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UBC Theses and Dissertations

An electrocortical investigation of word recognition in a backward masking paradigm Brandeis, Daniel Ulrich 1982

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AN ELECTROCORTICAL INVESTIGATION OF WORD RECOGNITION IN A BACKWARD MASKING PARADIGM. by DANIEL ULRICH BRANDEIS DIPL. NATW., EIDGENOESSISCHE TECHNISCHE HOCHSCHULE ZUERICH, 1 979 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS in THE FACULTY OF GRADUATE STUDIES PSYCHOLOGY DEPARTMENT We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA AUGUST 1982 © DANIEL ULRICH BRANDEIS, 1982 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. requirements for an advanced degree at the University Department The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6 (3/81) i i A b s t r a c t Three aspects of stimulus content, i . e . meaningfulness, f a m i l i a r i t y and task r e l e v a n c e , were manipulated without the. s u b j e c t s awareness. A number of s u b l i m i n a l (backward-masked) s t i m u l i were presented to the sub j e c t whose task i t was to estimate an i n t e r v a l of 1 sec ( s t a r t i n g with the p r e s e n t a t i o n -f l a s h ) by p r e s s i n g a button. S u p r a l i m i n a l words were randomly i n t e r s p e r s e d among these, s u b l i m i n a l s t i m u l i , appearing above or below the masked f i e l d . Whenever the sub j e c t d e t e c t e d a p r e v i o u s l y a s s i g n e d t a r g e t among the s u p r a l i m i n a l s t i m u l i , he/she was r e q u i r e d to press the button as f a s t as p o s s i b l e . The meaningfulness of the s u b l i m i n a l m a t e r i a l was manipulated using words, nonwords and blanks. Three groups of words were ' used: the t a r g e t s , the nontargets and other, 'new' words (which were never presented s u p r a l i m i n a l l y ) . Task relevance ( t a r g e t s vs. nontargets) and f a m i l i a r i t y ('new' words vs. other words) were thus manipulated. Unexpectedly, d e t e c t i o n performance was b e t t e r with words than with nonwords. T h i s suggests that d e t e c t i o n i s a l a t e process drawing on l e x i c a l i n f o r m a t i o n . S e v e r a l components of the event r e l a t e d p o t e n t i a l (ERP) d i f f e r e n t i a t e d as e a r l y as 140 msec p o s t s t i m u l u s between sub-and s u p r a l i m i n a l c o n d i t i o n s . More imp o r t a n t l y , d i f f e r e n c e s w i t h i n the s u b l i m i n a l c o n d i t i o n s were observed: f a m i l i a r i t y was d i s c r i m i n a t e d a f t e r 260 msec and simple presence of a s t r i n g a f t e r 300 msec. These r e s u l t s are c o n s i s t e n t with the c o n c l u s i o n s drawn from d e t e c t i o n performance, and they support the n o t i o n that backward masking does not d i s r u p t p r o c e s s i n g . i i i T able of Contents A b s t r a c t i i L i s t of Tables i v L i s t of F i g u r e s v Acknowledgement v i I. INTRODUCTION 1 1.1 D e t e c t i o n And Re c o g n i t i o n 4 1.2 Pat t e r n Masking 6 1.3 Coding And Recovery Of Information 9 1.4 R a t i o n a l e For The Present Study 17 11 . METHOD 21 2. 1 SUBJECTS 21 2.2 MATERIALS AND DESIGN 21 2.3 APARATUS 24 2.4 PROCEDURE 25 2.5 ANALYSIS 29 I I I . RESULTS 33 3.1 D e t e c t i o n Performance 33 3.2 Response L a t e n c i e s 34 3.3 Event Related P o t e n t i a l s 35 IV. DISCUSSION 41 4.1 S t a t i s t i c a l And Methodological C o n s i d e r a t i o n s 41 4.2 D e t e c t i o n Performance ' 42 4.3 Time Estimates 47 4.4 Event Related P o t e n t i a l s 47 4.5 General D i s c u s s i o n 50 BIBLIOGRAPHY 58 APPENDIX A - LIST OF STIMULI 64 APPENDIX B - GROUP MEAN ERPS AT P4 FOR ALL CONDITIONS 65 APPENDIX C - GROUP MEAN ERPS AT OZ FOR ALL CONDITIONS 66 APPENDIX D - GROUP MEAN EOG FOR ALL CONDITIONS 67 APPENDIX E - AVERAGED ERPS FOR ONE SUBJECT (S1) AT P3 68 APPENDIX F - AVERAGED ERPS FOR ONE SUBJECT (S2) AT P3 69 i v L i s t of Tables I. D e t e c t i o n performance: mean p r o b a b i l i t y of h i t s and d's ..34 I I . Mean time estimates and i n v a l i d t r i a l s 35 I I I . F - r a t i o s f o r c o n t r a s t s on time estimates 35 IV. Mean ERP component l a t e n c i e s and standard d e v i a t i o n s 36 V. ^ Mean ERP component l a t e n c i e s at P3 f o r a l l c o n d i t i o n s ....37 VI . Mean ERP component amplitudes at P3 f o r a l l c o n d i t i o n s ...38 V L i s t of F i g u r e s 1. Sequence of events i n a s i n g l e t r i a l ..25 2. Set of c o n t r a s t s 37 3. Group average ERPs at P3 f o r a l l c o n d i t i o n s .39 v i Acknowledgement I would l i k e to thank my committee members, Dr. A.M. Treisman and Dr. D. Rahneman f o r t h e i r encouragement and the h e l p f u l t h e o r e t i c a l guidance throughout the study. I am g r a t e f u l f o r the he l p of J e f f J u t a i and John L i n d , who introduced me to the Lab and a s s i s t e d generously whenever needed with p r a c t i c a l h e l p and d i s c u s s i o n s . S p e c i a l thanks go to my s u p e r v i s o r , Dr. Robert Hare, whose s e n s i b l e a d v i c e , constant support and g e n e r o s i t y were i n v a l u a b l e . T h i s r e s e a r c h was supported by Grant No. MT 4511 from the Medical Research C o u n c i l of Canada to Dr. R.D. Hare while the author was on a U n i v e r s i t y of B r i t i s h Columbia Graduate Student F e l l o w s h i p . 1 I . INTRODUCTION While reading i n the a d u l t i s a h i g h l y o v e r l e a r n e d s k i l l , remarkable i n i t s . speed and e f f i c i e n c y , there i s ; n o c l e a r evidence on the extent to which i t r e f l e c t s unique, s p e c i a l i z e d or u n i v e r s a l c o g n i t i v e f u n c t i o n s . The present study i s concerned with one aspect of r e a d i n g , word r e c o g n i t i o n , which preserves a c e n t r a l f e a t u r e of r e a d i n g : the t r a n s f o r m a t i o n of a sequence of a r b i t r a r y symbols i n t o s u b j e c t i v e meaning. C o g n i t i v e p s y c h o l o g i s t s have been reasonably s u c c e s s f u l i n t r e a t i n g word r e c o g n i t i o n w i t h i n a general framework of i n f o r m a t i o n p r o c e s s i n g , thus r e l a t i n g i t to other forms of p e r c e p t i o n . I t i s g e n e r a l l y assumed that word r e c o g n i t i o n , proceeds i n stages, with some amount of preconscious f e a t u r e e x t r a c t i o n preceding i d e n t i f i c a t i o n , r e c o g n i t i o n and, where r e q u i r e d , i n i t i a t i o n of a response. The e f f i c i e n c y of word r e c o g n i t i o n may be p a r t l y e x p l a i n e d by assuming that i t i s automatic to a l a r g e extent; we seem able to achieve a meaningful r e p r e s e n t a t i o n of p r i n t e d words q u i c k l y and with only l i t t l e a t t e n t i o n and e f f o r t . Posner and Snyder (1975) argue that (1) Automatic processes precede c o n t r o l l e d processes i n v o l v i n g c onscious a t t e n t i o n ; (2) they may occur without i n t e n t i o n ; (3) they may occur without i n t e r f e r i n g with other ongoing mental a c t i v i t y ; and (4) they may occur without g i v i n g r i s e to conscious awareness. 2 A recent r e p o r t by Marcel ( i n press) has shed l i g h t on the r e l a t i o n between word r e c o g n i t i o n and the involvement . of consciousness i n p r o c e s s i n g . He presented.evidence that l e x i c a l or semantic access f o r words-'under viewing c o n d i t i o n s p r e v e n t i n g conscious awareness i s p o s s i b l e . In b r i e f , Marcel ( i n press) c l a i m s t h a t : ( 1 ) At a stimulus onset asynchrony,(SOA, the i n t e r v a l between onset of the t a r g e t and onset of the masking stimulus) y i e l d i n g chance performance on both presence/absence and. graphic s i m i l a r i t y judgements, semantic s i m i l a r i t y judgments are s t i l l above chance, which means that there i s a ' s e n s i t i v i t y ' to the meaning of unseen words; (2) A s u b l i m i n a l word ( i . e . masked to y i e l d chance d e t e c t i o n performance) can produce s i g n i f i c a n t semantic f a c i l i t a t i o n or i n t e r f e r e n c e i n a Stroop ( c o l o r naming) task; (3) A s u b l i m i n a l prime word can f a c i l i t a t e a l e x i c a l d e c i s i o n about the t a r g e t , thus producing semantic priming. The e f f e c t i s obtained with p a t t e r n masking only; (4) R e p e t i t i o n of a s u b l i m i n a l prime i n c r e a s e s priming but leaves d e t e c t i o n performance unchanged at chance l e v e l . Marcel ( i n press) argues that d i f f e r e n t a spects of a word (e.g. form, l o c a t i o n , l e x i c a l i d e n t i t y , c o l o u r ) are coded independently and i n p a r a l l e l . For each of these aspects or 3 domains, p r o c e s s i n g proceeds a u t o m a t i c a l l y up to the highest p o s s i b l e l e v e l of r e p r e s e n t a t i o n . The r e s u l t i n g m u l t i p l e and separate codes must be recovered by e l a b o r a t i n g processes that i n t e g r a t e them i n t o a u n i t a r y p e r c e p t . P a t t e r n , masking supposedly i n t e r f e r e s with the f i g u r a l r e c o r d that i s e s s e n t i a l f o r c o n s c i o u s p e r c e p t i o n . Since records decay over time, the h i g h e s t l e v e l codes achieved l a s t are e a s i e s t to recover. P a r t i a l support f o r these claims comes from s t u d i e s by McCauley, Parmelee, Sperber & Carr (1980) and Fowler, Wolford, Slade & T a s s i n a r y (1981) but the v a l i d i t y of the f i n d i n g s has a l s o been questioned ( M e r i k l e , 1982; P u r c e l l , Stewart & Stanovich, Note 1). I f Marcel's argument i s tenable i t would have consequences that go beyond i s s u e s l i m i t e d to word r e c o g n i t i o n . More spec i f i c a l l y , - M a r c e l q u e s t i o n s commonly h e l d b e l i e f s by c l a i m i n g t h a t : (1) d e t e c t i o n may not be a p r e r e q u i s i t e f o r r e c o g n i t i o n ; (2) p a t t e r n masking may not i n t e r r u p t p r o c e s s i n g ; and (3) p e r c e p t u a l e f f e c t s b e l i e v e d to r e f l e c t encoding might a c t u a l l y r e f l e c t recovery p r o c e s s e s . The present study approaches these i s s u e s by examining both the c o r t i c a l event r e l a t e d p o t e n t i a l (ERP) and the b e h a v i o r a l responses of the s u b j e c t s to s u b l i m i n a l s t i m u l i . S e v e r a l components of the ERP have been a s s o c i a t e d with f u n c t i o n a l stages i n i n f o r m a t i o n p r o c e s s i n g (Dohchin, R i t t e r & McCallum, 1978). Since the temporal o r d e r i n g of events in the i n f o r m a t i o n 4 p r o c e s s i n g sequence i s . c r u c i a l to Marcel's p o s i t i o n , the ERP, with i t s high, temporal r e s o l u t i o n , might be a p a r t i c u l a r l y s u i t a b l e measure f o r t h i s purpose. 1.1 D e t e c t i o n And R e c o g n i t i o n D e t e c t i o n and r e c o g n i t i o n are t y p i c a l l y assumed to be h i e r a r c h i c a l l y organized, i . e . d e t e c t i o n i s viewed as a p r e r e q u i s i t e f o r r e c o g n i t i o n . T h i s leads to the p r e d i c t i o n that r e c o g n i t i o n must be at chance l e v e l s when a stimulus goes undetected (Coren, Porac & Ward, 1979). For s i g n a l d e t e c t i o n theory and i t s extension to r e c o g n i t i o n however (Green and B i r d s d a l l , 1978), r e c o g n i t i o n without d e t e c t i o n i s a teneable outcome. Rather than being h i e r a r c h i c a l l y organized, d e t e c t i o n and r e c o g n i t i o n are conceived of as r e f l e c t i n g the same b a s i c process, one i n which a set of i n t e r n a l d e t e c t o r s i s being monitored. In d e t e c t i o n , any of these d e t e c t o r s i s compared to a preset c r i t e r i o n . In r e c o g n i t i o n , the d e t e c t o r with the l a r g e s t output in the set i s chosen. The theory makes the c o u n t e r i n t u i t i v e p r e d i c t i o n that r e c o g n i t i o n performance can be s u p e r i o r to d e t e c t i o n performance, a p r e d i c t i o n that has been confirmed i n s e v e r a l experiments (e.g. Diener, 1981). A p p l i c a t i o n of the theory has so f a r been l i m i t e d to simple s t i m u l i (e.g. tones of a c e r t a i n p i t c h ) f o r which s p e c i a l i z e d d e t e c t o r s are l i k e l y to e x i s t . An important q u e s t i o n a r i s e s when more complex s t i m u l i , such as words are c o n s i d e r e d : what are the r e l e v a n t d e t e c t o r s that are being monitored ? Obviously when d e t e c t o r s are being monitored f o r i d e n t i f i c a t i o n or r e c o g n i t i o n , the i d e n t i t y of s i n g l e words must be s p e c i f i e d . 5 Probably only word d e t e c t o r s at a l e x i c a l l e v e l conform to t h i s requirement. For de t e c t i o n , however,.a small set of fe a t u r e d e t e c t o r s c o u l d s i g n a l presence, of p r i n t , but a set of l e t t e r or word d e t e c t o r s would serve the same purpose. What s i g n a l d e t e c t i o n theory p r e d i c t s f o r the r e l a t i o n between d e t e c t i o n and r e c o g n i t i o n holds only i f the.same se t s of d e t e c t o r s , at the same f u n c t i o n a l l e v e l , are monitored i n both d e t e c t i o n and r e c o g n i t i o n t a s k s . The- c o u n t e r i n t u i t i v e p r e r e q u i s i t e f o r an a p p l i c a t i o n to word d e t e c t i o n thus would be that to de t e c t a word, i t i s not the e a r l y encoding processes decomposing the word i n t o graphic f e a t u r e s that one monitors, but rather the l a t e r output at the l e x i c a l l e v e l . If t h i s assumption holds, any experimental manipulation a f f e c t i n g l e x i c a l access, r e g a r d l e s s of whether i t does so by i n f l u e n c i n g the f e a t u r e a n a l y s i s or by a f f e c t i n g a l a t e r stage, would have to i n f l u e n c e d e t e c t i o n . Recent research i n v o l v i n g the ERP i s r e l e v a n t to t h i s d i s c u s s i o n of d e t e c t i o n and r e c o g n i t i o n . Two components of the ERP, N100 and P300, have c o n s i s t e n t l y been shown to manifest s u c c e s s i v e stages of s e l e c t i o n i n in f o r m a t i o n p r o c e s s i n g , with N100 (a negative going wave peaking at around 100 msec) being s e n s i t i v e to e a r l y channel s e l e c t i o n a c c o r d i n g to simple sti m u l u s f e a t u r e s , and P300 ( a p o s i t i v e going wave peaking around 300 msec) r e f l e c t i n g s e l e c t i o n of a s p e c i f i c t a r g e t w i t h i n the a p p r o p r i a t e channel ( P i c t o n , Campbell, Baribeau-Braun & Prou l x , 1978). Parasuraman, Richer and Beatty (1982) p r e d i c t e d that N100 would be s e n s i t i v e to d e t e c t i o n only, while 6 P300 should vary with.both d e t e c t i o n and r e c o g n i t i o n . In t h e i r experiment both d e t e c t i o n and r e c o g n i t i o n judgements of tones d i f f e r i n g i n p i t c h were made on each t r i a l . The r e s u l t s p r o v i d e d c l e a r support f o r t h e i r h y p o t h e s i s : N100 v a r i e d with d e t e c t i o n only, while P300 was a f f e c t e d both by d e t e c t i o n and r e c o g n i t i o n . In a d d i t i o n , a slow, p o s i t i v e s h i f t (SPS), which was i d e n t i f i e d by p r i n c i p a l component a n a l y s i s (PCA) and peaked a f t e r P300, v a r i e d with r e c o g n i t i o n only, r e g a r d l e s s of d e t e c t i o n c o n f i d e n c e . An important f i n d i n g was that r e c o g n i t i o n was above chance on t r i a l s where (d o u b t f u l ) 'absent' judgements were made, i . e . when s u b j e c t s were f a i r l y c o n f i d e n t that the t a r g e t was not present. Moreover both P300 and the SPS y i e l d e d d i s c r i m i n a t i o n between c o r r e c t l y and i n c o r r e c t l y i d e n t i f i e d t a r g e t s . Thus both b e h a v i o r a l judgements and the ERP suggest that d e t e c t i o n and r e c o g n i t i o n are concurrent rather than s e q u e n t i a l p r o c e s s e s . 