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A critical role for endogenous processes in inhibition of return Tipper, Christine Marie 2003

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A C R I T I C A L R O L E F O R E N D O G E N O U S PROCESSES IN INHIBITION OF R E T U R N  by  CHRISTINE M A R I E TIPPER B.A., University of British Columbia, 2001  A THESIS SUBMITTED IN P A R T I A L F U L F I L M E N T OF T H E REQUIREMENTS FOR T H E D E G R E E OF M A S T E R OF ARTS in T H E F A C U L T Y OF G R A D U A T E STUDIES (Department of Psychology; Cognitive Systems Program)  We accept this thesis as conforming to the required standard  T H E UNIVERSITY OF BRITISH C O L U M B I A August 2003 © Christine M . Tipper, 2003  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 of  P^uOMolOCj^  The University of British Columbia Vancouver, Canada Date  DE-6 (2/88)  ABSTRACT  Response time to visual targets at peripheral locations can be delayed if the target location was previously cued, a phenomenon called inhibition of return (IOR). Given that IOR is found under what are assumed to be conditions of exogenous (reflexive), but not endogenous (volitional) covert attentional orienting, it is accepted that the IOR effect is the result of a cognitive mechanism that operates at an exogenous, stimulus-driven level. The cue in a classic IOR target detection task does, however, have a predictable temporal relationship with the target, which is evidenced by a foreperiod effect - decreasing RTs with increasing cue-target interval. Thus, whether or not the endogenous attentional system plays a role in the IOR effect remains unclear. The present study tested whether endogenous attentional mechanisms play a role in IOR by systematically decreasing the utility of the cue for preparing for target onset. This was achieved by presenting trials in which peripheral cues were not followed by targets (false alarms) on 0%, 5% or 25% of trials. Overall cue-target contingency was controlled by presenting trials without a peripheral cue preceding the target (misses) on 5% or 25% of trials. By eliminating the temporal utility of the cue, and thus removing a component of endogenous preparation, the IOR effect was attenuated, but not eliminated. The results suggest, contrary to widespread assumptions, that IOR is not solely an exogenous phenomenon, but is sensitive to contributions from endogenous mechanisms. The nature of this endogenous component of IOR is discussed with respect to existing literature as well as the current findings.  Ill  Table of Contents Abstract  ii  Table of Contents  iii  List of Tables  iv  List of Figures  v  Acknowledgements Introduction Method  vi 1 15  Participants  15  Apparatus & Stimuli  16  Procedure  16  Design  17  Results  18  Discussion  21  Footnotes  28  References  29  Figure Captions  39  LIST OF T A B L E S Table 1: Summary of Mean RTs Across Cue Error Groups  LIST OF FIGURES Figure 1: Mean R T as a Function of Trial Validity and SOA Figure 2: Size of the IOR Effect  ACKNOWLEDGEMENTS  The author would like to thank supervisors Dr. Alan Kingstone and Dr. Elton Ngan for their guidance, support, and countless hours spent teaching and talking. Thanks also to all of my B A R lab and SCI lab colleagues, who helped make this work fun. And finally, thank you to John, without whom this accomplishment could not have been made, and to my family, who gave me the strength to pursue my dreams.  1 A Critical Role for Endogenous Processes in Inhibition of Return Visual attention can be directed to particular regions of visual space, either in accordance with the direction of eye gaze, or independent of it (Posner, Nissen, & Ogden, 1978; Posner, 1988). Movements of attention that occur via the movement of the eyes or head are said to be overt shifts, while movements of attention that occur without such behaviors are said to be covert shifts. Both of these types of attentional shifts can take place with or without the observer's intention. Endogenous (volitional) attentional orienting refers to shifts of spatial attention that occur as a result of the observer's internal goals or intentions, while exogenous (reflexive) attentional orienting refers to shifts that occur without intention, driven by external stimuli in the visual scene (Jonides, 1981; Posner, 1981). The allocation of attention plays a major role in the efficiency of visual information processing, with more efficient detection of (awareness of and response to) stimuli at locations that are attended (Posner, Snyder, & Davidson, 1980; Mack & Rock, 1998). Importantly then, conscious visual perception is greatly influenced by the interplay of endogenous and exogenous attentional orienting (Posner 1980; Corbetta & Shulman, 2002; Posner & Rothbart, 1991; Rafal & Robertson, 1995). As such, there has been much interest in understanding the relationship between endogenous and exogenous attentional orienting processes, and a drive to identify not only their behavioral signatures, but also the conditions under which each type of attentional orienting will occur. In the laboratory, endogenous orienting has typically been manipulated by informing subjects that a response target has a high probability of appearing at a location indicated by a central or peripheral cue (Posner, 1980; Posner & Cohen, 1984). This  information is used to motivate participants allocate attention volitionally to the spatial location indicated by a cue in order to detect or identify a specific target with maximal efficiency. Exogenous orienting, however, is brought about typically by presenting an abrupt, high salience, high contrast luminance change at a location in the periphery (Jonides, 1981; Posner & Cohen, 1984; Taylor & Klein, 1998; Lambert & Hockey, 1991). Importantly, this exogenous cue does not predict with any reliability where the target will appear. The effects of attentional orienting can be observed via response times (RTs) for various tasks that involve detecting or making some decision about a target stimulus (Posner, 1978). The general finding is that RT (and/or response accuracy) is superior at locations that are attended relative to those that are unattended (Posner, Nissen & Ogden, 1978; Posner, 1980; Posner & Cohen, 1984; Taylor & Klein, 1998). The specific performance effects of attentional orienting are different depending on whether attention is oriented endogenously or exogenously. Although RT is facilitated for targets presented to attended locations regardless of whether attention is oriented to those locations endogenously or exogenously, the two types of orienting differ with respect to how and when attentional movements are made (Jonides, 1981; Muller & Rabbitt, 1989; Klein, Kingstone, & Pontefract, 1993; Rafal & Henik, 1994; Klein, 1994). Exogenous orienting occurs more quickly than endogenous orienting (Remington, 1978, as cited in Posner, 1980; Muller & Rabbitt, 1989; Cheal & Lyon, 1991), occurs without effort (Posner, 1990), occurs even amidst an ongoing task (Jonides, 1981), and has the potential to partially interrupt endogenous orienting (Jonides 1981, Muller & Rabbitt, 1989). Such dissociations in behavioral