , but show no oth e r a b n o r m a l i t i e s i n the component pr o c e s s e s t h a t c o n t r o l a t t e n t i o n . - i v -Table of Contents Abstract i i Table of Contents i v L i s t of Tables v i i L i s t of Figures v i i i Acknowledgements x i Introduction 1 Psychopathy 3 The D e f i n i t i o n and Assessment of Psychopathy 3 Evidence for Abnormal Cognitive Processing i n Psychopaths 4 Attentional Over-focussing 4 V i s u a l Attention 9 Covert Orienting 10 Cost Benefit Analysis 13 Possible Mechanisms of Over-focussing 15 Selection among Competing V i s u a l Stimuli 17 Interference 17 Habituation 19 Negative Priming 20 Possible Mechanisms of Over-focussing 21 Experimental Hypotheses 22 Experiments 1 & 2 22 -v-Experiments 3, 4 & 5 25 Experiment 1 26 Method 29 Subjects 29 Procedure 30 Data Analysis 3 6 Results 37 Discussion 44 Experiments 2-5 46 General Procedures 46 Subjects 47 Experiment 2 48 Design 50 Subjects 52 Procedure 53 Data Analysis 54 Results 56 Discussion 69 Experiment 3 73 Subjects 74 Design 75 Procedure 77 Data Analysis 78 Results 79 Discussion 84 - v i -Experiment 4 85 Subjects 87 Design 87 Procedure 91 Data Analysis 91 Results 93 Discussion 96 Experiment 5 98 Subjects 100 Design 100 Procedure 101 Data Analysis 101 Results 103 Discussion 110 General Discussion and Summary 117 References 121 Appendix A 129 - v i i -L i s t of Tables Table I. Component processes of attention assessed by each experiment and predicted group differences 23 Table II. Mean of median reaction times and percentage correct responses in Experiment 3 94 - v i i i -L i s t of Figures Figure 1. Relationships among the components processes underlying covert orienting of attention 18 Figure 2. Stimulus sequences and frequencies for the seven conditions used in Experiment 1 32 Figure 3. Stimulus Sequence for Condition 3 in Experiment 1: Validly cued target in the right visual f i e l d at 650 msec SOA 34 Figure 4. Experiment 1: Reaction times to valid and invalid t r i a l s for each SOA, visual f i e l d and group 38 Figure 5. Experiment 1: Reaction times to double-cued neutral t r i a l s for each SOA, visual f i e l d and group 39 Figure 6. Experiment 1: Difference in reaction time between invalidly and validly cued t r i a l s at each SOA for each group 40 Figure 7. Experiment 1: Difference in reaction time between invalidly cued and neutral t r i a l s at each SOA for each group 42 Figure 8. Experiment 2: Reaction times to valid and invalid peripherally cued t r i a l s for each SOA, visual f i e l d and group 57 - i x -F i g u r e 9. Experiment 2: R e a c t i o n times t o v a l i d and i n v a l i d c e n t r a l l y cued t r i a l s f o r each SOA, v i s u a l f i e l d and group 58 F i g u r e 10. Experiment 2: D i f f e r e n c e i n r e a c t i o n time between i n v a l i d l y and v a l i d l y cued t r i a l s a f t e r p e r i p h e r a l c u i n g f o r each SOA 59 F i g u r e 11. Experiment 2: D i f f e r e n c e i n r e a c t i o n time between i n v a l i d l y and v a l i d l y cued t r i a l s a f t e r c e n t r a l c u i n g f o r each SOA 60 F i g u r e 12. Experiment 2: R e a c t i o n times t o double-cued and s i n g l e - c u e d n e u t r a l t r i a l s i n the p e r i p h e r a l c u i n g c o n d i t i o n f o r each SOA, v i s u a l f i e l d and group 65 F i g u r e 13. Experiment 2: R e a c t i o n times t o e a r l y n e u t r a l cues i n the p e r i p h e r a l c u i n g c o n d i t i o n as a f u n c t i o n of v i s u a l f i e l d , b l o c k o r d e r and group 66 F i g u r e 14. Experiment 2: R e a c t i o n times t o l a t e n e u t r a l cues i n the p e r i p h e r a l c u i n g c o n d i t i o n as a f u n c t i o n of SOA, t r i a l type and group 67 F i g u r e 15. Experiment 3: R e a c t i o n times f o r each group t o i d e n t i f y t a r g e t c o l o u r f o r f o u r c o n d i t i o n s i n each b l o c k 80 -x-F i g u r e 16. Experiment 3: Mean number of c o r r e c t responses by each group f o r f o u r c o n d i t i o n s i n each b l o c k 81 F i g u r e 17. Experiment 3: The mean magnitude of i n t e r f e r e n c e , h a b i t u a t i o n and n e g a t i v e p r i m i n g f o r each group i n each b l o c k 82 F i g u r e 18. Experiment 5: R e a c t i o n times f o r each group f o r c o n t r o l and i n t e r f e r e n c e c o n d i t i o n s i n the prime d i s p l a y as a f u n c t i o n of the e c c e n t r i c i t y of the d i s t r a c t o r 104 F i g u r e 19. Experiment 5: Percentage of c o r r e c t responses by each group f o r c o n t r o l and i n t e r f e r e n c e c o n d i t i o n s i n the prime d i s p l a y as a f u n c t i o n of the e c c e n t r i c i t y o f the d i s t r a c t o r 105 F i g u r e 20. Experiment 5: I n t e r f e r e n c e f o r each group as a f u n c t i o n of d i s t r a c t o r e c c e n t r i c i t y 106 F i g u r e 21. Experiment 5: Mean r e a c t i o n times f o r each group f o r c o n t r o l and n e g a t i v e p r i m i n g c o n d i t i o n s i n the probe d i s p l a y as a f u n c t i o n o f d i s t r a c t o r e c c e n t r i c i t y i n the prime d i s p l a y 108 F i g u r e 22. Experiment 5: Percentage of c o r r e c t responses by each group f o r c o n t r o l and n e g a t i v e p r i m i n g c o n d i t i o n s i n the probe d i s p l a y as a f u n c t i o n o f the e c c e n t r i c i t y o f the d i s t r a c t o r i n the prime d i s p l a y 109 - x i -Acknowledgements I would l i k e to express my thanks to the many people who helped i n the research reported here. F i r s t l y I would l i k e to thank my research supervisor, Bob Hare, whose generous and unstinting support throughout my graduate career contributed greatly to t h i s research, and to many other enjoyable projects. Secondly I would l i k e to thank the other committee members, Jim Enns, Don Wilkie, and Tony P h i l i p s , f o r t h e i r supervision and thoughtful comments. Many fellow graduate students, research assistants and other members of the Psychology Department have helped me i n numerous ways while carrying out t h i s research. I am g r a t e f u l i n , p a r t i c u l a r , to Adelle Forth, Sherrie Green and Mike Laycock, who d i d many of the assessments and greatly f a c i l i t a t e d the l o g i s t i c s of carrying out t h i s study i n the prison; to Mike S a t t e r f i e l d and Gary Birch who spent time teaching me the rudiments of the hardware and software necessary to carry out these studies; and to B i l l Jacobs who knew nothing about t h i s thesis, but who taught me something about how to think. Most importantly I thank Sherrie f o r her love and support. The l a s t eight years would have been empty without her. -1-Introduction Psychopathy i s a severe disorder of personality and behaviour that i s evidenced early i n l i f e , usually by adolescence, and p e r s i s t s through much of the adult l i f e s p a n . I t has been variously described as consisting of some or a l l of the following c h a r a c t e r i s t i c features: Juvenile delinquency, persistent adult c r i m i n a l i t y , f a i l u r e to learn from experience, lovelessness, g u i l t l e s s n e s s , a lack of remorse, pathological egocentricity, manipulativeness, lack of anxiety, and a lack of empathy (see Cleckley, 1976; Hare, 1980, 1990; Karpman, 1961; M i l l o n , 1981). Theories of psychopathy have usually t r i e d to explain the behavioural features of the disorder with reference either to learning theory or to biology (e.g. Eysenck, 1964; Gray, 1987; Hare, 1970, 1978; Lykken, 1957; Gorenstein & Newman, 1980). However, more recent research has uncovered anomalies i n the cognitions of psychopaths, as well as i n t h e i r behaviour. Hare, Williamson, & Harpur (1988) reviewed considerable evidence for abnormalities i n how psychopaths process l i n g u i s t i c information, and Harpur & Hare (1990a) stated that there was " s u f f i c i e n t evidence to conclude that psychopaths are unusual i n t h e i r mobilization of attentional resources" (p. 440). I t may be that these cognitive abnormalities contribute to some extent to the behavioural and learning abnormalities studied more commonly in t h i s group (see e.g., Gorenstein, i n press; -2-Newman, 1987, 1989), but the precise mechanism by which t h i s might occur are unknown. The present research i s intended to explore abnormalities i n a t t e n t i o n a l processing i n psychopaths. The concept of over-focussing, which has been invoked to explain psychopaths' unusual performance on tasks requiring attention (Jutai & Hare, 1983; Harpur & Hare, 1990a), i s here given more precise operationalization i n terms of component processes currently theorized to underlie the control of v i s u a l attention. Two paradigms that have been used extensively i n cognitive psychology to investigate v i s u a l attention i n normal, brain-damaged, and psychopathological populations were employed. The f i r s t used covert orienting (Posner, 1978, 1980), which involves inducing subjects to focus attention on one region of the v i s u a l f i e l d , thereby allowing s t i m u l i which appear at that l o c a t i o n to be processed more quickly or e f f i c i e n t l y than s t i m u l i presented at other locations. This a l l o c a t i o n of attention occurs independent of eye-movements, and the d i s t r i b u t i o n of attention across the v i s u a l f i e l d can be e a s i l y assessed using reaction time (RT). The second paradigm investigated the processes of interference and negative priming (Eriksen & Eriksen, 1974; Tipper, 1985). These experiments examined how well psychopaths can screen out concurrently presented i r r e l e v a n t information, and how t h e i r success i n ignoring i r r e l e v a n t information -3-subsequently influences their a b i l i t y to process that same information. The use of these two paradigms permits the examination and dissociation of a number of component processes involved in controlling how we attend to different objects and events in the world. If the functioning of one or more of these processes i s abnormal in psychopaths, i t may provide important insights into the development and maintenance of this serious disorder, and into the mechanisms by which attentional processes in general control and influence behaviour. Psychopathy The Definition and assessment of psychopathy The construct of psychopathy has a long and complex history (see Millon, 1981; Pichot, 1978). Both the label, and the construct to which i t refers have undergone considerable change and refinement. At present, two definitions are in common use. Antisocial personality disorder i s defined by the American Psychiatric Association in the third revised edition of The diagnostic and s t a t i s t i c a l Manual of Mental Disorders. (DSM-III-R; APA, 1987). Psychopathy can also be assessed, at least in criminal populations, by the Psychopathy Checklist (PCL; Hare, 1990; Hare et a l . , 1990). The nature of these two conceptualizations, and the relationship between them, has been extensively investigated (Gerstley, Alterman, McLellan, & Woody, 1990; Hare, 1983, 1985; Harpur & Hare, 1990b; Harpur, -4-Hare, & Hakstian, 1989; Hart & Hare, 1989; Newman & Kosson, 1986) and need not concern us here. In keeping with extensive previous research, psychopathy i s assessed here using the PCL. Evidence for abnormal cognitive processing in psychopaths Considerable evidence has accrued that psychopaths, as defined by the PCL or similar assessment procedures, are abnormal in how they process certain kinds of information. In this section the literature relevant to the planning and design of these experiments w i l l be reviewed, although f u l l e r reviews may be found in Gorenstein (in press), Hare et a l . (1988), and Harpur & Hare (1990a). Attentional over-focussing One of the most prominent recent hypotheses concerning psychopaths' information-processing abnormalities has been that they are unusually proficient at attending to some stimuli and at ignoring others. This over-focussing hypothesis developed from experiments examining psychopaths' autonomic responses to aversive events. Prior to a predictable aversive event, psychopaths' electrodermal responses are consistently smaller than those of nonpsychopaths (Hare, 1978), a finding that i s consistent with the hypothesis that psychopaths are deficient in fear conditioning. However, this same group also demonstrates significantly greater heart-rate acceleration than do nonpsychopaths (Hare, 1978; Hare & Craigen, 1974; Hare, Frazelle, & Cox, 1978). To the extent that heart-rate -5-acceleration i s associated with fear arousal, these r e s u l t s are incompatible with a simple fear-conditioning model of psychopathy. Hare (1978) attempted to accommodate these r e s u l t s within an a t t e n t i o n a l model that has i t s basis i n research on the r e l a t i o n s h i p between cardiovascular a c t i v i t y and s e n s i t i v i t y to sensory stimulation. According to t h i s research, cardiac deceleration i s associated with increased s e n s i t i v i t y , and acceleration with decreased s e n s i t i v i t y , to the external environment (Lacey, 1967; Lacey & Lacey, 1974). Hare (1978) suggested that the anticipatory heart rate acceleration shown by psychopaths may be part of an adaptive coping response that helps them to "tune out" or otherwise reduce the impact of premonitory cues, and that the small electrodermal responses r e f l e c t the successful operation of t h i s coping e f f o r t . Subsequent studies by Hare (1982) and Ogloff & Wong (1990) supported t h i s hypothesis. They showed that the opportunity to cope a c t i v e l y with the stimulus, or to be d i s t r a c t e d by a d i f f e r e n t stimulus, thereby removing the need to cope by i n t e r n a l means, abolished the abnormal heart rate acceleration i n psychopaths. This model i m p l i c i t l y invokes differences i n the e f f i c i e n c y of s e l e c t i v e attention to account f o r the psychophysiological data. However, there i s r e l a t i v e l y l i t t l e data e x p l i c i t l y examining s e l e c t i v e attention i n psychopaths. -6-J u t a i & Hare (1983) tested the over-focussing hypothesis i n a s i t u a t i o n i n which subjects were asked to play video-games while ignoring a tone pip which they heard through earphones. The primary dependent measure of i n t e r e s t was the amplitude of the N100 event-related p o t e n t i a l (ERP) to the i r r e l e v a n t tones, an i n d i c a t i o n of the residual attentional capacity av a i l a b l e while performing the primary task. Although psychopaths and nonpsychopaths did not d i f f e r i n t h e i r responses to the tones presented alone, the N100 amplitude was smaller for psychopaths than f o r nonpsychopaths while playing the video games, consistent with the hypothesis that they were a l l o c a t i n g greater a t t e n t i o n a l resources to the primary task. Kosson & Newman (1986) used a dual-task procedure to t e s t the over-focussing hypothesis. Vi s u a l search and tone discrimination tasks were performed separately and concurrently under both divided and focussed attention i n s t r u c t i o n s . The pattern of r e s u l t s did not d i r e c t l y support the over-focussing hypothesis. Under instructions to focus on the v i s u a l search, psychopaths performed at the same l e v e l as nonpsychopaths on both the primary and secondary tasks. However, under divided attention conditions, psychopaths were less accurate than nonpsychopaths on the v i s u a l task, and slower on the auditory task. This pattern of r e s u l t s was interpreted as i n d i c a t i n g that psychopaths used an i n e f f i c i e n t p o l i c y f o r maintaining j o i n t a l l o c a t i o n of resources to two tasks (greater concurrence -7-costs). Although the r e s u l t s are consistent with t h i s i n t e r p r e t a t i o n , Harpur & Hare (1990a) pointed out that the r e s u l t s for t h i s study must be interpreted with caution. The performance of criminal nonpsychopaths, who formed the control group, d i d not conform to the expected pattern under divided and focussed attention i n s t r u c t i o n s . Since the putatively normal group did not behave normatively i n t h i s case, in t e r p r e t a t i o n of the r e s u l t s for the hypothetically abnormal group i s suspect. Although not designed to examine the over-focussing hypothesis, data from a study by Hare & McPherson (1984) provide an excellent t e s t of i t . They administered a t e s t of d i c h o t i c l i s t e n i n g to a large group of psychopaths and nonpsychopaths under both divided- and focussed-attention i n s t r u c t i o n s . Although they reported s i g n i f i c a n t differences i n the degree of l a t e r a l i z a t i o n shown by the two groups, there was no o v e r a l l difference i n the performance of the groups i n either i n s t r u c t i o n condition. Performance f o r t h i s task was well below c e i l i n g , and i t involved the processing of meaningful l i n g u i s t i c material, conditions which might be expected to maximize the chances of fi n d i n g differences i n att e n t i o n a l capacity i n the two groups (Harpur & Hare, 1990a; J u t a i , 1989). Nevertheless, psychopaths appear to have divided and focussed t h e i r attention p e r f e c t l y normally. On the basis of these r e s u l t s , and of other studies of -8-less d i r e c t relevance to s e l e c t i v e attention, Harpur & Hare (1990a) concluded that there was reasonable evidence f o r some kind of over-focussing of attention i n psychopaths, but that there was l i t t l e evidence to indicate the mechanism underlying t h i s abnormality. Of the studies they reviewed, only Hare & McPherson (1984) f a i l e d to f i n d evidence f o r some abnormality of a t t e n t i o n a l processing. One notable feature of t h i s study which might be relevant i s that i t was the only one i n which attention was assessed s o l e l y i n the auditory modality. Other studies used v i s u a l or both v i s u a l and auditory tasks, suggesting that the abnormalities i n attent i o n a l processing i n psychopaths may be p a r t i c u l a r l y linked to v i s u a l information processing. For t h i s reason, the experiments reported here were r e s t r i c t e d to examining v i s u a l attention. The over-focussing hypothesis has some inherent p l a u s i b i l i t y , p a r t i c u l a r l y i f i t allows subjects to screen out p o t e n t i a l l y aversive events. In t h i s guise i t o f f e r s a po t e n t i a l explanation for psychopaths' f a i l u r e to learn from experience. I t also has the advantage of characterizing the differences between psychopaths and others i n terms that do not imply a d e f i c i t i n the former group: An increased a b i l i t y to focus attention may be highly advantageous i n c e r t a i n circumstances. However, as expressed to date the hypothesis i s somewhat lacking i n s p e c i f i c i t y . No mechanism has been offered to explain why or how psychopaths are able to focus on s p e c i f i c -9-events or s t i m u l i , and no theory e x i s t s which can explain i n advance what events w i l l or w i l l not p a r t i c u l a r l y a t t r a c t psychopaths' attention. As discussed above, Hare & McPherson's (1984) f a i l u r e to f i n d evidence of over-focussing i n d i c h o t i c l i s t e n i n g has led the current research to concentrate on the v i s u a l modality. A second source guiding the design of t h i s research i s recent cognitive theory concerning the component processes underlying the a l l o c a t i o n of v i s u a l attention. These t h e o r e t i c a l developments provide the p o s s i b i l i t y of operationalizing the concept of over-focussing more pre c i s e l y , i n terms of abnormalities or imbalances i n one or more of these processes. The next section w i l l review research on these component processes and examine how abnormalities among these components might produce over-focussing of attention. Vi s u a l Attention The f i r s t assumption I w i l l make i s that over-focussing, as i t has been used to date, implies an enhanced a b i l i t y to s e l e c t or process a p a r t i c u l a r v i s u a l stimulus or feature. Enhanced s e l e c t i o n has been been studied i n two general ways. F i r s t l y , i t may be measured as an advantage f o r processing s t i m u l i at a given location i n v i s u a l space. This i s usually tested by presenting a single target stimulus but varying the l o c a t i o n of that target, and i s discussed below under the heading "covert orienting". The second approach i s to study the -10-a b i l i t y to choose among a number of competing stimuli, discussed below under the heading "selection among competing visual stimuli". As w i l l become apparent, a number of distinct processes have been identified within each paradigm that contribute to the control of visual attention. Covert orienting Attending to a location in visual space usually involves a change in orientation, either of the whole body or of the eyes, in order to bring the area of interest into central vision. However, there i s now ample evidence that the focus of attention within visual space i s not fixed at the fovea, but can move covertly to improve the processing of information at non-foveal locations (Posner, 1978). Such covert shifts in attentional focus are necessary for the performance of many skil l e d a c t i v i t i e s , such as driving or sports and they have been shown to play a role in the control of overt eye movements (Posner, Cohen, Choate, Hockey, & Maylor, 1984). Covert shifts in attention can be induced both voluntarily and involuntarily (Jonides, 1981). In most experiments, either peripheral physical cues or symbolic cues are used to prime a peripheral location, inducing automatic and voluntary shifts of attention respectively. Precuing of a location at which a subsequent target i s lik e l y to appear by presenting a cue at that same location (here termed "peripheral precuing") results in a rapid and -11-automatic s h i f t of attention to that location (Posner 1980; Jonides 1981; Yantis & Jonides, 1990). Targets presented at that l o c a t i o n w i l l usually be processed f a s t e r and/or more e f f i c i e n t l y than targets presented at other, non-cued locations. Peripheral precuing can have two primary e f f e c t s which have been experimentally dissociated. I n i t i a l l y i t f a c i l i t a t e s or primes responding to a target presented at the cued location (in comparison with targets presented at uncued lo c a t i o n s ) . This f a c i l i t a t i o n i s la r g e l y involuntary, and occurs r a p i d l y , at stimulus onset asynchronies (SOAs) of 50-150 msecs (e.g. Jonides, 1981). I f a target i s presented at a longer SOA (over 500 msecs), and attention has been moved away from the cued location, then responding to a target at the cued lo c a t i o n i s i n h i b i t e d (again i n comparison to targets at uncued loc a t i o n s ) , a phenomenon c a l l e d i n h i b i t i o n of return by Posner & Cohen (1984). F a c i l i t a t i o n and i n h i b i t i o n have been dissociated i n several ways. F a c i l i t a t i o n i s rapid and short-l i v e d , whereas i n h i b i t i o n has a longer time-course. Within the same experiment, therefore, a subject may be fa s t e r to respond to a target at a cued location, r e l a t i v e to an uncued location, i f the target follows the cue ra p i d l y ( f a c i l i t a t i o n ) , but slower to respond to a target at the cued l o c a t i o n i f i t follows the cue with a longer delay ( i n h i b i t i o n ) . F a c i l i t a t i o n has been shown to be coded i n ret i n o t o p i c coordinates, while i n h i b i t i o n i s environment-centred. This means that i n h i b i t i o n -12-w i l l continue to be seen at a s p e c i f i c environmental lo c a t i o n even i f the subject's eyes move, whereas f a c i l i t a t i o n w i l l move around the environment with the eyes, but w i l l