1.2 P a t t e r n Masking Backward masking with p a t t e r n e d masks can profoundly i n t e r f e r e with word r e c o g n i t i o n . The locus of t h i s form of masking i s c e n t r a l , s i n c e masking can be obtained d i c h o p t i c a l l y , with s t i m u l u s and mask each being presented to a d i f f e r e n t eye (Turvey, 1973) T h i s suggests that p a t t e r n masking cannot adequately be e x p l a i n e d i n terms of degradation of the stimulus by the mask. Turvey (1973) argues that the p a t t e r n mask i n t e r r u p t s - t h e p r o c e s s i n g of the t a r g e t . The f i n d i n g s of Marcel ( i n press) suggest a d i f f e r e n t i n t e r p r e t a t i o n : p a t t e r n masking a f f e c t s f i g u r a l codes or r e c o r d s , but leaves l e x i c a l or semantic 7 records of the stimulus l a r g e l y u n a f f e c t e d . M c C l e l l a n d & Rumelhart (1981) and Rumelhart & M c C l e l l a n d (1982) have developed an i n t e r a c t i v e a c t i v a t i o n model f o r l e t t e r and word r e c o g n i t i o n . I t s p e c i f i e s the e f f e c t s of p a t t e r n masking on p r i n t i n a way which seems b a s i c a l l y compatible with Marcel's ( i n press) i n t e r p r e t a t i o n . T h e i r model i s h i e r a r c h i c a l , i n that i t c o n s i s t s of a f e a t u r e - , a l e t t e r - and a wo r d - l e v e l . Despite i t s advanced f e a t u r e s , i t bears a strong s i m i l a r i t y to the i n f l u e n t i a l 'logogen' model,. (Morton,. 1969), i n that the word l e v e l c o n s i s t s of an a r r a y of d e t e c t o r s or nodes, each of which accumulates evidence f o r a s i n g l e word. However, c o n t r a r y to the logogen model, a c t i v a t i o n and i n h i b i t i o n are p o s s i b l e between and w i t h i n l e v e l s , i . e . feedback from higher to lower l e v e l s i s implemented and the nodes have no i n d i v i d u a l t h r e s h o l d s . The e f f e c t of p a t t e r n masking i n t h i s i n t e r a c t i v e model i s to l i m i t amount of time f o r which a ' l e g i b l e ' r e p r e s e n t a t i o n of the stimulus i s a v a i l a b l e . Information at the word l e v e l i s l e s s a f f e c t e d by i n t e r f e r e n c e from incompatible mask-features than at the f e a t u r e l e v e l , because feedback from the word l e v e l can s u s t a i n a c t i v a t i o n of the proper l e t t e r nodes, which i n turn r e a c t i v a t e the proper word node. Thus, the model e x p l a i n s why higher l e v e l , l e x i c a l or semantic i n f o r m a t i o n i s l e a s t a f f e c t e d by p a t t e r n masking. One c o u l d argue that with proper a c t i v a t i o n at the l e t t e r l e v e l some f i g u r a l i n f o r m a t i o n should be a v a i l a b l e . However, r e p r e s e n t a t i o n s at the l e t t e r l e v e l probably must be thought of as a b s t r a c t r a t h e r than f e a t u r e - p r e s e r v i n g ; E v e t t and Humphreys (1981) make a strong 8 case f o r access to the l e x i c o n v i a an a b s t r a c t graphemic code, where upper- and lower-case l e t t e r s are i n d i s t i n g u i s h a b l e . A c c o r d i n g l y , f i g u r a l i n f o r m a t i o n might not be d i r e c t l y a v a i l a b l e at that l e v e l . I t may w e l l be that the readouts from l e t t e r and word l e v e l must be i n t e g r a t e d with l e s s a b s t r a c t , f i g u r a l i n f o r m a t i o n to y i e l d the f i n a l percept ( A l l p o r t , 1977; Evet t and Humphreys, 1981) The e f f e c t s of backwardmasking on the ERP have been explo r e d i n some d e t a i l , and the c o n c l u s i o n s drawn are of major importance f o r the present experiment, although they are s o l e l y concerned with the impairment of f i g u r a l p e r c e p t i o n . .Andreassi, DeSimone & M e l l e r s (1976) and A n d r e a s s i , G a l l i c h i o and Young (Note 2) repor t e d a t t e n u a t i o n of a p o s i t i v e component around 200 msec p o s t s t i m u l u s , s p e c i f i c to p e r c e p t u a l masking, under masking c o n d i t i o n s s i m i l a r to metacontrast ( i . e . t a r g e t and mask have adjacent, nonoverlapping c o n t o u r s ) . The a t t e n u a t i o n was s p e c i f i c to the ERP recorded from Oz ( c e n t r a l o c c i p i t a l l o c a t i o n ) . Masking was assessed by ask i n g the s u b j e c t s to draw the sequence of s t i m u l i they saw. P e r c e p t u a l masking was d e f i n e d as the f a i l u r e to draw the t a r g e t s . Schwartz, W h i t t i e r & Schweitzer (1979) and Schwartz & P r i t s c h a r d (1981) examined ERP under both monoptic and d i c h o p t i c viewing c o n d i t i o n s . They re p o r t e d c o n s i s t e n t r e s i d u a l s ( i . e . waveform d i f f e r e n c e s between t a r g e t , f o l l o w e d by the mask and mask alone) with d i s c r i m i n a t i o n between l e t t e r s c l o s e to chance. However, the r e s i d u a l d i d not change when a second masked fo l l o w e d , while d i s c r i m i n a t i o n s i g n i f i c a n t l y improved. S i m i l a r l y , over a range 9 of SOAs y i e l d i n g a U-shaped masking f u n c t i o n , the- r e s i d u a l m o n o tonically decreased with s m a l l e r SOAs. The authors concluded that the ERP. does not c o r r e l a t e with performance or s u b j e c t i v e experience i n backwardmasking. The f i n d i n g s of these two groups (Andreassi et a l . , 1976, Note 2; Schwartz et al.., 1979, 1981) are c l e a r l y , at odds. While there are p r o c e d u r a l d i f f e r e n c e s which make a d i r e c t comparison d i f f i c u l t ( e.g. the former group used c e n t r a l , the l a t t e r p e r i p h e r a l s t i m u l a t i o n ) , i t i s c l e a r that Schwartz et a l . (1979, 1981) used a f a r narrower range of SOAs to induce changes i n p e r c e p t u a l masking ( i . e 0 to 60 msec i n s i x steps as opposed to 10, 40 and 110 msec by Andreassi et a l . , Note 2), along with a more s e n s i t i v e d e t e c t i o n measure (d' as opposed to the drawings i n Andreassi et a l . , 1976, Note 2). The f i n d i n g s of Andreassi et a l . (1976, Note 2) are t h e r e f o r e more d i f f i c u l t to i n t e r p r e t . However, an a d d i t i o n a l problem c h a r a c t e r i z e s the res e a r c h of both groups: the c o n d i t i o n s were not randomized, but rather presented i n bl o c k s , which c l e a r l y allows f o r d i f f e r e n t s t a t e v a r i a b l e s ( a r o u s a l , e x p e c t a t i o n s ) a c r o s s c o n d i t i o n s . To summarize, i t i s unclear whether c o r r e l a t e s f o r p e r c e p t u a l experience under backwardmasking can be found i n the ERP. S i m i l a r l y , i t i s unclear whether a r e s i d u a l , of whatever f u n c t i o n a l s i g n i f i c a n c e , i s present under c o n d i t i o n s where t a r g e t d e t e c t i o n i s at chance l e v e l s . 1.3 Coding And Recovery Of Information A c e n t r a l aspect of the work of Marcel (1980; i n press) i s that p a t t e r n masked words are shown to produce priming without 10 becoming c o n s c i o u s . Priming r e f e r s to the f i n d i n g that some responses to a word (e.g. a l e x i c a l d e c i s i o n , the c l a s s i f i c a t i o n of a l e t t e r s t r i n g as a r e g u l a r word or a nonword) are speeded when an a p p r o p r i a t e context (e.g. v i s u a l l y s i m i l a r or s e m a t i c a l l y a s s o c i a t e d ) precedes t h i s word (e.g. Meyer, Schvaneveldt & Ruddy, 1975). Marcel (1980; i n press) has argued that semantic priming, as w e l l as word frequency or f a m i l i a r i t y , a f f e c t word r e c o g n i t i o n a f t e r a word has gained l e x i c a l access r a t h e r than i n the encoding stage, i . e . that the e f f e c t s occur at a stage where the recovery of l e x i c a l i n f o r m a t i o n takes p l a c e . In h i s view then, l e x i c a l access i s l a r g e l y i n v a r i a n t and determined by the encoding of p h y s i c a l p r o p e r t i e s of the word o n l y . T h i s c o n t r a s t s with the logogen model (Morton, 1969) where the l o c u s of semantic priming i s i n the encoding stage. In t h i s model, the s u b j e c t i v e l e x i c o n c o n s i s t s of an a r r a y of d e t e c t o r s or logogens with i n d i v i d u a l t h r e s h o l d s . Each logogen accumulates evidence f o r a s i n g l e word from f e a t u r e a n a l y s e r s , from other logogens or from the c o g n i t i v e system. A s i n g l e mechanism, c r i t e r i o n b i a s , accounts f o r semantic priming and f o r the e f f e c t s of other v a r i a b l e s a f f e c t i n g word r e c o g n i t i o n , such as stimulus f a m i l i a r i t y and graphic c o n t e x t . Words primed by s e m a n t i c a l l y r e l a t e d context, as w e l l as f a m i l i a r or g r a p h i c a l l y primed words, a l l have the c r i t e r i o n of t h e i r c orresponding logogen lowered, so that these logogen u n i t s need l e s s evidence from f e a t u r e d e t e c t o r s to exceed t h e i r t h r e s h o l d . T h i s c r i t e r i o n b i a s e x p l a n a t i o n i s parsimonious; however, i t can not 11 account f o r a l l of the data (Becker and K i l l i o n , 1977). Schvaneveldt and McDonald (1981) r e c e n t l y presented evidence s u p p o r t i n g Marcel's ( i n press) view, namely .that semantic priming does not a f f e c t encoding. They argue that semantic priming i s due to a process t e s t i n g and v e r i f y i n g hypotheses about the i d e n t i t y of the stimulus a f t e r l e x i c a l a ccess. T h i s process i s c h a r a c t e r i z e d as memory d r i v e n and 'top-down' o p e r a t i n g . However, the immediate v e r b a l context i s only one determinant of semantic priming. There i s evidence that i n s t r u c t i o n s to attend to c e r t a i n words can a l s o r e s u l t i n some form of priming. For example, search f o r t a r g e t s among d i s t r a c t o r s i s c o n s i d e r a b l y a i d e d when membership i n a s i n g l e category d e f i n e s t a r g e t s and separates them from nontargets (e.g. l e t t e r s vs. d i g i t s , . Jonides & Gleitman 1972). K a r l i n and Bower (1976) have extended t h i s r e s u l t to words, where a search f o r exemplars of semantic c a t e g o r i e s , e.g the search f o r ' t r e e s ' among ' c o l o u r s ' , i s r e q u i r e d . Again, the search i s ai d e d when t a r g e t s belong to one semantic category and d i s t r a c t o r s to a d i f f e r e n t one. These 'category e f f e c t s ' have been i n t e r p r e t e d in terms of 'set' f o r a t a r g e t category (Gleitman & Jo n i d e s , 1978): a top-down, or memory d r i v e n form of pri m i n g . Thus, i n s t r u c t i o n s to a t t e n d to a t a r g e t category may r e s u l t i n semantic priming. Not every manipulation a f f e c t i n g word r e c o g n i t i o n does so at a semantic l e v e l , as the d i s c u s s i o n of the logogen model has a l r e a d y i n d i c a t e d . Priming e f f e c t s with g r a p h i c a l l y s i m i l a r 12 word- or nonword- primes have r e p e a t e d l y been demonstrated (e.g. Meyer, Schwanefeldt. & Ruddy, 1975; E v e t t & Humphreys, 1981). Word frequency or f a m i l i a r i t y a l s o a f f e c t s word r e c o g n i t i o n . Scarborough, Gerard and Cortese (1979) presented evidence that word frequency i s a h i g h l y p l a s t i c phenomenon. F a m i l i a r i t y e f f e c t s were r e a d i l y generated by the r e p e t i t i o n of words, they l a s t e d f o r a long time, and they o c c u r r e d a u t o m a t i c a l l y , without s u b j e c t s , r e a l i z i n g that the words had been repeated. However, no transfer-between f a m i l i a r i t y i n d i f f e r e n t m o d a l i t i e s was found. M u r r e l l and Morton (1974) r e p o r t e d s i m i l a r r e s u l t s . Warren & Morton (1982) have extended these l a t t e r f i n d i n g s to p i c t u r e r e c o g n i t i o n , where no t r a n s f e r from words to p i c t u r e s or v i c e versa occured. Since semantic priming i s not modality s p e c i f i c , i t seems t h a t f a m i l i a r i t y operates at a lower f u n c t i o n a l l e v e l than does semantic priming. To summarize, word r e c o g n i t i o n i s a f f e c t e d by a v a r i e t y of experimental m a n i p u l a t i o n s . E f f e c t s of unconscious words on the r e c o g n i t i o n of conscious words have y i e l d e d important new evidence about the temporal sequence of events in word r e c o g n i t i o n . I t may w e l l be that d i f f e r e n t f u n c t i o n a l l o c i underly the e f f e c t s of f a m i l i a r i t y and of semantic context on word r e c o g n i t i o n . Thus f a r unconscious reading has been examined by manipulating the immediate semantic c o n t e x t , as i n the Stroop or the semantic priming paradigm (Marcel, i n p r e s s ) . I t may be j u s t as important, however, to examine how other procedures which a f f e c t word r e c o g n i t i o n (e.g. the ones mentioned above, 13 semantic s e t , graphic priming or f a m i l i a r i t y ) i n turn a f f e c t the unconscious .processing of words. T h i s would l e a d to more c o n c l u s i v e evidence about the temporal o r d e r i n g of the f u n c t i o n a l events i n word r e c o g n i t i o n . E q u a l l y important, i t would a l s o h e l p to c h a r a c t e r i z e unconscious processes and to e x p l o r e t h e i r l i m i t s . There has been very l i t t l e ERP r e s e a r c h on the dynamics of i n f o r m a t i o n p r o c e s s i n g i n v o l v e d i n word r e c o g n i t i o n . T h i s does not mean, however, that research on ERP and l i n g u i s t i c s t i m u l i i s sparse, only that t h i s r e s e a r c h i s not d i r e c t l y concerned with word r e c o g n i t i o n . A few a r t i c l e s have examined ERP d i f f e r e n c e s between words and nonwords. Molfese, Papanicolaou, Hess & Molfese (1979) compared the ERP's to a u d i t o r i l y presented consonant-vowel-consonant (CVC) s y l l a b l e s , which c o u l d be meaningful [kaeb] or meaningless [kaek]. Subjects were to press a key i f they heard a word and another key i f they heard a nonsense s y l l a b l e . They found d i f f e r e n c e s i n the f a c t o r - a n a l y s e d ERP f o r three f a c t o r s , pea- king at 6-60, 240-280 and 320-440 msec p o s t s t i