measures provide evidence that endogenous and exogenous orienting are separate cognitive processes (Muller & Rabbitt, 1989), and raise  3 the possibility that they are subserved by different neural systems (Posner, Snyder, & Davidson, 1980; Posner, 1980; Posner, Cohen, & Rafal, 1981; Corbetta & Shulman, 2002). Covert and overt orienting regularly co-occur in ordinary circumstances, as both are needed for detection of and response to relevant stimuli in a manner that promotes coordinated interactions with the environment. Consistent with this viewpoint, exogenous attentional orienting is assumed to be tightly associated with the eye movement system (Posner, 1980; Rafal & Egly, 1994; Posner, Crippin, Cohen, & Rafal, 1986). This adaptive, reflexive orienting system, encompassing both eye movements and covert attentional orienting, is thought to be mediated in phylogenetically more primitive neural systems, including the superior colliculus (Posner, 1980; Posner, 1981; Rafal & Egly, 1994, Rafal, Posner, Friedman, Inhoff, & Bernstein, 1988). Evidence for the role of the superior colliculus in exogenous covert attentional orienting has been obtained with healthy participants on the basis that the temporal visual hemifield is more richly connected with the superior colliculus than is the nasal hemifield, and the effects of exogenous orienting are more pronounced for peripheral cues occurring in the temporal hemifield. Moreover, neurological studies suggest that midbrain regions, including the superior colliculus, are essential for effective exogenous covert attentional orienting, while phylogenetically newer cortical regions are strongly implicated in endogenous attentional orienting (Posner, 1981; Rafal, 1996). Corbetta and Shulman (2002) recently reviewed neuroimaging studies that have examined the neural basis of attentional functions (e.g. Corbetta, Meizin, Shulman, & Petersen, 1993; Hopfinger, Buonocore, & Mangun, 2000). They found evidence for two  4 distinct cortical networks that seem to map onto the functions of endogenous and exogenous attention (see also Posner & Rothbart, 1991; Posner, 1992; although see Posner, 1995 for a discussion of additional networks involved in attention). The first network Corbetta and Shulman describe is the dorsal fronto-parietal network, which they argue underlies top-down control of visual attention. This network includes bilaterally the dorsal parietal cortex along the intraparietal sulcus, the superior parietal lobule, and extends anteriorly to the frontal eye field in the dorsal frontal cortex. These regions are consistently activated specifically when endogenous attention is brought about by informing observers about a relevant aspect of the visual scene to which they must respond. The second network identified, however, is not activated under conditions of endogenously directed attention. Rather, the right-lateralized ventral fronto-parietal network, including the tempero-parietal junction and the ventral frontal cortex, is activated when orienting attention to salient stimuli outside the focus of processing (see also Posner & Petersen, 1990; Posner, 1987). This result prompted Corbetta and Shulman to argue that the ventral fronto-parietal network may be critically involved in exogenous orienting. Thus it appears that exogenous covert orienting is underlain by both primitive subcortical as well as more recently evolved cortical functions, while endogenous orienting is mediated predominantly by cortical mechanisms. One phenomenon in particular, coined inhibition of return (IOR) (Posner, Rafal, Choate, & Vaughan, 1985), is probably the most highly cited distinction between the effects of endogenous and exogenous attentional orienting (see Klein, 2000 for a review). IOR refers to an inhibitory process that occurs at relatively longer intervals following a peripheral cue (e.g. 300-500 ms after cue onset). Posner and Cohen (1984) first observed  5 this inhibitory phenomenon in a study that examined target detection performance at variable intervals following either a peripheral or a central cue (i.e., under conditions of either exogenous or endogenous orienting, respectively). Posner and Cohen found that when a visual transient that did not predict the location of the impending target occurred in the periphery, target detection at the location of the transient was slowed at relatively longer intervals following the cue (i.e. the IOR effect was observed). It is a widely accepted assumption that in conditions of covert attentional orienting, IOR is the product of the exogenous orienting system alone. There are several reasons for this assumption. First, in Posner and Cohen's original (1984) study of IOR, it was demonstrated that IOR occurred at relatively long intervals following a spatially nonpredictive peripheral cue, a visual event that is known to capture attention automatically. Importantly, however, IOR did not follow a spatially predictive cue. In this situation RT was facilitated at the cued location even at relatively long cue-target intervals suggesting that endogenous orienting was committed to and maintained at the location predicted by the cue. Although the view that attention per se is a necessary process in the IOR effect has since been challenged (Taylor & Klein, 1998; 2000), there is ample evidence to suggest that exogenous attentional orienting contributes to the IOR effect (Kingstone & Pratt, 1998; Abrams & Dobkin, 1994; Reuter-Lorenz, Jha, & Rosenquist, 1996; Handy, Jha, & Mangun, 1999). Secondly, there is evidence to suggest that IOR is mediated by the primitive neural system that is implicated in exogenous, stimulus-driven orienting. Posner et al. (1985) were the first to show a close relationship between IOR and the saccadic eye movement system, and that midbrain regions implicated in the control of eye movements,  6 including the superior colliculus, may be necessary to generate IOR. They found that patients with progressive supranuclear palsy, whose ability to make voluntary saccades is compromised, do not exhibit IOR. Other research has addressed the role for nasaltemporal visual field retino-tectal asymmetry in the IOR effect, finding that experimental manipulations that affect the time course of IOR in the nasal visual field do not affect IOR in the temporal visual field (Berger & Henik, 2000). Given that the temporal visual field is much more richly connected with the superior colliculus, these findings bolster claims that IOR is mediated in the primitive exogenous system. More direct evidence to suggest a crucial role for the superior colliculus in IOR was obtained by studying a patient with a rare unilateral superior colliculus lesion caused by a hemorrhage (Sapir, Soroker, Berger, & Henik, 1999). This unique study revealed that IOR emerged only in the visual hemifields that projected to the intact side of the superior colliculus. Finally, the argument that IOR is a phenomenon of the primitive exogenous orienting system also receives support from another branch of IOR research that investigates the functional significance of the phenomenon. Posner and Cohen's (1984) initial interpretation and many studies that followed, suggested