eye movements in reading and information processing: 20 years of research

7/30/2019 Eye Movements in Reading and Information Processing: 20 Years of Research

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Psychological Bulletin Copyright 1998 by the American Psychological Association, Inc.1998 , Vol. 124 , No . 3 , 372 -422 0033-2909/98 /$3.00

Eye Movements in Read ing and In format ion Proces s ing :20 Years o f ResearchK e i th Ra yne r ~University of Massachusetts at Amherst

Recent studies of eye movements n reading and other information processing tasks, such as musicreading, typing, visual search, and scene perception, are reviewed. The major emphasis of the reviewis on reading as a specific example of cognitive processing. Basic topics discussed with respect toreading are (a) the characteristics of eye movements, (b) the perceptual span, (c) integration ofinformation across saccades, (d) eye movement control, and (e) individual differences (includingdyslexia). Similar topics are discussed with respect to the other tasks examined. The basic themeof the review is that eye movementdata reflect moment-to-moment ognitiveprocesses in the varioustasks examined. Theoretical and practical considerations concerning the use of eye movement dataare also discussed.

Many studies using eye movements to investigate cognitiveprocesses have appeared over the past 20 years. In an earlierreview, I (Rayner, 1978b) argued that since the mid-1970s wehave been in a third era of eye movement research and that thesuccess of research in the current era would depend on theingenuity of researchers in designing interesting and informativestudies. It would appear from the vast number of studies usingeye movement data over the past 20 years that research in thisthird era is fulfilling he promise inherent in using eye movementbehav ior to infer cognitive processes. The first era of eye move-ment research extended from Javal's initial observations con-cerning the role of eye movements in reading in 1879 (see Huey,1908) up until about 1920. During this era, many basic factsabout eye movements were discovered. Issues such as saccadicsuppression (the fact that we do not perceive information duringan eye movement), saccade latency (the time that it takes toinitiate an eye movement) , and the size of the perceptual span(the region of effective vision) were of concern in this era. Thesecond era, which coincided with the behaviorist movement inexperimental psychology, tended to have a more applied focus,and little research was undertaken with eye movements to infercognitive processes. Although classic work by Tinker (1946)on reading and by Buswell (1935) on scene perception wascarried out dur ing this era, in retrospect, most of the work seemsto have focused on the eye movements per se (or on surfaceaspects of the task being investigated). Tinker's (1958) finalreview ended on the rather pessimistic note that almost every-

Preparation of this article was supported by a Research ScientistAward from the National Institute of Mental Health (MH01255) and byGrants HD 17246 and HD 26765 from the National Institutes of Health.Thanks are extended to Ken Ciuffreda, Charles Clifton, David Irwin,and Alexander Pollatsek for their helpful comments on prior versions ofthis article.Correspondence concerning this article should be addressed to KeithRayner, Department of Psychology, University of Massachusetts, Am-herst, Massachusetts 01003. Electronic mail may be sent to [email protected].

thing that could be learned about reading from eye movements(given the technology at the time) had been discovered. Perhapsthat opinion was widely held, because between the late 1950sand the mid-1970s little research with eye movements wasundertaken.

The third era of eye movement research began in the mid-1970s and has been marked by improvements in eye movementrecording systems that have allowed measurements to be moreaccurate and more easily obtained. It is beyond the scope of thepresent review to detail all of the technological advancementsthat have been made. Numerous works have dealt with methodsof analyzing eye movement data (see Kliegl & Olson, 1981;Pillalamarri, Barnette, Birkmire, & Karsh, 1993; Scinto & Bar-nette, 1986), and much has been learned about the characteris-tics of various eye-tracking systems (see Deubel & Bridgeman,1995a, 1995b; Muller, Cavegn, d'Ydewalle, & Groner, 1993).More important, the era has yielded tremendous technologicaladvances that have made it possible to interface laboratory com-puters with eye-tracking systems so that large amounts of datacan be collected and analyzed. These technological advanceshave also allowed for innovative techniques to be developed inwhich the visual display is changed contingent on the eye posi-tion. In the eye-contingent d isp lay change paradigm (McCon-kie, 1997; McConkie & Rayner, 1975; Rayner, 1975b; Reder,1973), eye movements are monitored, and changes are made inthe visual display that the reader is looking at, contingent onwhen the eyes move (or at some other critical point in thefixation). Finally, the development of general theories of lan-guage processing has made it possible to use eye movementrecords for a critical examination of the cognitive processesunderlying reading.

In the present article, recent studies of eye movements inreading and other informa tion processing tasks are examined.Since the last review in this jou rnal (Rayner, 1978b), there havebeen many reviews of eye movement research (Kennedy, 1987;L6vy-Schoen & O'Rega n, 1979; O'Regan , 1990; Pollatsek,1993; Rayner, 1984, 1993, 1995, 1997; Rayner & Pollatsek,1987, 1992; G. Underwood, 1985). However, none of them are

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EYE MOVEMENTS IN READING 373comprehensive: Some deal only with rea ding (or scene percep-tion), and most of them advocate a particular point of view.The goal of the present article is to provide a comprehensivereview of eye movement research over the past 20 years. Since1978, many eye movement studies have appeared in editedbooks. Because the quality of the research reported in suchbooks is somewhat variable, the focus of the current review ison studies that have appeared in peer-reviewed journals.