m u l u s , r e s p e c t i v e l y . Shelbourne (1972, 1978) compared v i s u a l ERPs to meaningful and meaningless CVC-trigrams in normal s u b j e c t s and i n reading d i s a b l e d c h i l d r e n . The l e t t e r s of the trigrams were presented one second a p a r t . No d i f f e r e n c e s between meaningful and meaningless trigr a m s were found, perhaps because the l e t t e r s of the t r i g r a m were presented one at a time r a t h e r than s i m u l t a n e o u s l y . Molfese et a l . ' s (1979) p o s i t i v e f i n d i n g , on the other hand, may have been the r e s u l t of. lower l e v e l 14 d i f f e r e n c e s between s t i m u l i , s i n c e the phonemes used f o r words and nonsense CVCs were not i d e n t i c a l . . ERP d i f f e r e n c e s between meaningful [kaeb] and meaningless [kaek] s t i m u l i occured long before the d e c i s i v e t h i r d phoneme of the CVC- was presented.. Sub j e c t s must have c o r r e c t l y a n t i c i p a t e d the c r i t i c a l t h i r d l e t t e r by u t i l i z i n g c o a r t i c u l a t o r y cues i n the e a r l i e r phonemes. Moreover, Sutton (1979) p o i n t s out that i n a task where the s u b j e c t has two c h o i c e s (meaningful vs. meaningless), the l i n g u i s t i c meaningfulness of only one set of s t i m u l i might render them more s a l i e n t or important. To conclude, there seems to e x i s t no c o n v i n c i n g demonstration of an ERP c o r r e l a t e of meaning!ulness in g e n e r a l . A s i z e a b l e number of s t u d i e s has been conducted on more s p e c i f i c a spects of meaning, e s p e c i a l l y on p o s s i b l e ERP c o r r e l a t e s of s i m i l a r i t i e s and d i f f e r e n c e s i n meaning. D i f f e r e n t ERPs to p h y s i c a l l y i d e n t i c a l s t i m u l i with d i f f e r e n t meanings have been obtained by Johnston & Chesney (1974), T e y l e r , Roemer, H a r r i s o n & Thompson (1973), and Brown & Lehmann (1979). In g e n e r a l , they used ambiguous s t i m u l i (e.g., a f i g u r e which c o u l d be read as "B" or as 13; ambiguous sounds i n sentences l i k e "a p r e t t y rose" vs. "a boatman rows") which were rendered unambiguous by the c o n t e x t . D i f f e r e n t ERPs f o r number vs. l e t t e r i n t e r p r e t a t i o n and noun vs. verb meaning were obt a i n e d . S e v e r a l papers have compared ERPs to d i f f e r e n t c l a s s e s of meaning. U s u a l l y , s u b j e c t s had to r a t e presented words on semantic or a f f e c t i v e s c a l e s . Chapman (1979) and Chapman, 15 McCrary, Chapman & Mart i n (1980) found that ERPs d i s t i n g u i s h e d w e l l between words i n d i f f e r e n t semantic c l a s s e s , r e p r e s e n t i n g the poles of Osgood's semantic d i f f e r e n t i a l (Osgood, 1964). I n t e r e s t i n g l y , they a l s o found s i m i l a r d i s c r i m i n a t i o n when su b j e c t s only l i s t e n e d to the words. B e g l e i t e r , P o r j e s z & Garozzo (1979) found d i f f e r e n t ERPs f o r word groups r a t e d d i f f e r e n t l y on an a f f e c t i v e s c a l e . Megela & T e y l e r (1978) have t r i e d t o assess the r e l a t i v e importance of semantic vs. p h y s i c a l or task s p e c i f i c manipulations f o r ERP changes. They compared the c o r r e l a t i o n s between ERPs to synonyms ("Throw the small ROCK/STONE") and homonyms ("Shuffle /walk on the DECK"). They found very s i m i l a r ERPs to the homonyms but v i r t u a l l y random c o r r e l a t i o n s between the ERPs to synonyms. Obviously, i n t h i s experiment low order e f f e c t s were much more powerful than semantic e f f e c t s . Thatcher (1977) compared ERPs to synonyms, antonyms and n e u t r a l words i n a semantic matching task. The s u b j e c t ' s task was to i n d i c a t e which of the three c o n d i t i o n s had occured. No d i f f e r e n c e s between synonyms and antonyms were found, but both these c o n d i t i o n s d i f f e r e d from the n e u t r a l c o n d i t i o n . The f a c t o r - a n a l y t i c a l l y i d e n t i f i e d component y i e l d i n g the best d i s c r i m i n a t i o n peaked around 400 msec p o s t s t i m u l u s , d i s c r i m i n a t i o n being l i m i t e d to p a r i e t a l and temporal leads (P3, T5) on the l e f t hemisphere. More r e c e n t l y , however, Vaughan, S h e r i f , 0 ' S u l l i v a n , Herrmann & Weldon (1982) have r e p o r t e d ERP d i f f e r e n c e s f o r synonyms and antonyms i n a s i m i l a r task i n a lat e n c y range of 250-650 msec. Boddy (1981) ana l y s e d ERPs i n a 16 semantic . c a t e g o r i s a t i o n task. D i f f e r e n c e s between p o s i t i v e and negative i n s t a n c e s of a category were r e f l e c t e d at a l a t e n c y e a r l i e r than 212 msec in the N1-P2 component. He i n t e r p r e t s the f i n d i n g s i n terms of category p r i m i n g . Some of the s t u d i e s mentioned are open to a number of i n t e r p r e t a t i o n s . Thatcher (1978) p o i n t s out the d i f f i c u l t y of d i s c r i m i n a t i n g between c o n t r i b u t i o n s of semantic content and of i n v a r i a n t processes o p e r a t i n g on t h i s semantic content (e.g. e f f e c t s of s y n t a c t i c c o n t e x t ) , e s p e c i a i l y when using ambiguous s t i m u l i i n d i f f e r e n t c o n t e x t s . In the s t u d i e s concerned with d i f f e r e n t semantic or a f f e c t i v e c l a s s e s , i t i s d i f f i c u l t to assess the r e l a t i v e c o n t r i b u t i o n s of the s p e c i f i c semantic content and the task s p e c i f i c c o n t e x t . I n t e r p r e t a t i o n s i n terms of d i f f e r e n c e s i n emotional involvement, d i f f e r e n c e s i n s u b j e c t i v e s a l i e n c e of s t i m u l i , or d i f f e r e n c e s ; in task d i f f i c u l t y can not be r u l e d out. The work of Chapman (1979) and Chapman et a l . ( l 9 8 0 ) seems to escape t h i s c r i t i c i s m . T h e i r use of v a r i o u s combinations of r a t i n g s c a l e s and word c l a s s e s shows that the d i f f e r e n c e s f o r the ERPs to d i f f e r e n t word c l a s s e s are independent of the semantic s c a l e used to judge them, and p e r s i s t when the words are simply read. S i m i l a r l y , Thatcher's (1977) use of e x t e n s i v e c o n t r o l s leads one to b e l i e v e that h i s c o n c l u s i o n s about c o r r e l a t e s of semantic matching are warranted. On the other hand, these l a t t e r s t u d i e s i l l u s t r a t e to what extent the r e s u l t s depend on the use of s o p h i s t i c a t e d m u l t i v a r i a t e techniques and manipulations of the raw ERP. Simple v i s u a l i n s p e c t i o n of the untransformed averaged ERPs to 1 7 the d i f f e r e n t word c l a s s e s only shows them to be extremely s i m i l a r . S e v e r a l r e s e a r c h e r s have suggested that i n order to o b t a i n r e l i a b l e language r e l a t e d E R P - e f f e c t s , t a s k s should be designed, to engage s u b j e c t s i n a c t i v e l i n g u i s t i c processing, (e.g. Friedmann,. 1978; Megela & T e y l e r , 1978). However the work of Chapman et a l . (1980) i n d i c a t e s that ERPs d i s c r i m i n a t e e q u a l l y well;between semantic, c l a s s e s independent of whether the su b j e c t simply repeats the words or r a t e s them on a semantic s c a l e . I t may be that ERP c o r r e l a t e s of e a r l y l i n g u i s t i c p r o c e s s i n g would be more apparent i n the ERP when the subject i s not a c t i v e l y engaged in d e c i s i o n making, s i n c e such higher order c o g n i t i v e a c t i v i t y might obscure e f f e c t s due to e a r l i e r processes such as l e x i c a l a c c e s s . I t may even be u s e f u l to prevent the subject from engaging i n i n t e r p r e t a t i v e processes and from b u i l d i n g up i n t e r p r e t a t i o n s of the experimental s t i m u l i , e.g by i n t e r p r e t i n g the words and nonwords as being d i f f e r e n t l y important. Backward masking with a p a t t e r n mask may be a p p r o p r i a t e f o r t h i s purpose, s i n c e i t seems to preserve the l e x i c a l code of the stimulus word while p r e v e n t i n g conscious experience ( A l l p o r t , 1977; M a r c e l , i n p r e s s ) . 1.4 R a t i o n a l e For The Present Study A primary purpose of the present study was to o b t a i n a s i n g l e t h r e s h o l d f o r d e t e c t i o n of p h y s i c a l l y s i m i l a r s t i m u l i (e.g. words and nonwords d i f f e r i n g only i n the sequence of t h e i r c o n s t i t u e n t l e t t e r s ) i n order to i n s u r e s u b l i m i n a l viewing c o n d i t i o n s . As suggested e a r l i e r i n d i s c u s s i n g the r e l a t i o n between word-detection and w o r d - r e c o g n i t i o n , i t seems 18 c o u n t e r i n t u i t i v e that Ss would r e l y on other than f i g u r a l i n f o r m a t i o n i n order to dete c t words. The study c o n t r o l l e d f o r t h i s p o s s i b i l i t y , however, by determining the t h r e s h o l d f o r words and nonwords with matched p h y s i c a l f e a t u r e s . The second reason f o r t h i s s t u d y , i s r e l a t e d to the c u r r e n t s t a t e of research on ERPs and backward masking. Most experimenters have been concerned with the ERP c o r r e l a t e s of p e r c e p t u a l experience. However, p e r c e p t u a l experience i s probably based on a complex sequence of i n f o r m a t i o n p r o c e s s i n g , with some processes r e f l e c t e d more and others l e s s d i r e c t l y i n ERP components. The supposedly complex s t r u c t u r e s u n d e r l y i n g conscious experience do not l e a d one to expect a simple ' r e l a t i o n s h i p with the ERP as a whole. The ^ i n t e r p r e t a t i o n of p a t t e r n masking mentioned above (e.g. Marcel, i n press) allows f o r a more s p e c i f i c q u e s t i o n : how i s i n f o r m a t i o n p r o c e s s i n g under c o n d i t i o n s of p a t t e r n masking manifested i n the ERP s t r u c t u r e ? By manipulating i n s t r u c t i o n a l set and stimulus f a m i l i a r i t y but not conscious experience, the present experiment attempts to examine s p e c i f i c i n f o r m a t i o n p r o c e s s i n g s t r u c t u r e s and to e s t a b l i s h a f u n c t i o n a l and temporal r e l a t i o n s h i p between ERP s t r u c t u r e and processes in word r e c o g n i t i o n . The t h i r d reason f o r the present experiment was to explore unconscious processes themselves. Marcel ( i n press) c l a i m s that unseen words access t h e i r l e x i c a l e n t r i e s and produce semantic priming, and he accounts f o r these f i n d i n g s by d i s t i n g u i s h i n g encoding and recovery of i n f o r m a t i o n . Word f a m i l i a r i t y may a f f e c t unconscious p r o c e s s i n g of words, s i n c e i t probably 1 9 operates at a lower f u n c t i o n a l l e v e l , than semantic priming, p o s s i b l y on the encoding stage. In a d d i t i o n , the present study, a l s o examined w h e t h e r : p r o c e s s i n g advances to the p o i n t where cont a c t i s made with semantic s e t , i . e . whether d i f f e r e n t i a l p r o c e s s i n g of t a r g e t s and t h e i r c o n t r o l s can be observed. For t h i s purpose the procedure i n c l u d e s an i n s t r u c t i o n a l m anipulation which i s thought to r e s u l t i n semantic s e t , a 'top-down' form of priming: the i n s t r u c t i o n to attend to a t a r g e t s i n one semantic category. Semantic set i s more l i k e l y to a i d recovery of l e x i c a l i n f o r m a t i o n than encoding of the stimulus and thus i s expected to a f f e c t a l a t e r stage of word p r o c e s s i n g than f a m i l i a r i t y . Marcel ( i n press) has demonstrated that a s u b l i m i n a l prime a f f e c t s p r o c e s s i n g of a conscious t a r g e t . The man i p u l a t i o n of set i n the present study can be viewed as a t e s t of whether conscious priming can a f f e c t p r o c e s s i n g . of a s u b l i m i n a l t a r g e t . Words (and the a p p r o p r i a t e c o n t r o l s ) were chosen because they supposedly invoke a s i g n i f i c a n t amount of mandatory, automatic p r o c e s s i n g under p a t t e r n masking. The time e s t i m a t i o n task was chosen mainly because the delayed response allows r e c o r d i n g of uncontaminated ERPs, and because i t has been shown to be s e n s i t i v e to a number of c o g n i t i v e manipulations, e.g. d i f f i c u l t y of i n f o r m a t i o n p r o c e s s i n g ( F r a i s s e , 1979), stimulus f a m i l i a r i t y (Avant, Lyman & Antes, 1975; Avant and Woods, Note 3), stimulus p r o c e s s i n g time (Thomas & Weaver, 1975). More s p e c i f i c a l l y , Avant and Woods (Note 3) found r e l a t i v e d u r a t i o n judgements to be a f f e c t e d by l e x i c a l s t a t u s of pattern-masked 20 l e t t e r s t r i n g s y i e l d i n g chance- d i s c r i m i n a t i o n of l e t t e r case. In a d d i t i o n , the task r e q u i r e d no overt response to the 'unseen' aspect of the stimulus, thereby a v o i d i n g the f r u s t r a t i n g s i t u a t i o n where s u b j e c t s have to judge - something they do not see.. I t was hypothesized t h a t with d e c r e a s i n g f a m i l i a r i t y , i . e . blanks. > t a r g e t s > nontargets > new words > nonwords, processing; would be more demanding and take longer, r e s u l t i n g in o v e r e s t i m a t i o n of r e a l time, f o r which the subject compensates by producing s h o r t e r 1 sec estimates ( F r a i s s e , 1979). 21 I I . METHOD 2.1 SUBJECTS The s u b j e c t s (Ss) were s i x female and s i x male students. : A l l were right-handed, n a t i v e E n g l i s h speakers ranging i n age from 18 to 23 years (mean= 20.3, standard d e v i a t i o n = 1.5 y e a r s ) . Payment was $5.00 per hour, amounting to $15.00 f o r the complete s e s s i o n of approximately three hours. A l l s u b j e c t s r e p o r t e d normal or corrected-to-normal v i s i o n and c o u l d e a s i l y read t a c h i s t o s c o p i c a l l y presented words. 