that IOR serves an adaptive role in effective visual search of the environment (Tipper, Driver & Weaver, 1991; Pratt, O'Donnell, & Morgan, 2000; Cheal, Chastain, & Lyon, 1998; Danzinger, Kingstone, & Snyder, 1998; Klein, 1988). Specifically, IOR seems to promote attending to novel locations in the visual scene by inhibiting return of attention to previously attended locations. Obviously, such a mechanism would be evolutionarily beneficial in terms of foraging for food or scanning the environment for dangers. This suggestive evolutionary connection lends further support to the argument that IOR is a function of  the primitive exogenous system. Although there is plenty of evidence to suggest that the exogenous orienting system plays a critical role in IOR, this does not rule out the involvement of endogenous factors. Granted, in studies of IOR utilizing covert attentional orienting, IOR is not found when attention ought to be voluntarily allocated to a particular location based on the spatially predictive value of the peripheral cue. Nevertheless, there are several reasons to question the ubiquity of the exogenous orienting system in IOR and to suspect a role for other forms of endogenous cognitive control. Rafal and Henik (1994) suggest the possibility that the inhibition seen in IOR may share some properties with the top-down inhibition seen when purposefully controlling overt or covert orienting of visual attention. They view inhibition involved in controlling covert orienting as an endogenous process that helps satisfy the need to solve what is often a competition between environmentally triggered reflexes, and a person's goal and intentions. One could not function coherently if distracted by every flash or movement in the periphery. In this regard, Rafal and Henik argue that IOR may well serve to promote effective interactions with the environment, at least in terms of controlling or mediating stimulus-driven attentional or occulomotor scanning of the scene (e.g. Law, Pratt, & Abrams, 1995; Snyder & Kingstone, 2000). Rafal and Henik submit that the neural system generating IOR and whether it is generated endogenously or exogenously may depend on the task at hand. Although these arguments are speculative, they certainly suggest that the widely accepted claim that IOR is a purely exogenous phenomenon may be questioned. There is further evidence suggesting the necessity to test the assumption that IOR is purely exogenous. First, contrary to initial assumptions, attentional capture by  8 peripheral cues is not completely stimulus-driven, as top-down control appears to be critical to its occurrence (Yantis & Jonides, 1990; Yantis & Johnston, 1990; Yantis, 1993; Theeuwes 1991; Folk, Remington, & Johnston, 1992). Rafal and Henik (1994) also argue against the view that exogenous orienting is like a reflex. They show that covert exogenous orienting can be inhibited at least partially by creating task demands that favour attending to a location opposite to a peripheral cue. Second, in the context of overt orienting, as measured by saccade latencies, IOR can be generated with endogenous saccades (Rafal & Egly, 1994). Third, the time course of IOR can be modulated by strategic factors (Lupianez, Milliken, Solano, Weaver, & Tipper, 2001). Lupianez et al. demonstrated that two different manipulations designed to increase task difficulty had differential effects on the time course of IOR, one increasing the cue-target interval at which IOR emerged, and one decreasing it. Specifically, increasing the perceptual difficulty of the target discrimination task by requiring " M " - " N " letter discriminations as opposed to " X " - " 0 " letter discriminations or simple luminance detection delayed the emergence of IOR. Conversely, presenting the target with an asterisk distractor at the location opposite the target, and thereby increasing the difficulty of target selection, speeded the emergence of IOR, regardless of the discrimination required. Lupianez et al. argued that presenting the distractor with the target changed the strategic configuration for the task, and that this difference in strategy is what altered the time course of the IOR effect. To bolster their argument for strategic reconfiguration, they cited a result from Lupianez and Milliken (1999) that showed that a cueing effect at 400 ms was altered not by the presence or absence of a distractor on a particular trial, but by the proportion of distractors in a set of trials. Thus, it was not the distractor stimulus per se that was  9 influencing the results, but the participant's expectations about whether a abstractor might occur. Here again we see the potential for the influence of endogenous attentional processes on IOR. Together, these lines of evidence suggest indirectly that IOR may not be solely a phenomenon of the exogenous system. The present research springboards from studies suggesting that the time course of IOR is tightly linked to strategy. In the context of the testing environment, where participants are required to perform a particular task, one strategy that makes sense regardless of the task is to prepare for an expected event. This preparation utilizes the ability to direct attention to the temporal domain in order to attempt to be maximally ready for the target when it occurs. In nearly all studies of IOR using abrupt peripheral onsets and multiple stimulus onset asynchronies, a classic foreperiod effect can be found to co-occur with the IOR phenomenon. This foreperiod effect is generally reflected as a systematic decrease in RT that occurs during approximately the first second of preparation time. In the context of IOR experiments, although the peripheral cue is not spatially predictive, it nevertheless serves as a temporal warning signal for the impending target, which motivates participants to get ready to detect and respond to the target. A warning signal brings about both immediate alerting processes that can be thought of as behaving like reflexes, as well as volitional processes that operate in accordance with the goals and intentions of the observer (Bertelson, 1967; Bernstein, Chu, Briggs & Schurman 1973; Sanders, 1972, 1975). While reflex-like alerting processes enable faster response times, they also increase error rates (Posner, Klein, Summers & Buggie, 1973; Posner 1978) suggesting that while alerting processes prime response systems to go, they do not do so in accordance with the intentions of the participant. Klein and Kerr (1974)  10 suggested that alerting operates not at sensory or motor stages, but at the level of a central "decision" mechanism, which when more alert, samples the results of sensory processing stages more rapidly. Thus, a "decision" is made perhaps before adequate information about the stimulus is available to the relevant cognitive operations. Voluntary preparation, on the other hand, reduces response times without a concomitant increase in error rate (Holender & Bertelson, 1975). It is this aspect of endogenously controlled voluntary preparation enabled by the warning signal, and evidenced as a foreperiod effect, that is of specific interest to the present study. Thomas (1974) pointed out that preparation goes hand in hand with expectancy, arguing that it makes little sense to prepare for something if it is not expected to happen. Consistent with this position, studies have shown that the timing of preparation is influenced by the distribution of possible cue-target intervals (e.g. Naatanen, 1970). Thus, the less certain a participant is about when a target will occur, the less prepared that participant will be to respond when that target does occur (Sanders & Wertheim, 1973). Holender & Bertelson (1975) point out that a reduction of the temporal window in which a stimulus might occur from 5000 ms to 500 ms improves both the speed and the accuracy of responding. This effect does not depend on preparing selectively for a particular response, but rather reflects a general readiness to respond. This nonselective preparation is maximized when participants are able to predict when they will need to make a response. Thus, temporal expectancy plays a role in a participant's readiness to respond regardless of what that response will have to be. Although the preparedness is nonspecific with respect to the response, the fact that temporal expectancy is a necessary factor bolsters the claim that this preparation process is generated endogenously (see also  11 Kingstone, 1992). Depending on the task, preparatory adjustments can begin as little as 50 ms after the warning signal (Bertelson, 1967), or as long as seconds after the signal. Therefore temporal preparation effects are very much in play at the intervals tested in most IOR experiments. Endogenously generated preparation is most certainly present in all studies of IOR that show an overall decline in reaction time with increasing SOAs. Therefore, it is possible that this endogenous component is a critical factor in the emergence of IOR, perhaps even playing a necessary role in the generation of IOR. There is some evidence to suggest such a link between voluntary preparation and IOR. Snyder and Kingstone (2001) showed that the IOR at multiple successive locations was eliminated when participants did not need to voluntarily attend to each cue. Multiple IOR, first observed by Danzinger, Kingstone and Snyder (1998), refers to the phenomenon whereby inhibition effects are found not only at the previously peripherally cued location, but also at the peripheral location cued before that, and so on. Snyder and Kingstone's original question was whether attention to each peripheral onset was necessary for multiple IOR to occur. In their first experiment, they tested whether multiple IOR occurred when participants knew in advance which onsets would be cues and which would be targets. A comparison was made between a random condition, in which cued 1-back, cued 2-back, and cued 3-back targets were randomly intermixed, and a blocked condition in which each type of trial was presented in its own consistent block. The logic was that if participants knew how many cues would precede a target in the blocked condition, then they would not need to attend to each onset, and multiple IOR should be abolished. Interestingly, this manipulation did not do away with multiple IOR,  12 which was found at all three sequentially cued locations. A subsequent experiment examined whether participants were actually attending to onsets in the predictable condition in order to keep track of the number of onsets that had occurred prior to target onset. This interpretation would explain why multiple IOR had persisted in the blocked condition. In this sense, and without intending to, Snyder and Kingstone were proposing an integral link between voluntary preparation and spatial attention in the context of their cue-target detection task, whereby attending voluntarily to the passing of cues in order to prepare for the target directed spatial attention to those cues. The results of this follow up study revealed that when the need to attend to onset cues in order to keep track of them was removed by putting a cue counter at fixation, multiple IOR was indeed eliminated in the blocked condition, but not in the random condition . They concluded that multiple 1  IOR is an attentional phenomenon that occurs when attention is directed to multiple onsets. What their results also suggest is that voluntary preparation for an impending target may be critical for the occurrence of IOR, at least in the case of multiple IOR. This raises the possibility that the voluntary foreperiod effect present in IOR studies is actually not independent from the IOR phenomenon at all, but rather an integral part of it. Thus we find that although IOR is assumed to be a strictly exogenously generated phenomenon, there are many lines of evidence to suggest that it may be critically modulate by endogenous mechanisms. The present study was designed to test whether endogenous mechanisms involved in temporal preparation for an impending target are critically involved in the emergence or modulation of IOR. The logic for the present study was that if endogenous mechanisms are an integral component of the emergence of the IOR effect, then removing endogenous mechanisms  13 should eliminate or reduce the IOR effect. Voluntary preparation, a process contributing a substantia] endogenous component in target detection tasks, can be prevented by abolishing the temporal utility of the cue for predicting the onset of the target. To this end preparation was eliminated by adding a large number of trials in which a peripheral cue was presented without subsequently presenting a target. If participants are using the cue as a warning signal to prepare for the impending target, and no target occurs, the temporal warning function of the cue can be said to have "false alarmed". The decision to eliminate preparation effects by including trials in which the cue false alarms was based on evidence from several studies. When considering alerting systems for hazardous situations, such as those used in aviation, an important aspect of the effectiveness of the system is its trustworthiness (Pritchett, Vandor, & Edwards, 2002). Trustworthiness refers to the extent to which an operator ought to rely on the warning signals given by the system. A common problem for trustworthiness in such systems is the tendency to false alarm. Getty, Swets, Pickett and Gonthier (1995) quantitatively tested the effect of false alarms, finding that responding to a warning signal was significantly retarded by lowering the probability that the warning would actually predict a pre-specified event. In an analogue of an automobile braking task (Nickerson, Collins & Markowitz, 1969), where depression of a foot pedal was required in response to a danger signal, the higher the probability of the danger signal following the warning signal, the greater the preparatory effect on the foot pedal press (i.e. the greater the difference between the warning and no warning RTs). Given these results showing that false alarms via warning signals detrimentally affect preparation, it was hypothesized that the foreperiod effect that accompanies most IOR findings, indicating voluntary temporal  14 preparation for the target, would be eliminated by presenting