remain stationary r e l a t i v e to the r e t i n a . F i n a l l y f a c i l i t a t i o n does not occur when two d i f f e r e n t locations are simultaneously cued but i n h i b i t i o n can. This seems to imply that f a c i l i t a t i o n i s an att e n t i o n a l phenomenon, requiring c e n t r a l processing resources, but i n h i b i t i o n i s sensory, serving to ensure non-redundant sampling of the v i s u a l environment (Jonides, 1981; Posner & Cohen, 1984; Posner et a l . , 1984). Posner and Snyder (1975) and Jonides (1981) have also distinguished between two v a r i e t i e s of f a c i l i t a t i o n . Exogenous  f a c i l i t a t i o n , occurs when a physical change i n a stimulus primes the location at which the change occurs. In t h i s case the s h i f t of attention i s caused by the change i n stimulation at the cued location, and the priming i s rapid and automatic (Posner & Snyder, 1975; Yantis & Jonides, 1990). Endogenous  f a c i l i t a t i o n occurs when a location i s cued by abstract or symbolic means. This may be achieved by presenting a ce n t r a l stimulus which indicates the primed location symbolically (an arrow pointing l e f t or r i g h t ) , or by manipulating the pr e d i c t i v e v a l i d i t y of the cue (subjects w i l l a l l o c a t e greater resources to a cued location i f the cue i s highly p r e d i c t i v e of the target than i f i t i s worthless as a pr e d i c t o r ) . Endogenous f a c i l i t a t i o n occurs when the s h i f t i n attention r e s u l t s from -13-the meaning of the cue as interpreted (whether conciously or not) by the subject. Endogenous f a c i l i t a t i o n depends upon the subject's knowledge of the s i g n i f i c a n c e of the cue, and therfore i t develops more slowly than exogenous f a c i l i t a t i o n . The former does not develop appreciably at SOAs of less than 100 msecs. This temporal difference means of course that the development of endogenous, but not exogenous, f a c i l i t a t i o n may overlap temporally with the development of i n h i b i t i o n of return. Exogenous f a c i l i t a t i o n i s more automatic (Kahneman & Treisman, 1984) than endogenous f a c i l i t a t i o n (Jonides, 1981; Muller & Rabbitt, 1989; Posner et a l . , 1984) Cost Benefit Analysis A further d i s t i n c t i o n , i n addition to that between endogenous f a c i l i t a t i o n , exogenous f a c i l i t a t i o n , and i n h i b i t i o n of return, has often been made i n studies of covert orienting. These studies have divided the f a c i l i t a t i o n r e s u l t i n g from cuing into two opposing processes, costs, which slow responding to a target presented at an uncued location, and benefits, which speed responding to a target at a cued l o c a t i o n (see Posner, 1978; Posner & Snyder, 1975). The difference between RTs to targets at cued and uncued locations i s assumed to be the sum of both the costs and the benefits induced by cuing. Posner and h i s colleagues have t r i e d to measure costs and benefits separately by including i n t h e i r experiments three conditions: One i n which the cue c o r r e c t l y predicts the target -14-location, another i n which i t i n c o r r e c t l y predicts the location, and a t h i r d i n which the cue i s "neutral", providing no s p a t i a l cue concerning the target l o c a t i o n . In t h i s paradigm, benefits can be measured by comparing the v a l i d cue with the neutral cue condition, and costs are measured by comparing the i n v a l i d cue with the neutral condition. Jonides and Mack (1984) presented a c r i t i q u e of the cost-benefit paradigm. They pointed out that i n t e r p r e t a t i o n of t h i s type of analysis r e l i e s on a c r i t i c a l assumption, namely that the nonspatial cue used i n the neutral condition i s i d e n t i c a l i n a l l respects other than i t s s p a t i a l informativeness to the v a l i d and i n v a l i d cues. This assumption i s never s t r i c t l y met, and the consequences of i t s v i o l a t i o n are r a r e l y tested. S t r i c t l y , therefore, the RT costs and benefits cannot be unambiguously attributed to the e f f e c t s of s p a t i a l cuing, since other factors (differences i n the degree of general a l e r t i n g , the speed of perceptual processing of the cue etc.) are also l i k e l y to d i f f e r with d i f f e r e n t kinds of cues. Their recommendation was to use the cued-uncued RT difference as a measure of covert orienting, and to i n t e r p r e t comparisons with neutral cues with great caution. The studies reported here r e l y primarily on cued-uncued RT differences to measure covert orienting. However, there are several reasons why a neutral condition, and analyses i n terms of costs and benefits, were also included. In the f i r s t place, -15-a neutral condition can be useful i n studies of i n d i v i d u a l differences as a control for group differences i n processes unrelated to attention, such as motor response times or v i s u a l acuity differences, which might vary between the groups i r r e s p e c t i v e of differences i n attention (see f o r example Enns & Brodeur, 1989). Secondly, although the p a r t i t i o n i n g of costs and benefits may be suspect (Jonides & Mack, 1984), we cannot assume that i t i s automatically i n v a l i d . In the study of i n d i v i d u a l differences, r e p l i c a b l e differences between groups are of i n t e r e s t , even i f t h e i r t h e o r e t i c a l s i g n i f i c a n c e i s unclear. I f psychopaths d i f f e r from others i n , say, the costs of v i s u a l s e l e c t i o n , but not the benefits, as tested i n a p a r t i c u l a r paradigm, then further research can be planned with the intention of t e s t i n g whether t h i s difference i s a t t r i b u t a b l e to the subjects reactions to the p a r t i c u l a r neutral cue used. Replication of the e f f e c t s using a v a r i e t y of neutral cues could go some way towards v a l i d a t i n g the i n t e r p r e t a t i o n of the e f f e c t i n terms of costs and benefits. Possible mechanisms of over-focussing There are several ways i n which the component processes described above might contribute to over-focussing i n psychopaths. Most obviously, a greater degree of f a c i l i t a t i o n , e i t h e r endogenous or exogenous, i n covert o r i e n t i n g to a cue would mean that psychopaths were a l l o c a t i n g a greater proportion of t h e i r resources to the cued l o c a t i o n than were -16-nonpsychopaths. If t h i s difference i n f a c i l i t a t i o n were r e s t r i c t e d to short SOAs, we could conclude that psychopaths' greater or i e n t i n g to s p a t i a l cues i s p r i m a r i l y exogenous and r e s u l t s from a stronger tendency for novel v i s u a l s t i m u l i to capture t h e i r attention (see Yantis & Jonides, 1990). A l t e r n a t i v e l y , i f the orienting difference developed more slowly, we could i n f e r that psychopaths a l l o c a t e greater at t e n t i o n a l resources as a r e s u l t of t h e i r i n t e r p r e t a t i o n of the meaning of the symbolic cues. This type of difference might derive from an inaccurate estimation of the r e l a t i o n s h i p between the cue and the target (e.g. over-estimation of the p r e d i c t i v e v a l i d i t y of the cue), or from s t r a t e g i c differences i n how they h a b i t u a l l y a l l o c a t e attention. Differences i n the b u i l d up of i n h i b i t i o n of return could also r e s u l t i n improved s e l e c t i o n f o r psychopaths, although i n t h i s case the d i r e c t i o n of the difference between the groups i s hard to predict. On the one hand, an active i n h i b i t o r y process might help to screen out i r r e l e v a n t or competing s t i m u l i , so greater i n h i b i t i o n of return might be seen for psychopaths. On the other hand, Posner et a l . (1984) have suggested that active attention may be required to overcome i n h i b i t i o n i f one wants to maintain attention on one spot. If t h i s i s the case, less i n h i b i t i o n than normal may allow psychopaths to over-focus on c e r t a i n locations. The relationships among the mechanisms of covert orienting described above are i l l u s t r a t e d schematically -17-i n F i g u r e 1. S e l e c t i o n among competing v i s u a l s t i m u l i S t u d i e s o f c o v e r t o r i e n t i n g examine how a t t e n t i o n i s d i s t r i b u t e d s p a t i a l l y , without imposing on the s u b j e c t any requirement t o f i l t e r o r scree n out i r r e l e v a n t o r competing s t i m u l i . However, a separate l i t e r a t u r e e x i s t s on t h e mechanisms which u n d e r l i e t h i s a b i l i t y . Experiments 3, 4 and 5 were intended t o examine whether psychopaths d i f f e r from other s u b j e c t s i n t h e i r a b i l i t y t o f i l t e r o r s e l e c t among competing v i s u a l s t i m u l i . I n t e r f e r e n c e I t i s a w i d e l y r e p l i c a t e d f i n d i n g t h a t the presence of an i r r e l e v a n t s t i m u l u s i n t e r f e r e s w i t h the p r o c e s s i n g o f a t a r g e t s t i m u l u s ( E r i k s e n & E r i k s e n , 1974; Underwood, 1976; Stroop, 1935). T y p i c a l l y i t i s assumed t h a t i n t e r f e r e n c e r e s u l t s from the i n v o l u n t a r y p r o c e s s i n g of the i r r e l e v a n t s t i m u l u s which reduces the e f f i c i e n c y w i t h which the t a r g e t s t i m u l u s i s proce s s e d . For i n s t a n c e , i n the Stroop colour-naming t a s k (Stroop, 1935), the naming of the c o l o u r i n which the word i s w r i t t e n i s slowed i f the word i t s e l f i s the name of a d i f f e r e n t c o l o u r . I n t e r f e r e n c e e f f e c t s have t y p i c a l l y been c o n s i d e r e d measures of the degree t o which the i r r e l e v a n t s t i m u l u s has been pro c e s s e d . T h i s c o n c l u s i o n i s supported by s t u d i e s showing t h a t i n c r e a s i n g the p h y s i c a l s e p a r a t i o n between the t a r g e t and the d i s t r a c t i n g items can reduce i n t e r f e r e n c e (e.g. E r i k s e n & -18-COVERT ORIENTING Exogenous Facilitation^ Inhibition of Return Endogenous Costs Benefits Figure 1. Relationships among the components processes underlying covert orienting of attention -19-Eriksen, 1974; Kahneman & Henik, 1981). However, Driver & Tipper (1989) have pointed out that, although the presence of interference may provide unequivocal evidence that the processing of an i r r e l e v a n t stimulus has taken place, the converse i s not true: The absence of interference need not mean that the i r r e l e v a n t stimulus has not been processed. They demonstrated using negative priming (see below) that i r r e l e v a n t d i s t r a c t o r s that have demonstrable e f f e c t s i n the form of negative priming (and therefore must have been processed) may produce l i t t l e or no interference. Interference, at l e a s t i n experiments s i m i l a r to those of Eriksen and h i s colleagues, appears therefore to measure the e f f i c i e n c y with which the v i s u a l a t t e n t i o n a l channel can be s p a t i a l l y tuned, so that nearby d i s t r a c t o r s cease to be able to influence response s e l e c t i o n . Habituation A second process which influences whether or not an i r r e l e v a n t stimulus i n t e r f e r e s with the processing of a target stimulus i s habituation. When a novel stimulus i s presented to an organism, i t provokes an orienting response (Sokolov, 1963). I f the stimulus i s i r r e l e v a n t , and i t s appearance coincides with the appearance of a target stimulus, then o r i e n t i n g to the i r r e l e v a n t stimulus may contribute to the interference produced by that stimulus (Lorch, Anderson, & Well, 1984; Reisberg, Baron, & Kemler, 1980). However, repeated presentation of an -20-i r r e l e v a n t stimulus should lead to habituation of the orienting response, and decreased interference. This reduced interference has been observed i n a va r i e t y of tasks (see Cowan, 1988). Importantly, the mechanisms of habituation and negative priming do not appear to be the same; by the second grade c h i l d r e n show evidence of at least adult l e v e l s of interference and habituation, but provide l i t t l e or no evidence f o r the development of i n h i b i t i o n (Tipper, Borque, Anderson, & Brehaut, 1989) . Negative priming Tipper and h i s colleagues have developed a paradigm which considerably extends our understanding of the mechanisms of v i s u a l s e l e c t i v e attention. The process they have studied, termed negative priming, acts to i n h i b i t the processing of unattended information (Dalrymple-Alford & Budayr, 1966; Greenwald, 1972; N e i l l , 1977; Tipper, 1985; Tipper & Cranston, 1985). In a t y p i c a l experiment, a subject i s asked to ignore one stimulus, but to respond to another (e.g. name a drawing outlined i n blue while ignoring an overlapping stimulus outlined i n red). Interference can be conventionally measured as the degree to which responding to the target i s slowed by the presence of the unattended stimulus. Active i n h i b i t i o n of the ignored stimulus (negative priming) can be measured i f the same stimulus i s presented again on the next t r i a l , but t h i s time as a target. Response times to the previously ignored -21-targets are slower than to targets presented f o r the f i r s t time, presumably because of the need to overcome the i n h i b i t i o n which developed on the previous t r i a l . In a ser i e s of studies Tipper has dissociated negative priming from the other components of attention. Thus negative priming may be seen with or without the presence of interference (Driver & Tipper, 1989; Tipper, Brehaut & Driver, 1990), i s absent i n young children who s t i l l show habituation to repeatedly presented d i s t r a c t o r s t i m u l i (Tipper et a l . , 1989), and i s unrelated to the modality of stimulus or response (Tipper & Driver, 1988; Tipper, MacQueen, & Brehaut, 1988). Negative priming appears to act either on the representations of i r r e l e v a n t a t t r i b u t e s of objects, or on the representations of i r r e l e v a n t objects themselves (Driver & Tipper, 1989), and i n the l a t t e r case the i n h i b i t i o n i s object-centred, moving through the environment with the object (Tipper et a l . , 1990). According to Tipper et a l . (1989), "the i n h i b i t i o n of c o n f l i c t i n g i r r e l e v a n t s t i m u l i i s confined to a c e n t r a l locus of processing between perception and action, common to a v a r i e t y of d i f f e r e n t perceptual inputs and response outputs" (p. 355). Possible mechanisms of over-focussing Any one of the three processes described above may contribute to over-focussing i n psychopaths. Increased s p a t i a l s e l e c t i v i t y would lead to a greater a b i l i t y to screen out -22-nearby irrelevant stimuli, thereby increasing the efficiency of selection. More rapid habituation to repeated distractor stimuli would achieve a similar end (but note that previous research on autonomic habituation suggests that psychopaths, i f they d i f f e r at a l l , may habituate more slowly than normal [Hare, 1968]). Finally, greater negative priming may allow psychopaths actively to inhibit irrelevant stimuli to a greater extent than other people. Experimental hypotheses The present studies were intended to test the performance of psychopaths in tasks designed to assess the functioning of each of the component processes described above. To do this, five experiments were performed which tested different facets of attentional processing using well-replicated paradigms developed to study normal populations. Table I illustrates schematically the component processes theoretically assessed by each experiment. Experiments 1 & 2 Experiments 1 and 2 investigated covert orienting across the visual f i e l d and assessed both inhibition and f a c i l i t a t i o n of reaction time using peripheral and central (symbolic) cuing to prime locations at which a target appeared. Experiment 1 was intended primarily to determine whether inhibition of return or exogenous orienting of attention distinguished psychopaths from nonpsychopathic criminals. Experiment 2 was intended to -23-Tab l e I Component Processes of A t t e n t i o n Assessed by Each Experiment and P r e d i c t e d Group D i f f e r e n c e s Exog. Endog. I n h i b . I n t e r f . E r i k s e n H a b i t . Neg. Expt. Fac. Fac. of R. E f f e c t P r i . 1 XXX XXX XXX 2 a) XXX XXX XXX b) XXX 3 XXX XXX XXX 4 XXX XXX 5 XXX XXX XXX Pred. P>NP P>NP P>NP P<NP P>NP P More P>NP or NP>P Rapid Note. Experimental C o n d i t i o n s : Expt. 1. P e r i p h e r a l c u i n g a t e a r l y and l a t e SOAs Expt. 2a. P e r i p h e r a l c u i n g a t e a r l y and l a t e SOAs, w i t h a d d i t i o n a l n e u t r a l t r i a l s 2b. C e n t r a l c u i n g a t e a r l y and l a t e SOAs Expt. 3. Stroop t a s k ( t a b l e continues) -24-T a b l e I c o n t i n u e d Expt. 4. Responding t o t a r g e t l o c a t i o n i n presence of a d i s t r a c t o r Expt. 5. Responding t o l e t t e r i d e n t i t y i n the presence of a d i s t r a c t o r XXX=Process ass e s s e d i n experiment; =Process not assessed i n experiment; Expt.=Experiment; Exog. Fac.=Exogenous F a c i l i t a t i o n ; Endog. Fac.=Endogenous F a c i l i t a t i o n ; I n h i b . R . = I n h i b i t i o n of Return; I n t e r f ^ I n t e r f e r e n c e ; H a b i t . = H a b i t u a t i o n of I n t e r f e r e n c e ; Neg. Pri.=Negative Priming; P r e d . = P r e d i c t i o n s t h a t might account f o r psychopaths' over-f o c u s s i n g of a t t e n t i o n ; P=Psychopaths; NP=Nonpsychopaths. -25-r e p l i c a t e the r e s u l t s of experiment 1 and to d i s t i n g u i s h unequivocally between the processes of endogenous f a c i l i t a t i o n and i n h i b i t i o n of return. Experiments 3, 4 & 5 Experiments 3, 4, and 5 were intended to examine the mechanisms which help subjects s e l e c t between competing v i s u a l s t i m u l i . They investigated the processes of interference, habituation of interference, s p a t i a l tuning of interference, and negative priming (see Table I ) . Each of these mechanisms might contribute to the a b i l i t y to s e l e c t s t i m u l i more e f f i c i e n t l y , thereby causing what I have termed over-focussing. Experiment 3 used a stroop colour naming task modelled a f t e r the design of Tipper et a l . (1989). The experiment measured the time i t takes to respond to a colour under four conditions, a neutral condition, a Stroop interference condition, a repeated d i s t r a c t o r condition f o r measuring habituation, and an ignored r e p e t i t i o n condition f o r measuring negative priming. Comparison of RTs i n the neutral and interference condition, the interference and repeated d i s t r a c t o r condition, and the interference and ignored r e p e t i t i o n condition provided measures of interference, habituation of interference, and negative priming respectively. Experiment 4 also examined the processes of interference and negative priming, but i n the s p a t i a l domain. Tipper has recently argued that i n h i b i t i o n seen i n language-based tasks -26-d i f f e r s fundamentally from and that seen i n spatially-based tasks (Tipper, 1990; Tipper et a l . , 1990). This r a i s e s the p o s s i b i l i t y that the influence of i n h i b i t i o n on s e l e c t i o n e f f i c i e n c y may d i f f e r i n only one domain fo r psychopaths, a fin d i n g which might be consistent with the l i t e r a t u r e showing abnormal cognitive functioning i n some language-based tasks (Hare et a l . , 1988; Williamson, Harpur, & Hare, i n press). In addition, the finding of group differences i n i n h i b i t i o n i n one but not the other of these two domains would provide additional evidence supporting the v a l i d i t y of Tipper's d i s t i n c t i o n . In any case, experiment 4 offered a t e s t of the generality of any group differences found i n experiment 3. Experiment 5 further evaluated the generality of the r e s u l t s of experiments 3 and 4 by examining interference and negative priming i n a t h i r d paradigm. In addition, one further a t t e n t i o n a l mechanism was assessed that contributes to the s p a t i a l s e l e c t i v i t y of the interference e f f e c t . Here termed the "Eriksen" e f f e c t , t h i s s p a t i a l s e l e c t i v i t y allows f o r the a b o l i t i o n of interference at increasing e c c e n t r i c i t y of the d i s t r a c t o r item, which again could underlie improved s e l e c t i o n i n psychopaths. Experiment 1 Experiment 1 employed a paradigm i n which a loc a t i o n i n v i s u a l space was primed by a cue some time p r i o r to the presentation of a target stimulus (Jonides, 1981; Posner, -27-1980). I t was assumed that r e l a t i v e l y pure measures of exogenous f a c i l i t a t i o n and i n h i b i t i o n could be obtained by using eit h e r short (50 and 150 msecs) or long (650 or 1000 msecs) SOAs. Targets were presented to the l e f t or r i g h t of f i x a t i o n either at a location that had been previously cued ( v a l i d t r i a l s ) , or on the side opposite to the cue ( i n v a l i d t r i a l s ) . The difference i n reaction time between the v a l i d and i n v a l i d t r i a l s provided the primary measure of f a c i l i t a t i o n at early SOAs and i n h i b i t i o n at l a t e SOAs. An addi t i o n a l double-cued condition was included i n which both l a t e r a l s i t e s were primed simultaneously. Because no f a c i l i t a t i o n occurs when more than one location i s cued (Kiefer, 1985, c i t e d i n Briand & Kle i n , 1987; Posner, Snyder, & Davidson, 1980; Posner & Cohen, 1984), a comparison of these t r i a l s with i n v a l i d t r i a l s provided a measure of the development of i n h i b i t i o n uncontaminated by f a c i l i t a t i o n . I t was expected, therefore, that group differences i n i n h i b i t i o n seen at l a t e SOAs using the v a l i d - i n v a l i d difference measure would also appear i n t h i s invalid-double cued comparison. Jonides and Mack (1984) have cautioned against the use of a neutral condition of t h i s type for analyzing the e f f e c t s of f a c i l i t a t i o n i n terms of costs and benefits. I t should be noted that i n t h i s paradigm the double-cued condition was not pr i m a r i l y used for t h i s purpose. I t was included to separate the e f f e c t s of i n h i b i t i o n of return from any overlapping -28-f a c i l i t a t i o n o c c u r r i n g a t l a t e SOAs. The v a l i d - i n v a l i d measure may c o n t a i n e f f e c t s of both i n h i b i t i o n and endogenous f a c i l i t a t i o n , due f o r i n s t a n c e t o the p r e d i c t i v e r e l a t i o n s h i p between the cue and the t a r g e t . I f f a c i l i t a t i o n i s p r e s e n t a t l a t e SOAs, i t may s t i l l be c o n c e p t u a l i z e d i n terms of c o s t s and b e n e f i t s , but these opposing pr o c e s s e s are o c c u r r i n g i n a d d i t i o n t o i n h i b i t i o n of r e t u r n . One of f o u r d e v i a n t p a t t e r n s c o n s i s t e n t w i t h over-f o c u s s i n g was c o n s i d e r e d p o s s i b l e when psychopaths were t e s t e d i n t h i s paradigm. F i r s t , psychopaths might show a g r e a t e r degree of exogenous f a c i l i t a t i o n , but normal i n h i b i t i o n . Second, psychopaths might show normal f a c i l i t a t i o n but g r e a t e r i n h i b i t i o n of r e t u r n . An u n u s u a l l y a c t i v e i n h i b i t o r y p r o c e s s c o u l d l e a d t o o v e r - f o c u s s i n g by h e l p i n g t o s c r e e n out i r r e l e v a n t or d i s t r a c t i n g s t i m u l i . T h i r d , psychopaths might show normal f a c i l i t a t i o n but l e s s i n h i b i t i o n than normal. The f a c t t h a t o p p o s i