Basic Characteristics of Eye Movementsin Information ProcessingWhen we read, look at a scene, or search for an object, we

continually make eye movements called saccades. Between thesaccades, our eyes remain relatively still during f i xat ions forabout 200 -30 0 ms. There are differences in these two measuresas a function of the particular task (see Table 1 ). Saccades arerapid movements of the eyes with velociti es as high as 500 per second, Sensitivity to visual i nput is reduced during eyemovements; this phenomenon is called saccadic suppression(Matin, 1974) and has been the topic of considerable debate.We do not obt ain new information during a saccade, becausethe eyes are moving so quickly across the stable visual stimulusthat only a blur would be perceived (Uttal & Smith, 1968).More important, however, masking caused by the informationavailable before and after the saccade makes it such that we donot perceive any type o f blurring effect (Brooks, Impe lman, &Lum, 1981; Campbell & Wurtz, 1979; Chekaluk & Llewellyn,1990). However, some suppression is found even when maskingis eliminated (Riggs, Merton, & Morton, 1974), which suggeststhat there is a central inhi bitory contribution to saccadic sup-pression as well.

The velocity of the saccade is a monotonic function of howfar the eyes move; it rapidly rises during the saccade to a maxi-mum that occurs slightly before the midp oint of the movementand then drops at a slightly slower rate until the target locationis reached. The duration of a saccade is also influenced by thedistance covered; a 2 saccade typical of reading takes around30 ms, whereas a 5 saccade, typ ical of scene perception, takesaround 40-50 ms (R. A. Abrams, Meyer, & Kornblum, 1989;Rayner, 1978a).

An issue that has received considerable attention recently is

whether or not cognitive processing activities are suspendedduring a saccade (Boer & van der Weijgert, 1988; W. Hans en &Sanders, 1988; Irwin & Carlson-Radvansky, 1996; Irwin, Carl-son-Radvansky, & Andrews, 1995; Matin, Shao, & Boff, 1993;Sanders & Houtmans, 1985; Sanders & Rath, 1991; Van Duren,1993; Van Duren & Sanders, 1992, 1995). Some of these studieshave found evidence to suggest that some cognitive activitiesare suppressed during saccades. Because the tasks used in mostof these studies are relatively simple, it will be interesting todetermine whether thinking is suspended during saccades inmore complex tasks, such as reading and scene perception. Cer-tainly, people are not aware of pauses in mental activity duringeye movements, but because saccade durations are so brief, a nydisruptions might not be particularly salient. Recently, Irwin(1998) reported some studies demonstrating that lexical pro-cessing is not suppressed during saccades.

Saccades need to be distinguished from three other types ofeye movements: pursuit, vergence, and vestibular eye move-ments. Pursuit eye movements occur when our eyes follow amoving target; the velocity of pursuit eye movements is mark-edly slower than saccades and, if the target is moving quicklyacross our visual field, we often make saccades to catch up withthe target (White, 1976). Vergence eye movements occur whenwe move our eyes inward, toward each other, in order to fixateon a nearby object. Vestibular eye movements occur when theeyes rotate to compensate for head and body movements inorder to ma intain the same direction of vision. Although pursuit,vergence, and vestibular eye movements are important and ex-tensively studied (see Ciuffreda & Tannen, 1995, and Leigh &Zee, 1991, for more details), saccadic eye movements are morerelevant in typical i nformation processing tasks. 1

Finally, three types of small movements of the eyes need tobe mentioned: nystagmus, drifts, and microsaccades. Althoughresearchers interested in eye movements in information pro-cessing tasks typically discuss fixations as the period of timewhen the eyes are still,, the term f i xat ion is something of amisnomer. The eyes are never really still, because there is aconstant tremor of the eyes called nystagmus. Such tremors ofthe eyes are quite small, and their exact nature is somewhatunclear, though it is often assumed that the movements are re-lated to perceptual activity and help the nerve cells in the retinato keep firing. Drifts and microsaccades tend to be somewhat

Table 1A pprox i mat e Me an F i xa t ion Dura t i on and Saccade L eng t h i nReading, Visual Search, Sce ne Perception,Mu sic Reading, and Typing

Mean fixation Mean saccade sizeTask duration (ms) (degrees)Silent reading 225 2 (about 8 letters)Oral reading 275 1.5 (about 6 letters)Visual search 275 3Scene perception 330 4Music reading 375 1Typing 400 1 (about 4 letters)Note. Valuesare taken from a number of sources and vary dependingon a number of factors (see Rayner, 1984).

1From a number of studies, it is known that the coordination ofhorizontal and vertical saccades is very accurate in adults when thestimulus s a visually presented arget (Bains, Crawford, Cadera, & Vilis,1992; Collewijn, Erkelens, & Steinman, 1988a, 1988b). It is typicallyassumed that the eyes move conjngately during tasks like reading. How-ever, Collewijnet al. (1988a) found that the movenaentsof the abducting(temporally moving) eye are somewhat larger than the correspondingmovements of the adducting (nasally moving) eye in simple scanningtasks. Similar observations were reported by Heller and Radach (1995)for reading and other complex tasks. Bassou, Pugh, Granie, and Morucci(1993) and Ygge and Jacobson (1994) reported that although the eyesof fifth-grade readers tended to be well-coordinatedspatially, hey werenot always closely conjugated spatially. Henriks (1996) recently exam-ined vergence movements of skilled readers and found that the eyesconverge during reading. As she noted, this finding s in contrast toearlier reports (E. A. Taylor, 1966) in which the eyes were found todiverge during reading.