a number of warning signal false alarms. A pilot study suggested that presenting false alarms on 25% of trials would eliminate the foreperiod effect. The elimination of the foreperiod effect by adding false alarms of the peripheral cue on 25% of trials can be interpreted as indicating that participants no longer attend endogenously to the cue in order to prepare for the target. Although the evidence discussed previously would suggest that this is the case, it is possible that one might argue that the foreperiod effect was eliminated not because of the presence of false alarms per se, but instead because of a break in the overall contingency between cue and target. It is possible that this element of uncertainty, or unpredictability about what events are to occur on a given trial may have induced a strategic process that emphasized cautious responding, thereby flattening the foreperiod function. In order to be certain that adding false alarms indeed prevents endogenous attentional mechanisms from being applied to the cue for the purpose of voluntary preparation, it is important to show that false alarms, and not just any break in cue-target contingency, remove the foreperiod effect. Therefore, not only was the effect of adding false alarms examined, but also the effect of adding trials in which a target is presented without having been preceded by a cue. These "misses" by the cue affect the overall cue-target contingency in a similar manner to false alarms, but they should not affect the utility of the cue for preparing for the target. In other words, unlike false alarm trials, presenting miss trials does not change the probability that a target will occur given the presentation of the cue. In summary, the present study tested whether the IOR effect could be modulated by abolishing voluntary preparation for the target based on temporal information  15 provided by the presentation of the peripheral cue. False alarms were used to manipulate whether participants did or did not use the cue to prepare for the target. The elimination of voluntary preparation was operationalized as an absence of the classic preparatory foreperiod effect of decreasing RT with increasing SOA. If IOR is modulated when voluntary preparation does not take place, then one may conclude that this endogenous mechanism (perhaps only one of several relevant endogenous mechanisms) plays a fundamental role in the generation or expression of the IOR effect. This would counter the traditional view that IOR is a phenomenon of the primitive exogenous attentional system alone. On the other hand, IOR remaining unaffected when voluntary preparation is eliminated would support the widely held view that IOR is a phenomenon of the exogenous system alone. Method Participants A total of 50 participants at the University of British Columbia participated in exchange for course credit. Participants were assigned randomly to one of five experimental groups (N = 10); a baseline group (BL), a 5% false alarm rate group (5FA), a 25% false alarm rate group (25FA), a 5% missed cue rate group (5MC), and a 25% missed cue rate group (25MC). Mean age was 20.1 years (s = 2.69) for the OFA group (6 females), 21.5 years (s = 6.08) for the 5FA group (8 females), 19.8 (s = 3.05) for the 25FA group (7 females), 20.1 years (s = 1.20) for the 5MC group (7 females), and 20.2 years (s = 1.55) for the 25MC group (5 females). A l l participants were naive as to the purpose of the experiment.  16 Apparatus and Stimuli Stimuli were presented on a 17-inch colour V G A monitor. A 486/33 I B M compatible computer running Presentation software (Neurobehavioral Systems) controlled stimulus presentation and data collection. The stimulus display consisted of white figures on a black background, including a fixation dot (subtending 0.3° visual angle) at the center of the screen, two square placeholder outlined boxes located 6.5° to the left and to the right of fixation, each subtending 2.5°. The target letter ' X ' , subtending 1.25°, could appear centered within the boundaries of either of the two boxes. The target stimulus was preceded by a peripheral cue, which consisted of the brightening of one of the boxes. This brightening effect was achieved by briefly increasing the thickness of the box outline from 1-point to 5-point. Participants responded to the target letter by pressing the space bar on a standard keyboard. Procedure Participants were tested individually in a small testing room equipped with a single computer. They were seated 57 cm from the monitor with the center of the monitor at eye level. Participants were instructed to maintain fixation on the central dot on each trial, and to press the space bar as quickly as possible when a target ' X ' appeared in the periphery. They were informed that the peripheral cues did not predict where the target would occur, but they were not told about the degree of cue-target contingency, or which, if any, type of cue error would occur. Each trial began with the presentation of the fixation dot and the boxes. 750 to 1250 ms after their onset (randomly selected within this range at 50 ms increments) one of the boxes brightened for 75 ms, then returned to its original state. The target could appear 100 ms, 500 ms, or 1000 ms after the onset of the  peripheral cue. Which of these durations preceded target onset was random and equiprobable, as was the location of the target. The target was as likely to appear at the location of the cue (valid trial) as the location opposite the cue (invalid trial). The target remained on the screen until the spacebar was pressed, after which the target was removed and the next trial began. Response times (RTs) were measured from the time of target onset to response execution. On false alarm trials, the timing of events was the same with the exception that no target was presented. As such, no response was to be executed and the trial timed out after 2500 ms (i.e. ranging from 1250 to 1750 ms after cue onset, in 50 ms increments). On missed cue trials, no cue was presented before the target appeared. On these trials, the timing of stimulus presentation was the same as it would have been had cues been included, but the cues were simply omitted. Rest breaks were provided every 160 trials. Participants terminated each rest break by pressing the spacebar when they felt ready to begin the next block. Design A 5 x 2 x 3 between-within design was employed, with Cue Error Group as a between-subjects factor (BL, 5FA, 25FA, 5MC, and 25MC), and trial Validity (valid and invalid) and SOA (100 ms, 500 ms, and 1000 ms) as within-subjects factors. For all groups, there were 5 blocks of 160 trials each, for a total of 800 trials for each participant. There were always an equal number of valid and invalid trials, and left and right targets. For the B L group, a target was presented on all 160 trials in each block. For the 5FA group, there were 8 false alarm trials per block (5% of each block). For the 25FA group, 40 of the trials in each block were false alarms (25% of each block). For the 5MC group, there were 8 missed cue trials per block (5% of each block). For the 25MC group, 40 of  18 the trials in