t e a b n o r m a l i t i e s i n the s t r e n g t h of i n h i b i t i o n c o u l d both be compatible w i t h the o v e r - f o c u s s i n g h y p o t h e s i s d e r i v e s from the d i f f e r e n t f u n c t i o n a l p r o p e r t i e s of i n h i b i t i o n and f a c i l i t a t i o n . As d i s c u s s e d p r e v i o u s l y , i n h i b i t i o n appears t o be a p a s s i v e p r o p e r t y of the sensory f i e l d . T h e r e f o r e , s u s t a i n e d v i s u a l a t t e n t i o n t o one l o c a t i o n may r e q u i r e t h a t an a c t i v e a t t e n t i o n a l process overcomes t h i s p a s s i v e b u i l d u p of sensory i n h i b i t i o n (Posner e t a l . , 1984), and a weak b u i l d u p of i n h i b i t i o n might r e s u l t i n an unusual a b i l i t y t o m a i n t a i n -29-attention on one spot. The reason that we cannot be sure which of these two differences i n i n h i b i t i o n would r e s u l t i n overfocussing as i t has been described i n psychopaths i s because we s t i l l have only l i m i t e d understanding of how i n h i b i t i o n and f a c i l i t a t i o n i n t e r a c t . Studies have concentrated on looking at the d i f f e r e n t time courses f o r the two processes, but we know l i t t l e of how they in t e r a c t when they both occur simultaneously at one location. S i m i l a r l y , most studies prime locations i n the peripheral v i s u a l f i e l d s . The i n t e r a c t i o n of these processes at the fovea and at the periphery may be d i f f e r e n t . Fourth, psychopaths might show normal exogenous f a c i l i t a t i o n and normal i n h i b i t i o n , but they may d i f f e r i n the degree of endogenous f a c i l i t a t i o n seen at l a t e SOAs. A f a i l u r e to f i n d any group differences would lead to the conclusion that over-focussing, i f i t occurs i n psychopaths, a f f e c t s a l a t e r , more ce n t r a l , stage of information processing. Method Subjects Subjects were male inmates from a Canadian federal penitentiary near Vancouver, B r i t i s h Columbia who had volunteered to p a r t i c i p a t e i n an ongoing research program. Psychopathy was assessed using the Psychopathy Checklist (PCL; Hare, 1980), a 22 item r a t i n g scale of proven r e l i a b i l i t y and v a l i d i t y (Hare, 1980, 1983, 1985; Hare et a l . , 1990; Harpur, Hakstian, & Hare, 1988; Harpur et a l . , 1989; Newman & Kosson, -30-1986; Schroeder, Schroeder, & Hare, 1983; Wong, 1984). The 22 behavioural and personality items are scored (0-2) on the basis of an extensive interview with the inmate and a review of his institutional f i l e . The summed scores provide a global measure of psychopathy which i s sensitive to both the behavioural and personality characteristics central to the diagnosis (see Harpur et a l . , 1989; Millon, 1981). Two raters (not the experimenter) completed the PCL on a l l inmates and their ratings were averaged to provide a f i n a l score. The intraclass correlation coefficient for the PCL calculated on a sample of 176 inmates from the same population was 0.87. In line with previous research, we selected for comparison groups of inmates who were clearly psychopathic (PCL score >31.5) or nonpsychopathic (PCL scores <24). Mean PCL scores for the psychopaths and nonpsychopaths were 35.3 (N = 15) and 19.6 (N = 16) respectively. Groups P and NP did not di f f e r significantly in age (M = 28.8 and 33.3 years respectively), formal education (M = 10.8 and 10.9 years respectively), or reported level of drug and alcohol use. Procedure A l l subjects were individually tested by a male experimenter in a quiet room in the prison. They were paid $3 for their participation in a single session lasting approximately 1 hour. They were able to win up to $4.20 more for fast and accurate responding on this task. The two groups -31-d i d not d i f f e r on the amount they were subsequently p a i d . The experimental procedure was modelled a f t e r t h a t used by Posner, R a f a l , Choate, & Vaughan (1985). S u b j e c t s s a t approximately 75 cm from a T e k t r o n i x g r a p h i c s monitor on which the s t i m u l i were d i s p l a y e d . Three hexagonal boxes were permanently d i s p l a y e d , white on a b l a c k background, on the s c r e e n , one c e n t r a l l y and one 4.6° t o l e f t and r i g h t . Because a h e a d r e s t was not used i n experiment 1, the angles g i v e n are o n l y approximate. The boxes subtended 1.4° of v i s u a l a ngle. The t a r g e t was a s t a r , subtending .7° of v i s u a l angle, which always appeared i n e i t h e r the l e f t o r r i g h t box but never i n the c e n t r a l box. Each t r i a l began w i t h a b r i g h t e n i n g of one or both of the l a t e r a l boxes and was t e r m i n a t e d when the s u b j e c t responded t o the t a r g e t . The seven p o s s i b l e sequences of s t i m u l i used i n experiment 1 are i l l u s t r a t e d i n F i g u r e 2. On a l l t r i a l s , one or both of the l a t e r a l boxes i n i t i a l l y b r i g h t e n e d f o r 150 msecs (0-150 msecs) and then r e t u r n e d t o normal b r i g h t n e s s . On some t r i a l s , i f a t a r g e t had not by then appeared, the c e n t r a l box b r i g h t e n e d from 500-650 msecs. T h i s m a n i p u l a t i o n was intended t o ensure t h a t a t t e n t i o n had moved away from the p r e v i o u s l y primed l a t e r a l l o c a t i o n by drawing i t back t o the c e n t r a l l o c a t i o n . On 40% of t r i a l s ( C o n d i t i o n s 1 and 2) the i n i t i a l b r i g h t e n i n g of one of the l a t e r a l boxes was r a p i d l y f o l l o w e d by the p r e s e n t a t i o n of the t a r g e t e i t h e r a t 50 msecs or 150 msecs - 3 2 -Conditions % of Trials 2 1 4 3 I l_ One Lateral Box One Lateral Box Central Box 20 20 i 20 20 7 6 I 1_ Both Lateral Boxes Both Lateral Boxes J 1 Central Box 6.7 6.7 6.7 150 650 SOA (msec) | Target Onset _TT_ Cue 1000 Figure 2. Stimulus sequences and frequencies f o r the seven conditions used i n Experiment 1 -33-SOA ( a l l SOAs are measured from the onset of the i n i t i a l brightening). These t r i a l s provided a measure of f a c i l i t a t i o n . On 40% of t r i a l s (Conditions 3 and 4), one or other l a t e r a l box brightened but no target occurred i n the i n i t i a l 500 msecs; the cen t r a l box then brightened from 500-650 msecs and a target appeared at either 650 msecs or 1000 msecs SOAs. On the remaining 20% of t r i a l s (Conditions 5, 6, and 7) both l a t e r a l boxes i n i t i a l l y brightened and the target appeared i n one of the l a t e r a l boxes equally often at 50, 650 and 1000 msecs SOAs. In the l a t t e r two conditions, the central box brightened from 500-650 msecs as i t did for the single cued t r i a l s . These seven conditions can be summarized as follows (see Figure 2): three double cued conditions with the target appearing at SOAs of 50, 650 and 1000 msecs i n equal proportions (20% of a l l t r i a l s ) and four s i n g l e cued conditions on which the target appeared at SOAs of 50, 150, 650 and 1000 msecs i n equal proportions (80% of t r i a l s ) . T r i a l s with targets at SOAs of 50 or 150 msecs w i l l be referred to as early, and those with targets at SOAs of 650 or 1000 msecs as l a t e . The brightening of the central box occurred only on l a t e t r i a l s . Figure 3 i l l u s t r a t e s the stimulus sequence f o r one condition. For each of the single cued conditions, t r i a l s were defined as v a l i d i f the target appeared at the previously cued loc a t i o n or as i n v a l i d i f the target appeared at the opposite loca t i o n . Eighty percent of early t r i a l s were v a l i d , and 20% - 3 4 -650 - Response Figure J3. Stimulus Sequence for Condition 3 i n Experiment 1: V a l i d l y cued target i n the r i g h t v i s u a l f i e l d at 650 msec SOA -35-were i n v a l i d . F i f t y percent of the l a t e t r i a l s were v a l i d and 50% were i n v a l i d . Subjects were not given any e x p l i c i t i n s t r u c t i o n s concerning the p r e d i c t i v e v a l i d i t y of the cue. They were simply t o l d that sometimes the target would appear on the side of the cue, and sometimes i t would appear on the opposite side. On a l l t r i a l s both v a l i d and i n v a l i d targets appeared equally often at the l e f t and r i g h t l o c a t i o n . Subjects were instructed to maintain f i x a t i o n on the c e n t r a l box and to respond to the targets as f a s t and as accurately as possible. They were e x p l i c i t l y instructed not to move t h e i r eyes, either when a target appeared or when any of the boxes brightened. Compliance with these in s t r u c t i o n s was encouraged by o f f e r i n g incremental pay for f a s t e r and more accurate responding, and by emphasizing that eye movements, either i n a n t i c i p a t i o n of a target or i n response to a box brightening, would be l i k e l y to slow t h e i r responses to targets. Subjects appeared highly motivated to comply with these instructions during the task. Subjects responded by depressing a morse key with t h e i r dominant hand as quickly as possible upon presentation of a target. Reaction time (to the nearest millisecond) was recorded by a Compaq computer which also controlled stimulus presentation. Subjects performed three blocks of 180 t r i a l s i n which a l l stimulus conditions were presented i n a d i f f e r e n t random order for each subject. I n t e r - t r i a l i n t e r v a l varied randomly from 3-5 -36-seconds. Between blocks they performed unrelated memory and word r a t i n g experiments. Data Analysis Median RT was calculated separately f o r each condition. Reaction times less than 100 msecs were considered anticipatory and were excluded. The data f o r early and l a t e t r i a l s were analyzed separately i n 2 (Group) X 2 (SOAs; 50 or 150 msecs for early t r i a l s and 650 or 1000 msecs f o r la t e t r i a l s ) X 2 (Cue side; r i g h t or l e f t ) X 2 (Cue V a l i d i t y ; v a l i d or invalid) X 3 (Blocks) ANOVAs with group as a between-subjects factor and the remaining factors within-subjects. Complete data were available for 15 psychopaths and 13 nonpsychopaths. The remaining 3 subjects did not have data for a l l three blocks. The major e f f e c t s reported below (excluding those involving the blocks factor) remained s i g n i f i c a n t whether or not these subjects were included and the data was collapsed across blocks. Analysis of the double-cued t r i a l s was performed s l i g h t l y d i f f e r e n t l y . Because we were interested i n the difference between double-cued and i n v a l i d t r i a l s as a measure of i n h i b i t i o n of return, the arithmetic difference between these two conditions was used as the dependent v a r i a b l e . For instance, for right-sided targets, the RT difference between double-cued t r i a l s and t r i a l s on which an i n v a l i d cue appeared on the l e f t was calculated f o r each subject. These analyses are comparable to those discussed above except that the Cue -37-Validity factor i s no longer explicit. Any main effects or interactions which occur in this analysis would be equivalent to the same effect in the previous analysis interacting with cue validity. Results Reaction times for psychopaths (P) and nonpsychopaths (NP) on valid and invalid t r i a l s in the right and l e f t visual fields (RVF and LVF respectively) at each SOA are shown in Figure 4. Results for the double-cued neutral t r i a l s are shown in Figure 5, and the valid minus invalid RT differences are shown in Figure 6, where values greater than zero indicate faster RTs for valid than for invalid t r i a l s . Analysis of early t r i a l s revealed significant effects for SOA (F(l,26) = 4.41, p_<.05), for Cue Side (F(l,26) = 7.37, p_<.02), and for Cue Validity (F(l,26) = 23.95, p_<.001). These main effects were moderated by a SOA X Cue Validity interaction (F(l,26) = 4.58, p_<.05). Subjects in both groups were faster to respond to targets following a cue on the right side (373 msecs) than on the l e f t (379 msecs). As expected, subjects were quicker to respond to valid than to invalid targets, but this vali d i t y effect was larger at 50 msecs SOA than at 150 msecs SOA (see Figure 6). However, there was no evidence that the groups differed in this invalid-valid (I-V) RT difference (p_>.40) or for any higher order interaction. Analysis of the late t r i a l s revealed main effects for SOA -38-400 r Stimulus Onset Asynchrony (msec) F i g u r e 4. Experiment 1: R e a c t i o n times t o v a l i d and i n v a l i d t r i a l s f o r each SOA, v i s u a l f i e l d and group -39-o CD C/) E CD E c o • mmmm ts CTJ CD DC 400 r 380 • 360 -340 " 320 300 -r>— P, Neutral, RVF P, Neutral, LVF NP, Neutral, RVF NP, Neutral, LVF 0 200 400 600 800 1000 Stimulus Onset Asynchrony (msec) Figure 5 . Experiment 1: Reaction times to double-cued neutral t r i a l s f or each SOA, v i s u a l f i e l d and group -40-F i g u r e 6 . E x p e r i m e n t 1 : D i f f e r e n c e i n r e a c t i o n t i m e b e t w e e n i n v a l i d l y a n d v a l i d l y c u e d t r i a l s a t e a c h SOA f o r e a c h g r o u p -41-(F(l,26) = 91.61, E<-001), for Blocks (F(2,52) = 4.48, p_<.03), and for Cue V a l i d i t y (F(l,26) = 149.96, p_<.001). Subjects were fa s t e r to respond at 1000 msecs than at 650 msecs, they responded i n the second (346 msecs) and t h i r d (348 msecs) fa s t e r than i n the f i r s t block (358 msecs), and they were slower to respond on v a l i d than on i n v a l i d t r i a l s . Tukey comparisons among the means fo r the 3 blocks found the f i r s t block to d i f f e r s i g n i f i c a n t l y from the second, but the comparison with the t h i r d block just f a i l e d to reach s i g n i f i c a n c e . There were also two s i g n i f i c a n t i n t e r a c t i o n s . The Group X Cue V a l i d i t y i n t e r a c t i o n (F(1,26)=4.46, &<.05) showed that the I-V RT difference was smaller for psychopaths than for nonpsychopaths (see Figure 6). There was also a Group X Cue side X Cue v a l i d i t y X Block i n t e r a c t i o n (F(2,52) = 3.55, p_<.05). This 4-way int e r a c t i o n was explored further using simple e f f e c t s analyses. The 3-way i n t e r a c t i o n of Cue side X Cue v a l i d i t y X Block f a i l e d to reach s i g n i f i c a n c e f o r either the nonpsychopaths (F(2,52) = 1.19, p>.30) or the psychopaths (F(2,52) = 2.65, p_>.08) separately. For t h i s reason t h i s unpredicted i n t e r a c t i o n was not examined further. If the group difference at la t e SOAs was due to less strong development of i n h i b i t i o n of return i n psychopaths than i n nonpsychopaths, then a s i m i l a r group difference should have emerged when we examined the RT difference between double-cued and i n v a l i d t r i a l s . This RT difference i s shown i n Figure 7. As -42-fX CO > I Td > c 50 Ms 650 Ms 1000 Ms Stimulus Onset Asynchrony ao Group NP Group P F i g u r e 7. Experiment 1: D i f f e r e n c e i n r e a c t i o n time between i n v a l i d l y cued and n e u t r a l t r i a l s a t each SOA f o r each group -43-expected, there was no evidence f o r the development of any i n h i b i t o r y e f f e c t at 50 msecs SOA. Analysis of t h i s early t r i a l revealed a main e f f e c t neither f o r group nor for the grand mean (both p_s>.25). At l a t e SOAs there was a main e f f e c t f o r the grand mean (F(l,26) = 121.95, p_<.001), equivalent to a main e f f e c t f or Cue v a l i d i t y i n previous analyses. However, the main e f f e c t f or group (equivalent to the Group X Cue V a l i d i t y i n t e r a c t i o n described above) did not even approach s i g n i f i c a n c e (F(l,26) = 0.03, p_>.85). Therefore, although there was cl e a r evidence for the development of i n h i b i t i o n of return, the evidence was not consistent with the hypothesis that psychopaths d i f f e r from nonpsychopaths i n the magnitude of t h i s i n h i b i t i o n . In addition, there was a s i g n i f i c a n t i n t e r a c t i o n of Group X Cue side (F(l,26) = 4.25, p<.05), although the Group X Cue side X Block i n t e r a c t i o n (equivalent to the s i g n i f i c a n t 4-way in t e r a c t i o n reported above) was not s i g n i f i c a n t f o r t h i s measure (F(2,52) = 1.33, p_>.25). The Group X Cue side i n t e r a c t i o n was due to the fac t that nonpsychopaths showed greater i n h i b i t i o n i n the l e f t v i s u a l f i e l d than i n the r i g h t , but that psychopaths showed the opposite pattern. Analysis of simple e f f e c t s confirmed t h i s conclusion. The e f f e c t of Cue side was s i g n i f i c a n t f or nonpsychopaths (F(l,26) = 4.41, p_<.05) but not for psychopaths (F(l,26) = 0.59). The d i f f e r e n t r e s u l t s obtained using i n v a l i d - v a l i d and -44-invalid-double cued measures could have been due simply to group differences i n RT to the double cued t r i a l s . To r u l e out t h i s p o s s i b i l i t y , we submitted subjects' RTs f o r the l a t e double cued t r i a l s to an ANOVA. Although there were s i g n i f i c a n t e f f e c t s f o r Blocks, SOA, and an i n t e r a c t i o n of Block X SOA X Cue side, there were no s i g n i f i c a n t main e f f e c t s or interactions involving groups ( a l l p_s > .19). Mean RTs to double cued t r i a l s were 383 and 371 msecs at 650 msec SOAs, and 335 and 330 msecs at 1000 msec SOAs for psychopaths and nonpsychopaths respectively. Discussion The r e s u l t s of Experiment 1 support the hypothesis that, under c e r t a i n conditions, psychopaths and nonpsychopaths may be d i f f e r e n t i a t e d by the way i n which they a l l o c a t e attention. On early t r i a l s both groups showed an equal amount of f a c i l i t a t i o n ; the r e f l e x i v e priming of a v i s u a l l o c a t i o n was equally e f f e c t i v e i n drawing psychopaths' and nonpsychopaths' attention to the cued location. The r e s u l t s for the l a t e t r i a l s were more complicated. Our measure of primary inte r e s t , comparing the difference between v a l i d and i n v a l i d t r i a l s , revealed the development of i n h i b i t i o n i n both groups; that i s , both groups were quicker to respond to a target i n a previously uncued lo c a t i o n than to one i n a previously cued location. This i n h i b i t o r y e f f e c t was less strong f o r psychopaths. However, by measuring the RT difference -45-between double-cued and uncued (invalid) t r i a l s , we were able to obtain a second measure of i n h i b i t i o n of return, t h e o r e t i c a l l y uncontaminated by f a c i l i t a t i o n . This measure showed no evidence for an o v e r a l l group difference i n i n h i b i t i o n of return, although i t did reveal a group difference i n the asymmetry of i n h i b i t i o n . This discrepancy can be most e a s i l y interpreted i n terms of a group difference i n the a l l o c a t i o n of endogenous or voluntary attention (Jonides, 1981, Muller & Rabbitt, 1989). In the present paradigm cue v a l i d i t y was manipulated with the intention of providing clear evidence f o r covert s h i f t s i n attention without encouraging overt eye movements or conscious guesses as to the location of targets. For early t r i a l s the cue was 80% p r e d i c t i v e of target location, but f o r l a t e t r i a l s the cue provided no i n d i c a t i o n as to the target l o c a t i o n (50% v a l i d i t y ) . However, early and l a t e t r i a l s were randomly interspersed. I f subjects did not d i s t i n g u i s h the two types of t r i a l (and t h e i r verbal reports indicated that they did not) the cue could have been interpreted as being 65% v a l i d on a l l t r i a l s . Such a r e l a t i o n s h i p between the cue and target leads to voluntary s h i f t s of attention to the primed lo c a t i o n (Jonides, 1981), but only a f t e r delays of at least 100 msecs. I t appears, therefore, that the RT difference on l a t e t r i a l s i s best considered as the sum of sensory i n h i b i t i o n at the cued location and an endogenously controlled s h i f t of -46-a t t e n t i o n towards the cued l o c a t i o n . The data from Experiment 1 i s c o n s i s t e n t w i t h the h y p o t h e s i s t h a t psychopaths over-a l l o c a t e endogenous a t t e n t i o n t o the cued s i d e , but t h a t they m a n i f e s t exogenous f a c i l i t a t i o n and i n h i b i t i o n o f r e t u r n normally. Experiments 2-5 General Procedures Procedures common t o the remaining experiments w i l l be d e s c r i b e d i n t h i s s e c t i o n . Experiments 2-5 were c a r r i e d out i n a s i n g l e s e s s i o n l a s t i n g approximately 2 hours. Experiment 2, which was intended t o r e p l i c a t e and extend the r e s u l t s o f Experiment 1, was always completed f i r s t . The o r d e r o f Experiments 3-5 was randomly a s s i g n e d t o one of s i x p o s s i b l e o r d e r s . S t i m u l i , under computer c o n t r o l , were p r e s e n t e d on the same c o l o u r g r a p h i c s monitor used i n Experiment 1. S u b j e c t s were p a i d $7.00 f o r t h e i r p a r t i c i p a t i o n , w i t h bonus p r i z e s t o t a l l i n g $45.00 p a i d t o the s u b j e c t s p e r f o r m i n g most q u i c k l y and a c c u r a t e l y i n the experiments. T h i s a d d i t i o n a l prize-money was a l l o c a t e d as f o l l o w s : For each experiment, RT and accuracy s c o r e s , averaged a c r o s s a l l c o n d i t i o n s i n the experiment, were s t a n d a r d i z e d a c r o s s a l l s u b j e c t s and summed. The h i g h e s t ranked s u b j e c t i n each experiment r e c e i v e d $5.00. In a d d i t i o n , the sc o r e s f o r each experiment were r e - s t a n d a r d i z e d and summed a c r o s s the f o u r experiments, and the s u b j e c t w i t h the h i g h e s t r a n k i n g a c r o s s a l l experiments r e c e i v e d an a d d i t i o n a l $25. -47-P r i o r t o each experiment, s u b j e c t s were reminded of the a v a i l a b i l i t y o f t h i s prize-money. R e a c t i o n time was r e c o r d e d u s i n g the same response keys used i n Experiment 1, and u s i n g the computer keyboard. Feedback and d e b r i e f i n g were g i v e n a t the end of the s e t of experiments. Speed and accuracy were e q u a l l y emphasized throughout. S u b j e c t s S u b j e c t s were d e f i n e d i n the same way as f o r Experiment 1, except t h a t the 20-item r e v i s e d PCL (PCL-R: Hare, 1990; Hare e t a l . , 1990) was used t o c l a s s i f y s u b j e c t s . T h i s r e v i s e d s c a l e i s s u b s t a n t i v e l y i d e n t i c a l t o the 22-item v e r s i o n used i n Experiment 1 (Hare e t a l . , 1990). F o r t y male inmates from the same p e n i t e n t i a r y used i n Experiment 1 v o l u n t e e r e d t o p a r t i c i p a t e i n these experiments. One s u b j e c t (a nonpsychopath) had p a r t i c i p a t e d i n Experiment 1, but t e s t i n g had taken p l a c e approximately 2 y e a r s p r e v i o u s l y , so t h i s s u b j e c t was not excluded. Two r a t i n g s were a v a i l a b l e f o r 11 s u b j e c t s , the remainder were r a t e d o n l y once. Again, r a t i n g s were averaged where a v a i l a b l e . The i n t r a c l a s s c o r r e l a t i o n c o e f f i c i e n t f o r a s i n g l e PCL-R r a t i n g c a l c u l a t e d on a sample of 241 inmates from the same p o p u l a t i o n was 0.78 (Hare e t a l . , 1990). In these experiments, the s u b j e c t s were d i v i d e d i n t o 20 psychopaths (PCL-R s c o r e > 30; range = 30.5-40; Mean = 34.0, S.D. = 3.0) and 20 nonpsychopaths (PCL-R s c o r e < 30; range = -48-13.5-28; Mean = 22.1, S.D. = 4.2). The d e f i n i t i o n o f psychopaths as s c o r i n g above 30 on the PCL-R i s c o n s i s t e n t w i t h p r e v i o u s r e s e a r c h u s i n g the PCL, and r e f l e c t s the s l i g h t l y reduced range of the PCL-R. Groups P and NP d i d not d i f f e r s i g n i f i c a n t l y i