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374 RAYNERl a r g e r m o v e m e n t s t h a n t h e n y s t a g m u s m o v e m e n t s . A l t h o u g h t h er e a s o n s f o r t h e s e m o v e m e n t s a r e n o t c o m p l e t e l y c l e at ; i t a p p e a r st h a t t h e e y e s o c c a s i o n a l l y d r i f t ( i . e . , m a k e s m a l l , s l o w m o v e -m e n t s ) b e c a u s e o f l e s s -t h a n - p e rf e c t c o n t r o l o f t h e o c u l o m o t o rs y s t e m b y t h e n e r v o u s s y s t e m . W h e n t h i s h a p p e n s , t h e r e is o f t e na s m a l l m i c r o s a c c a d e ( a m u c h m o r e r a p i d m o v e m e n t ) t o b r i n gt h e e y e s b a c k t o w h e r e t h e y w e r e . M o s t e x p e r i m e n t e r s i n t e r e s t e di n r ea d i n g a s s u m e t h a t t h e se s m a l l m o v e m e n ts a r e " n o i s e " a n da d o p t s c o r i n g p r o c e d u r e s t h a t i g n o r e t h e m . F O r e x a m p l e , m o s tr e s e a r c h e r s l u m p t o g e t h e r s u c c e s s i v e f i x a t io n s t h a t a r e o n a d j a -c e n t c h a r a c t e r s a s a s i n g l e f i x a t io n . A n o t h e r a l t e r n a t iv e i s a m o r es o p h i s t i c a t e d p r o c e d u r e i n w h i c h f i x a t i o n s a r e p o o l e d i f t h e t w of i x a t i o n s a r e o n a d j a c e n t c h a r a c t e r s a n d o n e i s s h o r t ( i . e . , l e s st h a n 1 0 0 m s ) .Saccade Latency

T h e r e i s a l a t e n c y p e r i o d a s s o c i a t e d w i t h m a k i n g a s a c c a d e ,b e c a u s e t h e y a r e m o t o r m o v e m e n t s t h a t r e q u i r e t i m e t o p l a n a n de x e c u t e . E v e n i f u n c e r t a i n t y a b o u t w h e n o r w h e r e t o m o v e t h ee y e s is e li m i n a t e d , s a c c a d e l a t e n c y i s a t l e a s t 1 5 0 - 1 7 5 m s ( R . A .A b r a m s & J o n i d e s , 1 9 8 8 ; R a y n e r , S l o w i a c z e k , C l i f t o n , & B e r -te ra , 1983 ; Sa l tho use & El l i s , 1980 ; Sa l thou se , E l l i s , D iener , &S o m b e r g , 1 9 8 1 ) , w h i c h s u g g e s t s t h a t s a c c a d e p r o g r a m m i n g i sd o n e i n p a r a l l e l w i t h c o m p r e h e n s i o n p r o c e s s e s i n r e a d i n g .

S t u d i e s d e a l i n g w i t h s a c c a d e l a t e n c y a r e l eg i o n , a n d a c o m p l e t er e v i e w i s b e y o n d t h e s c o p e o f t h e p r e s e n t a r t i c le . H o w e v e l ; s o m ei m p o r t a n t f a c t s h a v e b e e n l e a r n e d a b o u t s a c c a d e l a t e n c y th a t m a yh e r e l e v a n t t o u n d e r s t an d i n g e y e m o v e m e n t b e h a v i o r i n i n f o r m a -t ion p rocess ing t a sks (Bec ker & JUrgens, 1979; Cra wfo rd , 1996 ;F ind lay , 1992 ; F ind la y & W alker , in p ress ; Heyw ood & Churcher ,1 9 8 0 ). F i r s t , t h er e a r e s e p a r a t e d e c i s i o n p r o c e s s e s i n v o l v e d i nc o m p u t i n g w h e n a n d w h e r e t o m o v e t h e e y e s ( A s l i n & S h e a ,1987; Be cker & JUrgens, 1 979) . Seco nd , a l though sacca des ins i m p l e r e a c t i o n - t i m e e x p e r i m e n t s a r e o f t e n c h a r a c t e r i z e d a s r e -f l ex ive , the re i s a l so ev idence tha t cogn i t ive p rocesses can in f lu -e n c e t h e l a t e n c y ( D e u b e l , 1 9 9 5 ) . F o r e x a m p l e , i n t h e a n t i s a c c a d ep a r a d i g m ( H a U e t t, 1 9 7 8 ) , s a c c a d e s a r e v o l u n t a r i l y d i r e c t e d a w a yf rom a p e r iphera l t a rge t , and la tenc ies inc rease . L ikewise , whena n u m b e r o f s a c c a d e s a r e p l a n n e d i n a s e q u e n c e , l a t e n c ie s o f t h ein i t i a l saccad e inc rease (Craw ford , 1990; Inhof f , 1986 ; Z ing a le &Kowler , 1987 ) ; a s ecc en t r i c i ty o f the t a rge t inc reases , l a tenc iesc a n i n c r e a s e ( K a l e s n y k a s & H a l l e t t, 1 9 9 5 ) . T h i r d , i n c r e a s i n g th es a c c a d e l a t e n c y g e n e r a l l y l e a d s t o i n c r e a s e d a c c u r a c y i n l o c a t i n ga t a rge t ( Jacobs , 1987a ; Naz i r & Jacobs , 1991) . Four th , whens a c c a d e s a r e m a d e t o t a r g e ts c o n s i s t i n g o f t w o e l e m e n t s , i n r e a -s o n a b l y c l o s e p r o x i m i t y , t h e f i r s t sa c c a d e g o e s t o s o m e i n t e r m e d i -a te loca t ion . Th is i s r e fe r red to as the global o r center of gravityeffect (Deube l , Wol f , & Hauske , 1984 ; F ind lay , 1982 ; Ot tes , VanG i n s b e r g e n , & E g g e r m o n t , 1 9 8 4 ) . I f o n e e l e m e n t i s l a r g e r o rm o r e i n t e n s e ( o r b r i g h t e r ) , t h e n t h e s a c c a d e t e n d s t o l a n d c l o s e rt o t h a t t a rg e t i n c o m p a r i s o n t o a c o n d i t i o n i n w h i c h t h e t w oe l e m e n t s a r e i d e n t ic a l . I n st r u c t io n s t o b e m o r e c a r e f u l i n f l u e n cewhere the eyes l and (Cow, f6 & O 'Reg an , 1987; K ow ler & Blase r ,1995) bu t a l so inc rease saccade l a tency . F i f th , when a f ixa t ionp o i n t d i s a p p e a r s p r i o r t o t h e a p p e a r a n c e o f a t a r g e t, l a t e n c y d e -c r e a s e s ( M . E . C o h e n & R o s s , 1 9 7 7 ; K i n g s t o n e & K l e i n , 1 9 9 3 a ;L . E . Ross & Ross , 1980 ; S . M. Ross & Ross , 1981) . Th iss p e e d i n g u p ( c a l l e d t h e gap effect) r e l a t e s to t h e t e m p o r a l w a r n i n g