each block were misses (25% of each block). Results Mean RTs are listed in Table 1. RTs as a function of Validity and SOA are plotted graphically for each group in Figure 1. A l l analyses were performed on data obtained from trials in which both a cue and a target occurred. Response anticipations (< 100 ms) and failures to respond in a speeded manner (> 1000 ms) were removed from the analysis. As seen in Figure 1, the most striking aspect of the data is the complete elimination of the foreperiod effect in the 25FA group (Figure IE). This flattening of the foreperiod effect suggests that participants are no longer employing endogenous mechanisms to prepare for the target during the interval following the cue. In all other groups, there is a decline in RT with increasing SOA. IOR appears to be present in all five groups, but importantly, IOR is attenuated in the 25FA group. No such modulation of IOR occurs in the 25MC group. Thus it appears that when the cue does not serve as a useful means by which to direct endogenous attentional mechanisms, i.e., when the cue does not temporally predict the target with useful reliability, the IOR effect is reduced. The statistical significance of these observations was tested with a 3-factor between-within A N O V A , with Cue Error Group as a between-subjects factor (BL, 5FA, 25FA, 5MC, and 25MC), and Validity (valid and invalid) and SOA (100 ms, 500 ms, and 1000 ms) as within-subjects factors. There was a significant Cue Error Group X SOA interaction [F(8, 90) = 5.65, p < .001], indicating that the SOA effect differed significantly between groups. In order to assess the nature of the SOA effect in each group, the Cue Error Group X SOA interaction was followed up with a separate 2-factor (Trial Validity x SOA) within-subjects A N O V A for each group. These follow-up  19 analyses revealed main effects of SOA for the B L [F(2, 18) = 31.13, p < .001], 5FA [F(2, 18) = 7.525, p < .005], 5MC [F(2, 18) = 21.89, p < .001] and 25MC [F(2, 18) = 20.00, p < .001] groups. In contrast, there was no main effect of SOA for the 25FA group [F(2, 18) = .06, p > .50]. Linear contrasts based on the follow-up A N O V A s show that the main effects of SOA in the 0ER, 5FA, 5MC and 25MC groups represent roughly linear declines in response time with increasing SOA [F(l, 9) = 36.86, p < .001; F ( l , 9) = 9.07, p < .05; F ( l , 9) = 30.81, p < .001; F ( l , 9) = 34.83, and p < .001, respectively], indicating the presence of foreperiod effects. The overall 3-factor A N O V A also revealed a significant Validity X SOA interaction [F(2, 90) = 128.19, p < .001]. This interaction was followed up with separate 1-factor repeated measures A N O V A s testing the Validity effect at each SOA. The follow up analyses revealed that the Validity X SOA interaction represented faster RTs for valid than invalid trials at the 100 ms SOA [F(l, 49) = 15.48, p < .001], and slower valid than invalid trials at the 500 ms [F(l, 49) = 99.87, p < .001] and 1000 ms [F(l, 49) = 225.01, p < .001] SOAs. This early facilitation of RTs for valid trials followed by a later inhibition effect is the classic pattern of RTs associated with IOR. Importantly, this biphasic pattern of early facilitation and later IOR did not vary significantly across Cue Error Group, as evidenced by the absence of a significant 3-way Cue Error Group X Validity X SOA interaction [F (8, 90) = .52, p > .50]. Thus, IOR was not eliminated by making the cue useless for endogenous preparation. In order to examine specifically the modulation of the IOR effect caused by abolishing the temporal utility of the cue (as evidenced by the flattening of the foreperiod function), an additional set of analyses were conducted comparing baseline group  performance with each other group, for only the 500 ms and 1000 ms SOAs (i.e., only the SOAs relevant to IOR). Four 2 x 2 x 2 between-within A N O V A s with Cue Error Group as a between-subjects factor and Validity and SOA (500 ms, 1000 ms) as within-subjects factors were conducted. A significant Cue Error Group x Validity interaction in the B L vs. 25FA comparison showed that the IOR effect was attenuated in the 25FA group [F (1, 18) = 5.03, p < .05]. The size of the IOR effect was not significantly different from baseline in any of the other groups. Figure 2 compares the size of the IOR effect in the M C and F A cue error groups to that in the baseline group. The fact the size of the IOR effect was the same in the B L and 25MC groups suggests that the modulation of IOR in the 25FA group was indeed related to the reduction of temporal predictability and not merely a break in the cue-target contingency. In addition to the effects reported above, the overall 3-factor A N O V A revealed a significant main effect of Cue Error Group. By examining Figure 1, one might assume that this main effect was due to an overall slowing of RTs in the 25FA group compared to the rest of the groups. Indeed, if RT is averaged over Validity and SOA, an independent samples t-test between the B L group and the 25FA group shows that overall RTs are slower in the 25FA group [t(18) = 3.33, p < .01]. This difference, however, is not due to RTs being generally slowed in the 25FA condition, but due to the foreperiod effect being eliminated. In other words, there was no decline in RTs between the early (100 ms) and later (500 ms and 1000 ms) SOAs because the foreperiod effect was eliminated. This point is reinforced by the observation that RTs in the 25FA and B L conditions were equivalent at the 100 ms SOA, [t(18) = 2.02, p > .05]. The percentage of anticipatory responses was calculated for each participant.  21 Anticipatory responses did not vary in amount across Cue Error Group [F (4, 45) = 2.00, p > .10], and were rare ( M = 2.1%). Discussion This study investigated the widely held assumption that IOR is a phenomenon of the exogenous attentional system alone. Although peripheral cues in target detection tasks used to investigate IOR are nonpredictive with respect to the spatial location of the target, they do provide temporal information regarding the onset of the target. In fact, it has been argued that the pattern of declining RTs with increasing cue-target SOAs found in most IOR studies using a target detection task indicates that participants employ endogenous mechanisms to actively prepare for target onset based on the presentation of the cue. Thus, the peripheral cues in the traditional IOR paradigm are far from being irrelevant. While studies of IOR have assumed the involvement of exogenous attention alone based on the spatial irrelevance of the cues, they have overlooked the fact that the cues are actually highly relevant for preparing when to respond to the target. Thus the IOR effect as it is known in the literature may actually depend critically on this endogenously controlled preparatory process. The present experiment tested the effect of manipulating the temporal utility of the cue on IOR. It was hypothesized that if endogenous processes, preparation in particular, are critical to IOR, then setting up conditions in which they are not likely to occur (i.e. presenting a large percentage of false alarms) should