2.2 MATERIALS AND DESIGN The experimental procedure i n c l u d e d both sub- and supra-l i m i n a l c o n d i t i o n s . A l l experimental s t i m u l i were fo l l o w e d by a p a t t e r n mask; for the s u p r a l i m i n a l p r e s e n t a t i o n s , however, the mask was i n e f f e c t i v e s i n c e the words were typed above or below the masked c e n t r a l f i e l d . The complete set of p r a c t i c e and experimental s t i m u l i i s given i n Appendix A. The s t i m u l i f o r the s u b l i m i n a l p r e s e n t a t i o n s c o n s i s t e d of blank cards with a c e n t r a l , grey patch of 2 x 0.8 cm, corresponding to a v i s u a l angle of 2.4 x 1.0 degrees at a viewing d i s t a n c e of 48 cm. The use of the grey patch was necessary to reduce c o n t r a s t of the s t i m u l i . With other s t i m u l i masking was not severe enough to prevent d e t e c t i o n at reasonably high SOAs (above 20 msec). T h i s probably r e f l e c t s c h a r a c t e r i s t i c s of the t a c h i s t o s c o p e used. An IBM S e l e c t r i c was used to type e i t h e r words or nonwords on the grey patch. Typeface was l e t t e r g o t h i c , 12 l e t t e r s per i n c h . Words were three to seven l e t t e r s long, with a four l e t t e r word 22 corresponding to a c e n t r a l v i s u a l angle of 1.0 x 0.4 degrees. E i g h t words were chosen from each of three semantic c a t e g o r i e s , i . e . f u r n i t u r e , v e h i c l e s and body p a r t s , l i s t e d i n the B a t t i g & Montague (1969) category norms. Only words with at l e a s t ten occurences p e r / m i l l i o n (Kucera & F r a n c i s , 1967) were used. They were matched across categories, i n terms of mean word frequency (Kucera & F r a n c i s , 1967), mean l o g frequency and the r e s p e c t i v e standard d e v i a t i o n s , as w e l l as i n terms of word le n g t h and, to the extent s t i l l p o s s i b l e , i n terms of t y p i c a l i t y , i . e . p r o d u c t i o n frequency and p o s i t i o n rank. Nonwords were made by scrambling l e t t e r s of 8 experimental words, at l e a s t two from each category, so as to y i e l d nonpronounceable s t r i n g s bearing l i t t l e resemblance to the o r i g i n a l words. S t r i n g lengths i n t h i s group were matched with the word c a t e g o r i e s . Each word was used f o r two i d e n t i c a l s t i m u l i to y i e l d 16 s t i m u l i per category. The p a t t e r n mask c o n s i s t e d of a c e n t r a l white f i e l d s l i g h t l y l a r g e r than the grey patches c o n t a i n i n g fragments of l e t t e r s of the same typeface as used f o r the s t i m u l i . I t was produced by t r e a t i n g a densely typed f i e l d of l e t t e r s in random o r i e n t a t i o n s with l i q u i d paper to fragment the l e t t e r s . A high q u a l i t y Xerox copy was made and a f i e l d of 2 x 1 cm cut out and glued on the center of a white c a r d . For s u p r a l i m i n a l p r e s e n t a t i o n , the same words were used a g a i n . They were typed above or below the grey patch on otherwise i d e n t i c a l s timulus c a r d s . Each word occ u r r e d i n both p o s s i b l e p o s i t i o n s , y i e l d i n g 16 s t i m u l i per category. These words appeared o u t s i d e the masked f i e l d , c entered 0.8 cm (1.0 23 degree) above or below the c e n t e r of the c a r d . For the t h r e s h o l d determination) a separate ' d e t e c t i o n deck' was used. S t i m u l i were of the type used f o r s u b l i m i n a l p r e s e n t a t i o n s . Half of the 48 cards had a l e t t e r s t r i n g on the grey patch. Of these, h a l f c o n t a i n e d nouns, matched again i n frequency and wordlength to the ones in the experimental c o n d i t i o n s . No exemplars of the c a t e g o r i e s used i n the experimental c o n d i t i o n s were used. The remaining s t r i n g s were nonwords d e r i v e d from the corresponding words, as i n the experimental c o n d i t i o n (with the e x c e p t i o n that here every word had a corresponding nonword). The deck was d i v i d e d i n t o two 'subdecks', each with 50% s t r i n g s and balanced as w e l l as p o s s i b l e . Two of the semantic c a t e g o r i e s were assigned to. each subject as t a r g e t s and nontargets, r e s p e c t i v e l y . Only t a r g e t and nontarget words were presented s u p r a l i m i n a l l y , i . e . o u t s i d e the masked f i e l d . T h i s l e d to the f o l l o w i n g seven experimental c o n d i t i o n s : t a r g e t s and nontargets presented s u p r a l i m i n a l l y , i . e . above or below the c e n t e r ; nonwords, t a r g e t s , nontargets, and 'new' words (the remaining category, i . e . the words they never saw i n s u p r a l i m i n a l p r e s e n t a t i o n ) presented s u b l i m i n a l l y , i . e . c e n t r a l l y ; and a blank c o n d i t i o n (no p r i n t ) f o r c o n t r o l . Combinations of t a r g e t , nontarget and new word c a t e g o r i e s were counterbalanced across sex, with each p o s s i b l e combination a d m i n i s t e r e d once to a female and once to a male s u b j e c t . r 24 2.3 APARATUS S t i m u l i were presented i n a Cambridge t w o - f i e l d t a c h i s t o s c o p e ( t - s c o p e ) . Luminance of stimulus and masking f i e l d were e q u a l i z e d at 3.2 footlamberts (maximal s e t t i n g ! . EEG (Electroencephalogram) was recorded from Oz, C3 and C4 r e f e r r e d to the nose . EOG (Electrooculogram) was recorded between e l e c t r o d e s s u p r a o r b i t a l f o r the l e f t and at the. outer canthus f o r the r i g h t eye. 1 Grass e l e c t r o d e s i n combination with Grass EC-2 paste were used at a l l s i t e s . Grounding was v i a a Beckmann e l e c t r o d e on top of the s p i n e . R e s i s t a n c e was kept below 7k0hms f o r a l l l e a d s . A Beckmann R711 Polygraph was used f o r r e c o r d i n g . A time constant of 1 sec and ah a m p l i f i c a t i o n of 50 microvolts/cm were used f o r a l l channels. The s i g n a l s of the four p h y s i o l o g i c a l channels were m u l t i p l e x e d v i a a V e t t e r model 4 FM r e c o r d i n g adapter and s t o r e d on one channel of a c a s s e t t e tape deck. A 1000 Hz tone i n d i c a t i n g warning tone, stimulus onset and buttonpress response was recorded on the other channel. T a c h i s t o s c o p i c exposure and tone s i g n a l s to loudspeaker and c a s s e t t e tape were under c o n t r o l of an MCS-85 microcomputer. T r i a l s were i n i t i a t e d by the experimenter. The EOG was monitored throughout the experiment and the S was t o l d about the occurrence of e x c e s s i v e a r t i f a c t s i n the r e c o r d i n g , where pres e n t . 1 P i l o t s t u d i e s had i n d i c a t e d that t h i s procedure y i e l d e d comparable s e n s i t i v i t y f o r v e r t i c a l and h o r i z o n t a l eyemovements. 25 2.4 PROCEDURE . For a l l but three Ss the two s e s s i o n s were separated by a 15 min. break. For the remaining three Ss, s e s s i o n s were 2 days, 8 days and 15 days a p a r t . The f i r s t . s e s s i o n was used to determine, the S's t h r e s h o l d f o r d e t e c t i o n of backward-masked words. EOG e l e c t r o d e s were atta c h e d and the S was screened on the f i r s t few t r i a l s f o r e x c e s s i v e eye movement a r t i f a c t s . These a r t i f a c t s were present i n three Ss, and they were r e p l a c e d . The S was seated i n a dimly i l l u m i n a t e d , s h i e l d e d room. The general i n s t r u c t i o n s about the sequence of events i n a s i n g l e t r i a l were read to the S. Throughout the experiment important i n s t r u c t i o n s were accompanied by a summary presented i n the stimulus f i e l d of the t a c h i s t o s c o p e . Every t r i a l c o n s i s t e d of a warning tone of 750 msec, a w a i t i n g p e r i o d of 1 sec, a stimulus p r e s e n t a t i o n followed at a v a r i a b l e SOA by the p a t t e r n mask, a short tone of 10 msec o c c u r r i n g 1 sec a f t e r the stimulus p r e s e n t a t i o n , and an end tone of 200 msec, 1.5 sec a f t e r stimulus p r e s e n t a t i o n (see F i g u r e , ! ) . F i g u r e 1 • - Sequence of events i n a s i n g l e t r i a l mask ^st imulus ISOA P mask t a c h i s t o s c o D e ! warn i nq J • | • i ' r end r~r 1000 Hz t one \ • $ • t t • - 1750 -1000 t ime (msec) 0 1000 1500 1700 26 The S was t o l d not to move and to keep her 2 eyes centered i n the middle of the m a s k - f i e l d between warning tone and end tone. A head r e s t was used. to ensure a constant viewing d i s t a n c e (48cm). I n s t r u c t i o n s f o r the d e t e c t i o n task were then presented. In g e n e r a l , an attempt was made to prepare Ss o p t i m a l l y f o r the d e t e c t i o n task, and they were given c o n s i d e r a b l e advance i n f o r m a t i o n , s t r a t e g i c h i n t s and feedback. The S had to respond v o c a l l y with e i t h e r ' s t r i n g ' or 'blank' and was f i r s t given 5 t r i a l s at an SOA of 200 msec. Then the d e t e c t i o n cards were given to her to look a t . She was asked to look c a r e f u l l y at some of the s t i m u l i , s i n c e d e c i s i o n s would become very d i f f i c u l t , and was t o l d to v e r i f y , that h a l f of the cards contained l e t t e r s t r i n g s . The S was given the assurance, that only t h i s deck would be used f o r the d e t e c t i o n task. An i n s t r u c t i o n c a r d provided a summary of s t i m u l i and t h e i r r e l a t i v e frequency. The f o l l o w i n g statements were emphasized to optimize performance: Decide only on presence or absence, use any a v a i l b l e cue; don't be a f r a i d of guessing, r e l y on your f e e l i n g s ; don't give up when i t gets f r u s t r a t i n g ; s t r i n g s and blanks are h a l f and h a l f , so always use t h i s i n f o r m a t i o n to a d j u s t your s e n s i t i v i t y , and a v o i d using j u s t one response. A minimum of 3 t r i a l s , depending on how c o n f i d e n t the S was, were given at SOAs of 150, 120 and 100 msec each. Then SOA was 2 For the sake of s i m p l i c i t y , ' she.' and 'her' w i l l be used in the sense of 'she' or 'he' and 'her'.or ' h i s ' , r e s p e c t i v e l y . 27 reduced slowly u n t i l the S made a mistake. Feedback was then given on approximately 30 t r i a l s i n an attempt - ( g e n e r a l l y s u c c e s s f u l ) to improve the S's performance.. At the next lower SOA where the S made two mistakes i n a row, a ' s t a i r c a s e ' method was used f o r a subdeck (24 t r i a l s ) . For two c o n s e c u t i v e c o r r e c t responses, SOA was' reduced by 10 msec, and . f o r two i n c o r r e c t responses SOA was in c r e a s e d by 10 msec. To o b t a i n convergence towards the h i g h e s t SOA y i e l d i n g responses at a chance l e v e l an i n c o r r e c t t r i a l was a u t o m a t i c a l l y recorded a f t e r 12 t r i a l s (thus i f a S would have given a l t e r n a t i n g c o r r e c t and i n c o r r e c t responses throughout the 24 t r i a l s , the SOA would n e v e r t h e l e s s have been i n c r e a s e d by one step, a f t e r 13. or 14 t r i a l s , due to the p r eset i n c o r r e c t response between t r i a l 12 and 13). In a d d i t i o n , the SOA was not reduced below 20 msec. The SOA at which the maximal number of t r i a l s had been given was determined and 0, 5 or 10 msec were s u b t r a c t e d from i t (up to the experimenter). A subdeck was presented at the r e s u l t i n g SOA. Whenever performance exceeded 60% c o r r e c t responses, the SOA was f u r t h e r reduced, u s u a l l y i n steps of 5msec, but at l e a s t by 2 msec. The f i r s t SOA at which l e s s than 60% ( i . e . l e s s than 14 items) c o r r e c t responses were obtained i n two cons e c u t i v e subdecks ( i . e . 48 t r i a l s ) was used f o r the experimental s e s s i o n . The S f i l l e d out a q u e s t i o n n a i r e on the t h r e s h o l d d e t e r m i n a t i o n to i n d i c a t e s t r a t e g i e s , c onfidence and estimated performance. Ten t a r g e t s and nontargets of the s u p r a l i m i n a l c o n d i t i o n s were then presented at t h i s SOA while the S was asked 28 to report. . them. Subjects were g e n e r a l l y able to i d e n t i f y most of them. The S was then i n s t r u c t e d f o r the time e s t i m a t i o n task. She was to press a button 1 sec a f t e r the stim u l u s p r e s e n t a t i o n , i . e . concurrent with the short tone, with the r i g h t thumb. No s u p r a l i m i n a l t r i a l s were given f o r that purpose. Up t o . 60 p r a c t i c e t r i a l s were given i n order to t r a i n the S to press r e l i a b l y w i t h i n an i n t e r v a l of 900 to 1100 msec p o s t s t i m u l u s . The f i r s t s e s s i o n l a s t e d between 40 and 80 min. EEG and EOG e l e c t r o d e s were attached at the beginning of the second s e s s i o n . For Ss e n t e r i n g the second s e s s i o n on a d i f f e r e n t day, a subdeck of d e t e c t i o n t r i a l s was admi n i s t e r e d i n order to check the s t a b i l i t y of the p r e v i o u s l y determined SOA. As a r e s u l t of t h i s procedure, the SOA of one S was reduced by 5 msec. The time e s t i m a t i o n task was p r a c t i s e d f u r t h e r u n t i l performance became r e l i a b l e a g a i n . Then the S was i n s t r u c t e d f o r the semantic task. She was shown her t a r g e t s and nontargets, and was t o l d that nontargets were i r r e l e v a n t , that i t was s u f f i c i e n t to decide whether a word was a t a r g e t , and t h a t , only f o r t a r g e t s , she had to press a button as f a s t and a c c u r a t e l y as p o s s i b l e with the middle f i n g e r of her r i g h t hand. She was i n s t r u c t e d not to respond to words other than t a r g e t s . P r a c t i c e was given with the s u p r a l i m i n a l t a r g e t s and nontargets. The two tasks were then combined. When the S d i d not see a word she estimated one sec with the r i g h t thumb. When she saw a word she decided whether or not i t was a t a r g e t , i n the manner j u s t d e s c r i b e d f o r p r a c t i c e t r i a l s . 29 Accuracy was s t r e s s e d . When p r a c t i c e r e s u l t e d i n r e l i a b l e performance, p h y s i o l o g i c a l r e c o r d i n g was s t a r t e d and the experimental t r i a l s were given i n two blocks of 116 t r i a l s (7 x 16, p l u s 4 p r a c t i c e t r i a l s repeated at the end). P r e s e n t a t i o n sequence was randomized f o r each block s e p a r a t e l y , with the c o n s t r a i n t that no more than two exemplars of a s i n g l e s u p r a l i m i n a l c o n d i t i o n , and no more than 3 s u p r a l i m i n a l t r i a l s r e g a r d l e s s of c o n d i t i o n , followed each other. The S was encouraged to r e l a x and to ask f o r short breaks when her eyes f e l t t i r e d . Immediately a f t e r the r e c o r d i n g s e s s i o n , the S f i l l e d out another short q u e s t i o n n a i r e on her s t r a t e g i e s and on what she saw i n the time e s t i m a t i o n t r i a l s , and was then . shown the i n s t r u c t i o n c a r d f o r d e t e c t i o n t r i a l s and given 48 d e t e c t i o n t r i a l s (the two subdecks). She then f i l l e d out a f i n a l q u e s t i o n n a i r e ( s i m i l a r to the f i r s t one on d e t e c t i o n t r i a l s ) , was d e b r i e f e d about the nature of the experiment, and,asked f o r her comment. 