n age (M = 30.3 and 31.6 y e a r s r e s p e c t i v e l y ) , but Group NP r e p o r t e d r e c e i v i n g s i g n i f i c a n t l y more f o r m a l e d u c a t i o n (M = 11.1 years) than d i d Group P (M = 10.0 y e a r s ) . In g e n e r a l , s u b j e c t s were o n l y excluded from a n a l y s i s i n the f o l l o w i n g experiments i f t h e r e were c o m p e l l i n g reasons t o do so. For i n s t a n c e one s u b j e c t (a psychopath) r e p o r t e d s u f f e r i n g from m u l t i p l e s c l e r o s i s . Although c o n f i n e d t o a w h e e l - c h a i r , he performed w e l l w i t h i n normal l i m i t s i n a l l experiments on both RT and accuracy. Furthermore, h i s e x c l u s i o n from a n a l y s e s of each experiment f a i l e d t o a l t e r the r e s u l t s s u b s t a n t i v e l y . He was t h e r e f o r e i n c l u d e d i n a l l a n a l y s e s . Reasons f o r o m i t t i n g s u b j e c t s from one or more experiments w i l l be d e s c r i b e d i n the methods s e c t i o n of t h a t experiment. Experiment 2 Two obvious o b j e c t i o n s can be made t o the i n t e r p r e t a t i o n of the r e s u l t s of experiment 1. F i r s t l y , s i n c e t h e experiment was designed p r i m a r i l y t o examine the p r o c e s s e s of exogenous f a c i l i t a t i o n and i n h i b i t i o n o f r e t u r n , no attempt t o c o n t r o l o v e r t eye movements was made. Although psychopaths are g e n e r a l l y compliant and we11-motivated i n r e s e a r c h of t h i s k i n d , we cannot r u l e out the p o s s i b i l i t y t h a t the group -49-d i f f e r e n c e s we i n t e r p r e t e d as i n d i c a t i n g d i f f e r e n c e s i n the c o v e r t o r i e n t i n g of endogenous a t t e n t i o n were the r e s u l t of o v e r t eye movements by one of the groups. At SOAs of l e s s than 200 msecs t h i s i s u n l i k e l y t o be a problem, but the group d i f f e r e n c e s emerged o n l y on l a t e t r i a l s . Consequently, experiment 2 attempted t o r e p l i c a t e the r e s u l t s of experiment 1 w h i l e s i m u l t a n e o u s l y r e c o r d i n g l a t e r a l eye-movements. The second d i f f i c u l t y w i t h the i n t e r p r e t a t i o n r e s t s on the use of n e u t r a l t r i a l s . D i s t i n g u i s h i n g between the mechanisms of i n h i b i t i o n of r e t u r n and endogenous f a c i l i t a t i o n on t h i s b a s i s alone i s q u e s t i o n a b l e (Jonides & Mack, 1984). In experiment 2, t h e r e f o r e these two p r o c e s s e s were d i s t i n g u i s h a b l e i n two a d d i t i o n a l ways. F i r s t , two b l o c k s of t r i a l s were run, one u s i n g p e r i p h e r a l c u i n g as i n Experiment 1, the o t h e r u s i n g arrows as symbolic cues, always p r e s e n t e d c e n t r a l l y . In t h i s l a t t e r c o n d i t i o n n e i t h e r i n h i b i t i o n nor exogenous o r i e n t i n g i s induced, but endogenous o r i e n t i n g i s . Second, i n the p e r i p h e r a l l y cued block, two types of n e u t r a l cue were employed. For h a l f of the n e u t r a l t r i a l s a double-cue primed both the l a t e r a l boxes s i m u l t a n e o u s l y , as i n Experiment 1. For the remaining t r i a l s , the c e n t r a l box b r i g h t e n i n g from 0-150 msecs was used. In n e i t h e r case do the cues prime a s p a t i a l l o c a t i o n , but o n l y on double-cued n e u t r a l t r i a l s s h ould any i n h i b i t i o n develop a t p e r i p h e r a l l o c a t i o n s . I f experiment 2 r e v e a l s group d i f f e r e n c e s i n the e f f e c t s of c u i n g on l a t e -50-t r i a l s which occurs o n l y a f t e r p e r i p h e r a l , but not c e n t r a l c u i n g , t h e s e d i f f e r e n c e s would have t o be a t t r i b u t e d t o an i n h i b i t o r y p r o c e s s . S i m i l a r l y , group d i f f e r e n c e s i n the development of i n h i b i t i o n s hould be v i s i b l e i n comparisons of s i n g l e - and double-cued n e u t r a l t r i a l s . However, i f group d i f f e r e n c e s are s i m i l a r a f t e r both p e r i p h e r a l and c e n t r a l c u i n g , then t h i s d i f f e r e n c e would be a t t r i b u t a b l e t o endogenous f a c i l i t a t i o n , and should be accompanied by no d i f f e r e n c e s between the double- and s i n g l e - c u e d n e u t r a l t r i a l s . In t h i s experiment, then, the comparison of p e r i p h e r a l l y and s y m b o l i c a l l y cued l a t e r a l t r i a l s , and comparison of c e n t r a l and p e r i p h e r a l n e u t r a l t r i a l s p r o v i d e s e p a r a t e t e s t s , based on d i f f e r e n t c o n d i t i o n s w i t h i n the experiment, of t h e c e n t r a l h y p o t h e s i s . Experiment 2 , t h e r e f o r e , was designed t o r e p l i c a t e the e f f e c t found i n Experiment 1, t o i d e n t i f y unambiguously the mechanism u n d e r l y i n g t h i s e f f e c t as e i t h e r i n h i b i t i o n , or endogenous f a c i l i t a t i o n , and, should the group d i f f e r e n c e be a t t r i b u t a b l e t o f a c i l i t a t i o n , t o compare the two groups on the r e l a t i v e c o s t s and b e n e f i t s of s p a t i a l c u i n g . Design The experimental procedure was s i m i l a r t o t h a t used i n Experiment 1 . The same t h r e e boxes were d i s p l a y e d permanently on the screen, one t o the r i g h t , one t o the l e f t , and one a t f i x a t i o n (see F i g u r e 3 ). The t a r g e t was a g a i n a s t a r appearing -51-i n one or oth e r p e r i p h e r a l box. Two types of cue c o n d i t i o n were t e s t e d . P e r i p h e r a l Cuing. P e r i p h e r a l cues were i d e n t i c a l t o those used i n Experiment 1: One of the p e r i p h e r a l boxes b r i g h t e n e d f o r 150 msecs, f o l l o w e d a f t e r 500 msecs by a b r i g h t e n i n g o f the c e n t r a l box t o draw a t t e n t i o n back t o f i x a t i o n . Two k i n d s o f n o n - s p a t i a l , o r n e u t r a l , cues were used d u r i n g the p e r i p h e r a l c u i n g b l o c k . On double-cued n e u t r a l t r i a l s both p e r i p h e r a l boxes were b r i g h t e n e d f o r 150 msecs, f o l l o w e d a f t e r 500 msecs by the b r i g h t e n i n g of the c e n t r a l box. T h i s was the same n e u t r a l c o n d i t i o n used i n experiment 1. On s i n g l e - c u e d n e u t r a l t r i a l s o n l y the c e n t r a l box b r i g h t e n e d as the f i r s t cue. F i v e hundred msecs l a t e r the same box b r i g h t e n e d a g a i n as happened on ot h e r l a t e t r i a l s . C e n t r a l c u i n g . C e n t r a l cues c o n s i s t e d o f an arrow, appearing i n the f i x a t i o n box f o r 150 msecs, p o i n t i n g t o the r i g h t o r l e f t . For c o m p a r a b i l i t y w i t h p e r i p h e r a l c u i n g t r i a l s , a f t e r 500 msecs a second, n o n - s p a t i a l cue appeared f o r 150 msecs i n the c e n t r a l box. T h i s n e u t r a l cue c o n s i s t e d o f a double-headed arrow p o i n t i n g both l e f t and r i g h t . N e u t r a l t r i a l s c o n s i s t e d o f the appearance of the same double-headed arrow both i n i t i a l l y , and a f t e r 500 msecs. Because t h e r e were no group d i f f e r e n c e s i n Experiment 1 a t e a r l y SOAs, o n l y one e a r l y SOA (100 msecs), as w e l l as both l a t e SOAs (equal numbers of t r i a l s a t 650 msecs and 1000 msecs -52-SOAs) were t e s t e d . Each t r i a l c o n s i s t e d o f an i n i t i a l cue (sometimes d i r e c t i o n a l ) , f o l l o w e d a f t e r 500 msecs by a second cue (always c e n t r a l and n e u t r a l as t o d i r e c t i o n ) , f o l l o w e d by a t a r g e t i n the r i g h t o r l e f t box. When t a r g e t s appeared a t SOAs of 100 msecs, o n l y the i n i t i a l cue was pr e s e n t e d . P e r i p h e r a l and c e n t r a l c u i n g t r i a l s were run i n sep a r a t e b l o c k s , randomly counterbalanced f o r order a c r o s s s u b j e c t s . W i t h i n each type of cue, 20% were n e u t r a l t r i a l s , and 80% d i r e c t i o n a l l y cued t r i a l s . Of the d i r e c t i o n a l l y cued t r i a l s , 69% were v a l i d l y cued and 31% were i n v a l i d l y cued a t a l l t h r e e SOAs. A c r o s s a l l c o n d i t i o n s , h a l f the t a r g e t s appeared i n each v i s u a l f i e l d . These percentages c l o s e l y r e p l i c a t e d the c o n d i t i o n s used i n Experiment 1. W i t h i n each b l o c k a l l c o n d i t i o n s were presented i n a d i f f e r e n t random o r d e r f o r each s u b j e c t . As f o r Experiment 1, a v a l i d t r i a l c o n s i s t e d o f a p e r i p h e r a l cue, f o l l o w e d by a t a r g e t a p pearing on the same s i d e as the cue. For i n v a l i d t r i a l s , the cue o c c u r r e d on the s i d e o p p o s i t e t o the cue. Subi e c t s The a n a l y s e s d e s c r i b e d below were based on data from 19 nonpsychopaths and 18 psychopaths. One s u b j e c t r e p o r t e d s u f f e r i n g from d i a b e t i c r e t i n o p a t h y , r e s u l t i n g i n impaired p e r i p h e r a l v i s i o n . As a consequence, he found i t d i f f i c u l t t o d e t e c t t a r g e t s without moving h i s eyes, r e s u l t i n g i n l o n g e r -53-than u s u a l RTs. For the remaining s u b j e c t s , experimenter e r r o r r e s u l t e d i n the l o s s of data f o r e i t h e r the c e n t r a l l y o r the p e r i p h e r a l l y cued b l o c k . Procedure The procedures f o l l o w e d were v e r y s i m i l a r t o those d e s c r i b e d f o r Experiment 1. A f t e r having the procedures e x p l a i n e d t o them and s i g n i n g consent forms, Beckman s i l v e r e l e c t r o d e s were at t a c h e d l a t e r a l t o the e x t e r n a l canthus of the s u b j e c t ' s l e f t and r i g h t eye t o monitor l a t e r a l eye movements. The s i g n a l was a m p l i f i e d (x 10,000) v i a a P r i n c e t o n A p p l i e d Research p r e - a m p l i f i e r , band-passed a t .03-30Hz, d i g i t i z e d a t 100 Hz, and s t o r e d o f f - l i n e f o r subsequent a n a l y s i s . For v a r i o u s reasons d e s c r i b e d i n the r e s u l t s s e c t i o n d i f f e r e n t a m p l i f i c a t i o n and f i l t e r s e t t i n g s were used f o r some s u b j e c t s . The e l e c t r o - o c u l o g r a m was reco r d e d f o r 250 msecs p r i o r t o and 2.75 seconds a f t e r the onset of the cue f o r each t r i a l . To ensure a c c u r a t e d e t e c t i o n o f l a t e r a l eye movement s u b j e c t s used a c h i n - r e s t t o prevent movements of t h e i r head. Su b j e c t s performed the experiment i n the same way as Experiment 1. Two b l o c k s of 240 t r i a l s , one u s i n g p e r i p h e r a l b r i g h t e n i n g , the other c e n t r a l arrows as cues, were run i n a random ord e r . W i t h i n each block, 132 cues were v a l i d , 60 were i n v a l i d and 48 were n e u t r a l w i t h r e s p e c t t o l o c a t i o n . T a r g e t s o c c u r r e d e q u a l l y o f t e n a t SOAs of 100, 650 and 1000 msecs and a l l t r i a l s and c o n d i t i o n s were presented i n , a d i f f e r e n t random -54-o r d e r f o r each s u b j e c t . B efore each b l o c k s u b j e c t s performed 24 p r a c t i c e t r i a l s t o f a m i l i a r i z e them w i t h the sequence of t h a t b l o c k . The 240 t r i a l s were d i v i d e d i n t o s e t s of 80 between which s u b j e c t s were g i v e n a chance t o r e s t . S u b j e c t s responded t o the t a r g e t by d e p r e s s i n g a morse key w i t h t h e dominant hand as q u i c k l y as p o s s i b l e . I n s t r u c t i o n s emphasized t h a t the prize-money depended on the f a s t e s t and the most a c c u r a t e responding, w i t h e r r o r s o c c u r r i n g i f s u b j e c t s responded b e f o r e the s t a r appeared. These speed/accuracy i n s t r u c t i o n s were repeated a t each break. In f a c t , because the computer c o u l d not monitor the RT key c o n s t a n t l y , i t was im p o s s i b l e t o r e c o r d a n t i c i p a t o r y responses a c c u r a t e l y . Because no d i s c r i m i n a t i v e responding was r e q u i r e d , the o n l y e r r o r s r e c o r d e d were those d e s i g n a t e d as e r r o r s because they o c c u r r e d w i t h i n 100 msecs of the t a r g e t onset (See below). For t h i s experiment, t h e r e f o r e , performance was measured by RT alone, a lthough s u b j e c t s were not informed of t h i s . Data A n a l y s i s Median RT was c a l c u l a t e d s e p a r a t e l y f o r each c o n d i t i o n . RTs l e s s than 100 msecs were c o n s i d e r e d a n t i c i p a t o r y and were excluded. For e a r l y t r i a l s a 5-way ANOVA was c a r r i e d out w i t h between-subjects f a c t o r s of Group (P,NP) and Block Order ( P e r i p h e r a l l y or c e n t r a l l y cued b l o c k s f i r s t ) , and w i t h i n -s u b j e c t s f a c t o r s of Cue Type ( P e r i p h e r a l b r i g h t e n i n g o r c e n t r a l -55-arrow), Cue Side (Right, l e f t ) , and Cue V a l i d i t y ( V a l i d , i n v a l i d ) . A n a l y s i s of l a t e t r i a l s i n c l u d e d the a d d i t i o n a l f a c t o r o f SOA (650, 1000 msecs). A n a l y s i s o f n e u t r a l t r i a l s was c a r r i e d out f o r the p e r i p h e r a l l y cued b l o c k i n order t o p r o v i d e an a d d i t i o n a l t e s t of group d i f f e r e n c e s i n the magnitude of i n h i b i t i o n . As w i t h Experiment 1, group d i f f e r e n c e s i n the development o f i n h i b i t i o n were t e s t e d without the p o s s i b l e c o n t a m i n a t i o n of o v e r l a p p i n g f a c i l i t a t i o n . T h i s c o u l d be done more e f f e c t i v e l y i n Experiment 2 because the p e r i p h e r a l c u i n g c o n d i t i o n used two types o f n e u t r a l cues, a c e n t r a l l y b r i g h t e n e d box ( s i n g l e cue) and a b i l a t e r a l l y b r i g h t e n e d box (double c u e ) . N e i t h e r cue induces o r i e n t i n g , because n e i t h e r cue p r o v i d e s s p a t i a l i n f o r m a t i o n , but the double-cued c o n d i t i o n induces i n h i b i t i o n whereas the s i n g l e cue does not. An ANOVA w i t h Group, Block Order, T a r g e t Side (Right, l e f t ) , and N e u t r a l T r i a l Type (Double, s i n g l e ) as f a c t o r s was performed t o examine i n h i b i t i o n u s i n g t h e s e two types of n e u t r a l cue. U n f o r t u n a t e l y the r e c o r d i n g o f EOG i n t h i s experiment was plagued by a v a r i e t y of problems. The EOG data c o n t a i n e d a c o n s i d e r a b l e amount of a r t i f a c t u a l 60Hz n o i s e , which c o u l d not be e l i m i n a t e d because o f the nature of the r e c o r d i n g s i t u a t i o n . When necessary, the low-pass f i l t e r was reduced t o 10Hz t o t r y t o minimize contamination, and f o r some s u b j e c t s s i g n a l a m p l i f i c a t i o n had t o be reduced. T h i s i n t e r f e r e n c e , equipment -56-f a i l u r e , and experimenter e r r o r l e d t o the e l i m i n a t i o n of data f o r an a d d i t i o n a l f o u r s u b j e c t s . Furthermore, the amount of a r t i f a c t u a l n o i s e p r e s e n t i n the data of the remaining s u b j e c t s p r e c l u d e d u s i n g EOG i n f o r m a t i o n t o s c r e e n f o r eye-movements on a t r i a l - b y - t r i a l b a s i s . For t h i s reason, f u r t h e r d e t a i l s o f the EOG r e c o r d i n g procedures and r e s u l t s a re not r e p o r t e d here. However, a l e s s s e n s i t i v e t e s t o f group d i f f e r e n c e s was performed, r e v e a l i n g no evidence t h a t psychopaths were more l i k e l y t o move t h e i r eyes a f t e r the i n i t i a l l a t e r a l cue than were nonpsychopaths. D e t a i l s of these a n a l y s e s a r e g i v e n i n Appendix A. R e s u l t s Means of the median RTs f o r psychopaths and nonpsychopaths on v a l i d and i n v a l i d t r i a l s i n each v i s u a l f i e l d a t each SOA are shown i n F i g u r e 8 f o r p e r i p h e r a l l y cued t r i a l s , and i n F i g u r e 9 f o r c e n t r a l l y cued t r i a l s . The v a l i d minus i n v a l i d RT d i f f e r e n c e s are shown i n F i g u r e s 10 and 11. Values g r e a t e r than zero i n d i c a t e f a s t e r RTs f o r v a l i d than f o r i n v a l i d t r i a l s . E a r l y T r i a l s A n a l y s i s of e a r l y t r i a l s r e v e a l e d s i g n i f i c a n t e f f e c t s f o r Cue Type (F(l,33) = 28.15, p<.001), and Cue V a l i d i t y (F(l,33) = 9.41, p_<.005). A number of oth e r e f f e c t s approached s i g n i f i c a n c e (e.g., Side, p_=.055, and Cue V a l i d i t y X Si d e , p_=.08); however, no main e f f e c t o f Group, or i n t e r a c t i o n i n v o l v i n g Group X Cue V a l i d i t y approached s i g n i f i c a n c e ( a l l Fs -57-o CD t/) E, CD e o CTJ 0 DC 4 0 0 r 375 3 5 0 325 300 275 250 2 2 5 P, Valid, RVF P, Valid, LVF P, Invalid, RVF P, Invalid, LVF NP, Valid, RVF NP, Valid, LVF NP, Invalid, RVF NP, Invalid, LVF 0 200 400 6 0 0 8 0 0 1000 Stimulus Onset Asynchrony (msec) Figure 8. Experiment 2: Reaction times to v a l i d and i n v a l i d p e r i p h e r a l l y cued t r i a l s f or each SOA, v i s u a l f i e l d and group -58-380 r Stimulus Onset Asynchrony (msec) Figure 9. Experiment 2: Reaction times to v a l i d and i n v a l i d c e n t r a l l y cued t r i a l s f or each SOA, v i s u a l f i e l d and group -59-Figure 10. Experiment 2: Difference i n reaction time between i n v a l i d l y and v a l i d l y cued t r i a l s a f t e r peripheral cuing for each SOA -60-100 MS 650 MS 1000 MS Stimulus Onset Asynchrony a Group NP Group P F i g u r e 11. Experiment 2: D i f f e r e n c e i n r e a c t i o n time between i n v a l i d l y and v a l i d l y cued t r i a l s a f t e r c e n t r a l c u i n g f o r each SOA -61-< 1.96, ps > .15). Subjects responded faster to validly cued t r i a l s (358 msecs) than to invalidly cued t r i a l s (369 msecs) and to t r i a l s centrally cued using an arrow than to peripherally cued t r i a l s (350 vs 377 msecs respectively). It i s of some interest that the interaction of Cue Type and Cue Validity did not approach significance (F<1), indicating that both peripheral and central cues succeeded in inducing orienting of attention at this SOA. Late Trials Analysis of late t r i a l s revealed significant main effects of for Cue Type (F(l,33) = 166.09, p<.001), SOA (F(l,33) = 193.78, p_<.001) and Cue Validity (F(l,33) = 90.06, p_<.001). Again, subjects responded faster on centrally cued t r i a l s than on peripherally cued t r i a l s . They also responded faster at 1000 msec SOA than at 650 msec SOA. Finally, the main effect of Cue validit y demonstrated that validly cued targets were responded to more slowly than invalidly cued targets (see Figures 8 and 9). The effect of cue validity was moderated by a number of interactions. The Cue Validity X SOA interaction (F(l,33) = 9.96, p_<.004) indicated that the I-V RT difference was considerably greater at 1000 than at 650 msecs. In fact, as expected, no overall inhibition was seen for central cues. However, the amount of f a c i l i t a t i o n decreased from 650 to 1000 msecs after central cuing, and the amount of inhibition seen -62-a f t e r p e r i p h e r a l c u i n g i n c r e a s e d (see F i g u r e s 10 and 11). Because t h i s e f f e c t d i d not i n t e r a c t w i t h Cue Type (F(l,33) = 0.28, p_>.50), we can a t t r i b u t e the change between 650 and 1000 msecs t o a r e d u c t i o n i n the e f f e c t s of exogenous a l l o c a t i o n of a t t e n t i o n t o the cued l o c a t i o n , s i n c e endogenous a t t e n t i o n s h i f t s are e l i c i t e d by both types of cue. Of p a r t i c u l a r importance f o r t h i s study was the f a c t t h a t the Cue V a l i d i t y X SOA X Group i n t e r a c t i o n was a l s o s i g n i f i c a n t ( F ( l ,33) = 4.27, p_<.05). Planned comparisons of the e f f e c t s of c u i n g on psychopaths v e r s u s the e f f e c t s on nonpsychopaths were c a r r i e d out s e p a r a t e l y f o r 650 and 1000 msecs SOAs. For t h e s e comparisons, pooled e r r o r terms were used as recommended by K i r k (1982), and the c r i t i c a l t f o r c o n t r a s t s i n v o l v i n g d i f f e r e n t sources of v a r i a b i l i t y was c a l c u l a t e d t o be 2.04 (see K i r k , 1982, p. 508). At 650 msecs, the e f f e c t s of Cue V a l i d i t y was not d i f f e r e n t f o r the two groups ( t = 0.32). At 1000 msecs, the psychopaths demonstrated a s i g n i f i c a n t l y s m a l l e r I-V RT d i f f e r e n c e than the nonpsychopaths ( t = 2.62). T h i s i n t e r a c t i o n demonstrates t h a t , as p r e d i c t e d , the e f f e c t of cue v a l i d i t y was d i f f e r e n t f o r the two groups, but o n l y a t the l o n g e s t SOA. T h i s e f f e c t was not moderated by any s i g n i f i c a n t h i g h e r o r d e r i n t e r a c t i o n s . In p a r t i c u l a r , the 4-way i n t e r a c t i o n i n v o l v i n g Cue Type was not s i g n i f i c a n t (F(l,33) = 2.18, p>.14). T h i s i s c o n s i s t e n t w i t h the h y p o t h e s i s t h a t the reduced i n h i b i t i o n seen f o r psychopaths r e s u l t s from g r e a t e r endogenous o r i e n t i n g , -63-which should be apparent f o r both cue t y p e s , and not from the development of l e s s i n h i b i t i o n of r e t u r n , which would o n l y appear a f t e r p e r i p h e r a l c u i n g . S e v e r a l o t h e r i n t e r a c t i o n s not i n v o l v i n g groups were observed. The i n t e r a c t i o n of Cue Type X Cue V a l i d i t y ( F ( l ,33) = 224.70, p_<.001) demonstrated the e f f e c t i v e n e s s of the use of c e n t r a l and p e r i p h e r a l cues. A t l a t e SOAs, p e r i p h e r a l c u i n g l e d t o f a s t e r responding t o i n v a l i d l y cued t a r g e t s , but c e n t r a l c u i n g l e d t o f a s t e r responding t o v a l i d l y cued t a r g e t s (see f i g u r e s 10 and 11). The SOA X Cue V a l i d i t y i n t e r a c t i o n (F(l,33) = 4.75, p_<.04) demonstrated t h a t f o r both groups and f o r both cue types t h e r e was a s m a l l e r I-V RT d i f f e r e n c e a t 1000 msec SOA than a t 650 msec SOA. T h i s was not a f u n c t i o n of the cue type ( f o r the 3-way i n t e r a c t i o n , F ( l , 3 3 ) = 0.28, p_>.50), s u g g e s t i n g t h a t t h i s r e f l e c t s the g r a d u a l waning of the e f f e c t s of endogenous o r i e n t i n g . The SOA X Cue V a l i d i t y X B l o ck Order i n t e r a c t i o n was a l s o s i g n i f i c a n t (F(l,33) = 5.47, p_<.03). Because no i n t e r a c t i o n s w i t h Block order were p r e d i c t e d , and t h i s i n t e r a c t i o n d i d not i n v o l v e a group e f f e c t , no attempt w i l l be made t o i n t e r p r e t i t . No o t h e r s i g n i f i c a n t e f f e c t s were observed. N e u t r a l T r i a l s A n a l y s e s of n e u t r a l t r i a l s i n the p e r i p h e r a l c u i n g b l o c k were c a r r i e d out f o r e a r l y and l a t e t r i a l s s e p a r a t e l y i n order t o t e s t the magnitude of the i n h i b i t i o n e f f e c t i n the two -64-groups. Mean RTs f o r these t r i a l s a t each SOA are shown i n F i g u r e 12. At 100 msecs SOA the o n l y s i g n i f i c a n t e f f e c t was a 3-way i n t e r a c t i o n between Group X Block Order X Cue S i d e (F(l,33) = 4.68, p_<.04). The group mean RTs f o r p e r i p h e r a l c u i n g i n the f i r s t and the second b l o c k are shown i n F i g u r e 13. Simple main e f f e c t s a n a l y s e s r e v e a l e d t h a t the Group X S i d e i n t e r a c t i o n was s i g n i f i c a n t when the p e r i p h e r a l c u i n g c o n d i t i o n o c c u r r e d as the second of the two b l o c k s (F(l,33) = 4.95, p_<.05), but not when i t o c c u r r e d f i r s t ( F ( l , 