reduce or eliminate the IOR effect. This is precisely what was found. When the utility of the cue for predicting target onset was reduced to a level at which participants no longer used the cue to prepare to respond (25FA), the IOR effect was significantly diminished relative to a baseline condition (BL). This result suggests that the endogenous process of temporal  22 preparation is a critical factor in the IOR effect. Thus, IOR is not solely an exogenous phenomenon, but rather depends on the deployment of endogenous mechanisms for its fullest expression. Importantly, the reduction of the IOR effect did not occur in the 25MC condition, although the same reduction in overall cue-target contingency was present as in the 25FA group. Thus the reduction of IOR can not be attributed to general uncertainty about what events were to occur on each trial, or to a general break in the relation between the cue and the target. Rather, the reduction of IOR that occurred in the 25FA group can be attributed solely to the elimination of voluntary preparation for when the target will occur in response to the presentation of the cue. I have argued that the reduction of IOR in the 25FA group is the result of removing a substantial endogenous component from the cognitive operations involved in performing the task. It is possible, however, that one might argue that the reduction of IOR in the 25FA group was due to a general slowing in RT. As described in the results, the comparison of overall RTs averaged over Validity and SOA between the B L and 25FA groups showed significantly slower RTs in the 25FA group than in the B L group. This difference, however, can be attributed to the lack of a foreperiod effect in the 25FA group, as there was no significant difference in RT between the B L and 25FA groups when only the 100 ms SOA is considered. Nevertheless, one may still wish to argue that the IOR effect is modulated in the 25FA group because of a ceiling effect, whereby RTs for the valid trials can not get any slower than approximately 400 ms, thereby reducing the difference in RT between valid and invalid trials. The present data, however, do not support this argument. First, there was no significant difference in overall RTs between  23 the 25FA and 5FA groups [t(18) = 1.97, p > .05]. Thus, while RTs in the 25FA group were not significantly slower overall than those in the 5FA group, there was an attenuation of the IOR effect in the 25FA group that was not present in the 5FA group. Second, although this potential ceiling effect is described in terms of RTs for valid trials being unable to get any slower, and thus compressing the gap between valid and invalid RTs, it is important to note that IOR slows RT at the valid location and speeds it at the invalid location (Klein, 2000). In that regard, there is every opportunity for RTs at the invalid location to improve. Third, the largest facilitation effect (invalid - valid RT) at the 100 ms SOA is seen in the 25FA group (see Figure IE). This suggests that the 25FA condition was sensitive to express any attentional differences between valid and invalid trials that were present. Moreover, the robust facilitation effect that remains despite the modulation of the IOR effect in fact represents a dissociation between facilitation and IOR, a finding in line with claims that different cognitive and neural mechanisms may underlie the two effects (e.g. Pratt, Sekuler, & McAuliffe, 2001; Danzinger & Kingstone, 1999). While the results of the present study provide evidence that endogenous attentional mechanisms play an integral role in the IOR effect, a previous study by Pratt, Sekuler, and McAuliffe (2001) concluded that attentional control settings might not have any influence on IOR. Experiment 2 of their study examined all four combinations of onset and colour cues and targets in a cue-target discrimination paradigm. They looked for differences in the IOR effect depending on whether the cue-target combinations were blocked or random. They hypothesized that if attentional control settings play a role in IOR (as they do in early attention cueing), there should be significant differences between  24 IOR effects in the blocked and random conditions. According to their logic, if attentional control settings are critical to IOR, then when participants expect an onset target IOR should only occur for onset cues, and when participants expect a colour target IOR should only occur for colour cues. Such a pattern was not expected in the random condition. Their results showed no such pattern, and no differences in IOR across blocked and random conditions, which led them to confirm the null hypothesis in concluding that attentional control settings have no effect on IOR. If attentional control settings, endogenous mechanisms that allow participants to prepare for a particular stimulus, do not in fact influence the IOR effect, it becomes difficult to interpret the influence of temporal predictability on IOR found in the present research. I propose that temporal preparation may be one of several ways that the endogenous attention system uses information conveyed by the spatially irrelevant cue to prepare to respond to the target. If attentional control settings do not influence IOR, then this proposal may need to be reconsidered in favor of an interpretation for the present results specific to the process of temporal preparation. Working from the view that temporal preparation and attentional control settings are two instances from the same "pool" of non-spatial endogenous processes, then the result of the present study would seem to contradict that of Pratt et al. While it is suggested here that endogenous mechanisms do influence the IOR effect, Pratt et al. conclude that endogenous mechanisms do not. It is important to note, however, that IOR only occurred in their experiment in the onset-onset cue-target combination for both blocked and random conditions. The fact that IOR did not occur in the random condition for any of the other cue-target combinations or in the colour-colour combination in the blocked condition suggests that the particular task and stimulus parameters employed  25 simply did not provide conditions conducive to the emergence of IOR. The lack of differentiation of the IOR effect across the blocked cue-target combinations is thus not surprising. Simply put, something that does not exist is not able to differentiate. Therefore, the fact that there are no systematic differences between IOR effects in the blocked and random conditions may not speak to the absence of any effect of attentional control settings on IOR per se, but rather to the absence of any IOR. It is intriguing to question the specific nature of the role played by endogenous mechanisms in the emergence of IOR. One may argue that there is actually a component of endogenous attention in the IOR effect. That is, a portion of the IOR effect arises specifically as a result of endogenous attention being directed to some aspect of the cue. Alternatively, one may argue that IOR has no endogenous attentional component per se, but that there is an interaction between the mechanisms subserving IOR (e. g. the