2.5 ANALYSIS Percent c o r r e c t responses and the s i g n a l d e t e c t i o n parameter d', i n d i c a t i n g s e n s i t i v i t y to a s t i m u l u s , were c a l c u l a t e d f o r the pre- and postexperimental t h r e s h o l d s e s s i o n s . Both response l a t e n c y data and ERPs were r e t r i e v e d from magnetic tape. During the experiment response l a t e n c i e s were only a v a i l a b l e i n hexadecimal form and the only records w r i t t e n were on the sequence of t r i a l s . In order to a v o i d p o s s i b l e experimenter b i a s , data a n a l y s i s was d e f e r r e d u n t i l the l a s t S was run. Data from both p h y s i o l o g i c a l channels and marker 30 channel were d i g i t i z e d and averaged o f f l i n e . Sampling rate was 100 Hz f o r the p h y s i o l o g i c a l channels and 3000 Hz f o r the marker channel. Response l a t e n c i e s were averaged f o r each c o n d i t i o n while the ERPs were averaged : f o r each combination of s i t e and c o n d i t i o n . Only buttonpress responses between 200 and 1500 msec p o s t s t i m u l u s were i n c l u d e d . Time e s t i m a t i o n responses o u t s i d e a l a t e n c y window of 700 to 1300 msec were d i s c a r d e d as i n v a l i d . T a rgets t r i a l s with responses slower than 1000 msec were excluded, as were nontarget t r i a l s where a button was pressed. Planned orthogonal c o n t r a s t s between the c o n d i t i o n means were performed using the BMDP4V program (Dixon, 1981). The time estimates, i . e . the response l a t e n c i e s f o r the s u b l i m i n a l c o n d i t i o n s , were subjected to the f o l l o w i n g c o n t r a s t s 3 : Blanks vs. s t r i n g s ('presence'), words vs. nonwords ( ' l e x i c a l i t y ' ) , f a m i l i a r vs. u n f a m i l i a r words ( ' f a m i l i a r i t y ' ) and t a r g e t s vs. nontargets ('task r e l e v a n c e ' ) . Sampling and averaging of the p h y s i o l o g i c a l s i g n a l s was f o r a p e r i o d of 3.25 sec, s t a r t i n g with the warning tone (-1750 msec, i . e . 1750 msec pr e s t i m u l u s ) and extending to the endtone (1500 msec p o s t s t i m u l u s ) . However, sampling with 100 Hz only a p p l i e d to a 1600 msec p e r i o d , s t a r t i n g at -100 msec. A r t i f a c t r e j e c t i o n of EOG contaminated t r i a l s was based . on three c r i t e r i a : (1) Absolute amplitude: amplitude of EEG or EOG 3 The s u p r a l i m i n a l c o n d i t i o n s were not c o n s i d e r e d , because f o r nontargets, a no-go s i t u a t i o n ( i . e . no responses) r e s u l t e d , and the r e l a t i v e l y short l a t e n c i e s f o r the t a r g e t s were i n s t r u c t e d , obvious and t h e r e f o r e t r i v i a l . 31 exceeded preset upper or lower l i m i t s . (2) R e l a t i v e amplitude: the absolute d i f f e r e n c e between amplitude and average amplitude i n the EEG or EOG of a t r i a l exceeded p r e s e t c r i t e r i a . (3) C o r r e l a t e d amplitude: f a s t amplitude changes exceeded c r i t e r i a for, EEG and EOG simultaneously or with a short l a g (+•/-' 10 msec). The P3 d e r i v a t i o n was used as the c r i t i c a l EEG channel. A c o n j u n c t i o n r u l e was a p p l i e d to the r e l a t i v e and the c o r r e l a t e d amplitude c r i t e r i o n , i . e . both types of a r t i f a c t s had to occur f o r a t r i a l to be r e j e c t e d . C r i t e r i a were a d j u s t e d i n d i v i d u a l l y when a f i r s t run f a i l e d to y i e l d f l a t EOG r e c o r d i n g s with l e s s than 20%' r e j e c t i o n . A c r i t i c a l p e r i o d of at l e a s t 700 msec po s t s t i m u l u s was scanned. The ERPs of i n d i v i d u a l Ss were p l o t t e d f o r a l l combinations of c o n d i t i o n s and s i t e s . ERP amplitude was s c a l e d a c c o r d i n g to recorded c a l i b r a t i o n s i g n a l s and r e f e r e d to a b a s e l i n e , d e f i n e d as the average of the 50 msec p e r i o d preceeding stimulus p r e s e n t a t i o n . Components o c c u r r i n g c o n s i s t e n t l y i n most of the Ss were i d e n t i f i e d and scored. Six components, l a b e l l e d , here NI, P1, N2, P2, N3, P3, were i d e n t i f i e d . Amplitude and l a t e n c y measures were analysed i n c o n t r a s t s s i m i l a r to the ones f o r the time e s t i m a t e . However, an a d d i t i o n a l c o n t r a s t between s u b l i m i n a l and s u p r a l i m i n a l c o n d i t i o n s was performed, and each comparison was done f o r .a s p e c i f i c s i t e , i . e . at Oz f o r the blanks vs. s t r i n g s c o n t r a s t , and at P3 f o r the remaining comparisons, presumably i n v o l v i n g 32 l i n g u i s t i c i n f o r m a t i o n p r o c e s s i n g (see a l s o F i g . 2, p.37) 4 . C o n t r a s t s were run with BMDP4V (Dixon, 1 9 8 1 ) . Analyses were performed on a l l component l a t e n c i e s , a l l peak-to-trough amplitude measures and, i n a d d i t i o n , N1 and P3 amplitude ( r e f e r r e d to the b a s e l i n e ) 5 .. For the p h y s i o l o g i c a l data, a s i g n i f i c a n c e l e v e l of . 0 1 r a t h e r than the usual .05 , l e v e l was adopted in order to reduce the familywise type-I e r r o r r a t e . The .05 l e v e l was used when i n t e r p r e t i n g t r e n d s . C o n t r a s t s were performed using the e r r o r terms corresponding to the i n d i v i d u a l c o n t r a s t s r a t h e r than the c o n v e n t i o n a l pooled estimate common to a l l c o n t r a s t s . M i t z e l & Games ( 1 9 8 1 ) have shown that t h i s robust approach s a c r i f i c e s r e l a t i v e l y l i t t l e power, and that the c o n v e n t i o n a l s o l u t i o n i s o f t e n i n a c c u r a t e . * As mentioned in the i n t r o d u c t i o n , Andreassi (Note 2) found changes in the ERP with backwardmasking s p e c i f i c to Oz; and Thatcher (1977) found e f f e c t s of semantic r e l a t e d n e s s (synonyms or antonyms) at l e f t hemisphere leads (P3 and T5) o n l y . These f i n d i n g s were thus i n c o r p o r a t e d i n the design of the c o n t r a s t s . 5 Peak-to-trough measures were f e l t to be more immune to b a s e l i n e f l u c t u a t i o n s . N1 and P3 amplitudes were analysed because these bordering components are underrepresented i n the f i v e d i f f e r e n c e - a m p l i t u d e s , i . e . because they enter only one d i f f e r e n c e as opposed to two f o r the other components, and because a major t h e o r e t i c a l framework has been b u i l t around N1 and P3. 33 I I I . RESULTS 3.1 D e t e c t i o n Performance Of the 14 Ss run o r i g i n a l l y , two were reruns f o r Ss whose data were d i s c a r d e d . One S was excluded because i n the f i r s t t h r e s h o l d s e s s i o n c r i t e r i o n was not reached at an SOA as short as 15 msec. Since i t was f e l t that n e i t h e r the c o n t r o l l i n g switches nor the t a c h i s t o s c o p e were accurate at such short exposures, SOA was not reduced f u r t h e r . T h i s r e s u l t e d i n 71% c o r r e c t responses i n the postexperimental d e t e c t i o n t r i a l s . The second S was excluded because there was not enough time to give d e t e c t i o n t r i a l s at the beginning of the second s e s s i o n , two days a f t e r the f i r s t s e s s i o n . T h i s S gave 75% c o r r e c t responses i n the postexperimental d e t e c t i o n t r i a l s and repo r t e d having seen one of the targetwords i n the time e s t i m a t i o n task. The f o l l o w i n g analyses are based on the counterbalanced design with 12 Ss. Experimental SOAs ranged from 23 to 60 msec, with a mean of 36 msec and a standard d e v i a t i o n of 9.7 msec. For a l l Ss i n c l u d e d i n the a n a l y s i s , c o r r e c t responses i n the postexperimental d e t e c t i o n t r i a l s were l e s s than 60%. Table I summarizes d e t e c t i o n performance at the experimental SOA f o r both pre- and postexperimental t h r e s h o l d . 34 Table I - De t e c t i o n performance: mean p r o b a b i l i t y of h i t s and d's EJ CPERIMENTAI POST-- EXPERIMEf JTAL ALL WORD, NONWORD ALL WORD NONWORD HIT : d\ HIT d' HIT d' HIT d' HIT d* HIT d' M .45 -.13 .49 -.05 .42 -.25* .48 .11 .53 .23* .42 -.04 SD .07 .26 .13 .47 .12 .30 .10 .22 .10 .27 . 1 6 . 4 1 Note - M: mean; SD: standard d e v i a t i o n ; * p < .05. The same f a l s e alarm r a t e was used i n determining the d' f o r o v e r a l l s e n s i t i v i t y as w e l l as f o r s e n s i t i v i t y to words or nonwords o n l y . S e n s i t i v i t y measures (d') were analyzed f o r d e v i a t i o n s from chance performance. In the preexperimental s e s s i o n , s e n s i t i v i t y to nonwords was below chance, t ( l l ) = -2.88, p < .05. In the postexperimental s e s s i o n , s e n s i t i v i t y to words was above chance, t ( l 1 ) = 3.05,1, p < .05. F a l s e alarm r a t e s were .50 f o r the pre- and .43 f o r the postexperimental s e s s i o n . For the preexperimental s e s s i o n , Ss responded c o r r e c t l y on 47.4% of the t r i a l s ; 49.1% and 45.6% were the r e s p e c t i v e values f o r words and nonwords. For the postexperimenatal s e s s i o n , Ss responded c o r r e c t l y on 52.3% of the t r i a l s , 54.9% f o r words and 49.7% f o r nonwords. 3.2 Response L a t e n c i e s Table II shows the mean response l a t e n c i e s f o r the time e s t i m a t i o n s and for the t a r g e t i d e n t i f i c a t i o n , together with the corresponding standard d e v i a t i o n s and percentage of i n v a l i d t r i a l s . 35 Table II - Mean time estimates and i n v a l i d t r i a l s Sl JBLIMINAI SUPRALIh 1INAL BLANK NONWOR TARGET NONTAR NEWORD TARGET NONTAR M SD -% 939.0 38.8 2.1 932.1 37.4 3.4 937.8 45.9 2.9 944.9 .'. 32.5 2.6 931 .7 35.1 3.4 659.8 40.8 ; 10.4 8.3 Note - NONWOR=nonword, NONTAR=nontarget, NEWORD=new word. M=mean estimated i n t e r v a l i n msec; SD=standard d e v i a t i o n ; -%=percentage i n v a l i d t r i a l s . None of the d i f f e r e n c e s between.the s u b l i m i n a l c o n d i t i o n s was s i g i f i c a n t ; the F values are given i n Table I I I . The a s s o c i a t e d type-I e r r o r p r o b a b i l i t i e s were a l l above 0.1. Table III - F - r a t i o s f o r c o n t r a s t s on time estimates BLANK vs. WORD vs. FAMILIAR vs. TARGET vs. STRING NONWORD NEW WORD NONTARGET F( 1 , 1 1 ) 0.17 1 .00 3.01 1.16 3.3 Event R e l a t e d P o t e n t i a l s S i x components were i d e n t i f i e d and scored. They are l a b e l e d N1 , P1, N2, P2, N3, P3; with 'N' and 'P' corresponding to the p o l a r i t y ( i . e . p o s i t i v e or negative) of the wave. Not a l l components were equaly prominent a c r o s s s u b j e c t s , with P2 and N3 o f t e n c h a r a c t e r i z e d by changes i n slope rather than by c l e a r p o l a r i t y r e v e r s a l s . The windows used f o r s c o r i n g the components were 90-130 msec f o r N1, 110-180 msec f o r P1, 160-220 msec f o r N2, 200-300 msec f o r P2, 250-340 msec f o r N3 and 360-36 440 msec f o r P3. An attempt was made to achieve high c o n s i s t e n c y w i t h i n a s i n g l e S's data. In d o u b t f u l cases the wave c l o s e s t to the one scored i n the c l e a r e s t t r a c e of the S's data was chosen. One sub j e c t d i d not show a P3 component. In t h i s case, l a t e n c i e s were d e f i n e d as the cente r of the window ( i . e . 400 msec) f o r a l l s i t e s and c o n d i t i o n s . Amplitudes were d e f i n e d as the average of the three c e n t r a l time p o i n t s ( i . e . 390, 400, 410 msec). Table IV d e p i c t s the mean l a t e n c i e s of the scored components, c o l l a p s e d a c r o s s Ss, s i t e s and c o n d i t i o n s , with the corresponding standard d e v i a t i o n s . Table IV - Mean ERP component l a t e n c i e s and standard d e v i a t i o n s LATENCY N1 P1 N2 P2 N3 P3 mean 111.1 141.5 183.3 259. 1 301 .3 400.7 SD 11.8 12.5 15.6 2.5.9 23.8 18.4 Sets of c o n t r a s t s were performed on the component l a t e n c i e s , on the peak-to-trough amplitude measures (e.g. N1-P1, P1-N2...) and on N1 and P3 amplitudes ( r e f e r r e d to b a s e l i n e ) . C o n t r a s t s were e s s e n t i a l l y i d e n t i c a l with the ones done f o r the time e s t i m a t e s ; i n a d d i t i o n , s u b l i m i n a l and s u p r a l i m i n a l c o n d i t i o n s were compared. The f o l l o w i n g f i g u r e d e p i c t s the set of c o n t r a s t s used, along with the s i t e ( s ) at which they were t e s t e d . The f i r s t four c o n t r a s t s i n v o l v e only means of s u b l i m i n a l c o n d i t i o n s . 37 Figu r e 2 - Set of c o n t r a s t s (1) Blank vs. s t r i n g : at Oz (2) Words vs. nonword: at P3 (3) F a m i l i a r vs. new words: at P3 (4) Ta r g e t s vs. nontargets: at P3 (5) S u b l i m i n a l vs. s u p r a l i m i n a l t r i a l s : at a l l s i t e s Table V g i v e s the mean latency-measures measures at the P3 d e r i v a t i o n , and Table VI.does so f o r the amplitude measures. F i g u r e 3 d e p i c t s the group average ERPs at P3. Furthe r ERP averages are shown in Appendices B-D (group averages) and E-F ( i n d i v i d u a l s u b j e c t averages). Table V - Mean ERP component l a t e n c i e s at P3 f o r a l l c o n d i t i o n s Sl JBLIMINJ SUPRAL] .MINAL BLANK NONWOR TARGET NONTAR NEWORD TARGET NONTAR N1 113.8 117.5 116.3 118.3 118.3 117.5 115.4 P1 1 42. 1 145.4 1 46.7 1 46.7 145.0 147. 1 1 45.8 N2 . 184.2 185.8 186.7 187. 1 184.2 190.0 190.8 P2 264.2 259.6 265.4 262.9 260.0 259.2 261 .3 N3 311.3 310.0 307.9 310.4 308.8 305.4 305.4 P3 406.7 399.2 404.2 398.8 399.6 411.7 407.5 Note - NONWOR=nonword, NONTAR=nontarget, NEWORD=new word. L a t e n c i e s i n msec p o s t s t i m u l u s . 38 For the l a t e n c i e s , the only d i f f e r e n c e occurred between sub- and s u p r a l i m i n a l p r e s e n t a t i o n s , with N2 being e a r l i e r f o r s u b l i m i n a l p r e s e n t a t i o n s (F=20.02, p <.01). ) Table VI - Mean ERP component amplitudes at P3 fo r a l l c o n d i t i o n s St JBLIMINi ^L SUPRAL] [MINAL BLANK NONWOR TARGET NONTAR NEWORD TARGET NONTAR BASELINE -8.96 -8.03 -8.99 -8.64 -8.93 -10.20 -9.52 N1 -1.18 -1 .58 -1 .28 -0.73 -0.61 -1 .08 -0.26 P1 1 .32 0.50 1.07 1 .63 1 .07 2.29 2.45 N2 -3.28 -4.64 - 4.06 -3.33 -4.03 -2.62 -3.88 P2 7.67 6.54 5.58 7.06 7.30 4.94 3.60 N3 5.49 4.33 5.57 6.43 4.99 4.48 2.98 P3 13.79 12.17 13.81 14.45 1 3.63 16.72 14.97 Note - NONWOR=nonword, NONTAR=nontarget, NEWORD=new word. Component amplitudes i n m i c r o v o l t s r e f e r r e d to b a s e l i n e . Signs r e f l e c t p o l a r i t y of v o l t a g e . 39 F i g u r e 3 - Group average ERPs at P3 f o r a l l c o n d i t i o n s Note - the upper two t r a c i n g s d e p i c t the s u p r a l i m i n a l , and the lower f i v e t r a c i n g s the s u b l i m i n a l c o n d i t i o n s , r e s p e c t i v e l y . Epoch 500 msec p o s t s t i m u l u s ; n e g a t i v i t y upwards; dashed l i n e s ( b a s e l i n e s ) 10 m i c r o v o l t s a p a r t . 40 For the amplitude measures, the b a s e l i n e was more negative (by 1.08 m i c r o v o l t s ) f o r s u p r a l i m i n a l as opposed to s u b l i m i n a l p r e s e n t a t i o n s (F=11.09, p <.01). T h i s c o n t r a s t a l s o d i f f e r e d f o r N1-P1 amplitude (F=11.83, p <.01), N1-P1 being 1.19 m i c r o v o l t s l e s s i n the s u b l i m i n a l c o n d i t i o n s ; f o r P1-N2 amplitude (F=16.35, p <.01), with P1-N2 by 1.8 m i c r o v o l t s s m a l l e r i n the s u b l i m i n a l c o n d i t i o n s ; and f o r N3-P3 amplitude (F=13.93, p <.01), N3-P3. being smaller again, by 3.49 m i c r o v o l t s , i n the s u b l i m i n a l c o n d i t i o n s . Comparisons w i t h i n the s u b l i m i n a l c o n d i t i o n s y i e l d e d an e f f e c t on P2-N3 amplitude f o r f a m i l i a r vs. new words (F=10.42, p <.01, P2-N3 being 1.99 m i c r o v o l t s smaller f o r f a m i l i a r words) and on N3-P3 for. blank vs. s t r i n g s (F=11.64, p <.0l); N3-P3 amplitude was .98 m i c r o v o l t s s m a l l e r f o r t r i a l s p r e s e n t i n g a l e t t e r - s t r i n g . A trend was observed f o r d i s c r i m i n a t i o n between words and nonwords i n terms of P3 amplitude (F=4.87, p <.05), with P3 amplitude 1.79 m i c r o v o l t s l a r g e r ( i . e . more p o s i t i v e ) for words. 