33) = 0.73). For s u b j e c t s r e c e i v i n g the p e r i p h e r a l c u i n g c o n d i t i o n second, simple simple main e f f e c t s r e v e a l e d a s i g n i f i c a n t d i f f e r e n c e i n RTs t o s t i m u l i i n the two v i s u a l f i e l d s f o r nonpsychopaths (F(l,33) = 6.50, p_<.05), but not f o r psychopaths (F(l,33) = 0.42). I t i s apparent from F i g u r e 13 t h a t nonpsychopaths i n b l o c k 2, who had a l r e a d y performed 240 t r i a l s w i t h c e n t r a l c u i n g , were responding q u i c k e r t o t a r g e t s i n the l e f t v i s u a l f i e l d , whereas f o r psychopaths t h e r e was a t r e n d i n the o p p o s i t e d i r e c t i o n . The l a c k of other e f f e c t s i n t h i s c o n d i t i o n i s i n l i n e w i t h the e x p e c t a t i o n t h a t no i n h i b i t i o n would be apparent on e a r l y t r i a l s . A n a l y s i s of l a t e t r i a l s r e v e a l e d s i g n i f i c a n t e f f e c t s of SOA (F(l,33) = 190.38, p_<.001), N e u t r a l T r i a l Type (F(l,33) = 14.09, p_<.001), and the SOA X N e u t r a l T r i a l Type i n t e r a c t i o n ( F ( l ,33) = 4.40, p_<.05). T h i s i n t e r a c t i o n i s i l l u s t r a t e d i n F i g u r e 14. S u b j e c t s were f a s t e r t o respond a t 1000 than a t 650 -65-o CD (f) E CD E o CTJ CD DC 4 0 0 r 3 7 5 350 3 2 5 3 0 0 2 7 5 2 5 0 2 2 5 -o P, Single, RVF P, Single, LVF P, Double, RVF P, Double, LVF NP, Single, RVF NP, Single, LVF NP, Double, RVF NP, Double, LVF 0 200 4 0 0 600 8 0 0 1000 Stimulus Onset Asynchrony (msec) Figure 12. Experiment 2: Reaction times to double-cued and single-cued neutral t r i a l s i n the peripheral cuing condition for each SOA, v i s u a l f i e l d and group -66-420 Figure 13. Experiment 2: Reaction times to early neutral cues i n the peripheral cuing condition as a function of v i s u a l f i e l d , block order and group -67-360 650 MS 1000 MS Stimulus Onset Asynchrony i SINGLE CUED DOUBLE CUED Figure 14. Experiment 2: Reaction times to l a t e neutral cues i n the peripheral cuing condition as a function of SOA, t r i a l type and group -68-msecs SOAs, demonstrating the well-known e f f e c t s of general a l e r t i n g i n cued reaction time studies. The development of i n h i b i t i o n was apparent i n slower RTs to double-cued than to single-cued t r i a l s , and the i n t e r a c t i o n of the two e f f e c t s indicates that the magnitude of the i n h i b i t i o n was reduced at the longer SOA. Most importantly f o r t h i s experiment, the Group X Neutral T r i a l Type i n t e r a c t i o n d i d not approach s i g n i f i c a n c e (F(l,33) = 1.23, p_>.25), which supports the i n t e r p r e t a t i o n of the v a l i d - i n v a l i d cuing differences as r e s u l t i n g from differences i n endogenous orienting, and not from differences i n the development of i n h i b i t i o n . Cost-Benefit Analysis Analysis of costs and benefits was performed separately for the c e n t r a l l y - and peripherally-cued conditions and for early and l a t e t r i a l s . In each case a difference measure was calculated subtracting the RT for the neutral condition (the single-cued neutral condition i n the case of p e r i p h e r a l l y cued t r i a l s ) from the RT for v a l i d or i n v a l i d t r i a l s . Using t h i s procedure, a s i g n i f i c a n t benefit or cost was tested by comparing the constant term i n the ANOVA with zero. A l l s i g n i f i c a n t main e f f e c t s and interactions should be interpreted as interactions of that e f f e c t with the cost or benefit involved. In general, these analyses revealed l i t t l e of a d d i t i o n a l i n t e r e s t concerning the two groups. While s i g n i f i c a n t costs and - 6 9 -benefits were observed f o r both early and l a t e p e r i p h e r a l l y cued t r i a l s , there were no s i g n i f i c a n t e f f e c t s involving the Group factor. Following symbolic cuing, only costs were observed f o r early t r i a l s and only benefits f o r l a t e t r i a l s . Again, no interactions were observed with the Group factor. Because of the lack of any e f f e c t s involving Group, the cost benefit analyses w i l l not be pursued further. I t appears that the difference i n endogenous orie n t i n g observed using v a l i d - i n v a l i d differences i s not confined s o l e l y e i t h e r to costs or benefits. Presumably the group difference can be a t t r i b u t e d to influences on both processes, but ones too small to be detected i n the present study. Discussion Experiment 2 was intended as a conceptual r e p l i c a t i o n of Experiment 1, with some additional controls included to permit unequivocal int e r p r e t a t i o n of the r e s u l t s i n terms of the component processes underlying the control of attention. The r e s u l t s were generally i n l i n e with those of Experiment 1. Analysis of early t r i a l s revealed no consistent group differences, and only a single, unpredicted, and t h e o r e t i c a l l y opaque i n t e r a c t i o n involving group was observed on neutral t r i a l s . These r e s u l t s strongly support the contention that exogenous orienting of attention function i n an equivalent manner i n the two groups. Experiment 1 l e f t open the p o s s i b i l i t y that group -70-d i f f e r e n c e s on l a t e t r i a l s c o u l d have emerged as a r e s u l t o f d i f f e r e n c e s i n the magnitude of i n h i b i t i o n , s i n c e the v a l i d -i n v a l i d RT d i f f e r e n c e a t l a t e SOAs c o u l d p o t e n t i a l l y i n c l u d e the o p p o s i t e i n f l u e n c e s of f a c i l i t a t i o n and i n h i b i t i o n . S i m i l a r l y the i n v a l i d - d o u b l e cued RT d i f f e r e n c e s used i n experiment 1 compared response times t o t a r g e t s a t a p r e v i o u s l y uncued l o c a t i o n and a t the same l o c a t i o n cued p h y s i c a l l y (by b r i g h t e n i n g ) but not s p a t i a l l y (both t a r g e t l o c a t i o n s b r i g h t e n e d ) , thereby t h e o r e t i c a l l y measuring o n l y the development of i n h i b i t i o n . However, i n the former c o n d i t i o n , a d i f f e r e n t l o c a t i o n had been cued, i n d u c i n g o r i e n t i n g t o another l o c a t i o n , and p o s s i b l y confounding the magnitude of o r i e n t i n g t o t h i s o t h e r l o c a t i o n w i t h the measurement of i n h i b i t i o n . In the p r e s e n t experiment, t h i s confounding was c o m p l e t e l y removed i n two ways. F i r s t , by the use of a s y m b o l i c a l l y cued c o n d i t i o n , i n which no i n h i b i t i o n should be p r e s e n t . Second, by comparing two types of n e u t r a l cues, n e i t h e r of which p r o v i d e d s p a t i a l i n f o r m a t i o n . These two comparisons p r o v i d e d two ways t o t e s t whether the groups d i f f e r e d i n the development of i n h i b i t i o n . In the f i r s t i n s t a n c e , a s i g n i f i c a n t Group X Cue Type X Cue v a l i d i t y i n t e r a c t i o n would have been i n t e r p r e t a b l e as i n d i c a t i n g t h a t the two groups d i f f e r e d i n the development of i n h i b i t i o n . The second comparison, of n e u t r a l t r i a l s , measured o n l y the development of i n h i b i t i o n , uncontaminated by f a c i l i t a t i o n . A s i g n i f i c a n t Group X Cue Type i n t e r a c t i o n here -71-would a l s o have been a t t r i b u t a b l e t o group d i f f e r e n c e s i n i n h i b i t i o n . In n e i t h e r case was t h e r e any evidence f o r a d i f f e r e n c e between the groups i n the magnitude of i n h i b i t i o n . A n u l l r e s u l t must always be i n t e r p r e t e d w i t h c a u t i o n , s i n c e i t may r e s u l t p u r e l y from a l a c k of power. In the p r e s e n t i n s t a n c e , a f a i l u r e t o f i n d d i f f e r e n c e s i n i n h i b i t i o n on n e u t r a l t r i a l s was accompanied by a s i g n i f i c a n t e f f e c t of Cue type, showing t h a t i n h i b i t i o n d i d indeed develop f o r both groups. S i m i l a r l y , group d i f f e r e n c e s i n o r i e n t i n g a f t e r s p a t i a l l y cued l a t e t r i a l s were s t a t i s t i c a l l y s i g n i f i c a n t , a l though the i n t e r a c t i o n w i t h Cue Type was not. T h i s suggests t h a t a t b e s t any group d i f f e r e n c e s i n i n h i b i t i o n were s m a l l i n magnitude r e l a t i v e t o d i f f e r e n c e s i n endogenous o r i e n t i n g . In f a c t , examination of the mean RTs f o r the n e u t r a l t r i a l s shown i n F i g u r e 12 r e v e a l s what appears t o be s l i g h t l y g r e a t e r i n h i b i t i o n a t the 650 msec SOA i n the p s y c h o p a t h i c group than i n the nonpsychopaths. Although not s t a t i s t i c a l l y r e l i a b l e , t h i s d i f f e r e n c e i s i n the o p p o s i t e d i r e c t i o n t o t h a t expected i f i n h i b i t i o n were t o be used t o account f o r the d i f f e r e n c e s seen a f t e r d i r e c t i o n a l c u i n g . What t h i s means i s t h a t the magnitude of the endogenous o r i e n t i n g d i f f e r e n c e s observed between the groups i n experiments 1 and 2 may have been underestimated due t o the c o n c u r r e n t l y g r e a t e r i n h i b i t i o n o c c u r r i n g a f t e r p e r i p h e r a l c u i n g . Future r e s e a r c h s h o u l d aim t o examine t h i s p o s s i b l e d i f f e r e n c e i n i n h i b i t i o n f u r t h e r by -72-i n c l u d i n g a g r e a t e r number of s p a t i a l l y n o n - i n f o r m a t i v e t r i a l s than were i n c l u d e d here t o p r o v i d e a more r e l i a b l e e s t i m a t e of i n h i b i t i o n . In t h i s experiment, u n l i k e experiment 1, the group d i f f e r e n c e i n o r i e n t i n g was r e s t r i c t e d t o 1000 msecs SOA. Although the v a l i d i t y o f the cue i n the two experiments was approximately equal o v e r a l l , the v a l i d i t i e s o f e a r l y and l a t e t r i a l s were not. S p e c i f i c a l l y , 80% and 50% v a l i d i t i e s f o r e a r l y and l a t e t r i a l s r e s p e c t i v e l y i n experiment 1 were changed t o 69% v a l i d i t i e s f o r a l l t r i a l s i n experiment 2. The change i n the r e s u l t s f o r the 650 msec SOA i n the two experiments c o u l d t h e r e f o r e have r e s u l t e d from the i n d u c t i o n o f d i f f e r e n t e x p e c t a n c i e s i n the two s t u d i e s . In a d d i t i o n , the use of o n l y a s i n g l e e a r l y SOA (at 100 msecs) i n Experiment 2 may have a l t e r e d the g e n e r a l a l e r t i n g p r o p e r t i e s o f t h e cues i n a way t h a t i n t e r a c t e d w i t h group membership t o equate o r i e n t i n g a t 650 msecs. I t i s apparent from F i g u r e s 8 and 9 t h a t t h e r e were no o v e r a l l group d i f f e r e n c e s i n RT a c r o s s SOAs. Both groups demonstrated the expected r e d u c t i o n i n RT a t l o n g e r SOAs. We might conclude t h e r e f o r e t h a t the e f f e c t s o f changing the number or l o c a t i o n of SOAs i n t h i s type of paradigm are l i k e l y t o be r e l a t i v e l y s u b t l e and s p e c i f i c . N e v e r t h e l e s s , evidence f o r the o v e r a l l o c a t i o n of a t t e n t i o n t o the cued l o c a t i o n by psychopaths was agai n forthcoming. -73-Exper intent 3 Experiment 3, was designed t o p r o v i d e measures of i n t e r f e r e n c e , h a b i t u a t i o n of i n t e r f e r e n c e , and n e g a t i v e p r i m i n g (see T a b l e I ) . The d e s i g n was based on t h a t of T i p p e r e t a l . (1989) . There are s e v e r a l ways i n which any one o f t h e s e p r o c e s s e s might c o n t r i b u t e t o more e f f i c i e n t s e l e c t i o n , and hence t o the appearance of o v e r - f o c u s s i n g i n psychopaths. Less i n t e r f e r e n c e from a d i s t r a c t i n g s t i m u l u s would c e r t a i n l y improve s e l e c t i o n . However, p r e v i o u s unpublished r e s e a r c h u s i n g the s t a n d a r d s t r o o p paradigm found t h a t i n t e r f e r e n c e d i d not d i f f e r f o r psychopaths and nonpsychopaths (see Hare, 1984). The p r e s e n t experiment used a s l i g h t l y d i f f e r e n t paradigm t o t h a t of Hare, i n which RT i s measured on each t r i a l r a t h e r than c u m u l a t i v e l y over a l i s t o f items. The p r e s e n t methodology may prove more s e n s i t i v e , but i t would n e v e r t h e l e s s be s u r p r i s i n g t o f i n d r e s u l t s s h a r p l y a t odds w i t h t h i s p r e v i o u s work. An a l t e r n a t i v e mechanism f o r o v e r - f o c u s s i n g c o u l d be a more r a p i d development of h a b i t u a t i o n , l e a d i n g t o l e s s i n t e r f e r e n c e f o r repeated d i s t r a c t o r s . Hare (1968) has r e p o r t e d t h a t , i f anything, psychopaths h a b i t u a t e l e s s q u i c k l y than do nonpsychopaths. However, t h i s c o n c l u s i o n was based on the h a b i t u a t i o n of autonomic responses, which may be under q u i t e d i f f e r e n t c o n t r o l from t h a t f o r c o g n i t i v e mechanisms. F i n a l l y , the magnitude of n e g a t i v e p r i m i n g i s g e n e r a l l y -74-i n v e r s e l y r e l a t e d t o the magnitude of i n t e r f e r e n c e e f f e c t s ( T i p p e r & B a y l i s , 1987; T i p p e r e t a l . , 1989) a l t h o u g h the two can be d i s s o c i a t e d ( D r i v e r & T i p p e r , 1989). I n d i v i d u a l d i f f e r e n c e s i n the e f f i c i e n c y of s e l e c t i o n have been l i n k e d t o d i f f e r e n c e s i n the s t r e n g t h of i n h i b i t o r y p r o c e s s e s i n c h i l d r e n ( T i p p e r e t a l . , 1989), i n s u b j e c t s showing f r e q u e n t f a i l u r e s i n everyday use of s e l e c t i v e a t t e n t i o n ( T i p p e r & B a y l i s , 1987), and i n s c h i z o p h r e n i c s (Beech, Powell, McWilliams, & C l a r i d g e , 1989). I t i s p l a u s i b l e , t h e r e f o r e , t o c o n s i d e r t h i s as a p o s s i b l e mechanism u n d e r l y i n g e f f i c i e n t s e l e c t i o n i n psychopaths a l s o . The magnitude of each of these p r o c e s s e s was assessed by comparing RTs t o the d i f f e r e n t c o n d i t i o n s d e s c r i b e d below. The d i r e c t i o n of the p r e d i c t e d group d i f f e r e n c e s , based on the assumption t h a t psychopaths w i l l show enhanced s e l e c t i o n , are shown i n T a b l e I. S u b j e c t s The a n a l y s e s d e s c r i b e d below were based on d a t a from 19 nonpsychopaths and 17 psychopaths. The remaining 4 s u b j e c t s were omitted because they c o r r e c t l y i d e n t i f i e d the s e q u e n t i a l r e l a t i o n s h i p between t r i a l s i n the n e g a t i v e p r i m i n g c o n d i t i o n (see p.xx). With t h i s knowledge s u b j e c t s were a b l e t o a n t i c i p a t e c o r r e c t l y the forthcoming t a r g e t , p r o v i d i n g i n v a l i d d a t a i n t h i s c o n d i t i o n . -75-Desiqn The s u b j e c t s ' t a s k was t o i d e n t i f y the c o l o u r o f t h e l e t t e r s i n which words appeared on the c o l o u r monitor (the t a r g e t c o l o u r ) . The c o l o u r s r e d , green, b l u e , and y e l l o w were used and f o u r response keys on t h e Compaq computer keyboard were i d e n t i f i e d by tape of the co r r e s p o n d i n g c o l o u r s . S u b j e c t s ' RT t o respond t o the key co r r e s p o n d i n g t o t h e c o l o u r on the sc r e e n was measured. L i s t s o f s t i m u l i c o n s i s t i n g of the words "RED", GREEN", "BLUE", and "YELLOW", or of rows of Xs, were prepared a c c o r d i n g t o the p r i n c i p l e s d e s c r i b e d below f o r the f o u r c o n d i t i o n s i n v e s t i g a t e d . The c o l o u r words s p e l l e d by the l e t t e r s c o n s t i t u t e i n t e r f e r i n g s t i m u l i , and are r e f e r r e d t o as d i s t r a c t o r c o l o u r s . The f o u r c o n d i t i o n s i n v e s t i g a t e d were: 1) N e u t r a l c o n d i t i o n : items on the s c r e e n c o n s i s t e d o f rows of Xs w i t h from t h r e e t o s i x X's per d i s p l a y , p r e s e n t e d i n d i f f e r e n t t a r g e t c o l o u r s . 2) Stroop I n t e r f e r e n c e c o n d i t i o n : items on the s c r e e n were c o l o u r words c o n f l i c t i n g w i t h the t a r g e t c o l o u r on t h a t t r i a l . There was no r e l a t i o n s h i p between s u c c e s s i v e items, except t h a t sequences i n d u c i n g h a b i t u a t i o n or n e g a t i v e p r i m i n g were excluded. 3) Stroop H a b i t u a t i o n c o n d i t i o n : Each item i n the l i s t was the same c o l o u r word presented r e p e a t e d l y , but i n v a r y i n g c o l o u r s (a repeated d i s t r a c t o r ) . On most t r i a l s t h i s word -76-c o n f l i c t e d w i t h the t a r g e t c o l o u r , although the t a r g e t c o l o u r and the d i s t r a c t o r c o l o u r were i d e n t i c a l on one q u a r t e r o f the t r i a l s . 4) Stroop Negative Pr i m i n g c o n d i t i o n : Each item i n the l i s t was a c o l o u r word which c o n f l i c t e d w i t h the c u r r e n t t a r g e t c o l o u r . However, the c u r r e n t t a r g e t c o l o u r was always i d e n t i c a l t o the d i s t r a c t o r c o l o u r on the p r e v i o u s t r i a l . Two d i f f e r e n t randomly ordered l i s t s o f s t i m u l i were prepared f o r each c o n d i t i o n . For C o n d i t i o n s 1, 2, and 4 each l i s t c o n s i s t e d of 40 items pr e s e n t e d s e q u e n t i a l l y as a b l o c k of 40 t r i a l s . B l o c k s 1-4 c o n s i s t e d o f one l i s t from each of the f o u r c o n d i t i o n s . Choice o f which l i s t from each c o n d i t i o n was pre s e n t e d f i r s t was randomized a c r o s s s u b j e c t s . B l o c k s 5-8 c o n s i s t e d o f the remaining 4 l i s t s . The or d e r o f p r e s e n t a t i o n of the f o u r c o n d i t i o n s was randomized a c r o s s s u b j e c t s i n Blocks 1-4, and the order of p r e s e n t a t i o n of c o n d i t i o n s i n B l o c k s 5-8 was always the r e v e r s e of t h a t i n Bl o c k s 1-4. Data from the f i r s t f o u r t r i a l s o f each b l o c k were d i s c a r d e d . In C o n d i t i o n s 1, 2, and 4, each of the c o l o u r s appeared e q u a l l y o f t e n f o r the remaining 36 t r i a l s o f each b l o c k . In c o n d i t i o n 3, because the same d i s t r a c t o r c o l o u r was used throughout, i n t e r f e r e n c e c o u l d o n l y be asse s s e d when the t a r g e t c o l o u r was one of the t h r e e remaining c o l o u r s . T h e r e f o r e , t o ensure t h a t estimates o f h a b i t u a t i o n were based on approximately equal numbers of t r i a l s as i n the o t h e r -77-c o n d i t i o n s , each b l o c k c o n s i s t e d of 52 t r i a l s , o f which the f i r s t f o u r were agai n d i s c a r d e d , 12 were t r i a l s on which t h e t a r g e t and d i s t r a c t o r were i d e n t i c a l , and 36 were used t o measure h a b i t u a t i o n of i n t e r f e r e n c e . Procedure Words were pre s e n t e d s i n g l y a t f i x a t i o n , on a b l a c k background, i n the c e n t r e of the s c r e e n . They remained on the s c r e e n u n t i l the s u b j e c t responded, and the next t r i a l began 1500 msecs a f t e r the s u b j e c t ' s response. The words or Xs subtended from 1.1° of v i s u a l angle f o r 3 l e t t e r s t o 2.3° of v i s u a l angle f o r 6 l e t t e r s , h o r i z o n t a l l y . The l e t t e r s subtended approximately 0.5° v e r t i c a l l y . S u b j e c t s were asked t o respond t o the c o l o u r by p r e s s i n g one of the computer keyboard keys Z, C, B, or M which were l a b e l l e d by b l u e , green y e l l o w and r e d c o l o u r e d tape r e s p e c t i v e l y , u s i n g the f i r s t two f i n g e r s o f each hand. R e a c t i o n time was reco r d e d t o the n e a r e s t m i l l i s e c o n d and was s t o r e d f o r l a t e r a n a l y s i s . I n i t i a l l y , s u b j e c t s were g i v e n a b l o c k of p r a c t i c e t r i a l s t o a l l o w them t o l e a r n which key corresponded t o which c o l o u r . These t r i a l s were i d e n t i c a l t o those of the main experiment except t h a t r e c t a n g u l a r b l o c k s of c o l o u r appeared on the scre e n and s u b j e c t s were r e q u i r e d t o p r e s s the c o r r e s p o n d i n g key as q u i c k l y as p o s s i b l e . F o r t y p r a c t i c e t r i a l s were g i v e n , and the p r a c t i c e s e t was repeated f o r a few s u b j e c t s who c o n t i n u e d t o make e x c e s s i v e e r r o r s on the f i r s t s e t . A l l s u b j e c t s were responding a c c u r a t e l y on the p r a c t i c e t r i a l s p r i o r t o commencing the experiment. Each b l o c k of t r i a l s was i n i t i a t e d by the experimenter when the s u b j e c t i n d i c a t e d t h a t he was ready, and was t e r m i n a t e d upon completion of e i t h e r 40 or 52 t r i a l s . In g e n e r a l s u b j e c t s performed the b l o c k s w i t h o n l y a s h o r t break between each, but a lo n g e r break was g i v e n (2-3 minutes) p r i o r t o commencing b l o c k s 5-8. However, s u b j e c t s were encouraged t o pace themselves as they saw f i t f o r o p t i m a l performance, and were f r e e t o take l o n g e r breaks i f d e s i r e d . I n s t r u c t i o n s emphasizing both speed and accuracy were re p e a t e d b e f o r e b e g i n n i n g each b l o c k , and g e n e r a l feedback c o n c e r n i n g both speed and accuracy was g i v e n by the experimenter a t the end of each b l o c k . Data A n a l y s i s Median RTs ( f o r c o r r e c t t r i a l s only) and number of c o r r e c t responses were c a l c u l a t e d s e p a r a t e l y f o r each b l o c k . Accuracy and RT data were submitted t o 3-way ANOVAs w i t h Group (P, NP) as a between-subjects f a c t o r and Block (1-4, 5-8) and C o n d i t i o n ( C o n t r o l , H a b i t u a t i o n , I n t e r f e r e n c e , Negative Priming) as w i t h i n - s u b j e c t s f a c t o r s . Where e f f e c t s i n v o l v i n g r e p e a t e d measures were s i g n i f i c a n t and the assumption o f s p h e r i c i t y was not t e n a b l e , Greenhouse-Geisser c o r r e c t e d degrees of freedom were used t o determine the s i g n i f i c a n c e o f the e f f e c t s . -79-R e s u l t s R e a c t i o n time and accuracy f o r each group, b l o c k and c o n d i t i o n are shown i n F i g s 15 and 16. A n a l y s e s of RT r e v e a l e d s i g n i f i c a n t main e f f e c t s f o r Block (F(l,34) = 35.39, p_<.001) and C o n d i t i o n (F(3,102) = 21.78, p_<.001) and a s i g n i f i c a n t B l o c k X C o n d i t i o n i n t e r a c t i o n (F(3,102) = 8.43, p_<.01). Anal y s e s f o r the simple main e f f e c t s f o r C o n d i t i o n were s i g n i f i c a n t f o r both Block 1 (F(3,102) = 29.31, p_<.01) and Block 2 (F(3,102) = 3.25, p_<.05). To e x p l o r e f u r t h e r the presence of the t h r e e a t t e n t i o n a l components of i n t e r e s t , t h r e e comparisons were made a c c o r d i n g t o the method of Dunnet (Glass & Hopkins, 1984) t o compare the C o n t r o l , the Stroop H a b i t u a t i o n and the Stroop Negative P r i m i n g c o n d i t i o n s w i t h the Stroop I n t e r f e r e n c e c o n d i t i o n . T h i s t e s t e d f o r the presence of i n t e r f e r e n c e , h a b i t u a t i o n of i n t e r f e r e n c e and n e g a t i v e p r i m i n g r e s p e c t i v e l y . For Block 1, a l l t h r e e comparisons were s i g n i f i c a n t (t(102) = 5.83, 4.05, and 2.61 r e s p e c t i v e l y , a l l ps<.05). For Block 2, however, a s i g n i f i c a n t e f f e c t was p r e s e n t f o r i n t e r f e r e n c e (t(102) = 2.52, P<.05), but not f o r h a b i t u a t i o n (t(102) =1.79) or n e g a t i v e p r i m i n g (t(102) = 0.04). F i g u r e 17 shows the magnitude of i n t e r f e r e n c e , h a b i t u a t i o n and n e g a t i v e p r i m i n g p r e s e n t f o r each group i n each b l o c k . P o s i t i v e v a l u e s i n d i c a t e the presence of each p r o c e s s . I t i s apparent t h a t a l l t h r e e p r o c e s s e s are v i s i b l e d u r i n g the f i r s t b l o c k of t r i a l s , and t h a t a l l t h r e e d i m i n i s h i n magnitude -80-850 800-CD 750-c o tj 700 to CD rr 650-600 I Si! CONTROL HABIT. STROOP NEG. PRI. Condition Grp NP, B1 HH G r P p . B 1 ^ Grp NP, B2 |ffg Grp P, B2 F i g u r e 15. Experiment 3: R e a c t i o n times f o r each group t o i d e n t i f y t a r g e t c o l o u r f o r f o u r c o n d i t i o n s i n each b l o c k 35.5 Grp P, B2 Figure 16. Experiment 3: Mean number of correct responses by-each group for four conditions i n each block -82-Fiqure 17. Experiment 3: The mean magnitude of interference, habituation and negative priming f o r each group i n each block -83-f o r the second b l o c k . Although f a i l i n g t o r e a c h s i g n i f i c a n c e , examination of the means f o r the second b l o c k suggests t h a t h a b i t u a t i o n of i n t e r f e r e n c e i s s t i l l apparent f o r both groups. The presence of n e g a t i v e p r i m i n g seems t o have been completely e l i m i n a t e d i n the second b l o c k , however. Such a r e d u c t i o n of n e g a t i v e p r i m i n g w i t h repeated t e s t i n g has not, t o my knowledge, been r e p o r t e d elsewhere i n the l i t e r a t u r e . As i s apparent from F i g u r e s 15 and 17, any d i f f e r e n c e s between the groups were t r i v i a l i n a l l f o u r c o n d i t i o n s and i n both b l o c k s . The l a r g e s t F f o r any e f f e c t i n v o l v i n g the Group f a c t o r was 0.08. A n a l y s i s of number of c o r r e c t responses r e v e a l e d o n l y one s i g n i f i c a n t e f f e c t , f o r Block (F(l,34) = 5.50, p_<.03). Both groups were more a c c u r a t e f o r the second b l o c k than the f i r s t . Comparison of F i g u r e s 15 and 16 w i l l r e v e a l t h a t f o r both groups, t h e r e was a g e n e r a l tendency f o r f a s t e r responses i n one c o n d i t i o n a l s o t o be more a c c u r a t e . T h i s suggests t h a t d i f f e r e n t t r a d e o f f s between speed and accuracy are u n l i k e l y t o have c o n t r i b u t e d t o the d i f f e r e n t RTs observed i n t h i s experiment. W i t h i n each c o n d i t i o n and b l o c k , the c o r r e l a t i o n s between number c o r r e c t and RT were g e n e r a l l y n e g a t i v e or n o n s i g n i f i c a n t l y p o s i t i v e , a g a i n s u g g e s t i n g l i t t l e i n f l u e n c e of speed-accuracy t r a d e o f f s i n these data. -84-D i s c u s s i o n Experiment 3 p r o v i d e d measures of t h r e e components of a t t e n t i o n not assessed by the v i s u a l o r i e n t i n g s t u d i e s used p r e v i o u s l y . Components of a t t e n t i o n measured here have been shown t o be d i s s o c i a b l e i n s t u d i e s of c h i l d r e n and s c h i z o p h r e n i c s . In the p r e s e n t experiment no evidence was found t h a t psychopaths d i f f e r from nonpsychopaths on any of t h e s e components. The f o u r c o n d i t i o n s used i n the experiment were a l l s i g n i f i c a n t l y d i f f e r e n t i a t e d from one another, a t l e a s t on the f i r s t b l o c k of t r i a l s , s u g g e s t i n g t h a t the m a n i p u l a t i o n m o b i l i z e d these a t t e n t i o n a l p r o c e s s e s e f f e c t i v e l y . T h i s i s an important f i n d i n g i n a number of ways. F i r s t , i t was observed on the same sample of s u b j e c t s who demonstrated the v i s u a l o r i e n t i n g d i f f e r e n c e s i n Experiment 2. T h i s h i g h l i g h t s the s p e c i f i c i t y o f the group d i f f e r e n c e we are examining and p r o v i d e s f u r t h e r j u s t i f i c a t i o n f o r the assumption, i m p l i c i t i n the d e s i g n of t h i s and r e l a t e d r e s e a r c h , t h a t d i f f e r e n t components of a t t e n t i o n are d i s s o c i a b l e and must be examined s e p a r a t e l y i n s t u d i e s of abnormal a t t e n t i o n a l f u n c t i o n i n g . Second, the e q u a l i t y of group performance on t h i s t a s k emphasizes the f a c t t h a t psychopaths do not have a g e n e r a l a t t e n t i o n a l or performance d e f i c i t . T h i r d , the p r e s e n t r e s u l t p r o v i d e s evidence t h a t the i n f o r m a t i o n p r o c e s s i n g a b n o r m a l i t i e s of psychopaths are i n one way d i s t i n c t from those of s c h i z o p h r e n i c p a t i e n t s , who have -85-been shown t o be d e f i c i e n t i n n e g a t i v e p r i m i n g i n a s i m i l a r s t r o o p t a s k (Beech e t a l . , 1989). Such a r e s u l t p r o v i d e s f u r t h e r evidence, a t the i n f o r m a t i o n - p r o c e s s i n g l e v e l , f o r the d i f f e r e n t i a t i o n of psychopaths from s c h i z o p h r e n i c s , a d i s t i n c t i o n t h a t some t h e o r e t i c i a n s seem r e l u c t a n t t o make (e.g. Eysenck & Gudjonsson, 1989; Eysenck, 1978). Experiment 4 One d i f f e r e n c e between the s p a t i a l o r i e n t i n g s t u d i e s of Experiments 1 and 2 and the study of i n t e r f e r e n c e i n Experiment 3 was the f a i l u r e o f the l a t t e r t o r e q u i r e any s p a t i a l o r i e n t i n g . Experiment 4 examined i n t e r f e r e n c e and n e g a t i v e pr i m i n g , but i n the s p a t i a l domain. The l i n g u i s t i c nature of the s t r o o p t a s k means t h a t the mechanisms c o n t r o l l i n g a t t e n t i o n i n t h i s s i t u a t i o n may not g e n e r a l i z e t o o t h e r c o n t e x t s . T i p p e r e t a l . (1990) have r e c e n t l y demonstrated t h a t the development of i n h i b i t i o n apparent i n n e g a t i v e p r i m i n g appears t o be c e n t r e d on the o b j e c t b e i n g ignored, r a t h e r than on the l o c a t i o n of the o b j e c t . T h i s i n h i b i t i o n can s t i l l be seen even i f the o b j e c t appears t o move and i s next p r e s e n t e d a t a d i f f e r e n t environmental and r e t i n a l l o c a t i o n . T i p p e r (1990) has a l s o c l a i m e d t h a t o b j e c t - c e n t r e d i n h i b i t i o n t e s t e d s p a t i a l l y d i f f e r s fundamentally from the i n h i b i t i o n seen i n language based i d e n t i f i c a t i o n p r o c e s s e s . He examined the performance of c h i l d r e n on a t a s k which r e q u i r e d them t o s e l e c t a t a r g e t on the b a s i s of i t s i d e n t i t y , and then t o respond t o the l o c a t i o n -86-of the t a r g e t . Note t h a t most s e l e c t i o n t a s k s r e q u i r e the o p p o s i t e , t h a t i s s e l e c t i o n on the b a s i s o f l o c a t i o n and then responses determined by the i d e n t i t y of the o b j e c t a t t h a t l o c a t i o n . As d i s c u s s e d above (T i p p e r e t a l . , 1990), a d u l t s show evidence of both i n t e r f e r e n c e and n e g a t i v e p r i m i n g on t h i s t a s k . C h i l d r e n of 5-6 y ears a l s o show thes e e f f e c t s , but s i g n i f i c a n t l y they showed no g r e a t e r i n t e r f e r e n c e and no l e s s n e g a t i v e p r i m i n g e f f e c t s than d i d a d u l t s ( T i p p e r , 1990). P r e v i o u s work by T i p p e r e t a l . (1989) has shown t h a t on a s t r o o p t a s k young c h i l d r e n showed g r e a t e r i n t e r f e r e n c e and l e s s i n h i b i t i o n than do a d u l t s . T i p p e r e x p l a i n s t h e d i s c r e p a n c y between these two r e s u l t s i n terms of the d i f f e r i n g e c o l o g i c a l v a l i d i t y of the two t a s k s , and the consequent p r a c t i c e c h i l d r e n w i l l have had w i t h one, r a t h e r than the o t h e r . S e l e c t i o n on the b a s i s of o b j e c t i d e n t i t y , f o l l o w e d by a manual response t o the l o c a t i o n of t h a t o b j e c t , i s the most common and n a t u r a l way i n which s t i m u l i c o n t r o l our behaviour. A c c o r d i n g t o T i p p e r (1990), "manual responses t o the s p a t i a l l o c u s of a s t i m u l u s are an example of a ' p r i v i l e g e d l o o p ' (Posner & McLeod, 1984) devoted t o s p e c i f i c s o r t s of i n p u t - o u t p u t t r a n s f o r m a t i o n s " (p. 206) . I f t h i s d i s t i n c t i o n i s v a l i d , i t r a i s e s the i n t e r e s t i n g p o s s i b i l i t y t h a t d i f f e r e n c e s i n mechanisms of s e l e c t i v e a t t e n t i o n i n psychopaths may be r e s t r i c t e d t o e i t h e r language p r o c e s s e s , as t e s t e d i n experiment 3, or t o v i s u o s p a t i a l - m a n u a l -87-t a s k s as t e s t e d i n experiment 4. The experiment was modelled on t h a t of T i p p e r e t a l . (1990), and r e q u i r e d manual responses t o i n d i c a t e the l o c a t i o n of a t a r g e t c h a r a c t e r , e i t h e r i n t h e presence or absence of a d i s t r a c t o r c h a r a c t e r . Each t r i a l c o n s i s t e d of a prime d i s p l a y f o l l o w e d by a probe d i s p l a y w i t h s u b j e c t s responding t o the presence of a t a r g e t i n each d i s p l a y . I n t e r f e r e n c e was a s s e s s e d by comparing RTs t o t a r g e t s p r e s e n t e d i n the prime d i s p l a y e i t h e r i n the presence or the absence of an i r r e l e v a n t d i s t r a c t o r . I n h i b i t i o n was measured by comparing RTs t o t a r g e t s i n the probe d i s p l a y e i t h e r when they occur a t a l o c a t i o n which was blank on the p r e v i o u s t r i a l , or a t a l o c a t i o n which was p r e v i o u s l y i g n o r e d . S u b j e c t s Data f o r t h i r t y - n i n e s u b j e c t s was i n c l u d e d f o r a n a l y s i s i n t h i s experiment. Data from one s u b j e c t (a psychopath) was excluded because of unacceptably low accuracy i n c e r t a i n c o n d i t i o n s (see below). Design The d e s i g n of the experiment was intended t o a l l o w measurement of i n t e r f e r e n c e from a d i s t r a c t i n g s t i m u l u s as w e l l as n e g a t i v e p r i m i n g a f t e r i n h i b i t i o n of a d i s t r a c t i n g s t i m u l u s a t a g i v e n s p a t i a l l o c a t i o n . Measurement of t h e s e p r o c e s s e s was a c h i e v e d by the s e q u e n t i a l p r e s e n t a t i o n of two d i s p l a y s on each t r i a l , w i t h s u b j e c t s responding t o the l o c a t i o n o f a t a r g e t s t i m u l u s i n each d i s p l a y . The i n t r o d u c t i o n of a d i s t r a c t o r -88-s t i m u l u s on the f i r s t d i s p l a y p r o v i d e d a measurement of i n t e r f e r e n c e . Placement of the t a r g e t s t i m u l u s i n t h e second d i s p l a y a t a l o c a t i o n t h a t had h e l d the d i s t r a c t o r s t i m u l u s i n the f i r s t d i s p l a y allowed f o r the assessment o f n e g a t i v e p r i m i n g . Each t r i a l o f the experiment c o n s i s t e d o f two d i s p l a y s , a prime d i s p l a y f o l l o w e d by a probe d i s p l a y . S u b j e c t s were asked t o respond i n each d i s p l a y t o the s p a t i a l l o c a t i o n o f a t a r g e t (the s i g n "#") w h i l e i g n o r i n g the d i s t r a c t o r (the s i g n "&"). T a r g e t s and d i s t r a c t o r s appeared, white on a grey background, a t one of f o u r l o c a t i o n s . These l o c a t i o n s were marked by b l a c k columns which remained permanently on the scr e e n . Because the hea d r e s t was not used f o r t h i s study, v i s u a l a ngles g i v e n below are approximate. H o r i z o n t a l angles between the i n n e r edges o f the columns were approximately 3.2° f o r t he i n n e r two columns and 7.6° f o r the o u t e r two columns. The columns themselves subtended 0.9° of v i s u a l angle h o r i z o n t a l l y , and 3.9° v e r t i c a l l y . The two i n n e r columns were lower than the out e r two columns by approximately 1°. The t a r g e t and d i s t r a c t o r s t i m u l i subtended approximately .5° of v e r t i c a l and .4° of h o r i z o n t a l angle. In t he prime d i s p l a y the t a r g e t appeared d i r e c t l y above the top of one of the columns, approximately 1.3° from the top edge, and appeared t o move v e r t i c a l l y down towards the top of the column f o r about 200 msecs. When i t reached t h e edge of the -89-column, i t disappeared, g i v i n g the appearance o f p a s s i n g behind the o c c l u d i n g b l a c k column. I f p r e s e n t i n the prime d i s p l a y , the d i s t r a c t o r appeared i n the same way above a d i f f e r e n t column and moved a t the same r a t e . The i l l u s i o n o f movement was c r a t e d by p r e s e n t i n g the s t i m u l u s i n f o u r l o c a t i o n s f o r 50 msecs each, s h i f t i n g each s u c c e s s i v e l o c a t i o n by .33°, which r e s u l t e d i n an approximate v e l o c i t y o f 6.5°/sec. f o r the s t i m u l i . In the probe d i s p l a y , e i t h e r the t a r g e t , or the t a r g e t and the d i s t r a c t o r , reappeared a t the bottom of the d i s p l a y , a g a i n moving v e r t i c a l l y down. Three hundred and f i f t y msecs a f t e r the s u b j e c t had responded t o the probe d i s p l a y , the s t i m u l i reappeared c e n t r e d d i r e c t l y below the bottom edge of one (two i f the d i s t r a c t o r was present) of the columns. They moved f o r 200 msecs v e r t i c a l l y downward a t the same r a t e as i n the probe d i s p l a y , then vanished. S u b j e c t s responded t o both the prime and t h e probe d i s p l a y s w i t h a button p r e s s t o one of f o u r keys on the computer keyboard. Keys A, X, N, and K, marked w i t h tape, were used t o i n d i c a t e the l e f t outer, l e f t i n n e r , r i g h t i n n e r and r i g h t o u t e r l o c a t i o n s r e s p e c t i v e l y , and s u b j e c t s were asked t o respond t o the h o r i z o n t a l l o c a t i o n of the t a r g e t s t i m u l u s by p r e s s i n g the a p p r o p r i a t e key. Prime D i s p l a y s . The prime d i s p l a y s were of two t y p e s . In the No D i s t r a c t o r c o n d i t i o n (80 t r i a l s ) o n l y the t a r g e t -90-s t i m u l u s was presented. In the D i s t r a c t o r c o n d i t i o n (120 t r i a l s ) the t a r g e t and d i s t r a c t o r s t i m u l i appeared s i m u l t a n e o u s l y a t d i f f e r e n t l o c a t i o n s . The d i f f e r e n c e i n RT t o these two c o n d i t i o n s p r o v i d e d a measure of i n t e r f e r e n c e . Probe D i s p l a y s . The probe c o n d i t i o n s of t h e o r e t i c a l i n t e r e s t i n t h i s study always f o l l o w e d the D i s t r a c t o r c o n d i t i o n f o r the prime d i s p l a y . These t r i a l s were f u r t h e r d i v i d e d i n t o t h r e e c o n d i t i o n s i n the Probe d i s p l a y . In the C o n t r o l c o n d i t i o n (48 t r i a l s ) , both the t a r g e t and d i s t r a c t o r reappeared a t h o r i z o n t a l l o c a t i o n s d i f f e r e n t from those used i n the prime d i s p l a y . In the Ignored R e p e t i t i o n c o n d i t i o n (48 t r i a l s ) , the t a r g e t appeared a t the h o r i z o n t a l l o c a t i o n of the d i s t r a c t o r i n the prime d i s p l a y , a t the l o c a t i o n t h a t had presumably been i n h i b i t e d on the p r e v i o u s d i s p l a y . The d i s t r a c t o r a g a i n appeared a t a new l o c a t i o n . In the No S e l e c t i o n c o n d i t i o n (24 t r i a l s ) , no d i s t r a c t o r was p r e s e n t i n the probe d i s p l a y , and the t a r g e t appeared e i t h e r a t the p r e v i o u s l y i g n o r e d l o c a t i o n (12 t r i a l s ) or a t a d i f f e r e n t l o c a t i o n (12 t r i a l s ) . These t r i a l s i n the No S e l e c t i o n c o n d i t i o n corresponded t o the Ignored R e p e t i t i o n and C o n t r o l c o n d i t i o n s r e s p e c t i v e l y , but w i t hout the presence of a d i s t r a c t o r , a m a n i p u l a t i o n t h a t has been r e p o r t e d t o a b o l i s h n e g a t i v e p r i m i n g ( T i p p e r & Cranston, 1985). T h i s c o n d i t i o n c o u l d be t r e a t e d as an added c o n t r o l t o c o n f i r m t h a t any group d i f f e r e n c e s i n n e g a t i v e p r i m i n g found under c o n d i t i o n s of t a r g e t s e l e c t i o n were a b o l i s h e d when -91-s e l e c t i o n was unnecessary. I f t h i s were t o occur, t h e e f f e c t c o u l d be a t t r i b u t e d w i t h g r e a t e r c o n f i d e n c e t o d i f f e r e n c e s i n n e g a t i v e p r i m i n g . Although not of d i r e c t i n t e r e s t , t h e same t h r e e t r i a l s types o c c u r r e d w i t h s i m i l a r frequency on probe t r i a l s f o l l o w i n g No D i s t r a c t o r prime t r i a l s . Procedure A f t e r e x p l a i n i n g the t a s k t o the s u b j e c t s a b l o c k o f 50 p r a c t i c e t r i a l s was g i v e n t o f a m i l i a r i z e them w i t h the t a s k and t o a l l o w them t o p r a c t i c e p e r c e i v i n g the s w i f t l y moving s t i m u l i . They were i n s t r u c t e d t o respond as q u i c k l y and a c c u r a t e l y as p o s s i b l e t o the l o c a t i o n o f the t a r g e t s t i m u l u s by p r e s s i n g one of the f o u r response keys w i t h the f i r s t and second f i n g e r s o f each hand. Throughout the experiment i t was emphasized t h a t speed and accuracy were e q u a l l y important. F o l l o w i n g the p r a c t i c e s e s s i o n , s u b j e c t s completed f o u r b l o c k s o f 51 t r i a l s , w i t h a s h o r t break between b l o c k s . A l l c o n d i t i o n s were pre s e n t e d i n the same randomized o r d e r t o a l l s u b j e c t s , and w i t h i n each c o n d i t i o n , t a r g e t s and d i s t r a c t o r s appeared e q u a l l y o f t e n a t a l l l o c a t i o n s . Data A n a l y s i s The f i r s t t r i a l from each b l o c k was omitted from a n a l y s i s . For the remaining t r i a l s , f o r each s u b j e c t , median RTs were c a l c u l a t e d , f o r c o r r e c t responses on l y , i n the d i s t r a c t o r and no d i s t r a c t o r c o n d i t i o n s f o r the prime d i s p l a y , and f o r the c o n t r o l , the ign o r e d r e p e t i t i o n and the two no s e l e c t i o n -92-c o n d i t i o n s i n the probe d i s p l a y . In the probe d i s p l a y , o n l y t r i a l s f o l l o w i n g a c o r r e c t response on the prime d i s p l a y were c o n s i d e r e d f o r a n a l y s i s . As a r e s u l t , t he number o f t r i a l s on which the probe data were based was s l i g h t l y d i f f e r e n t f o r each s u b j e c t . For t h i s reason the p r o p o r t i o n o f c o r r e c t t r i a l s was used i n p l a c e o f the t o t a l number c o r r e c t as a measure of accuracy. For both accuracy and RT data, s e p a r a t e ANOVAs were c a l c u l a t e d f o r prime and probe d i s p l a y s . In the former the f a c t o r s o f Group (P,NP), and C o n d i t i o n ( D i s t r a c t o r , No D i s t r a c t o r ) were i n c l u d e d , t e s t i n g the e f f e c t s o f i n t e r f e r e n c e . For the l a t t e r , n e g a t i v e p r i m i n g was measured by comparing C o n t r o l and Ignored R e p e t i t i o n c o n d i t i o n s . So a s i m i l a r 2-way ANOVA was performed f o r these data. A supplementary a n a l y s i s was performed on the data from the No S e l e c t i o n c o n d i t i o n , comparing the C o n t r o l and Ignored R e p e t i t i o n t r i a l s under c o n d i t i o n s which d i d not r e q u i r e s e l e c t i o n . One s u b j e c t performed so i n a c c u r a t e l y i n the presence o f the d i s t r a c t o r i n both the prime and the probe d i s p l a y s t h a t h i s d ata c o u l d not be i n c l u d e d as a v a l i d measure of i n t e r f e r e n c e or ne g a t i v e p r i m i n g . H i s accuracy, a l t h o u g h adequate f o r the c o n t r o l c o n d i t i o n i n the prime d i s p l a y , dropped t o 46% f o r the d i s t r a c t o r c o n d i t i o n (chance b e i n g 25%). T h i s l e f t o n l y 55 u s a b l e t r i a l s f o r a n a l y s i s i n the probe d i s p l a y , o f which he a c c u r a t e l y i d e n t i f i e d 36% (8 t r i a l s ) and -93-32% (7 t r i a l s ) i n the c o n t r o l and i g n o r e d r e p e t i t i o n c o n d i t i o n s . T h i s psychopath had, i t appears, a s e l e c t i v e i n a b i l i t y t o pr o c e s s any d i s p l a y s c o n t a i n i n g a d i s t r a c t o r , a l t h o u g h t h i s extreme i n t e r f e r e n c e e f f e c t was not apparent i n e i t h e r Experiment 3 or 5. The f a c t t h a t the s t i m u l i were pr e s e n t e d b r i e f l y and moving r a p i d l y may have c o n t r i b u t e d t o t h i s d e f i c i t , but the data c l e a r l y r e p r e s e n t e d an o u t l i e r from e i t h e r group and were t h e r e f o r e d i s c a r d e d . R e s u l t s The mean RT and percentage c o r r e c t f o r each group i n each c o n d i t i o n a re shown i n Tab l e I I . There was a s i g n i f i c a n t e f f e c t o f the d i s t r a c t o r i n the prime d i s p l a y ( F ( l,37) = 69.08, p_<.001), but no main e f f e c t s o r i n t e r a c t i o n w i t h group ( a l l F s < l ) . The presence of a d i s t r a c t o r slowed RT by 56 and 45 msecs f o r nonpsychopaths and psychopaths r e s p e c t i v e l y . I n t e r f e r e n c e was a l s o m a n i f e s t i n the accuracy data (F(l,37) = 27.23, p_<.001) where i t produced l e s s a c c u r a t e responding. A n a l y s i s of the probe d i s p l a y r e v e a l e d a s i g n i f i c a n t e f f e c t of n e g a t i v e p r i m i n g f o r RT (F(l,37) = 19.50, p_<.001) and accuracy (F(l,37) = 8.56, p_<.01). Both groups were slower (by 33 msecs f o r nonpsychopaths and 23 msecs f o r psychopaths) and l e s s a c c u r a t e i n the Ignored R e p e t i t i o n c o n d i t i o n , demonstrating the development of n e g a t i v e p r i m i n g , but t h e r e was no evidence f o r e i t h e r measure of a d i f f e r e n c e between the groups ( a l l F s < l ) . -94-Tab l e I I Mean of median r e a c t i o n times and percentage c o r r e c t responses i n Experiment 4 Group C o n d i t i o n Nonpsychopaths RT % C o r r e c t Psychopaths RT % C o r r e c t Prime D i s p l a y No D i s t r a c t o r D i s t r a c t o r 597 654 98.6 95.3 601 646 97.8 94.8 Probe D i s p l a y : S e l e c t i o n C o n t r o l 675 93.3 Ignored R e p e t i t i o n 708 91.7 643 665 93.5 90.8 Probe D i s p l a y : No S e l e c t i o n C o n t r o l 575 Ignored R e p e t i t i o n 629 97.0 99.1 580 99.1 633 94.9 -95-A n a l y s i s of the two types of No S e l e c t i o n t r i a l s i n the probe d i s p l a y was planned as a secondary check on the v a l i d i t y of our i n t e r p r e t a t i o n of group d i f f e r e n c e s i n the development of n e g a t i v e p r i m i n g . These d i f f e r e n c e s were expected t o d i s a p p e a r i n the absence of n e g a t i v e p r i m i n g i n the no s e l e c t i o n c o n d i t i o n . Although no group d i f f e r e n c e s i n n e g a t i v e p r i m i n g were observed under c o n d i t i o n s r e q u i r i n g s e l e c t i o n , the No S e l e c t i o n t r i a l s were n e v e r t h e l e s s a n a l y s e d . In c o n t r a s t t o T i p p e r & Cranston (1985), RT data showed a s i g n i f i c a n t e f f e c t of n e g a t i v e p r i m i n g (F(l,37) = 39.73, p_<.001), w i t h RT slowed by 54 and 53 msecs f o r the two groups. The e f f e c t , t h e r e f o r e , was not a b o l i s h e d on t r i a l s f o r which s e l e c t i o n was unnecessary; i n f a c t i t almost doubled i n magnitude. Once