superior colliculus) and the utility of the peripheral cue with respect to some aspect of the target that serves to enhance IOR, irrespective of whether attention is oriented to the cue exogenously or endogenously. While there is little evidence to suggest that endogenous attentional orienting per se is critical to the IOR effect, there is good reason to support the latter view that cue utility serves to enhance IOR. For example, consider the finding that IOR occurs in a visual search task as a result of eye movements between items in the field (Pratt & Abrams, 1995). These eye movements are clearly not the result of exogenous orienting alone, but nevertheless, IOR is found. This example of IOR in visual search illustrates that IOR occurs in the context of purposeful, goal-directed overt orientations of visual attention and eye gaze. Furthermore, Rafal, Calabresi, Brennan, and Sciolto (1989) demonstrated that preparing  26 an endogenously generated saccade was sufficient to produce the IOR phenomenon. The fact that IOR occurs in the absence of purely exogenous attentional shifts necessitates a distinction between the mechanisms that subserve IOR and the cognitive process of exogenous orienting (e.g. Taylor & Klein, 2000; Kingstone & Pratt, 1999). These two concepts have been conflated in the literature because of the invocation of exogenous orienting in the definition of IOR (e. g. Mondor, 1999) and the invocation of IOR in the definition of exogenous orienting (e. g. Theeuwes & Godijn, 2002). It makes little sense to limit the conceptualization of IOR to exogenous orienting because IOR occurs under conditions of endogenous attention when the attended items provide information relevant to the performance of the task at hand. In the case of visual search, the essential information provided by a non-target is that the target is not present at that location. Thus, the non-target item (which can be thought of as the cue) informs the participant to continue searching. This view of IOR as being enhanced in the context of a meaningful, useful cue is consistent with Rafal and Henik's (1994) argument discussed previously that IOR serves to promote effective visual interaction with the environment. In this vein, the distinction between exogenous and endogenous orienting with respect to IOR is second to the nature of the task and the observer's goals. Rafal and Henik argue that IOR may even be a mediating process in the constant competition and interaction of task-driven behavior and environmentally triggered reflexes. The fact that IOR was modulated, but not eliminated, in the present experiment suggests that perhaps the IOR effect is maximized when there is an interaction of exogenous and endogenous attentional mechanisms. Such a condition is met when the cue in an IOR task has attributes that promote the orienting of both  exogenous and endogenous attention, i.e., if the cue has utility. If indeed IOR is a process that serves people in a useful way, it makes sense that it would be maximized under conditions that most closely resemble those found in everyday life. As such, it would be expected that IOR would not occur in a situation where visual cues contained absolutely no relevant information that could be used to act accordingly on a visual target. Under this view, the residual IOR effect (the lessened, but still present IOR in the 25FA group) in the present experiment may be attributed to the cue still containing some relevant information about the target, for example colour, horizontal plane, or approximate size. Whether or not completely irrelevant cues would come into play at all in a real-world visual scene during some goal-driven behavior is highly questionable. Conversely, it is also unlikely that there are real-world situations where visual attention is guided solely by endogenous mechanisms. Several authors have argued that orientation of visual attention is always the result of an interplay between endogenous and exogenous processes, and their neural mechanisms (e. g. Corbetta & Shulman, 2002; Rafal & Robertson, 1995). As such, experimental situations in which attention must be oriented solely endogenously and held in wait are artificial and contrived, and do not likely reflect the scope of attentional processes at work in an individual behaving in the real world. From this perspective, then, it is perhaps not at all surprising that IOR does not occur when attention is oriented endogenously alone. Although this line of reasoning is speculative, it is relevant to understanding the significance of the phenomenon of IOR in terms of a cognitive process that occurs in naturally behaving people. The present research has examined the question of whether endogenous  28 mechanisms play a role in the IOR effect as it is described in the literature. Although the cue in a classic IOR task has traditionally been assumed to be irrelevant with respect to the target, it has been argued here that peripheral cues actually provide very relevant information regarding not where, but when the target will occur. When the endogenous process of temporal preparation is eliminated, the IOR effect is reduced. The results of this study suggest, contrary to popular assumption, that IOR is not in fact a phenomenon of the exogenous attentional system alone. The interaction of exogenous and endogenous processes in IOR is interpreted here as indicating that IOR is maximized when the cue has some meaningful utility in the task at hand. The importance of utility in IOR is an intriguing link between isolated cognitive mechanisms studied in the laboratory and people functioning in a meaningful world, and should be examined in future research. 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Abrupt visual onsets and selective attention: Voluntary versus automatic allocation. Journal of Experimental Psychology: Human Perception and Performance, 16, (1) 121-134.  38 Table 1 Summary of Mean RTs Across Cue Error Groups Cue Error Group SOA (ms) 100  500  1000  Validity (V/I)  BL  5MC  25MC  5FA  25FA  V  349  360  343  362  380  I  356  367  355  369  396  V  353  358  347  359  399  I  320  328  314  335  380  V  330  336  326  360  399  I  302  308  299  331  381  39  A) BL  420 400 -  - Valid  380 360 -  •- Invalid  340 320 300 280 L  100  500  1000  S O A (ms)  B) 5MC  420  C) 25MC  400 380  E  360 340 320 300 280 100  500 SOA (ms)  D)  420  1000  100  500 S O A (ms)  1000  E)25FA  5FA  400  ~  380  •§• 360 340 320 300 280 100  500 S O A (ms)  1000  100  500 S O A (ms)  1000  Figure 1. Mean RT as a function of trial validity and SOA, plotted separately for each cue error group. B L refers to the baseline group; 5MC to the 5% missed cue group; 25MC to the 25% missed cue group; 5FA to the 5% false alarms group; and 25FA to the 25% false alarms group.  40  40  •H  30 p"  ~  >  o  s  £  r-  ^  a: g2  •  FA MC BL  20 h  io h 5  25  Cue Error Probability (%)  Figure 2. Size of the IOR effect as a function of cue error type (MC vs. FA) and cue error probability (5 vs. 25). The size of the IOR effect in the B L group is indicated with a dotted line for comparison.  

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