41 IV. DISCUSSION ; 4.1 S t a t i s t i c a l And Me t h o d o l o g i c a l C o n s i d e r a t i o n s The number of s t a t i s t i c a l t e s t s performed i n t h i s study i s c o n s i d e r a b l e . On the ERP data alone, 14 sets of 5 orthogonal a p r i o r i hypotheses were t e s t e d . The adjustment of the s i g n i f i c a n c e l e v e l s • made here i s not n e a r l y s u f f i c i e n t to keep the experimentwise e r r o r r a t e at a nominal 0.05 l e v e l ( i t does so f o r one of the 14 se t s o n l y ) . Of these 70 c o n t r a s t s , 14 compared the s u b l i m i n a l and the s u p r a l i m i n a l c o n d i t i o n s . F i v e s i g n i f i c a n t e f f e c t s were found t h e r e . The remaining 56 c o n t r a s t s i n v o l v e d only the s u b l i m i n a l c o n d i t i o n s . Two s i g n i f i c a n t e f f e c t s and a trend (at the .01 and the .05 l e v e l , r e s p e c t i v e l y ) r e s u l t e d . C o n s i d e r i n g t h i s , i t i s of some concern that the s i g n i f i c a n c e of none of the e f f e c t s encountered w i t h i n the s u b l i m i n a l c o n d i t i o n s i s s t r i k i n g , i n f a c t , none of them reaches s i g n i f i c a n c e at a next lower l e v e l (e.g. at the 0.01 l e v e l f o r e f f e c t s t e s t e d at the 0.05 l e v e l ) . Since planned orthogonal comparisons r e f l e c t a powerful procedure, we are c l e a r l y d e a l i n g with weak e f f e c t s . To exclude the p o s s i b i l i t y that they are the r e s u l t of random processes r e p l i c a t i o n of the present f i n d i n g s seems e s s e n t i a l . . The p o s s i b i l i t y of methodological a r t i f a c t s must a l s o be c o n s i d e r e d . Whether the t h r e s h o l d obtained was too l i b e r a l i s a p o i n t to be d i s c u s s e d , s i n c e the use of the s e n s i t i v i t y parameter d' and the separate assessment of d e t e c t i o n performance f o r words and nonwords y i e l d e d a d i s t i n c t p a t t e r n of d e t e c t i o n a c c u r a c i e s , d i f f e r e n t from what would be expected by chance. 42 However, there i s some evidence i n d i c a t i n g t h at the r e s u l t s o btained are at l e a s t i n t e r n a l l y c o n s i s t e n t . F i r s t , i t i s f e l t t h a t they lend themselves to a c o n s i s t e n t i n t e r p r e t a t i o n , f o r which the ERP measures and the d e t e c t i o n performance measures pro v i d e converging evidence. Secondly, while the r e s u l t s are arguably weak, they are at l e a s t s p e c i f i c , i n that they do not seem to g e n e r a l i z e from the set of a p r i o r i hypotheses chosen to a number of other p o s s i b l e hypotheses. Each c o n t r a s t was hypothesized to y i e l d maximal d i s c r i m i n a t i o n at s p e c i f i c r e c o r d i n g s i t e s . To assess the value of these s p e c i f i c hypotheses, each c o n t r a s t on the peak-to-trough amplitudes was performed f o r the remaining s i t e s . T h i s set of c o n t r a s t s , i n c l u d i n g over twice the number of the s p e c i f i c c o n t r a s t s performed, y i e l d e d two trends (p .•-<•' .05) as opposed to two s i g n i f i c a n c e s (p <. .01) and one t r e n d f o r the s p e c i f i c hypotheses. While these arguments c l e a r l y do not q u e s t i o n the need f o r a r e p l i c a t i o n of the present f i n d i n g s , n e i t h e r do they favor the view that the r e s u l t s should be d i s m i s s e d as being due to chance. 4.2 D e t e c t i o n Performance While the o v e r a l l r e s u l t s i n d i c a t e that s u b j e c t s judged presence or absence of a s t r i n g no b e t t e r than chance, the d e t a i l e d a n a l y s i s of the d's y i e l d e d d i f f e r e n t p i c t u r e s f o r words and nonwords. I t seems l i k e l y t h a t i n the preexperimental s e s s i o n the c r i t e r i o n (two blocks i n sequence with l e s s - t h a n 60% c o r r e c t .responses) a r t i f i c i a l l y depressed the estimate of the Ss d e t e c t i o n performance below the a c t u a l performance l e v e l , i . e . 43 that i t i n t r o d u c e d a sampling b i a s towards the blocks of t r i a l s with poor o v e r a l l performance. I t seems that Ss were a c t u a l l y s l i g h t l y above chance f o r d e t e c t i o n of words, as r e f l e c t e d i n the (unbiased) second session., while., f o r nonwords t h e i r s e n s i t i v i t y was at chance l e v e l . I t i s assumed that t h i s r e l a t i o n h e l d f o r both s e s s i o n s ; i n the f i r s t one, however, the b i a s f o r c e d a c t u a l random performance ( f o r nonwords) below chance l e v e l , and f o r c e d the a c t u a l above chance performance ( f o r words) to a l e v e l no more d i f f e r e n t from chance. An obvious q u e s t i o n then i s whether ' s u b l i m i n a l ' or 'unconscious' p e r c e p t i o n i s an adequate term to d e s c r i b e the word t r i a l s i n the time e s t i m a t i o n t a s k . S e v e r a l f i n d i n g s bear on t h i s i s s u e . F i r s t , maximum s e n s i t i v i t y ( f o r words in the postexperimental s e s s i o n ) was s t i l l very low, y i e l d i n g a d' of 0.23 and 55% c o r r e c t responses. Of a l l Ss (other than the excluded ones) questioned, only one r e p o r t e d with some confidence having seen l e t t e r s or words, a f t e r the f i r s t d e t e c t i o n s e s s i o n . An a d d i t i o n a l 48 d e t e c t i o n t r i a l s were run for t h a t S, and he was to r e p o r t a l l he c o u l d from t r i a l s i n which he f e l t he had a c t u a l l y seen something. The S responded to these i n s t r u c t i o n s on 5 t r i a l s . He r e p o r t e d l e t t e r s or words on three ' s t r i n g ' and on two 'blank' p r e s e n t a t i o n s . For the s t r i n g p r e s e n t a t i o n s , he r e p o r t e d ' t i e ' as 'hat' (both words were among the 12 words i n the d e t e c t i o n deck), 'AHT* as s t a r t i n g with 'S', and 'FEOECF' as a nonword s t a r t i n g with 'MB'. For one of the blanks he r e p o r t e d 'ROOF', f o r the other blank 'MBL' i n the middle. These data are c l e a r l y at odds with h i s •44 c o n f i d e n t r e p o r t of having seen l e t t e r s and words. A l l but one subject d e b r i e f e d a f t e r the experiment, were c l e a r l y amazed, when t o l d that s t r i n g s had been presented on 80% of the t r i a l s , although the t r i a l s looked, i d e n t i c a l i n , d e t e c t i o n , and time e s t i m a t i o n t r i a l s . The response l a t e n c y data make a s i m i l a r p o i n t : There was no s i g n that ' s u b l i m i n a l ' p r e s e n t a t i o n of t a r g e t s or nontargets l e d to responses s i m i l a r to those obtained under normal viewing c o n d i t i o n s , nor was there any evidence fo r an induced response c o n f l i c t . Furthermore, the r e s u l t s i n d i c a t e that the term to q u e s t i o n i s ' d e t e c t i o n ' rather than ' s u b l i m i n a l ' or 'unconscious' p e r c e p t i o n . O v e r a l l , Ss proved unable to judge, at b e t t e r than chance accuracy, whether any stimulus had preceded the p a t t e r n mask. T h i s i s how d e t e c t i o n was o r i g i n a l l y d e f i n e d i n the experiment. While the f i n d i n g that presence/absence of some s t r i n g s (i.e.words) was judged with s l i g h t l y b e t t e r than chance accuracy i s i n need of an e x p l a n a t i o n , i t does not r e f l e c t what i s commonly understood as ' d e t e c t i o n ' . S i m i l a r l y , the e a r l y ERP components a s s o c i a t e d with d e t e c t i o n and stimulus set (Parasuraman et a l . , 1982) d i s c r i m i n a t e d between s u b l i m i n a l and s u p r a l i m i n a l c o n d i t i o n s but not between blanks and ' s u b l i m i n a l ' s t r i n g s . Parasuraman et a l . (1982) re p o r t e d that N100 r e f l e c t e d d e t e c t i o n performance. The r e s u l t s obtained here f o r the components in the same l a t e n c y range i n d i c a t e that d e t e c t i o n accuracy, where above chance, was not accompanied by the expected e a r l y ERP e f f e c t s . T h i s might again i n d i c a t e that 45 d e t e c t i o n , when confounded with the Content of the s t i m u l u s , can not be equated with 'simple' d e t e c t i o n . To assess the p o s s i b l e c o n t r i b u t i o n s of ' d e t e c t i o n ' performance to the l a t e ERP e f f e c t s of f a m i l i a r i t y and presence of a s t r i n g , c o r r e l a t i o n s between the c r i t i c a l ERP d i f f e r e n c e s and the s e n s i t i v i t y to words ( i n the second, unconstrained s e s s i o n ) were c a l c u l a t e d . , The c o r r e l a t i o n s were not s i g n i f i c a n t , r ( l O ) = -.25 f o r f a m i l i a r i t y and r(!0) = -.26 f o r presence ( p > .10 i n each c a s e ) . Together with the negative values of the c o r r e l a t i o n s , t h i s r e s u l t most probably p r e c l u d e s an i n t e r p r e t a t i o n of the ERP e f f e c t s i n terms of r e s i d u a l awareness of some aspect of the s t i m u l i . F i n a l l y i t should be noted that the s e n s i t i v i t y measures were obtained under optimal c o n d i t i o n s . Great care was taken to assure t h a t Ss had a c l e a r idea of the s t i m u l i they were co n f r o n t e d with, and that r e l i a n c e on i n t u i t i v e f e e l i n g s and vague impressions r a t h e r than c o n f i d e n c e was emphasized. In a d d i t i o n , c o n s i d e r a b l e amounts of p r a c t i c e and feedback were gi v e n . To summarize, s e v e r a l l i n e s of evidence favor the c o n c l u s i o n that the o v e r a l l l e v e l of performance, the lack of confidence accompanying the judgements, and the p e c u l i a r p a t t e r n of accuracy do not support the view that words were 'detected'. However, the r e s u l t s a l s o i n d i c a t e that d i s c r i m i n a t i n g ( r a t h e r than d e t e c t i n g ) v e r b a l behavior d i d occur. A complete d i s s o c i a t i o n between v e r b a l r e p o r t and i n d i r e c t measures of stimulus d i s c r i m i n a t i o n , which i s the focus of a r a t h e r hot debate around the is s u e of s u b l i m i n a l p e r c e p t i o n (e.g. M e r i k l e , 46 1982; P u r c e l l et a l . , Note 1), was not found i n t h i s study. The d i f f e r e n t i a l s e n s i t i v i t y to words and nonwords i s i n t e r p r e t e d i n l i n e with recent r e s u l t s r e p o r t e d b y A v a n t .& Woods (Note 3). They found that l e x i c a l judgements on two s u c c e s s i v e l y presented, pattern-masked l e t t e r s t r i n g s ( i . e . to judge the s t r i n g s as 'same' or ' d i f f e r e n t ' with respect to l e x i c a l s t a t u s ) were made with b e t t e r than chance accuracy, while f o r the same s t i m u l i f i g u r a l judgements ( i . e . 'same' or ' d i f f e r e n t ' with respect to l e t t e r case) were at chance. In the present study Ss performed as i f making a l e x i c a l d e c i s i o n ; i . e . , they d i s c r i m i n a t e d words, but not nonwords, from blanks. C o n s i s t e n t with t h i s i s the f i n d i n g ( f o r the unconstrained postexperimental s e s s i o n ) that only 42% h i t s were scored f o r nonwords. T h i s y i e l d s 58% 'blank' responses to nonwords, a f i g u r e comparing f a v o r a b l y with the 57% 'blank' responses to a c t u a l blanks. S u b j e c t s might a c t u a l l y have responded with 'blank' i n the sense of 'no word', thus s u c c e s s f u l l y performing a l e x i c a l d e c i s i o n task.. U n f o r t u n a t e l y , r e i n t e r p r e t i n g the 'blank' response to a nonword as a h i t i n a h y p o t h e t i c a l l e x i c a l d e c i s i o n task confounds s e n s i t i v i t y and response b i a s : thus the f i g u r e s might simply i n d i c a t e a general tendency to respond 'blank' along with an i n c r e a s e d s e n s i t i v i t y to words. Whatever task Ss a c t u a l l y performed i t seems that they monitored i n t e r n a l evidence confounded with l e x i c a l p r o c e s s i n g . T h i s extends the r e s u l t s of Avant & Woods (Note 3) to the domain of 'simple' d e t e c t i o n . D e t e c t i o n under c o n d i t i o n s of p a t t e r n 47 masking, i . e . when f i g u r a l p r o p e r t i e s of. the t a r g e t are i n t e r f e r e d with, thus might r e l y on i n f o r m a t i o n at a higher l e v e l than p r e v i o u s l y assumed.. In t h i s r e s p e c t , i t i s an i n t e r e s t i n g p o s s i b i l i t y that the i n s t r u c t i o n s given to optimize performance, with t h e i r emphasis on 'simple' p h y s i c a l f e a t u r e s , were perhaps d e t r i m e n t a l r a t h e r than u s e f u l - d e t e c t i n g 'simple' p h y s i c a l p r o p e r t i e s might be d i f f e r e n t from, and more demanding than, d e t e c t i n g some i n t e r n a l events confounding p h y s i c a l and l e x i c a l p r o p e r t i e s of s t i m u l i . 4.3 Time Estimates The negative f i n d i n g s i n terms of response l a t e n c i e s a r e . d i f f i c u l t to d i s c u s s . U n f o r t u n a t e l y , the experiment does not t e l l us whether the time e s t i m a t i o n procedure chosen would be s e n s i t i v e to s i m i l a r stimulus manipulation under normal viewing c o n d i t i o n s . The f i n d i n g of Avant and Woods (Note 3), that r e l a t i v e d u r a t i o n s were a f f e c t e d by l e x i c a l s t a t u s of p a t t e r n masked m a t e r i a l , presented i n the compared i n t e r v a l s , might be l i m i t e d to r e l a t i v e d u r a t i o n judgements. However, there are no p o s i t i v e r e s u l t s to support such s p e c u l a t i o n s at t h i s p o i n t . 