again, however, t h e r e was no evidence f o r any group d i f f e r e n c e s ( F s < l ) . No main e f f e c t s were observed f o r accuracy. However the Group X C o n d i t i o n i n t e r a c t i o n was s i g n i f i c a n t ( F ( l ,37) = 4.18, p_<.05). As shown i n T a b l e I I , Psychopaths were l e s s a c c u r a t e i n the Ignored D i s t r a c t o r c o n d i t i o n than i n the C o n t r o l c o n d i t i o n , whereas f o r nonpsychopaths the r e v e r s e was t r u e . T h i s r e s u l t must be i n t e r p r e t e d w i t h c o n s i d e r a b l e c a u t i o n , however. S u b j e c t s r e c e i v e d a t most 12 t r i a l s i n each of the No S e l e c t c o n d i t i o n s , i n some cases fewer due t o i n a c c u r a t e responding on the Prime d i s p l a y . Examination of the d i s t r i b u t i o n of accuracy s c o r e s r e v e a l e d an extremely skewed d i s t r i b u t i o n w i t h the m a j o r i t y of s u b j e c t s (76%) responding w i t h 100% accuracy. Only -96-two s u b j e c t s performed a t l e s s than 90% accuracy, one of these i d e n t i f y i n g o n l y 63% of l o c a t i o n s a c c u r a t e l y i n t h e No S e l e c t i o n - I g n o r e d r e p e t i t i o n c o n d i t i o n . Under the s e c o n d i t i o n s , the use of ANOVA i s u n j u s t i f i e d , and few c o n c l u s i o n s can be drawn from the data. For t h i s reason the e f f e c t i s not c o n s i d e r e d f u r t h e r . D i s c u s s i o n As i n Experiment 3, t h i s experiment y i e l d e d no evidence f o r group d i f f e r e n c e s i n e i t h e r n e g a t i v e p r i m i n g o r i n t e r f e r e n c e e f f e c t s , even though the p r e s e n t study used s p a t i a l p r i m i n g s i m i l a r t o t h a t used t o demonstrate group d i f f e r e n c e s i n o r i e n t i n g i n the f i r s t two experiments. One can conclude, t h e r e f o r e , t h a t the mechanisms u n d e r l y i n g endogenous o r i e n t i n g i n the f i r s t two s t u d i e s a re d i s t i n c t from those o p e r a t i n g t o s e l e c t among competing s t i m u l i i n t h e Experiments 3 and 4. The m a n i p u l a t i o n used i n t h i s study p r o v i d e d the expected p a t t e r n o f r e s u l t s f o r both i n t e r f e r e n c e and n e g a t i v e p r i m i n g , w i t h one e x c e p t i o n . T i p p e r & Cranston (1985) have r e p o r t e d t h a t removing the requirement t o s e l e c t among competing s t i m u l i a b o l i s h e s n e g a t i v e p r i m i n g . The p r e s e n t r e s u l t s demonstrate t h a t under c e r t a i n c o n d i t i o n s n e g a t i v e p r i m i n g can be observed i n t he absence of d i s t r a c t o r s t i m u l i . In many ways t h i s c o n c l u s i o n appears more reasonable than t h a t o f T i p p e r & Cranston. These authors proposed a response i n h i b i t i o n -97-h y p o t h e s i s t o account f o r the a b o l i t i o n o f n e g a t i v e p r i m i n g i n the absence of s e l e c t i o n on the probe d i s p l a y . T h i s account has been superseded by r e s e a r c h showing t h a t n e g a t i v e p r i m i n g i s not response s p e c i f i c , but operates c e n t r a l l y on t h e r e p r e s e n t a t i o n s of o b j e c t s ( T i p p e r e t a l . , 1988). T h e r e f o r e the problem of e x p l a i n i n g why i n h i b i t i o n i s absent when s e l e c t i o n f o r a p r e v i o u s l y i g n o r e d s t i m u l u s i s not r e q u i r e d remains. L o g i c a l l y , such a pro c e s s should be invoked upon p r e s e n t a t i o n of D i s p l a y 1, r e g a r d l e s s of the nature o f the D i s p l a y 2 which has y e t t o be presented. The p r e s e n t r e s u l t s o f f e r some evidence t h a t r o b u s t i n h i b i t o r y e f f e c t s can be observed without s e l e c t i o n , although i t remains t o be determined why i n h i b i t i o n was not found by T i p p e r & Cranston (1985) . Some doubt might be c a s t on t h i s c o n c l u s i o n by p o i n t i n g out t h a t a confound e x i s t s i n the s p a t i a l t a s k between i n h i b i t i o n r e s u l t i n g from n e g a t i v e p r i m i n g and i n h i b i t i o n r e s u l t i n g from i n h i b i t i o n of r e t u r n . I n h i b i t i o n o f r e t u r n , o f course, can be demonstrated i n the absence of any requirement t o s e l e c t among competing s t i m u l i , as was the case i n Experiments 1 and 2, l e a d i n g one t o expect the r e s u l t s f o r n e g a t i v e p r i m i n g t h a t are r e p o r t e d here. T i p p e r , D r i v e r , & Weaver ( i n press) have shown t h a t i n h i b i t i o n o f r e t u r n can be o b j e c t - c e n t r e d , i n t h a t i t can move w i t h a moving o b j e c t . In t h i s i n s t a n c e , then, i n h i b i t i o n o f r e t u r n induced by the -98-d i s t r a c t o r i n the prime d i s p l a y , may be r e t a r d i n g RTs t o the probe t a r g e t s appearing a t the d i s t r a c t o r ' s l o c a t i o n . Although the presence of i n h i b i t i o n o f r e t u r n i s a d i s t i n c t p o s s i b i l i t y i n t h i s paradigm, t h i s e x p l a n a t i o n f a i l s t o account f o r the i n c r e a s e i n magnitude of the i n h i b i t o r y e f f e c t from the s e l e c t i o n c o n d i t i o n . Presumably, under c o n d i t i o n s r e q u i r i n g s e l e c t i o n , i n h i b i t i o n of r e t u r n and n e g a t i v e p r i m i n g both c o n t r i b u t e t o slowed RTs. The absence of one of the s e p r o c e s s e s ought t o reduce t h i s i n h i b i t i o n somewhat. Experiment 5 Experiment 5 was designed t o examine t h e i n t e r a c t i o n of s p a t i a l s e l e c t i v i t y , i n t e r f e r e n c e and n e g a t i v e p r i m i n g and t o t e s t the g e n e r a l i t y of the f i n d i n g s from experiments 3 and 4 i n a d i f f e r e n t paradigm. E r i k s e n and E r i k s e n (1974) demonstrated t h a t the s p a t i a l p r o x i m i t y of d i s t r a c t o r s t i m u l i s t r o n g l y i n f l u e n c e d the amount of i n t e r f e r e n c e seen when s u b j e c t s had t o d i s c r i m i n a t e s t i m u l i p r e s e n t e d a t f i x a t i o n (the E r i k s e n e f f e c t ) . They argued t h a t the i n t e r f e r e n c e o c c u r r e d a t the stage of response s e l e c t i o n and was due t o the need t o i n h i b i t a competing response e l i c i t e d by the d i s t r a c t o r s t i m u l u s . Response s e l e c t i o n depends, however, on a c c u r a t e l o c a l i z a t i o n of the t a r g e t and d i s t r a c t o r s t i m u l i , and the more d i s c r i m i n a b l e the d i f f e r e n c e s i n l o c a t i o n i n the d i s p l a y , the f a s t e r w i l l be the s e l e c t i o n p r o c e s s . U s i n g s i m i l a r paradigms D r i v e r & T i p p e r (1989) have shown -99-t h a t t h e s e i n t e r f e r e n c e e f f e c t s are not the r e s u l t of a f a i l u r e t o i d e n t i f y more d i s t a n t d i s t r a c t o r s , but must be a t t r i b u t e d t o the ease w i t h which s u b j e c t s can d i s c r i m i n a t e s p a t i a l l o c a t i o n . In t h e s e s t u d i e s n e g a t i v e p r i m i n g of equal magnitude was o b t a i n e d whether or not i n t e r f e r e n c e was observed (see a l s o T i p p e r e t a l . , 1988). T h i s d i s s o c i a t i o n o f n e g a t i v e p r i m i n g and i n t e r f e r e n c e suggests t h a t the mechanisms u n d e r l y i n g t h e s e two p r o c e s s e s are not i d e n t i c a l , even though they have been shown t o covary i n a number of s t u d i e s (e.g. T i p p e r & B a y l i s , 1987; T i p p e r e t a l . , 1989). Furthermore the i m p l i c a t i o n t h a t the s e l e c t i v i t y u n d e r l y i n g the i n t e r f e r e n c e seen i n the E r i k s e n e f f e c t i s s p a t i a l l y based makes i t a l i k e l y c a n d i d a t e f o r demonstrating d i f f e r e n c e s i n the e f f i c i e n c y of s e l e c t i o n between psychopaths and o t h e r s , s i n c e a s i m i l a r d i f f e r e n c e has a l r e a d y been demonstrated i n experiments 1 and 2. The experiment i t s e l f was modelled a f t e r t h e experiments of E r i k s e n & E r i k s e n (1974) and T i p p e r e t a l . (1988). S u b j e c t s responded t o l e t t e r s p r e s e n t e d a t the p o i n t o f f i x a t i o n . As f o r experiments 4, each t r i a l c o n s i s t e d of a prime d i s p l a y f o l l o w e d by a probe d i s p l a y , and s u b j e c t s responded t o both d i s p l a y s . I n t e r f e r e n c e between l e t t e r s was measured by RTs t o the prime d i s p l a y , and n e g a t i v e p r i m i n g was measured by RTs t o p r e v i o u s l y i g n o r e d s t i m u l i presented as t a r g e t s i n the probe d i s p l a y . In the prime d i s p l a y , d i s t r a c t o r s t i m u l i o c c u r r e d a t f o u r h o r i z o n t a l d i s t a n c e s from the t a r g e t t o t e s t the e f f e c t of -100-s p a c i n g on i n t e r f e r e n c e . S u b j e c t s Data from a l l s u b j e c t s was i n c l u d e d i n t h i s study. Design As i n Experiment 4, s u b j e c t s were shown two d i s p l a y s (prime and probe) and were asked t o respond t o a t a r g e t i n each d i s p l a y . S u b j e c t s always responded t o the i d e n t i t y o f the t a r g e t l e t t e r p r e s e n t e d a t f i x a t i o n . S t i m u l i c o n s i s t e d o f the l e t t e r s A, B, C, and D, and responses were made by p r e s s i n g one of f o u r marked keys on the computer keyboard. For the prime d i s p l a y , a t a r g e t l e t t e r always appeared a t the f i x a t i o n p o i n t and a d i s t r a c t o r l e t t e r appeared a t one of f o u r d i s t a n c e s t o the l e f t o r r i g h t o f the t a r g e t . The i n n e r edge of the d i s t r a c t o r l e t t e r s appeared a t approximately .2°, 1.1°, 2.8°, and 4.1°, from f i x a t i o n . In the No I n t e r f e r e n c e c o n d i t i o n (64 t r i a l s ) , t he t a r g e t and d i s t r a c t o r l e t t e r s were i d e n t i c a l . In the I n t e r f e r e n c e c o n d i t i o n (192 t r i a l s ) the d i s t r a c t o r l e t t e r was one of the t h r e e l e t t e r s r e q u i r i n g a competing response. For both c o n d i t i o n s , a l l l e t t e r s appeared e q u a l l y o f t e n a t a l l p o s i t i o n s on the l e f t and the r i g h t o f f i x a t i o n i n a random ord e r . Again, the Probe d i s p l a y o f i n t e r e s t f o l l o w e d t h e I n t e r f e r e n c e c o n d i t i o n i n the prime d i s p l a y . In the C o n t r o l c o n d i t i o n (96 t r i a l s ) , a t a r g e t and d i s t r a c t o r d i f f e r e n t from e i t h e r o f the l e t t e r s i n the prime d i s p l a y were both presented. -101-In t he Negative P r i m i n g c o n d i t i o n (96 t r i a l s ) , t he t a r g e t l e t t e r was the same as the d i s t r a c t o r l e t t e r i n the prime d i s p l a y . In both c o n d i t i o n s the d i s t r a c t o r appeared e q u a l l y o f t e n d i r e c t l y above or below the t a r g e t l o c a t i o n t o a v o i d s p a t i a l o v e r l a p w i t h the p o s i t i o n s o f the prime d i s t r a c t o r s . Again, a l l l e t t e r s appeared e q u a l l y o f t e n i n a l l p o s i t i o n s i n a random o r d e r . S t i m u l i appeared white on a b l a c k background. A c e n t r a l f i x a t i o n dot was p r e s e n t between the p r e s e n t a t i o n o f each d i s p l a y . T a r g e t and d i s t r a c t o r l e t t e r s subtended approximately 0.26° h o r i z o n t a l l y and 0.48° v e r t i c a l l y . Procedure S u b j e c t s were g i v e n 26 p r a c t i c e t r i a l s , f o l l o w e d by f o u r b l o c k s o f 65 t r i a l s each. The f i r s t t r i a l o f each b l o c k was d i s c a r d e d . The remaining t r i a l s appeared i n the same random order f o r a l l s u b j e c t s . For both the prime and probe d i s p l a y s , the t a r g e t s t i m u l u s and the d i s t r a c t o r were p r e s e n t e d f o r 167 msecs. The probe d i s p l a y f o l l o w e d the prime d i s p l a y 350 msecs a f t e r the s u b j e c t had responded. The f o l l o w i n g t r i a l began t h r e e seconds a f t e r the response t o the probe d i s p l a y . As i n p r e v i o u s experiments, speed and accuracy were encouraged e q u a l l y a t the b e g i n n i n g of each b l o c k and o r a l feedback was g i v e n about performance a f t e r each b l o c k . Data A n a l y s i s Median RT (usi n g c o r r e c t responses only) and percentage of -102-c o r r e c t responses were c a l c u l a t e d f o r each s u b j e c t i n t h e prime d i s p l a y ' s I n t e r f e r e n c e and No I n t e r f e r e n c e c o n d i t i o n s s e p a r a t e l y f o r each e c c e n t r i c i t y o f d i s t r a c t o r . In t h e probe d i s p l a y , o n l y t r i a l s f o l l o w i n g a c o r r e c t response on the prime d i s p l a y were c o n s i d e r e d f o r a n a l y s i s . As a r e s u l t , t he number of t r i a l s on which the probe data were based was s l i g h t l y d i f f e r e n t f o r each s u b j e c t . Again median RT and percentage o f c o r r e c t responses were c a l c u l a t e d . Only data f o l l o w i n g i n t e r f e r e n c e t r i a l s i n the prime d i s p l a y were analysed, and the measures were c a l c u l a t e d s e p a r a t e l y f o r C o n t r o l and Negative P r i m i n g C o n d i t i o n s f o r each e c c e n t r i c i t y o f t h e d i s t r a c t o r i n the p r e v i o u s d i s p l a y . Measures from the prime and probe d i s p l a y s were submitted t o ANOVA w i t h Group (NP,P), C o n d i t i o n (No I n t e r f e r e n c e , I n t e r f e r e n c e and C o n t r o l , Negative P r i m i n g r e s p e c t i v e l y ) , S ide (Prime d i s t r a c t o r on the r i g h t o r l e f t ) , and E c c e n t r i c i t y (.2°,1.1°,2.8°,4.1°) as f a c t o r s . Because the i n f l u e n c e o f the d i s t r a c t o r s was expected t o d e c l i n e w i t h i n c r e a s i n g e c c e n t r i c i t y , the r e s u l t s were a l s o a n a l y s e d u s i n g o n l y data from the s m a l l e s t e c c e n t r i c i t y . I t was h y p o t h e s i z e d t h a t t h i s a n a l y s i s would maximize the l i k e l i h o o d of f i n d i n g group d i f f e r e n c e s i n e i t h e r i n t e r f e r e n c e o r n e g a t i v e p r i m i n g . Where the ANOVA r e q u i r e d the assumption o f s p h e r i c i t y , Mauchley's t e s t was a p p l i e d and, i f s i g n i f i c a n t , t he Greenhouse-Geisser c o r r e c t i o n was a p p l i e d t o the degrees o f -103-freedom ( d f ) . P r o b a b i l i t y l e v e l s f o r these c o r r e c t e d df are r e p o r t e d . R e s u l t s Mean of the median RTs and p e r c e n t c o r r e c t f o r the probe d i s p l a y are shown f o r both groups under a l l c o n d i t i o n s i n F i g u r e s 18 and 19. A n a l y s i s of RT y i e l d e d a main e f f e c t f o r E c c e n t r i c i t y (F(3,114) = 49.83, p_<.001), moderated by s e v e r a l h i g h e r - o r d e r i n t e r a c t i o n s . I n t e r a c t i o n s of C o n d i t i o n X E c c e n t r i c i t y (F(3,114) = 12.10, p_<.001), Side X E c c e n t r i c i t y (F(3,114) = 4.04, p_<.02), and C o n d i t i o n X S i d e X E c c e n t r i c i t y (F(3,114) = 6.92, p_<.001) were a l s o s i g n i f i c a n t . Of t h e e f f e c t s i n v o l v i n g Group, o n l y the Group X C o n d i t i o n X S i d e i n t e r a c t i o n approached s i g n i f i c a n c e (F(l,38) = 3.14, p_<.10). Simple e f f e c t s a n a l y s e s were used t o examine the 3-way i n t e r a c t i o n f u r t h e r . Examining the e f f e c t of C o n d i t i o n a t each e c c e n t r i c i t y on the r i g h t and on the l e f t r e v e a l e d s i g n i f i c a n t d i f f e r e n c e s f o r 0.2° of v i s u a l angle on both s i d e s . As expected, a t t h i s e c c e n t r i c i t y a d i f f e r e n t d i s t r a c t o r item i n t e r f e r e d w i t h responding t o the t a r g e t r e l a t i v e t o a t a r g e t -i d e n t i c a l d i s t r a c t o r (see F i g u r e 20). However, a t e c c e n t r i c i t i e s of 1.1° and 2.8° on the l e f t and 4.1° on the r i g h t s i g n i f i c a n t f a c i l i t a t i o n was seen i n the presence of non-i d e n t i c a l d i s t r a c t o r items. I t appears t h a t a t wider e c c e n t r i c i t i e s the p r e s e n t a t i o n of an i d e n t i c a l item as a d i s t r a c t o r i n t e r f e r e s more than does a n o n - i d e n t i c a l - 1 0 4 -800 CD E c o 'o 700H CO CD DC 2.8 1.1 0.2 0.2 1.1 2.8 L Distractor Eccentricity (deg.) R NP, CNTR - s - P, CNTR NP, INTR P, INTR Figure 18. Experiment 5: Reaction times f o r each group f o r control and interference conditions i n the prime display as a function of the e c c e n t r i c i t y of the d i s t r a c t o r -105-100 92-91-90 1 1 1 1 1 1 1 r~ 4.1 2.8 1.1 0.2 0.2 1.1 2.8 4.1 L Distractor Eccentricity (deg.) R NP, CNTR - e - P, CNTR -~*~- NP, INTR P, INTR Figure 19. Experiment 5: Percentage of correct responses by each group for control and interference conditions i n the prime display as a function of the e c c e n t r i c i t y of the d i s t r a c t o r -106-CD O C CD 1_ CD CD 2.8 1.1 0.2 0.2 1.1 2.8 L Distractor Eccentricity (deg.) R 4.1 GROUP NP - e - GROUP P F i g u r e 20. Experiment 5: I n t e r f e r e n c e f o r each group as a f u n c t i o n of d i s t r a c t o r e c c e n t r i c i t y -107-d i s t r a c t o r . The o n l y s i g n i f i c a n t e f f e c t f o r accuracy was a main e f f e c t of E c c e n t r i c i t y (F(3,114) = 5.02, p_<.01). A second s t i m u l u s of e i t h e r type p r e s e n t e d a t wider e c c e n t r i c i t i e s r e s u l t e d i n more a c c u r a t e responding (see F i g u r e 19). However, none of the comparisons among the f o u r means reached s i g n i f i c a n c e u s i n g Tukey comparisons ( a l l qs<2.72). The r e s u l t s f o r D i s p l a y 2 are shown i n F i g u r e s 21 and 22. A n a l y s i s of RT r e v e a l e d s i g n i f i c a n t i n t e r a c t i o n s of Side X E c c e n t r i c i t y (F(3,114) = 3.90, p_<.02) and of C o n d i t i o n X Side X E c c e n t r i c i t y (F(3,114) = 2.69, p<.05). Once again , no group d i f f e r e n c e s approached s i g n i f i c a n c e ( a l l p_s>.10). To e x p l o r e f u r t h e r the 3-way i n t e r a c t i o n the e f f e c t of C o n d i t i o n was a g a i n t e s t e d a t each e c c e n t r i c i t y on both s i d e s u s i n g simple e f f e c t s comparisons. In t h i s i n s t a n c e , the C o n t r o l and Negative Priming c o n d i t i o n s d i f f e r e d o n l y a t a s i n g l e e c c e n t r i c i t y , 1.1° on the r i g h t . In t h i s c o n d i t i o n , however, responses i n the Negative P r i m i n g C o n d i t i o n were f a s t e r than those i n the C o n t r o l c o n d i t i o n . In o t h e r words no evidence f o r n e g a t i v e p r i m i n g was o b t a i n e d i n t h i s paradigm, but a s i g n i f i c a n t f a c i l i t a t i o n was seen when responding t o i g n o r e d items p r e v i o u s l y p r e s e n t e d 1° t o the r i g h t of f i x a t i o n . The o n l y s i g n i f i c a n t e f f e c t f o r accuracy data was a Side X E c c e n t r i c i t y i n t e r a c t i o n (F(3,114) = 6.43, p_<.001). Si n c e the e f f e c t i n v o l v e d n e i t h e r Group nor C o n d i t i o n i t was not examined -108-E r-C o 780 760-740 720-§ 700 rr 680-660 2.8 1.1 0.2 0.2 1.1 2.8 L Distractor Eccentricity (deg.) R NP, INT -e- p, INT - - NP, NEGP P, NEGP Figure 21. Experiment 5: Mean reaction times f o r each group for control and negative priming conditions i n the probe display as a function of d i s t r a c t o r e c c e n t r i c i t y i n the prime display - 1 0 9 -100 o CD o o 90 4.1 2.8 1.1 0.2 0.2 1.1 2.8 4.1 L Distractor Eccentricity (deg.) R NP, INT - e - P, INT - NP, NEGP P, NEGP Figure 22. Experiment 5: Percentage of correct responses by each group for control and negative priming conditions i n the probe display as a function of the e c c e n t r i c i t y of the d i s t r a c t o r i n the prime display -110-f u r t h e r . A n a l y s i s of the data f o r the c l o s e s t e c c e n t r i c i t y d i d not r e v e a l any evidence f o r group d i f f e r e n c e s even i n the c o n d i t i o n when i n t e r f e r e n c e and n e g a t i v e p r i m i n g s h o u l d have been s t r o n g e s t . For D i s p l a y 1 a s i g n i f i c a n t e f f e c t o f C o n d i t i o n (F(l,38) = 25.14, p/c.001) was observed f o r RT, and a C o n d i t i o n X Side i n t e r a c t i o n (F(l,38) = 4.53), p_<.04) was p r e s e n t f o r accuracy. The former e f f e c t was d i r e c t l y i n l i n e w i t h the f u l l a n a l y s i s , but the l a t t e r was not. Whereas a d i f f e r e n t d i s t r a c t o r i n t e r f e r e d w i t h the accuracy o f responding when i t was pr e s e n t e d t o the l e f t o f f i x a t i o n , i t a c t u a l l y f a c i l i t a t e d r e sponding when presented t o the r i g h t . For D i s p l a y 2, No s i g n i f i c a n t e f f e c t s were observed f o r e i t h e r RT or accuracy. D i s c u s s i o n C o n s i s t e n t w i t h Experiments 3 and 4, Experiment 5 p r o v i d e d no support f o r the h y p o t h e s i s t h a t psychopaths can be d i s t i n g u i s h e d from nonpsychopaths on the b a s i s o f the components of a t t e n t i o n u n d e r l y i n g i n t e r f e r e n c e between s t i m u l i and n e g a t i v e p r i m i n g . In t h i s experiment the added e f f e c t o f s p a t i a l t u n i n g of i n t e r f e r e n c e e f f e c t s was examined, on the premise t h a t t h i s c o u l d p r o v i d e a mechanism f o r d i f f e r e n t i a l s e l e c t i v i t y between the groups. The r e s u l t s f o r both the i n t e r f e r e n c e and n e g a t i v e p r i m i n g e f f e c t s were complicated by the presence o f s e v e r a l unexpected f i n d i n g s . Although c l e a r i n t e r f e r e n c e e f f e c t s were observed - I l l -w i t h d i s t r a c t o r s a t 0.2° of v i s u a l angle, t h i s i n t e r f e r e n c e was a b o l i s h e d a t 1.1° and wider. In f a c t s i g n i f i c a n t f a c i l i t a t i o n o c c u r r e d a t c e r t a i n e c c e n t r i c i t i e s . T h i s i s q u i t e d i f f e r e n t from the e f f e c t s r e p o r t e d elsewhere (e.g. E r i k s e n & E r i k s e n , 1974; Murphy & E r i k s e n , 1987), i n which i n t e r f e r e n c e i s observed when competing s t i m u l i a re pre s e n t e d a t up t o 1.5° from a t a r g e t , w i t h a gr a d u a l r e d u c t i o n i n the magnitude of the e f f e c t w i t h i n c r e a s i n g e c c e n t r i c i t y . In f a c t t he p e c u l i a r i t y of the r e s u l t i n the p r e s e n t experiment was l a r g e l y a t t r i b u t a b l e t o the p s y c h o p a t h i c s u b j e c t s , f o r whom the f a c i l i t a t i o n was p a r t i c u l a r l y marked when d i s t r a c t o r s were presented t o the l e f t o f f i x a t i o n (See F i g u r e 20). There was l i t t l e evidence f o r t h i s r e v e r s a l o f the i n t e r f e r e n c e e f f e c t i n nonpsychopaths, except a t the most extreme e c c e n t r i c i t y on the r i g h t . Although not r e a c h i n g s i g n i f i c a n c e , t h i s o b s e r v a t i o n i s supported by the presence o f a t r e n d f o r the 4-way Group X C o n d i t i o n X Si d e X E c c e n t r i c i t y i n t e r a c t i o n (F(3,114) = 2.15, p_<.10). F i g u r e 18 shows t h e RTs of both groups i n the presence o f t a r g e t - i d e n t i c a l ( C o n t r o l c o n d i t i o n ) and t a r g e t - n o n i d e n t i c a l ( I n t e r f e r e n c e c o n d i t i o n ) d i s t r a c t o r s as a f u n c t i o n of the e c c e n t r i c i t y o f the d i s t r a c t o r . The RT f u n c t i o n s o f the two groups are q u i t e s i m i l a r f o r the I