p r o v i d e d b y t h e f i x a t i o n - p o i n t o f f s e t; v i s u a l o f f s e t i s m o r e e f f e c -t i ve t h a n a n e u t r a l ( a u d i t o r y ) c u e , w h i c h i n t u r n i s m o r e e f f e c ti v et h a n o n s e t o f v i s u a l s t i m u l a t i o n a t t h e f i x a t i o n p o i n t ( F i n d l a y ,1 9 9 2 ) . T h i s p a t t e r n o f r e s u l t s s u g g e s t s t h a t s o m e p r o c e s s t h a tm a y b e t e r m e d relinquishing of attention s invo lved in genera t inga sacc ade . In te res t in these resu l t s has in tens i f i ed recen t ly becauseo f t h e s u g g e s t i o n t h a t t h e r e i s a s e p a r a t e c a t e g o r y o f s a c c a d e s ,c a l l e d express saccades, with v e r y s h o r t l a t e n c i e s ( C a v e g n &d 'Y dew al le , 1996 ; B . F i scher, 1992 ; B . F i scher & Boch , 1983;B . F i scher & Rampsp erger , 1984 ; B . F i sch er & Weber , 1993) . A tt h e m o m e n t , t h e r e i s s o m e d e b a t e a b o u t ( a ) w h e t h e r o r n o t t h e r e isa b i m o d a l d i s t r i b u t io n o f s a c c a d e l a t e n c ie s ( w i t h e x p r e s s s a c c a d e sr e p r e s e n t i n g o n e p e a k o f t h e d i s t r i b u t i o n a n d n o r m a l s a c c a d e sr e p r e s e n t in g t h e o t h e r) a n d ( b ) t h e p h e n o m e n o n i n g e n e r a l ( F i n d -lay , 1992 ; Kings tone & Kle in , 1993b ; A . B . Se reno , 1992) . Eveni f t h e r e w e r e n o c o n t r o v e r s y s u r r o u n d i n g e x p r e s s s a c c a d e s p e rse , the re a re ques t ions abou t the func t iona l u t i l i ty o f such shor t -l a t e n c y s a c c a d e s fo r n o r m a l i n f o r m a t i o n p r o c e s s i n g t a sk s ( M . H .F ische r & Rayner , 199 3) : Inhof f , Topo lsk i , V i tu , and O 'R ega n( 1 9 9 3 ) f o u n d n o e v i d e n c e f o r e x p r e s s s a c c a d e s o r a b i m o d a ld i s t r i b u ti o n o f f i x a ti o n d u r a t i o n s d u r i n g r e a d i n g .

The Visual Field and AcuityW e m a k e s a c c a d e s s o f r e q u e n t l y b e c a u s e o f a c u i t y l i m i t a t i o n s .