4.4 Event Re l a t e d P o t e n t i a l s The d i f f e r e n c e i n b a s e l i n e v a l u e s between the s u b l i m i n a l and the s u p r a l i m i n a l c o n d i t i o n s i s p u z z l i n g . There are s e v e r a l p o s s i b i l t i e s that c o u l d produce such an e f f e c t . The p o s s i b i l i t y that the e f f e c t was a r t i f a c t u a l was c o n s i d e r e d . Since p r e s t i m u l u s n e g a t i v i t y does c o r r e l a t e with performance i n some s i t u a t i o n s (Donchin et a l . , 1978), i t i s p o s s i b l e that the t r i a l s excluded as i n v a l i d i n the s u b l i m i n a l and i n the 48 s u p r a l i m i n a l c o n d i t i o n s (as r e f l e c t i n g poor.performance) were c h a r a c t e r i s e d by d i f f e r e n t a n t i c i p a t o r y . n e g a t i v i t y , s i n c e d i f f e r e n t types of p r e p a r a t i o n might be useful, or d e t r i m e n t a l in d i f f e r e n t types of t a s k s . The data, were t h e r e f o r e d i g i t i z e d again, with a l l c r i t e r i a f o r t r i a l e x c l u s i o n (except f o r experimentor e r r o r s ) removed. The c o n t r a s t between s u b l i m i n a l and s u p r a l i m i n a l c o n d i t i o n s performed on t h i s new set of b a s e l i n e s s t i l l y i e l d e d F(1,11) = 8.82 with p =.013. Thus b a s e l i n e d i f f e r e n c e s were present i n the 'raw' averages obtained from a l l t r i a l s . Since there i s no evidence that the e f f e c t i s s p u r i o u s , i t seems very l i k e l y that Ss had some s o r t of advance in f o r m a t i o n as to what type of t r i a l would occur. The p o s s i b i l i t y that the experimenter communicated to the S nonverbal cues based on h i s b i a s f o r a s p e c i f i c outcome seems u n l i k e l y , p a r t l y because the experimenter was f u l l y occupied with changing c a r d s , r e c o r d i n g the codes, and m o nitoring the eye movements of the S, and p a r t l y because the main i n t e r e s t of the study was i n d i f f e r e n c e s w i t h i n the s u b l i m i n a l c o n d i t i o n s , where no b a s e l i n e d i f f e r e n c e s were observed. However, the p o s s i b i l i t y cannot be completely r e f u t e d . W a s t e l l and Kleinman (1980) suggested that i n experiments with random permutations of s t i m u l i , p r e d i c t a b i l i t y of a stimulus type i s s t i l l above chance, due to the c o n s t r a i n t of equal (or j u s t f i x e d ) numbers of s t i m u l i per type. The a d d i t i o n a l c o n s t r a i n t , that no more than three s u p r a l i m i n a l s t i m u l i and no more than two s u p r a l i m i n a l s t i m u l i of one type were allowed i n sequence might have i n c r e a s e d p r e d i c t a b i l i t y to the p o i n t where i t r e s u l t e d i n 49 d i f f e r e n t i a l p r e p a r a t i o n . I t i s argued here that the v a l i d i t y of the main c o n c l u s i o n s i s not a f f e c t e d by t h i s f i n d i n g of b a s e l i n e d i f f e r e n c e s , be i t spurious or not. I f the d i f f e r e n c e s r e f l e c t a v a i l a b i l i t y of advance i n f o r m a t i o n , then the lack of d i f f e r e n c e w i t h i n the more i n t e r e s t i n g s u b l i m i n a l c o n d i t i o n s would seem to imply t h a t w i t h i n these c o n d i t i o n s no cues were a v a i l a b l e . N e v e r t h e l e s s , care must, be taken i n t e r p r e t i n g d i f f e r e n c e s between s u b l i m i n a l and s u p r a l i m i n a l c o n d i t i o n s . The d i f f e r e n c e in.N1-P1, s t a r t i n g before approximately 140 msec p o s t s t i m u l u s , most probably r e f l e c t s e a r l y e f f e c t s , of s e l e c t i v e a t t e n t i o n . No d i f f e r e n c e was obtained f o r NI, which i s t e n t i v e l y assumed to be homologous with N100. W a s t e l l and Kleinman (1980) s i m i l a r l y found no e f f e c t of s e l e c t i v e a t t e n t i o n on N1 i n an experiment where t a r g e t s and nontargets d i f f e r e d i n simple p h y s i c a l cues, such as shape and i n t e n s i t y , but appeared at the same l o c a t i o n . They argue that N1 r e f l e c t s mainly a t t e n t i o n to a s i n g l e s p a t i a l source. I t i s unclear to what extent the two p o s s i b l e s p a t i a l p o s i t i o n s i n the present experiment can be c o n s i d e r e d as such a s i n g l e source. In the present experiment, N1 occured somewhat e a r l i e r than i s usual f o r the v i s u a l modality. However, the f i n d i n g , t h a t d i f f e r e n c e s s t i l l do occur before 140 msec p o s t s t i m u l u s i s g e n e r a l l y i n agreement with other data on e a r l y s e l e c t i o n ( P i c t o n et a l . , 1978). I t i s a l s o p o s s i b l e that an even e a r l i e r e f f e c t i s obscured by the d i f f e r e n t b a s e l i n e s , e.g. the high p r e s t i m u l u s n e g a t i v i t y f o r the s u p r a l i m i n a l c o n d i t i o n s might have l e d t o a c e i l i n g e f f e c t for the e a r l y N1 n e g a t i v i t y . The other 50 d i f f e r e n c e s w i l l not be d i s c u s s e d i n d e t a i l , s i n c e d i f f e r e n c e s i n s t i m u l i , task and b a s e l i n e cannot be separated. I t should be noted, however, that the d i f f e r e n c e s are major and obvious on simple v i s u a l i n s p e c t i o n . The d i f f e r e n c e s w i t h i n the s u b l i m i n a l c o n d i t i o n s were small and not obvious on simple v i s u a l i n s p e c t i o n . Components of the ERP d i s c r i m i n a t e d between f a m i l i a r and u n f a m i l i a r words at 250-300 msec, while presence vs. absence of a s t r i n g was d i s c r i m i n a t e d by l a t e r components, at 350-400 msec. T h i s r e s u l t i s c o n s i s t e n t with the view t h a t d e t e c t i o n under c o n d i t i o n s of backward-masking i s a l a t e process which draws on evidence from s p e c i a l i z e d l e x i c a l (and maybe other) p r o c e s s o r s , an i n t e r p r e t a t i o n supported by the trend f o r words vs. nonwords: d i s c r i m i n a t i o n of l e x i c a l s t a t u s a l s o occured a f t e r the e f f e c t of f a m i l i a r i t y . , at a l a t e n c y s i m i l a r t o the d e t e c t i o n e f f e c t . However, i t a l s o seems p o s s i b l e that the e f f e c t of l e x i c a l s t a t u s i s s p u r i o u s . 4.5 General D i s c u s s i o n The r e s u l t s provide . converging evidence from s e n s i t i v i t y and ERP measures that d e t e c t i o n under the present c o n d i t i o n s i s a l a t e process. They a l s o argue a g a i n s t the view that p a t t e r n -masking d i s r u p t s p r o c e s s i n g : E R P - e f f e c t s d i d not occur before 260 msec p o s t s t i m u l u s ( l a t e n c y of P2), and were found prominently in comparisons i n v o l v i n g even l a t e r components (N3 at 300 msec, P3 at 400 msec).. A r e i n t e r p r e t a t i o n of the e f f e c t of f a m i l i a r i t y i n terms of task relevance i s not supported because of the negative f i n d i n g f o r the t a r g e t vs. nontarget 51 comparisons, and i t seems as i f the words were i d e n t i f i e d by the p e r c e p t u a l system,, but not r e c o g n i z e d as being t i e d to d i f f e r e n t i n t e r p r e t a t i o n s w i t h i n the task. The present study i n d i c a t e s that s p e c i f i c ERP c o r r e l a t e s of stimulus p r o c e s s i n g can be obtained under c o n d i t i o n s of. p a t t e r n masking. However, l i t t l e can be concluded about the c o r r e l a t e s f o r the simple s t i m u l i commonly used in backward masking paradigms (e.g. Andreassi et a l . , 1976; Schwartz et a l . , 1981). The e f f e c t s reported here are content s p e c i f i c , p o t e n t i a l l y i n d i c a t i n g the u s e f u l n e s s of complex s t i m u l i i n the study of the ERP under backward masking. An i n t e r e s t i n g f i n d i n g i n the present study was the apparent convergence between ERP e f f e c t s and i n t e r p r e t a t i o n s d e r i v e d from b e h a v i o r a l measures. That f a m i l i a r i t y i s coded e a r l i e r than presence/absence of a l e t t e r s t r i n g has been i n t e r p r e t e d as r e f l e c t i n g the dependence of ' d e t e c t i o n ' on l e x i c a l i n f o r m a t i o n under c o n d i t i o n s of p a t t e r n masking. Even more i n t r i g u i n g i s the f a c t that the trend f o r d i s c r i m i n a t i o n between words and nonwords in the ERP appears temporally confounded ( i . e . occurs in the same l a t e n c y range of 300-400 msec) with the d i s c r i m i n a t i o n between s t r i n g s and blanks. T h i s f i n d i n g i s p a r a l l e l e d i n the b e h a v i o r a l domain - d e t e c t i o n performance was confounded with content of the presented s t i m u l u s . Taken together, the f i n d i n g s extend the u s e f u l n e s s of the ERP i n the study of human inf o r m a t i o n p r o c e s s i n g to s i t u a t i o n s where automatic ( i n the sense of unconscious) p r o c e s s i n g p r e v a i l s . 52 F a m i l i a r i t y e f f e c t s may occur a u t o m a t i c a l l y , i .e. without the S being aware of d i f f e r e n t i a l , f a m i l i a r i t y (Scarborough et a l . 1979). T h e i r l o c u s seems to be l e x i c a l r a t h e r than semantic (Warren & Morton, 1982) s i n c e they do not show t r a n s f e r a c r o s s m o d a l i t i e s . Most r e c e n t l y , T u l v i n g , Stark & Schacter (1982) have succeeded i n s e p a r a t i n g e f f e c t s of ' f a m i l i a r i t y on priming and r e c o g n i t i o n . In t h e i r study words showed e f f e c t s of priming ( i n a fragment completion task) from p r e v i o u s exposure without being recognized; and the e f f e c t s were found to have d i f f e r e n t decay f u n c t i o n s . Priming thus seems to be u n r e l a t e d to e p i s o d i c memory and might be i n d i c a t i v e of a, lower l e v e l memory system. T h i s seems to p a r a l l e l the present study in which the ERP i n d i c a t e s that items were i d e n t i f i e d as f a m i l i a r , but not recognized as being of d i f f e r e n t task r e l e v a n c e . That f a m i l i a r i t y i s a powerful v a r i a b l e with long r e t e n t i o n , and that i t i s r e a d i l y a f f e c t e d by experimental manipulations has r e p e a t e d l y been shown (e.g. M u r r e l l and Morton, 1974; Scarborough et a l . , 1979). However, the main i n t e r e s t i n word r e c o g n i t i o n has focussed on semantic e f f e c t s over short i n t e r v a l s (e.g. semantic p r i m i n g ) . Research e x p l i c i t l y concerned with the e f f e c t s of v e r b a l i n f o r m a t i o n over longer p e r i o d s , as w e l l as the f i n d i n g s of the present study, suggest a-somewhat d i f f e r e n t emphasis: The view of word r e c o g n i t i o n as the temporary a c t i v a t i o n of a complex s t r u c t u r e might be s l i g h t l y m i s l e a d i n g , s i n c e i t n e g l e c t s the important r o l e of input i n updating p e r c e p t u a l and c o g n i t i v e s t r u c t u r e s with respect to f u t u r e events. 53 The f a i l u r e to o b t a i n d i f f e r e n c e s between the s u b l i m i n a l t a r g e t s and nontargets might i n d i c a t e that s u b l i m i n a l s t i m u l i do not i n t e r a c t with task r e l e v a n c e , here conceived of as semantic s e t . However i t may w e l l be that f o r semantic e f f e c t s to become apparent, some response to a meaningful stimulus (not n e c e s s a r i l y the s u b l i m i n a l one, though) i s r e q u i r e d . In cases where s u b l i m i n a l s t i m u l i prime a conscious t a r g e t . (Marcel, i n press) t h i s requirement i s met. I t i s not met, however, in the present study where e f f e c t s of (conscious) semantic set on s u b l i m i n a l t a r g e t s were examined. P o s s i b l y a conscious t a r g e t i s needed to 'carry' semantic e f f e c t s through the c o g n i t i v e system up to a p o i n t where they a f f e c t ongoing p r o c e s s e s . More s p e c i f i c a l l y , recovery processes a c t i n g on a l e x i c a l r e c o r d may not occur a u t o m a t i c a l l y to p a t t e r n masked s t i m u l i , but when i n i t i a t e d by a normally presented t a r g e t they may act on any l e x i c a l r e c o r d a v a i l a b l e , i n c l u d i n g those from sources that w i l l never become c o n s c i o u s . . However, more s e n s i t i v e experiments must be designed to answer t h i s q u e s t i o n . How do the f i n d i n g s f i t with the models of r e c o g n i t i o n and, more s p e c i f i c a l l y , word r e c o g n i t i o n , as i n t r o d u c e d at the beginning? The r e s u l t that d e t e c t i o n accuracy i s a f f e c t e d by l e x i c a l s t a t u s supports the view adopted by s i g n a l d e t e c t i o n t h e o r i s t s (e.g. Green and B i r d s d a l l , 1978). D e t e c t i o n and r e c o g n i t i o n thus may r e f l e c t a u n i t a r y p rocess, with the same set of i n t e r n a l d e t e c t o r s being monitored in both s i t u a t i o n s . The f i n d i n g might a l s o imply that the s i g n a l d e t e c t i o n model a p p l i e s not only to simple s t i m u l i . However the r e s u l t s do not 54 seem to favor a s i n g l e model of word r e c o g n i t i o n . The strength, of the logogen model of Morton (1969) with respect to the present f i n d i n g s i s that i t e x p l i c i t l y accounts for f a m i l i a r i t y e f f e c t s and the updating of the logogen u n i t s w i t h . r e s p e c t to f u t u r e events. The i n t e r a c t i v e a c t i v a t i o n model (Rumelhart & M c C l e l l a n d , 1982) i s h e l p f u l i n e x p l a i n i n g the s e l e c t i v e e f f e c t s of backward masking on f i g u r a l p r o p e r t i e s of a word, and i t might give a s l i g h t l y more d i r e c t account for the higher d e t e c t i o n accuracy f o r words than f o r nonwords. In the framework pro v i d e d by the logogen model (Morton, 1969), t h i s r e s u l t c o u l d i n d i c a t e that Ss monitored the l e x i c a l system f o r the d e t e c t i o n task. I t seems u n l i k e l y , however, that s i n g l e logogen u n i t s exceeded t h r e s h o l d , i . e . that words were a c t u a l l y recognized; r a t h e r Ss must have had some i n f o r m a t i o n about a c t i v a t i o n below the t h r e s h o l d l e v e l . In the framework provided by the i n t e r a c t i v e a c t i v a t i o n model, evidence a v a i l a b l e at the l e x i c a l or word l e v e l i n f l u e n c e s lower l e v e l s of r e p r e s e n t i o n v i a feedback. Thus in t h i s model judgements based on evidence from lower l e v e l s are expected to show i n f l u e n c e s of higher l e v e l i n f o r m a t i o n such as l e x i c a l -status. However, as mentioned e a r l i e r , the present experiment can not decide at which l e v e l Ss a c t u a l l y monitored evidence fo r the d e t e c t i o n task. M o n i t o r i n g e i t h e r the l e x i c a l l e v e l or a f i g u r a l l e v e l r e c e i v i n g feedback from the l e x i c a l l e v e l c o u l d both y i e l d the p a t t e r n of r e s u l t s a c t u a l l y o b t a i n e d . A l a s t general p o i n t adresses the i s s u e of the proper t h r e s h o l d f o r s u b l i m i n a l p e r c e p t i o n . Chances are that the 55 outcome of the debate -whether or hot r e s u l t s l i k e the ones obtained by Marcel ( i n press), are demonstrations of unconscious, p e r c e p t i o n w i l l be f a r l e s s i n t e r e s t i n g than the r e s u l t s themselves, u n l e s s a broader view of the 'proper' t h r e s h o l d i s adopted. M e r i k l e (1982), has argued f o r the need to use s i g n a l d e t e c t i o n , parameters along with a s u f f i c i e n t number of o b s e r v a t i o n s f o r determining a d e t e c t i o n t h r e s h o l d , and he o b v i o u s l y suspects the t h r e s h o l d s i n the paprs by Marcel ( i n p r e s s ) , Fowler et a l . ; (1981) and McCauley et a l . (1980), to be too l i b e r a l to warrant an i n t e r p r e t a t i o n i n terms of unconscious p e r c e p t i o n . P u r c e l l et a l . - (Note 1.) have p o i n t e d out that c o n d i t i o n s f o r the t h r e s h o l d d e t e r m i n a t i o n and f o r the a c t u a l experiment, while d i f f e r i n g i n seemingly t r i v i a l d e t a i l s , may r e s u l t i n d r a s t i c a l l y d i f f e r e n t e s t i m a t e s - o f the i d e n t i f i c a t i o n or d e t e c t i o n accuracy. They demonstrated that a d a p t a t i o n d i f f e r e n c e s c o u l d be r e s p o n s i b l e f o r the r e s u l t s obtained by McCauley et a l . (1980). I t seems indeed