n t e r f e r e n c e c o n d i t i o n , and they have t h e form expected on the b a s i s of p r e v i o u s l i t e r a t u r e o f d e c r e a s i n g RT wi t h i n c r e a s i n g t a r g e t - d i s t r a c t o r d i s t a n c e . The RT f u n c t i o n s -112-f o r the C o n t r o l c o n d i t i o n are l e s s s i m i l a r t o one another. They a l s o show d e c r e a s i n g RT w i t h i n c r e a s i n g t a r g e t - d i s t r a c t o r d i s t a n c e , but the shape of the f u n c t i o n i s q u i t e d i f f e r e n t from the I n t e r f e r e n c e c o n d i t i o n , the e f f e c t b e i n g l e s s s h a r p l y tuned t o a narrow angle around the focus of a t t e n t i o n . Psychopaths, i n p a r t i c u l a r , show s u b s t a n t i a l d i f f e r e n c e s i n RT t o a t a r g e t -i d e n t i c a l d i s t r a c t o r p r e s e n t e d 2.8° t o the l e f t o f f i x a t i o n , compared t o one presented 4.1° t o the l e f t . I t i s t h i s r a t h e r l a r g e i n t e r f e r e n c e e f f e c t a t wider v i s u a l angles f o r t a r g e t -i d e n t i c a l d i s t r a c t o r s , p a r t i c u l a r l y f o r psychopaths, t h a t appears t o be r e s p o n s i b l e f o r the r e v e r s a l of the i n t e r f e r e n c e e f f e c t . A c c e p t i n g f o r the moment t h a t these e f f e c t s are more than chance occurrences, they would seem t o run counter t o e x p e c t a t i o n s t h a t r e sponse-incompatible d i s t r a c t o r s should r e t a r d RT ( E r i k s e n & E r i k s e n , 1974; E r i k s e n & S t . James, 1986; Murphy & E r i k s e n , 1987), and t a r g e t - i d e n t i c a l d i s t r a c t o r s might f a c i l i t a t e RT due t o c o a c t i v a t i o n ( F o u r n i e r & E r i k s e n , 1990). The most l i k e l y e x p l a n a t i o n r e s i d e s i n the frequency of o ccurrence of the c o n d i t i o n s used i n t h i s experiment. T a r g e t -i d e n t i c a l d i s t r a c t o r s o c c u r r e d on o n l y 25% of t r i a l s , making t h e i r o c c u rrence a s u r p r i s i n g event. I f s u b j e c t s developed an e x p e c t a t i o n of having t o suppress responses t o response-i n c o m p a t i b l e d i s t r a c t o r s on the m a j o r i t y of t r i a l s , the presence of a response-compatible d i s t r a c t o r might have a -113-number of e f f e c t s . In the f i r s t p l a c e , i t might l e a d d i r e c t l y t o slowed RT due t o the tendency t o suppress o r i n h i b i t r e sponding t o the d i s t r a c t o r on a l l t r i a l s . Secondly, the presence of an unexpected s t i m u l u s might induce o r i e n t i n g o f a t t e n t i o n , p a r t i c u l a r l y when i t f a l l s some way o u t s i d e o f the foc u s o f a t t e n t i o n . The f i r s t o f these mechanisms might be expected t o have a s i m i l a r s p a t i a l d i s t r i b u t i o n as the i n t e r f e r e n c e e f f e c t s , w i t h r e l a t i v e l y narrow s p a t i a l t u n i n g . The l a t t e r mechanism might "cap t u r e " a t t e n t i o n r e g a r d l e s s of i t s c u r r e n t f o c u s . The v a l i d i t y o f these s p e c u l a t i o n s can o n l y be assessed by f u r t h e r s t u d i e s , but one f u r t h e r p o s s i b i l i t y deserves mention. The n o n - s i g n i f i c a n t group d i f f e r e n c e s we have d i s c u s s e d , p a r t i c u l a r l y i n the RT f u n c t i o n f o r t a r g e t - i d e n t i c a l d i s t r a c t o r s , might have a r i s e n on the b a s i s o f the degree of e x p e c t a t i o n t h a t the d i s t r a c t o r would be d i f f e r e n t from the t a r g e t . By c o i n c i d e n c e s , t h i s assumption has approximately equal v a l i d i t y (75% v a l i d ) as d i d the s p a t i a l cues used i n Experiments 1 and 2 (67% v a l i d i t y ) . In the s e experiments psychopaths s i g n i f i c a n t l y o v e r - a l l o c a t e d t h e i r a t t e n t i o n t o the cued l o c a t i o n d e s p i t e the r e l a t i v e l y poor v a l i d i t y o f the cue. In t h e p r e s e n t study a s i m i l a r over-investment o f r e s o u r c e s i n the e x p e c t a t i o n t h a t the d i s t r a c t o r would be d i f f e r e n t from the t a r g e t might have r e s u l t e d i n the r e l a t i v e disadvantage t h a t psychopaths appear t o d i s p l a y when f a c e d w i t h t a r g e t - i d e n t i c a l d i s t r a c t o r s . -114-The r e s u l t s f o r D i s p l a y 2 were, i f a n y t h i n g , more unusual. There was no evidence a t a l l f o r the development of n e g a t i v e p r i m i n g i n any of the c o n d i t i o n s . In f a c t , o v e r a l l , s u b j e c t s were f a s t e r on n e g a t i v e p r i m i n g t r i a l s whatever the e c c e n t r i c i t y of the d i s t r a c t o r on the p r e v i o u s d i s p l a y . The s t r o n g i n t e r f e r e n c e e f f e c t s found f o r d i s t r a c t o r s a t .2° e c c e n t r i c i t y p r o v i d e s evidence t h a t , a t l e a s t i n t h i s c o n d i t i o n , the d i s t r a c t o r s were e f f e c t i v e i n d i s r u p t i n g performance, and t h e r e f o r e s u b j e c t s should have b e n e f i t e d from the a c t i v e s u p p r e s s i o n of these s t i m u l i . Yet even i n t h i s c o n d i t i o n , responses t o p r e v i o u s l y i g n o r e d s t i m u l i were f a s t e r than t o newly pre s e n t e d t a r g e t s . A l s o Experiments 3 and 4 have c l e a r l y demonstrated t h a t these same s u b j e c t s show evidence f o r a c t i v e i n h i b i t i o n i n o t h e r paradigms. The c o n c l u s i o n must be, t h e r e f o r e , t h a t the c o n d i t i o n s of t h i s experiment changed the use of a c t i v e i n h i b i t i o n such t h a t i t no l o n g e r induced n e g a t i v e p r i m i n g . One obvious p o s s i b i l i t y i s t h a t the i n t e r v a l between the prime and probe d i s p l a y s was s u f f i c i e n t l y l o n g t o a l l o w the decay of i n h i b i t i o n . T h i s i s u n l i k e l y i n view of the r o b u s t e f f e c t r e p o r t e d by T i p p e r e t a l . (1988) u s i n g a v e r y s i m i l a r paradigm w i t h an i d e n t i c a l i n t e r - d i s p l a y i n t e r v a l , and the e f f e c t s r e p o r t e d i n Experiments 3 and 4. A more p l a u s i b l e e x p l a n a t i o n might d e r i v e from the asymmetrical p r o b a b i l i t i e s a s s o c i a t e d w i t h i n t e r f e r i n g and n o n - i n t e r f e r i n g d i s t r a c t o r s and -115-the f a c t t h a t the d i s t r a c t o r s appeared i n v a r i a b l e and u n p r e d i c t a b l e l o c a t i o n s . In p r e v i o u s s t u d i e s of n e g a t i v e p r i m i n g i n h i b i t i o n has been a s s o c i a t e d w i t h t h e i n t e r n a l r e p r e s e n t a t i o n of the o b j e c t (Tipper & D r i v e r , 1988) or w i t h the l o c a t i o n i n space a t which the o b j e c t p r e v i o u s l y appeared ( T i p p e r e t a l . , 1990). In another model o f a t t e n t i o n , however, i n h i b i t i o n has been proposed as a mechanism f o r s u p p r e s s i n g the p r o c e s s i n g of i r r e l e v a n t f e a t u r e s d u r i n g v i s u a l s e a r c h (Treisman & Sato, 1990). In t h i s model, knowledge of the i r r e l e v a n t f e a t u r e s p r e s e n t o n l y i n d i s t r a c t o r items a l l o w s s u b j e c t s s t r a t e g i c a l l y t o i n h i b i t the p r o c e s s i n g of t h e s e f e a t u r e s a t a l l l o c a t i o n s , l e a v i n g a c t i v e o n l y those l o c a t i o n s which c o n t a i n none of the i n h i b i t e d f e a t u r e s . The p r e s e n t experiment p r o v i d e s an analogous s i t u a t i o n , i n which the p o s i t i o n of the t a r g e t i s f i x e d , but the p o s i t i o n of the d i s t r a c t o r i s u n p r e d i c t a b l e . In t h i s s i t u a t i o n , t h e i n h i b i t i o n (or p a r t i a l i n h i b i t i o n ) of s p a t i a l l o c a t i o n s o t h e r than a t f i x a t i o n would be an e f f i c i e n t s t r a t e g y , perhaps more e f f i c i e n t than the i n h i b i t i o n of the r e p r e s e n t a t i o n s of i n d i v i d u a l items. The i d e a t h a t the l o c a t i o n map can be i n h i b i t e d i s not, o f course, d e r i v a b l e from Treisman's theory, but i t i s c o n s i s t e n t w i t h the t h e o r y ' s g e n e r a l development (e.g. Treisman, 1988; Treisman & Gelade, 1980; Treisman & Sato, 1990) i n a l l o w i n g i n c r e a s i n g l y f l e x i b l e s t r a t e g i e s f o r the p r o c e s s i n g of v i s u a l i n f o r m a t i o n . The a b i l i t y t o i n h i b i t s t r a t e g i c a l l y a l l n o n - f o c a l -116-v i s u a l l o c a t i o n s has not been s t u d i e d e i t h e r w i t h i n the v i s u a l o r i e n t i n g o r the n e g a t i v e p r i m i n g l i t e r a t u r e , but i t might p r o v i d e an e x p l a n a t i o n f o r the absence o f n e g a t i v e p r i m i n g i n the p r e s e n t study. The use of t h i s g l o b a l i n h i b i t i o n might w e l l r e p l a c e o r supersede the c a p a c i t y t o i n h i b i t s p e c i f i c o b j e c t or l o c a t i o n r e p r e s e n t a t i o n s . I f i n h i b i t i o n i s indeed an a c t i v e p r o c e s s , as T i p p e r proposes, i t may be l i m i t e d i n i t s c a p a c i t y , j u s t as are oth e r a c t i v e a t t e n t i o n a l mechanisms, and the s t r a t e g i c d e c i s i o n t o i n h i b i t non-attended l o c a t i o n s i n space may d e t r a c t from the a b i l i t y t o i n h i b i t a s p e c i f i c s t i m u l u s even when t h e r e i s evidence t h a t i t i n t e r f e r e s w i t h t a r g e t d e t e c t i o n . T h i s i n h i b i t i o n o f no n - f o v e a l l o c a t i o n s , o f course, would be e q u a l l y a p p l i c a b l e t o t a r g e t - i d e n t i c a l as t o non-i d e n t i c a l d i s t r a c t o r s , i n l i n e w i t h the d i s c u s s i o n o f the i n t e r f e r e n c e data above. I f the s t r a t e g i c use of i n h i b i t i o n i n t h i s paradigm l e d t o both the l a r g e i n t e r f e r e n c e seen f o r t a r g e t - i d e n t i c a l d i s t r a c t o r s i n d i s p l a y 1 and the l a c k of n e g a t i v e p r i m i n g i n d i s p l a y 2, why have s i m i l a r e f f e c t s not been seen i n o t h e r r e p o r t s of these phenomena? There are s e v e r a l p o s s i b l e answers, a l l o f whose c o r r e c t n e s s can o n l y be a s c e r t a i n e d by f u t u r e r e s e a r c h . In the f i r s t p l a c e , although E r i k s e n & E r i k s e n (1974) used t a r g e t - i d e n t i c a l d i s t r a c t o r s i n o n l y 20% of t r i a l s , t h e i r experiment c o n t a i n e d a much l a r g e r v a r i e t y o f t a r g e t and d i s t r a c t i n g s t i m u l i , p o s s i b l y d i s c o u r a g i n g s u b j e c t s from -117-r e c o g n i z i n g t h a t a s i n g l e s t r a t e g y employing s p a t i a l i n h i b i t i o n would be b e n e f i c i a l . In a d d i t i o n , the i n h i b i t i o n s t r a t e g y might have been disadvantageous f o r the 20% of t r i a l s i n which response-compatible d i s t r a c t o r s were p r e s e n t e d as w e l l as f o r the 20% of t r i a l s i n which t a r g e t - i d e n t i c a l d i s t r a c t o r s were presented. That would make the s t r a t e g y advantageous on o n l y 60% o f t r i a l s , c o n s i d e r a b l y l e s s than the 75% o f t r i a l s i n the pr e s e n t study. S t u d i e s by T i p p e r and c o l l e a g u e s o f n e g a t i v e p r i m i n g have never used a paradigm i n which t h e l o c a t i o n of the t a r g e t was f i x e d but t h a t o f the d i s t r a c t o r was v a r i a b l e , so t h e i r s t u d i e s p r o v i d e no evidence t o t e s t the p o s s i b i l i t y t h a t o b j e c t - c e n t r e d i n h i b i t i o n can be a b o l i s h e d by s t r a t e g i c use of s p a t i a l i n h i b i t i o n . General D i s c u s s i o n and Summary The r e s u l t s of the experiments r e p o r t e d here are, i n g e n e r a l , s t r a i g h t f o r w a r d . The c o n c l u s i o n s t h a t can be l e g i t i m a t e l y drawn from them can be summarized as f o l l o w s . Under c e r t a i n circumstances, p s y c h o p a t h i c c r i m i n a l s can be shown t o a l l o c a t e a g r e a t e r p r o p o r t i o n o f t h e i r a t t e n t i o n a l r e s o u r c e s on the b a s i s of cues of o n l y moderate v a l i d i t y than do nonpsychopathic c r i m i n a l s . The f u n c t i o n i n g o f a v a r i e t y o f components of v i s u a l a t t e n t i o n i d e n t i f i e d as important i n c o n t r o l l i n g the d i s t r i b u t i o n o f a t t e n t i o n were shown t o be o p e r a t i n g e g u i v a l e n t l y i n the two groups. These p r o c e s s e s i n c l u d e d the o r i e n t i n g of a t t e n t i o n on the b a s i s o f exogenous -118-cues, i n h i b i t i o n of r e t u r n , the i n t e r f e r i n g e f f e c t s o f i r r e l e v a n t s t i m u l i , the h a b i t u a t i o n o f t h a t i n t e r f e r e n c e , and n e g a t i v e p r i m i n g . The experimental m a n i p u l a t i o n s designed t o induce each of these p r o c e s s e s was s u c c e s s f u l i n d o i n g so, l e a d i n g t o the c o n c l u s i o n t h a t e i t h e r the groups d i d not d i f f e r i n t h e i r use of any of these c o g n i t i v e p r o c e s s e s , o r t h a t the d i f f e r e n c e s were of too s m a l l a magnitude t o observe i n a study of t h i s s i z e . T h i s c o n c l u s i o n was strengthened by the r e p l i c a t i o n of these f i n d i n g s of group e q u i v a l e n c e u s i n g d i f f e r e n t s u b j e c t s i n s i m i l a r paradigms i n experiments 1 and 2, and by u s i n g the same s u b j e c t s i n q u i t e d i f f e r e n t paradigms i n experiments 3, 4, and 5. The group d i f f e r e n c e s i n o r i e n t i n g t h a t were observed i n experiments 1 and 2 were t h e r e f o r e a t t r i b u t e d t o d i f f e r e n c e s i n endogenous a l l o c a t i o n of a t t e n t i o n on the b a s i s of symbolic cues. The s t r e n g t h of t h i s c o n c l u s i o n was b o l s t e r e d by the f a c t t h a t a s i m i l a r group d i f f e r e n c e was r e p l i c a t e d on d i f f e r e n t samples i n experiments 1 and 2. The term "endogenous o r i e n t i n g " has been used throughout t o r e f e r t o a c l a s s of p r o c e s s e s t h a t a c t a t a more a b s t r a c t l e v e l t o c o n t r o l the a l l o c a t i o n o f a t t e n t i o n than do most of the o t h e r components of a t t e n t i o n examined i n the p r e s e n t study. In t h i s sense one might t h i n k of the o t h e r p r o c e s s e s , n e g a t i v e priming, i n h i b i t i o n of r e t u r n , e t c . , as more o b l i g a t o r y , f i x e d and i n f l e x i b l e i n t h e i r o p e r a t i o n , and t h e r e f o r e i n f l u e n t i a l i n a narrower area of the -119-s u b j e c t s ' b ehavior and c o g n i t i o n s . T h e r e f o r e the endogenous f a c i l i t a t i o n i n the p r e s e n t study may be thought o f as r e s u l t i n g from a more g e n e r a l s e t of p r o c e s s e s f o r s t r a t e g i c a l l y c o n t r o l l i n g a t t e n t i o n a l a l l o c a t i o n i n a v a r i e t y of s i t u a t i o n s . Why t h i s o v e r - a l l o c a t i o n was o b s e r v a b l e i n the c o v e r t o r i e n t i n g paradigm used here i s not apparent from these s t u d i e s , but the p o s s i b i l i t i e s i n c l u d e the o v e r - e s t i m a t i o n of the p r e d i c t i v e v a l i d i t y of the cue, or the h a b i t u a l o v er-a l l o c a t i o n of a t t e n t i o n t o the most l i k e l y outcome d e s p i t e o n l y moderate p r e d i c t i v e v a l i d i t y . I t i s i n t e r e s t i n g t o note t h a t t h e r e was some evidence from the r e s u l t s of experiment 5 t h a t might be s p e c u l a t i v e l y i n t e r p r e t e d i n s i m i l a r terms. The d e t e r m i n a t i o n t h a t d i f f e r e n c e s i n a t t e n t i o n cannot be a t t r i b u t e d t o l o w e r - l e v e l components i s a n e c e s s a r y s t e p i n narrowing down the l o c u s of these d i f f e r e n c e s . The f ocus f o r f u t u r e r e s e a r c h can now approach the i s s u e of the s t r a t e g i c a l l o c a t i o n of a t t e n t i o n i n psychopaths w i t h g r e a t e r c o n f i d e n c e t h a t the observed d i f f e r e n c e s are not the r e s u l t of some more b a s i c d e f e c t i n a t t e n t i o n a l c o n t r o l . Presumably the f ocus of f u t u r e r e s e a r c h should be the f a c t o r s t h a t c o n t r i b u t e t o the s t r a t e g i c a l l o c a t i o n of r e s o u r c e s by psychopaths. A s i d e from the o v e r - e s t i m a t i o n of p r e d i c t i v e r e l a t i o n s h i p s mentioned above, s e v e r a l other c a n d i d a t e mechanisms can be i d e n t i f i e d t h a t may or may not have been o p e r a t i v e i n the p r e s e n t experiments. Newman and h i s c o l l e a g u e s have shown t h a t -120-psychopaths m a n i f e s t an i n a b i l i t y t o modulate t h e i r responses o n l y i n the presence of competing cues f o r both reward and punishment (Newman & Kosson, 1986), which might suggest t h a t s t r a t e g i c o v e r - a l l o c a t i o n of a t t e n t i o n i s an attempt t o r e s o l v e c o n f l i c t s a r i s i n g from competing g o a l s . An a l t e r n a t i v e approach might d e r i v e from the o b s e r v a t i o n s t h a t psychopaths d i s p l a y abnormal c o g n i t i v e and autonomic responses t o emotional m a t e r i a l (e.g. Hare, 1978; W i l l i a m s o n e t a l . , i n p r e s s ) . The r e l a t i o n s h i p between emotional responses and the c o n t r o l of a t t e n t i o n i s c u r r e n t l y p o o r l y understood, but most models of e i t h e r a t t e n t i o n or emotion assume a f u n c t i o n a l l i n k between these p r o c e s s e s (e.g. Gray, 1982) . 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For the remaining subjects, the EOG data contained a considerable amount of a r t i f a c t u a l 60Hz noise, which could not be eliminated because of the nature of the recording s i t u a t i o n . When necessary, the low-pass f i l t e r was reduced to 10Hz to t r y to minimize contamination, and f o r some subjects s i g n a l a m p l i f i c a t i o n had to be reduced. Two further subjects were eliminated because excessive a r t i f a c t necessitated reducing ampli f i c a t i o n to l e v e l s too low to be use f u l . This l e f t data from 18 nonpsychopaths and 15 psychopaths. At the s t a r t of the experiment subjects performed a b r i e f c a l i b r a t i o n procedure, consisting of v i s u a l l y tracking a white dot which moved ra p i d l y from a central location to locations 1.5°, 3.0°, 4.5°, and 6.0° to the l e f t or r i g h t of f i x a t i o n i n a random order. For experiment 2 the use of a chin-rest ensured that head-movements were kept to a minimum. Three t r i a l s were recorded f o r eye-movements to each of these locations. For each t r i a l , an area measure was calculated f o r a 100 msec window beginning 30 msecs p r i o r to the peak EOG amplitude occurring -130-w i t h i n 1000 msecs of the movement of the dot. These ar e a measurements were subsequently averaged a c r o s s the t h r e e t r i a l s f o r each v i s u a l angle t o the r i g h t and l e f t t o determine the A/D u n i t s c o r r e s p o n d i n g t o a movement of t h e s u b j e c t ' s eyes t o each l o c a t i o n . L i n e a r r e g r e s s i o n was used f o r each s u b j e c t t o determine the number of A/D u n i t s c o r r e s p o n d i n g t o a l a t e r a l movement of the eyes of 2.5°. A t h r e s h o l d f o r d e t e c t i o n o f movement on each t r i a l was then s e t a t the number of A/D u n i t s c o r r e s p o n d i n g t o 2.5° of v i s u a l angle. Because of the poor r e c o r d i n g c o n d i t i o n s , i t appeared i n a p p r o p r i a t e t o use the EOG r e c o r d as a c o n t r o l on a t r i a l - b y -t r i a l b a s i s . However, the h y p o t h e s i s t h a t , f o l l o w i n g a cue, psychopaths may be moving t h e i r eyes more o f t e n than nonpsychopaths c o u l d s t i l l be t e s t e d i n g e n e r a l by examining the number of t r i a l s on which s u b j e c t s ' EOG exceeded t h r e s h o l d . Assuming t h a t EOG contamination a f f e c t e d a l l s u b j e c t s i n a s i m i l a r manner, group d i f f e r e n c e s might s t i l l be v i s i b l e , a l though made l e s s d i s t i n c t by the i n c r e a s e d t r i a l - b y - t r i a l v a r i a b i l i t y . For each s u b j e c t , the EOG o c c u r r i n g from 100 msecs t o 650 msecs a f t e r the onset of the f i r s t cue was scanned f o r EOG amplitude i n excess of the t h r e s h o l d p r e v i o u s l y determined. The EOG was f u r t h e r smoothed by measuring the amplitude u s i n g the mean amplitude of a 100 msec window s h i f t e d by a s i n g l e data p o i n t through the epoch of i n t e r e s t . The number of t r i a l s on -131-which EOG beyond t h r e s h o l d was i d e n t i f i e d was the dependent measure o f i n t e r e s t . Although some t r i a l s would exceed t h r e s h o l d by chance, average group d i f f e r e n c e s i n l a t e r a l eye-movements f o l l o w i n g a cue ought t o have remained v i s i b l e . However the presence of n o i s e i n the data may have reduced the s e n s i t i v i t y o f the measurement too g r e a t l y t o be u s e f u l . As a check f o r t h i s , the c a l i b r a t i o n data was an a l y s e d i n a s i m i l a r way t o determine f i r s t whether the method used would i d e n t i f y e x c e s s i v e eye-movements when none were present, and second t o see whether eye movements of 3°, 4.5°, and 6° used d u r i n g c a l i b r a t i o n would be a c c u r a t e l y d e t e c t e d , but those of 1.5° would not. T h i s procedure was performed on two epochs from the c a l i b r a t i o n s e t , a 500 msec p r e - b a s e l i n e epoch d u r i n g which the c e n t r a l dot d i d not move, and a 1000 msec epoch f o l l o w i n g the movement of the c a l i b r a t i o n dot. The r e s u l t s o f t h i s check on the s e n s i t i v i t y of the procedure were q u i t e s a t i s f a c t o r y . During the p r e - b a s e l i n e p e r i o d , when no movements were expected t o occur, movement was s p u r i o u s l y d e t e c t e d on 5.8% of t r i a l s . P o s t - b a s e l i n e measurement d e t e c t e d movement on 51.6% of t r i a l s . I t must be remembered t h a t 25% of these t r i a l s c o n t a i n e d movement t h a t was below the t h r e s h o l d used by t h i s procedure. Another 25% c o n t a i n e d movements j u s t above t h r e s h o l d . I t i s apparent t h a t the procedure does s u c c e s s f u l l y d e t e c t eye movements, although not those below 3° of v i s u a l angle. In -132-a d d i t i o n , i t d i d not i d e n t i f y an e x c e s s i v e number of s p u r i o u s movements. For t h i s reason we can have some c o n f i d e n c e t h a t i t may be s u f f i c i e n t l y s e n s i t i v e t o i d e n t i f y group d i f f e r e n c e s s hould they occur. Eye-movements above t h r e s h o l d o c c u r r i n g w i t h i n 600 msecs of cue onset were d e t e c t e d on 40% of t r i a l s i n the p e r i p h e r a l l y cued c o n d i t i o n and 38% of c e n t r a l l y cued t r i a l s . No s i g n i f i c a n t d i f f e r e n c e s were found between the groups on t h e frequency of eye-movements (F(l,31) = 0.03, p>.50). Although some movement of the eyes appeared t o be common i n t h i s paradigm, t h e r e was no evidence t h a t one group moved t h e i r eyes more than t h e o t h e r . 

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