A s w e l o o k s t r a i g h t a h e a d , t h e v i s u a l f i e ld c a n b e d i v i d e d i n t ot h r e e r e g i o n s : foveal, parafoveal, and peripheral. A l t h o u g h a c u -i t y i s v e r y g o o d i n t h e f o v e a ( t h e c e n t r a l 2 o f v i s i o n ) , i t i s n o tn e a r l y s o g o o d i n t h e p a r a f o v e a ( w h i c h e x t e n d s o u t t o 5 o ne i t h e r s i d e o f f i x a t i o n ) , a n d i t i s e v e n p o o r e r i n t h e p e r i p h e r y( t h e r e g i o n b e y o n d t h e p a r a f o v e a ) . H e n c e , w e m o v e o u r e y e ss o a s t o p l a c e t h e f o v e a o n t h a t p a r t o f t h e s t i m u l u s w e w a n t t os e e c l e a r ly . O f c o u r s e , c h a r a c t e r i s t i c s o f t h e s t i m u l u s i n p a r a f o -v e a l o r p e r i p h e r a l v i s i o n i n f l u e n c e w h e t h e r o r n o t a s a c c a d en e e d s t o b e m a d e t o i d e n t i f y it . F o r e x a m p l e , i f a w o r d o f n o r m a l -s i z e p r i n t i s p r e s e n t e d i n p a r a f o v e a l v i s i o n , i t i s i d e n t i f i e d m o r eq u i c k l y a n d a c c u r a t e l y w h e n a s a c c a d e i s m a d e ( J a c o b s , 1 98 6 ,1 9 8 7 a; R a y n e r & M o r r i s o n , 1 9 8 1 ) . H o w e v e r , i f a n o b j e c t o rl a r g e l e t t e r is p r e s e n t e d a s t h e s t i m u l u s , i t c a n o f t e n b e i d e n t i f i e di n p e r i p h e r a l v i s i o n w i t h o u t a s a c c a d e ( P o l l a t s e k , R a y n e r , &C o l l i n s , 1 9 8 4 ) . S a n d e r s ( 1 9 9 3 ) s h o w e d t h a t th e v i s u a l fi e l d c a nb e d i v i d e d i n t o r e g i o n s w h e r e ( a ) a s t i m u l u s c a n b e i d e n t i f ie dw i t h o u t a n e y e m o v e m e n t , ( b ) i t i s n e c e s s a r y t o m a k e a n e y em o v e m e n t t o i d e n t i f y t h e s t i m u l u s , a n d ( c ) i t i s n e c e s s a r y t om a k e a h e a d m o v e m e n t t o i d e n t i f y t h e s t i m u l u s.

Eye Movements and AttentionA l t h o u g h i t i s o f t e n n e c e s s a r y t o m o v e o u r e y e s t o i d e n t i f y

o b j e c t s in o u r e n v i r o n m e n t , w e c a n m o v e a t t e n t i o n w i th o u t m o v -i n g o u r e y e s ( P o s n e r, 1 9 8 0 ) . T h e r e l a t i o n s h i p b e t w e e n a t t e n t i o na n d e y e m o v e m e n t s h a s b e e n e x t e n s i v e l y i n v e s t i g a t e d ( M . H .F i s c h e r, i n p r e s s ; K l e i n , 1 9 8 0 ; K l e i n , K i n g s t o n e , & P o n t e f r a c t ,1 9 9 2 ; R a f a l , C a l a b r e s i , B r e n n a n , & S c i o l t o , 1 9 8 9 ; R e m i n g t o n ,1 9 8 0 ; R e u t e r - L o r e n z & F e n d r i c h , 1 9 9 2 ; S h e p h e r d , F i n d l a y , &H o c k e y , 1 9 8 6 ) b u t i s b e y o n d t h e s c o p e o f t h e p r e s e n t r e v i e w .H o w e v e r , w i t h c o m p l e x s t i m u l i , it i s m o r e e f f i c i e n t t o m o v e o u re y e s t h a n t o m o v e a t t e n t i o n ( H e & K o w l e r , 1 9 9 2 ; S c l i n g e n s i e -


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EYE MOVEMENTS IN READING 37 5p e n , C a m p b e l l , L e g g e , & W a l k e r , 1 9 8 6 ). F u r t h e r m o r e , t h e r e i se v i d e n c e s u g g e s t i n g t h a t a t t e n t i o n p r e c e d e s a s a c c a d e t o a g i v e nl o c a t i o n i n s p a c e ( H o f f m a n & S u b r a m a n i a m , 1 9 9 5 ; K o w l e r ,A n d e r s o n , D o s h e r , & B l a s e r , 1 9 9 5 ; R a y n e r , M c C o n k i e , & E h r -l i c h , 1 9 7 8 ; R e m i n g t o n , 1 9 8 0 ) a n d t h a t a tt e n t i o n a l m o v e m e n t sa n d s a c c a d e s a r e o b l i g a t o r i ly c o u p l ed ( D e u b e l & S c h n e id e r ,1 9 9 6 ; b u t s e e S t e l m a c h , C a m p s a l l , & H e r d m a n , 1 9 9 7 , f o r c o n -f l ic t in g d a t a ) . A l t h o u g h w e c a n e a s i l y d e c o u p l e t h e l o c u s o fa t t e n t i o n a n d e y e l o c a t i o n i n s i m p l e d i s c r i m i n a t i o n t a s k s( P o s n e r , 1 9 8 0 ) , i n c o m p l e x i n f o r m a t i o n p r o c e s s i n g t a s k s s u c ha s r e a d i n g , t h e l i n k b e t w e e n t h e t w o i s p r o b a b l y q u i t e t i g h t .Developmental Changes in Eye Movements