unfortunate t h a t the methods used to determine d e t e c t i o n t h r e s h o l d s leave so much space f o r d i f f e r i n g i n t e r p r e t a t i o n s of the l e v e l of performance and. experience they r e f l e c t . In the experiment d e s c r i b e d here an attempt was made to a v o i d some of the more obvious c r i t i c i s m s , e.g. by g i v i n g r a t h e r e x p l i c i t i n s t r u c t i o n s , by f a m i l i a r i z i n g Ss with the s t i m u l i and the task, and by a s s e s s i n g d e t e c t i o n performance i n some d e t a i l with s i g n a l d e t e c t i o n parameters. However, the r e s u l t s i n d i c a t e that c o g n i t i v e m anipulations a f f e c t d e t e c t i o n 56 to such .an extent that t h r e s h o l d . d e t e r m i n a t i o n should probably c o n t r o l f o r them, too. T h i s might a c t u a l l y mean that two experiments with i d e n t i c a l setup ( i n c l u d i n g a l l manipulations of interest,) but d i f f e r e n t tasks should be run, one to assess d e t e c t i o n performance and one as the actuals experiment. The suggestion o b v i o u s l y i s s i m p l i s t i c and l i m i t s the range of p o s s i b l e experiments. I t may, however, serve the purpose of i l l u s t r a t i n g what c o u l d at l e a s t p a r t l y underly the much d i s c u s s e d 'complete d i s s o c i a t i o n ' between v e r b a l report and i n d i r e c t measures of behavior: d i f f e r e n c e s i n i n s t r u c t i o n s and t a s k s . A more v i a b l e a l t e r n a t i v e i s the procedure used by Avant & Woods (Note 3) who compared f i g u r a l and l e x i c a l , semantic or temporal judgements to p a i r s of s t i m u l i . T h i s approach examines what i n f o r m a t i o n i s a v a i l a b l e f o r a c o n s i d e r a b l e range of t a s k s . An important f e a t u r e w i t h i n t h i s approach i s the use of f i g u r a l f o r c e d c h o i c e judgements, i . e . a case d i s c r i m i n a t i o n . While t h i s approach might arguably address rather a b s t r a c t f i g u r a l q u a l i t i e s , i t has the advantage of being l e s s confounded with l e x i c a l p r o c e s s i n g than 'simple' ' d e t e c t i o n . A l t e r n a t i v e l y , the use of concurrent d e t e c t i o n and r e c o g n i t i o n judgements (e.g. Parasuraman et a l . , 1982) might serve b e t t e r to c h a r a c t e r i z e d e t e c t i o n under d i f f i c u l t c o n d i t i o n s . T h e i r a d d i t i o n a l use of confidence r a t i n g s r e s u l t s i n a more d e t a i l e d p i c t u r e of the r e l a t i o n s h i p between performance and experience i n complex d e t e c t i o n tasks than simple presence/absence judgements. F i n a l l y , a more r a d i c a l approach would be to abandon the 57 concept of d e t e c t i o n as a. b a s i c , simple process. T h i s approach has some appeal because the preoccupation with 'simple' d e t e c t i o n might be founded on a misconception, namely that an e a r l y , content-independent process c l o s e to the sensory end mediates d e t e c t i o n and thus must b e . a c c e s s i b l e f o r the purpose of v e r b a l r e p o r t about the s t i m u l u s . The argument a g a i n s t s u b l i m i n a l p e r c e p t i o n then seems to be that i f such an e a r l y , simple f u n c t i o n i s precluded, l a t e r complex f u n c t i o n s are • even l e s s l i k e l y to o c u r r . The present study, however, i n d i c a t e s that d e t e c t i o n under c o n d i t i o n s of pattern-masking might be a r a t h e r l a t e , c o n t e n t - s p e c i f i c process. Thus, occurrence of an (incomplete) d i s s o c i a t i o n between d e t e c t i o n accuracy and i n d i r e c t measures of semantic p r o c e s s i n g may not i n d i c a t e a c o u n t e r i n t u i t i v e d i s s o c i a t i o n between e a r l y , simple and complex, l a t e processes, but between e q u a l l y l a t e and complex processes of d i f f e r e n t s p e c i a l i z a t i o n . If the l a t t e r i n t e r p r e t a t i o n i s c o r r e c t , then d e t e c t i o n of complex and meaningful s t i m u l i under d i f f i c u l t c o n d i t i o n s might be i n t e r e s t i n g i n i t s e l f and thus be worth f u r t h e r i n v e s t i g a t i o n . A l l p o r t (1980, p.51) i n d i s c u s s i n g 'New D i r e c t i o n s ' f o r c o g n i t i v e psychology s t a t e s that "... A d i f f e r e n t and c o n t r a s t i n g o r i e n t a t i o n focusses d i r e c t l y on i n f o r m a t i o n content, and on content-s p e c i f i c (hence d i s t r i b u t e d ) mechanisms for i t s r e p r e s e n t a t i o n and use..." T h i s contemporary c h a r a c t e r i s a t i o n of c o g n i t i v e r e s e a r c h seems to leave much more room f o r r e s u l t s of the kind obtained i n t h i s explorato-ry study than does the n o t i o n of 'simple' d e t e c t i o n . 58 BIBLIOGRAPHY i . REFERENCE NOTES 1. P u r c e l l , D.G,, Stewart, A.L. & Stanovich, K.E. Another look at semantic priming without awareness. Paper i n p r e p a r a t i o n . 2. A n d r e a s s i , J.L., G a l l i c h i o , J.A. & Young, N.E. Evoked c o r t i c a l p o t e n t i a l s and i n f o r m a t i o n p r o c e s s i n g . S i x t h  Annual Report (Baruch C o l l e g e , C i t y U n i v e r s i t y of New York) . Contract N00014-77-C-01-14, June, 1978. . -3. 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Semantic category e f f e c t s i n v i s u a l search. Memory & C o g n i t i o n , 1976, 19, 417-424. Kucera, H. , & F r a n c i s , W.N. Computational A n a l y s i s of Present- Day E n g l i s h . Providence: Brown U n i v e r s i t y Press, 1967. M a r c e l , A.J. E x p l a i n i n g s e l e c t i v e e f f e c t s of p r i o r context on p e r c e p t i o n : the need to d i s t i n g u i s h conscious and pre-conscious p r o c e s s e s . In J . Requin (Ed.), A n t i c i p a t i o n and  Behaviour. Centre N a t i o n a l de l a Recherche S c i e n t i f i q u e : P a r i s , 1980. M a r c e l , A.J. Conscious and unconscious reading: the e f f e c t s of masking on word p e r c e p t i o n . C o g n i t i v e Psychology, 1982, i n p r e s s . McCauley, C., Parmelee, CM., Sperber, R.D. & C a r r , T.H. E a r l y e x t r a c t i o n of meaning from p i c t u r e s and i t s r e l a t i o n to conscious i d e n t i f i c a t i o n . J o u r n a l of Experimental  Psychology: Human P e r c e p t i o n and Performance, 1980, 6, 265-276. M c C l e l l a n d , J.L. & Rumelhart, D.E. An i n t e r a c t i v e a c t i v a t i o n model Of context e f f e c t s i n l e t t e r p e r c e p t i o n : p a r t I. An account of b a s i c f i n d i n g s . P s y c h o l o g i c a l Review, 1981, 88, 375-407. Megela, A.L. & T e y l e r , T.J. E v e n t - r e l a t e d p o t e n t i a l s a s s o c i a t e d with l i n g u i s t i c s t i m u l i : Semantic vs. lower-order e f f e c t s . In D.A. Otto (Ed.), M u l t i d i s c i p l i n a r y  P e r s p e c t i v e s i n Event R e l a t e d B r a i n P o t e n t i a l Research (EPA 600/9-77-043) . Washington,D.C.: U.S. Gov't. P r i n t i n g O f f i c e , 1978. M e r i k l e , P.M. Unconscious p e r c e p t i o n r e v i s i t e d . P e r c e p t i o n &  Psychophysics, 1982, 31, 298-301. Meyer, D.E., Schvaneveldt, R.V. & Ruddy, M.G. L o c i of c o n t e x t u a l e f f e c t on v i s u a l word r e c o g n i t i o n . In P.M.A. Rabbi t t and S. Dornic (Eds.), A t t e n t i o n and Performance V. New York: Academic Press, 1975. M i t z e l , H.C & Games, P.A. C i r c u l a r i t y and m u l t i p l e comparisons in repeated measure designs.- B r i t i s h J o u r n a l 61 of Mathematical and S t a t i s t i c a l Psychology, 1981, 34, 253-- 259. Molfese, D.L., Papanicolaou, A., Hess, T.H. & Molfese, V.J. Neuroel.ee t r i e c o r r e l a t e s of semantic p r o c e s s e s . In H . B e g l e i t e r (Ed.), Evoked B r a i n P o t e n t i a l s and Behavior. New York: Plenum Press, 1979. Morton,. J . The i n t e r a c t i o n of i n f o r m a t i o n i n word r e c o g n i t i o n . P s y c h o l o g i c a l Review, 1969, 76, 165-178. M u r r e l l , G.A. & Morton, J . Word r e c o g n i t i o n and morphemic s t r u c t u r e . J o u r n a l of Experimental Psychology, 1974, 102, 963-968. Osgood, C E . Semantic d i f f e r e n t i a l techniques i n the comparative study of c u l t u r e s . American Anthropology, 1964, 66j_ 171-200. Parasuraman, R. , R i c h e r , F. & Beatty, J . Detection, and r e c o g n i t i o n : concurrent processes i n p e r c e p t i o n . P e r c e p t i o n & Psychophysics, 1982, 31, 1-12.: P i c t o n , T.W., Campbell, K.B., Bar ibeau-Braun, J . & Proulx, G..B. The neurophysiology of human a t t e n t i o n : a t u t o r i a l review. In J . Requin (Ed.), A t t e n t i o n and Performance V I I . H i l l s d a l e , N.J: Erlbaum, 1978. Posner, M.i. & Snyder, C R . .Attention and c o g n i t i v e c o n t r o l . In R.L. Solso (Ed.), Information p r o c e s s i n g and c o g n i t i o n :  The Loyola-Symposium. H i l l s d a l e , N.J.: Erlbaum, 1975. Rumelhart, D.E. & M c C l e l l a n d , J.L. An i n t e r a c t i v e a c t i v a t i o n model f o r -context e f f e c t i n l e t t e r p e r c e p t i o n : p a r t 2. The c o n t e x t u a l enhancement e f f e c t and some t e s t s and extensions of the model. P s y c h o l o g i c a l Review, 1982, 89, 60-94. Scarborough, D.L., Gerard, L. & Cortese, C. A c c e s s i n g l e x i c a l memory: the t r a n s f e r of word r e p e t i t i o n e f f e c t s across task and modality. Memory & C o g n i t i o n , 1979, 3-12. Schwartz, M., W h i t t i e r , O.M. & Schweitzer, P.K. Evoked responses to r e t r o a c t i v e l y masked s t i m u l i . P h y s i o l o g i c a l  Psychology, 1979, 107-111. Schwartz, M. & P r i t s c h a r d , W.S. AERs and d e t e c t i o n i n tasks y i e l d i n g U-shaped backward masking f u n c t i o n s . Psychophysiology, 1981, j j ^ 678-685. Schvaneveldt, R.W. & McDonald, J.E. Semantic context and the encoding of words: evidence f o r two modes of stimulus a n a l y s i s . J o u r n a l of Experimental Psychology: Human  Pe r c e p t i o n and Performance, 1 9 8 1 , 2J. 673-687. 62 Shelbourne, S.A. V i s u a l evoked responses to word and nonsense s y l l a b l e s t i m u l i . Electroencephalography and C l i n i c a l  Neurophysiology, 1972, 32, 17-25. Shelbourne, S.A. V i s u a l evoked p o t e n t i a l s ' t o language s t i m u l i . in c h i l d r e n with reading d i s a b i l i t i e s . In D.A. Otto (Ed.), M u l t i d i s c i p l i n a r y , P e r s p e c t i v e s i n Event R e l a t e d  B r a i n P o t e n t i a l Research (EPA 600/9-77-043) . ~~ Washington,D.C. : U.S.. Gov't. P r i n t i n g O f f i c e , 1978. Sutton, S. P300 - t h i r t e e n years l a t e r . In H . B e g l e i t e r (Ed.), Evoked B r a i n P o t e n t i a l s and Behavior. New York: Plenum Press, 1979. T e y l e r , T.J., Roemer, R.A., H a r r i s o n , T.F. & Thompson, R.F. Human s c a l p - r e c o r d e d e v o k e d - p o t e n t i a l c o r r e l a t e s of l i n g u i s t i c s t i m u l i . B u l l e t i n of the Psychonomic S o c i e t y , 1 973, lj_ 333-334. Thatcher, R.W. 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Priming e f f e c t s i n word-fragment completion are independent of r e c o g n i t i o n memory. J o u r n a l of Experimental Psychology: L e a r n i n g ,  Memory and C o g n i t i o n , 1982, 8j_ 336-342. Turvey, M.T. On p e r i p h e r a l and c e n t r a l processes i n v i s i o n : i n f e r e n c e s from an i n f o r m a t i o n - p r o c e s s i n g a n a l y s i s of masking with p a t t e r n e d s t i m u l i . P s y c h o l o g i c a l Review, 1973, 80^ 1-52. Vaughan, J . , S h e r i f , K., O ' S u l l i v a n , R.L., Hermann, D.J., & Weldon, D.A. C o r t i c a l evoked responses to synonyms and antonyms. Memory & C o g n i t i o n , 1982, 10, 225-231. Warren, C. & Morton, J . The e f f e c t s of priming on p i c t u r e r e c o g n i t i o n . B r i t i s h J o u r n a l of Psychology, 1982, 73, 117-129. W a s t e l l , D.G. & Kleinman, D. Evoked p o t e n t i a l c o r r e l a t e s of v i s u a l s e l e c t i v e a t t e n t i o n . Acta P s y c h o l o g i c a , 1980, 46, 63 129-140. 64 APPENDIX A - LIST OF STIMULI i . S t i m u l i f o r t h e - d e t e c t i o n task WORDS NONWORDS FIG 72 TIE ....... 23 IFG AHT LBLA NTTE IEBBL FEOECF EIT RDOW NY I WE FEIRL OMSEU SEINNT HAT . .. 56 WORD .... .274 BALL .110 WINE 72 TENT ...... 20 RIFLE 63 BIBLE 59 MOUSE ..... 1 0 COFFEE . . . .78 TENNIS .-. .15 i i . S t i m u l i f o r the experimental tasks WORDS NONWORDS CAR 274 BED .. . . 127 TOE . ..19 ' DBL BUS .34 RUG 13 EAR 38 RAE TAXI ... .16 DESK .. ...65 LEGS .. . .67 EPJE JEEP. . . . .16 LAMP .. ..18 ARMS .. . 1 2 1 SAMR BOAT . . . .72 TABLE . . 1 9 8 NECK .. . . 8 1 CNEBH TRAIN .. .82 CHAIR . . .66 HEART . . 1 7.3 NRIAT TRUCK .. .57 BENCH . . .°35 BRAIN . . .45 IHACR TRACTOR .24 MIRROR . .27 BREAST . . 1 1 OTRTAC Note - numbers r e f l e c t frequency counts from Kucera & F r a n c i s (1967).. In a few cases, counts given do not r e f l e c t the numerosity of a given item (e.g. count given f o r 'ear' r e f l e c t s a c t u a l count f o r ' e a r s ' ) . 65 APPENDIX B - GROUP MEAN ERPS AT P4 FOR ALL CONDITIONS Note - the upper two t r a c i n g s d e p i c t the s u p r a l i m i n a l , and the lower f i v e t r a c i n g s the s u b l i m i n a l c o n d i t i o n s , r e s p e c t i v e l y . Epoch 500 msec p o s t s t i m u l u s ; n e g a t i v i t y upwards; dashed l i n e s ( b a s e l i n e s ) 10 m i c r o v o l t s a p a r t . APPENDIX C - GROUP MEAN ERPS AT OZ FOR ALL CONDITIONS GM Oz 100 200 300 *400 msec ' i • i Note - the upper two t r a c i n g s d e p i c t the s u p r a l i m i n a l , and the lower f i v e t r a c i n g s the s u b l i m i n a l c o n d i t i o n s , r e s p e c t i v e l y . Epoch 500 msec p o s t s t i m u l u s ; • n e g a t i v i t y upwards; dashed l i n e s ( b a s e l i n e s ) 10 m i c r o v o l t s a p a r t . 67 APPENDIX D - GROUP MEAN EOG FOR ALL CONDITIONS GM EOG NONTARGET TARGET NEW WORD NONTARGET TARGET NONWORD BLANK 100 i 200 i — 300 I — *t00 msec — I Note - the upper two t r a c i n g s d e p i c t the s u p r a l i m i n a l , and the lower f i v e t r a c i n g s the s u b l i m i n a l c o n d i t i o n s , r e s p e c t i v e l y . Epoch 500 msec p o s t s t i m u l u s ; n e g a t i v i t y upwards; dashed l i n e s ( b a s e l i n e s ) 10 m i c r o v o l t s a p a r t . 68 APPENDIX E - AVERAGED ERPS FOR ONE SUBJECT (S1) AT P3 Note - the upper two t r a c i n g s d e p i c t the s u p r a l i m i n a l , and the lower f i v e t r a c i n g s the s u b l i m i n a l c o n d i t i o n s , r e s p e c t i v e l y . Epoch 500 msec p o s t s t i m u l u s ; n e g a t i v i t y upwards; dashed l i n e s ( b a s e l i n e s ) 10 m i c r o v o l t s a p a r t . 69 APPENDIX F - AVERAGED ERPS FOR ONE SUBJECT (S2) AT P3 S2 P3 100 200 300 400 msec _> » i i Note - the upper two t r a c i n g s d e p i c t the s u p r a l i m i n a l , and the lower f i v e t r a c i n g s the s u b l i m i n a l c o n d i t i o n s , r e s p e c t i v e l y . Epoch 500 msec p o s t s t i m u l u s ; n e g a t i v i t y upwards; dashed l i n e s ( b a s e l i n e s ) 10 m i c r o v o l t s a p a r t . 

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