T h e c h a r a c te r i s ti c s o f c h i l d r e n ' s e y e m o v e m e n t s d i f f e r s o m e -w h a t f r o m t h o s e o f a d u l t s , P r e s c h o o l c h i l d r e n e x h i b i t m o r e f r e -q u e n t s m a l l s a c c a d e s a n d d r i f t s d u r i n g m a i n t a i n e d f i x a t i o n ; s a c -c a d i c l a t e n c y i s u s u a l l y l o n g e r , a n d s a c c a d e a c c u r a c y i s u s u a l l yl e s s p r e c i s e i n p r e s c h o o l c h i l d r e n t h a n i n a d u l t s w h e n s c a n n i n ga s c e n e ( K o w l e r & M a r t i n s , 1 9 8 5 ) . H o w e v e r , t h e s h a p e s o f t h ef r e q u e n c y d i s t r i b u t i o n s o f f i x a t i o n d u r a t i o n s f o r c h i l d r e n , a d u l t s ,a n d e v e n i n f a n t s a r e q u i t e s i m i l a r ( H a i n l i n e , T u r k e l , A b r a m o v ,L e m e r i s e , & H a r r i s , 1 9 8 4 ; H a r r i s , H a i n l i n e , A b r a m 0 v , L e m e r -i s e , & C a m e n z u l i , 1 9 8 8 ) . A l t h o u g h f r e q u e n c y d i s t r i b u t i o n s o ff i x a t i o n d u r a t i o n s o f e l d e r l y a d u l t s l o o k l i k e t h o s e o f y o u n g e ra d u l t s , s a c c a d e l a t e n c y i n c r e a s e s w i t h a g e ( A b e l , T r o o s t , &D e l l ' O s s o , 1 9 8 3 ; P i r o z z o l o & H a n s c h , 1 9 8 1 ) .Measuring Eye Movements

E y e m o v e m e n t s a r e m o n i t o r e d i n m a n y d i f fe r e n t w a y s . E y e -t r a c k i n g s y s t e m s a r e c u r r e n t l y i n u s e t h a t r e l y o n ( a ) s u r f a c ee l e c t ro d e s ( w h i c h a r e f a i r ly g o o d a t m e a s u r i n g s a c c a d e l a t e n c yb u t n o t g o o d a t m e a s u r i n g l o c a t i o n ) , ( b ) i n f r a r e d c o r n e a l r e -f l e c t io n s , ( c ) v i d e o - b a s e d p u p i l m o n i t o r i n g , ( d ) i n f r a r e d P u r -k i n j e i m a g e t r a c k i n g , a n d ( e ) s e a r c h c o i l s a t t a c h e d l i k e c o n t a c tl e n s e s t o th e s u r f a c e o f t h e e y e s . A l t h o u g h t h e r e h a s b e e n s o m ed i s c u s s i o n c o n c e r n i n g t h e m e a s u r e m e n t , e v a l u a t i o n , a n d r e -p o r t i n g o f e y e m o v e m e n t d a t a ( H a r r i s , A b r a m o v , & H a i n l i n e ,1 9 8 4 ; H e ll e r , 1 9 8 3 ; In h o f f & R a d a c h , 1 9 9 8 ; M c C o n k i e , 1 9 8 1 ;M c C o n k i e , W o l v e r t o n , & Z o l a , 1 9 8 4 ; N o d i n e , K u n d e l , T ot o , &K r u p i n s k i , 1 9 9 2 ) , n o m e a s u r e m e n t s t a n d a r d s h a v e b e e na d o p t e d , a n d m a n y m e t h o d o l o g i c a l i s s u e s r e m a i n u n a d d r e s s e do r u n r e s o l v e d ( s e e I n h o f f & R a d a c h , 1 9 9 8 , f o r a g o o d d i s c u s s i o no f t h e s e i s s u e s ) . D e s p i t e t h i s f a c t , m o s t o f t h e i m p o r t a n t f i n d i n g sd i s c u s s e d i n t h i s r e v i e w h a v e b e e n r e p l i c a t e d a c r o s s d i f f e re n tl a b s .

E y e M o v e m e n t s i n R e a d in gE y e m o v e m e n t s d i f f e r s o m e w h a t f o r r e a d i n g s i l e n t l y v e r s u s

a l o u d ( s e e T a b l e 1 ) . W h e n r e a d i n g a l o u d , o r w h e n r e a d i n gs i l e n t l y w h i l e l i s t e n i n g t o a v o i c e r e a d i n g t h e s a m e t e x t , m e a nf i x a t i o n d u r a t i o n s a r e l o n g e r th a n i n s i l e n t r e a d i n g , a n d t h e e y e st e n d t o g e t a h e a d o f t h e v o i c e ; c o n s e q u e n t l y , t h e r e a r e m a n yf i x a t i o n s i n w h i c h t h e e y e s a p p e a r t o b e h o l d i n g i n p l a c e s o a st o n o t g e t t o o f a r a h e a d o f t h e v o i c e ( L 6 v y - S c h o e n , 1 9 8 1 ) . T h ev a s t m a j o r i t y o f t h e r e s e a r c h o n r e a d i n g r e v i e w e d h e r e i s f o rs i l e n t r e a d i n g .

W h e n r e a d i n g E n g li s h , e y e fi x a ti o n s l a s t a b o u t 2 0 0 - 2 5 0 m sa n d t h e m e a n s a c c a d e s i z e i s 7 - 9 l e t t e r s p a c e s ( s e e T a b l e 1 ) .L e t t e r s p a c e s a r e t h e a p p r o p r i a t e m e t r i c t o u s e , b e c a u s e t h en u m b e r o f l e t t e rs t r a v e r s e d b y s a c c a d e s i s r e l a t i v e l y in v a r i a n tw h e n t h e s a m e t e x t i s r e a d a t d i f f e r e n t d i s t a n c e s , e v e n t h o u g h t h el e t t e r s p a c e s s u b t e n d d i f f e r e n t v i s u a l a n g l e s ( M o r r i s o n , 1 9 8 3 ;M o r r i s o n & R a y n e r , 1 9 8 1 ; O ' R e g a n , 1 9 8 3 ; O ' R e g a n , L 6 v y -S c h o e n , & J a c o b s , 1 9 83 ).2 T h e p r i m a r y f u n c t i o n o f a s a c c a d ei s t o b r i n g a n e w r e g i o n o f t e x t i n t o f o v e a l v i s i o n f o r d e t a i l e da n a l y s i s , b e c a u s e r e a d i n g o n t h e b a s i s o f o n l y p a r a f o v e a l o rp e r i p h e r a l i n f o r m a t i o n i s d if f i c u l t t o i m p o s s i b l e ( R a y n e r & B e r t -e r a , 1 9 7 9 ; R a y n e r , I n h o f f , M o r r i s o n , S l o w i a c z e k , & B e r t e r a ,1 9 8 1 ) . W h e r e a s a m a j o r i t y o f th e w o r d s i n a t e x t a r e f i x a t e dd u r i n g r e a d i n g , m a n y w o r d s a r e s k i p p e d s o t h a t f o v e a l p r o -c e s s i n g o f e a c h w o r d i s n o t n e c e s s a r y . F o r e x a m p l e , c o n t e n tw o r d s a r e f i x a t e d a b o u t 8 5 % o f t h e t im e , w h e r e a s f u n c t i o nw o r d s a r e f i x a t e d a b o u t 3 5 % o f t h e t i m e ( C a r p e n t e r & J u s t ,1 9 8 3 ; R a y n e r & D u f f y , 1 9 8 8 ) . F u n c t i o n w o r d s a r e f i x a t e d le s sf r e q u e n t l y t h a n c o n t e n t w o r d s , b e c a u s e t h e y t e n d t o b e s h o r t , a n dt h e r e i s a c l e a r r e l a t i o n s h i p b e t w e e n t h e p r o b a b i l i t y o f f i x a t i n g aw o r d a n d i t s l e n g th : A s l e n g t h i n c r e a s e s , t h e p r o b a b i l i t y o ff i xa t in g a w o r d i n cr e a s e s ( R a y n e r & M c C o n k i e , 1 9 7 6 ); 2 - 3l e t t e r w o r d s a r e o n l y f i x a t e d a r o u n d 2 5 % o f t h e t i m e , w h e r e a sw o r d s 8 l e t t e r s o r l o n g e r a r e a l m o s t a l w a y s f i x a t e d ( a n d o f t e nf i x a t e d m o r e t h a n o n c e ) .

A l t h o u g h m o s t s a c c a d e s i n r e a d i n g E n g l i s h a r e m a d e f r o ml e f t t o r i g h t , re a d e r s d o n o t r e l e n t l e s s l y g o f o r w a r d : A b o u t 1 0 -1 5 % o f t h e s a c c a d e s a r e regressions ( r i g h t - to - l e f t m o v e m e n t sa l o n g t h e li n e o r m o v e m e n t s b a c k t o p r e v i o u s l y r e a d l i n e s ) .M a n y r e g r e s s i o n s t e n d t o b e o n l y a f e w l e t t e r s l o n g a n d c o u l db e d u e t o t h e r e a d e r m a k i n g t o o l o n g o f a s a c c a d e , i n w h i c hc a s e a s h o r t s a c c a d e t o t h e l e f t m a y b e n e c e s s a r y f o r r e a d i n gt o p r o c e e d e f f i c i e n t l y . S h o r t w i t h i n - w o r d r e g r e s s i v e s a c c a d e sm a y a l s o b e d u e t o p r o b l e m s t h a t t h e r e a d e r h a s p r o c e s s i n g t h ec u r r e n t l y f i x a te d w o r d . L o n g e r r e g r e s s i o n s ( m o r e t h a n 1 0 le t t e rs p a c e s b a c k a l o n g t h e l i n e o r t o a n o t h e r l i n e ) o c c u r b e c a u s e t h er e a d e r d i d n o t u n d e r s t a n d t h e t e x t . I n s u c h c a s e s , g o o d r e a d e r sa r e v e r y a c c u r a t e i n s e n d i n g t h e i r e y e s t o t h a t p a r t o f t e x t t h a tc a u s e d t h e m d i f f i c u l t y ( F r a z i e r & R a y n e r , 1 9 8 2 ; K e n n e d y , 1 9 8 3 ;K e n n e d y & M u r r a y , 1 9 8 7 a , 1 9 8 7 b ; M u r r a y & K e n n e d y , 1 9 8 8 ) ,w h e r e a s p o o r r e a d e r s e n g a g e i n m o r e b a c k t r a c k i n g t h r o u g h t h et e x t ( M u r r a y & K e n n e d y , 1 9 8 8 ) .

O n r e t u r n s w e e p s f r o m t h e e n d o f o n e l i n e t o t h e b e g i n n i n go f t h e n e x t , r e a d e r s o f t e n u n d e r s h o o t a n d m a k e s m a l l c o r r e c t i v em o v e m e n t s t o t h e l e f t . B e c a u s e c o r r e c t i v e s a c c a d e s a r e o f t e nm a d e f o l l o w i n g r e t u r n s w e e p s , i t s h o u l d n o t b e a s s u m e d t h a tr e a d e r s p l a c e t h e i r f i x a t i o n t o c o r r e s p o n d t o t h e b e g i n n i n g o f al ine . Ra the r , the f i r s t and la s t f ixa t ions on a l ine a re genera l ly5 - 7 l e t t e r s p a c e s f r o m t h e e n d s o f a l i n e. T h u s , a b o u t 8 0 % o ft h e t e x t t y p i c a l l y f a l l s b e t w e e n t h e e x t r e m e f i x a t io n s . T h e f i r s tf i x a t io n o n a l i n e t e n d s t o b e l o n g e r t h a n o t h e r f i x a t io n s ( H e l l e r ,1982 ; Rayner , 1977) , an d the l a s t i s shor te r (Rayn er , 19 78b) .

2 However, it should b e noted that fixation time increases somew hatwhen the visual angle subtended by a letter is appreciably smaller thanin normal reading. This is because the letters are more difficult to dis-criminate when the text is further away from the eyes. Thus, letter spacesare the appropriate metric of saccade size for relatively normal-sizedprint; if the text is too small or too large, the principle would not hold.


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376 RAYNERF u r t h e r m o r e , r e a d e r s t e n d t o n o t f i x a t e i n t h e b l a n k s p a c e s b e -t w e e n s e n t e n c e s ( S . G . A b r a m s & Z u b e r , 1 9 7 2 ; R a y n e r , 1 9 7 5 a ) .

A l t h o u g h a v e r a g e v a l u e s f o r f i x a t i o n d u r a t i o n , s a c c a d e l e n g t h ,a n d f r e q u e n c y o f r e g r e s s i o n a r e c i t e d a b o v e , t h e r e i s c o n s i d e r -a b l e b e t w e e n - r e a d e r v a r i a b i l i t y f o r a l l t h r e e m e a s u r e s . M o r ei m p o r t a n t , t h e r e i s v a r i a b i l i t y fo r a g i v e n r e a d e r w i t h i n a s i n g l ep a s s a g e o f t e x t s o th a t f i x a t i o n d u r a t i o n s r a n g e f r o m u n d e r 1 0 0m s t o o v e r 5 0 0 m s , a n d s a c c a d e s v a r y f r o m 1 t o o v e r 1 5 l e t t e rs p a c e s ( s e e F i g u r e 1 ) . A c t u a l l y , f i x a t io n s a s s h o r t a s 5 0 m ss o m e t i m e s a p p e a r i n t h e e y e m o v e m e n t r e c o r d d u r i n g r e a d i n g .S a c c a d e s a s l o n g a s 1 5 l e t t e r s p a c e s a r e q u i t e r a r e a n d o f t e no c c u r i m m e d i a t e l y f o l lo w i n g a r e g r e s s i o n i n w h i c h r e a d e r s t y p i -c a l l y m a k e a l o n g s a c c a d e t o p l a c e t h e e y e s a h e a d o f w h e r e t h e yw e r e p r i o r t o m a k i n g t h e r e g r e s s i o n .

E y e m o v e m e n t s a r e a l s o i n f l u e n c e d b y t e x t u a l a n d t y p o g r a p h i -c a l v a r i a b l e s . F o r e x a m p l e , a s t e x t b e c o m e s c o n c e p t u a l l y m o r ed i f f i cu l t , f i x a t i o n d u r a t i o n i n c r e a s e s , s a c c a d e l e n g t h d e c r e a s e s ,a n d t h e f r e q u e n c y o f r e g r e s s i o n s in c r e a s e s ( J a c o b s o n & D o d -

1 4 -1 2 -10-

~ ' 8 - ,.

.8 8 _o.4 -2 -

/0 f0 600

\I I I I1 00 200 300 400 500

Fixation Duration ( m s )

12-1 0 -

8 -c 6 -n 4 -

2 -J0 0

Y

S a c c a d e LengthFigure 1. Frequency distributions for fixation durations and forwardsaccade lengths. Fixation durations are in milliseconds, and saccadelength is in character spaces.

w e l l , 1 9 7 9 ; R a y n e r & P o l l a t s e k , 1 9 8 9 ) . I f t h e t e x t l o o k s f a i r l yn o r m a l , t y p o g r a p h i c a l v a r i a b l e s t e n d t o h a v e a r e l a t i v e l y m i n o ri n f l u en c e . H o w e v e r , f a c t o r s s u c h a s t h e q u a l i t y o f t h e p r i n t ( v a r i -a t i o n s i n f o n t s ) , l i n e l e n g t h , a n d l e t t e r s p a c i n g ( K o l e r s , D u c h -n i c k y , & F e r g u s o n , 1 9 8 1 ; M o r r i s o n & I n h o f f , 1 9 8 1 ) i n f l u e n c ee y e m o v e m e n t s . C h a r a c t e r i s t i c s o f t h e w r i t i n g s y s t e m a l s o i n -f l u e n c e e y e m o v e m e n t s ( O s a k a , 1 9 8 9 ; P e n g , O r c h a r d , & S t e m ,1983 ; Sun , Mor i ta , & S ta rk , 1985) .

A c r u c i a l p o i n t t h a t h a s e m e r g e d r e c e n t l y i s t h a t e y e m o v e -m e n t m e a s u r e s c a n b e u s e d t o i n f e r m o m e n t - to - m o m e n t c o g n i -t i v e p r o c e s s e s i n r e a d i n g ( J u s t & C a r p e n t er , 1 9 8 0 ; M c C o n k i e ,H o g a b o a m , W o l v e r t o n , Z o l a , & L u c a s , 1 9 7 9 ; R a y n e r, 1 9 7 8 b ;R a y n e r , S e r e n o , M o r r i s , S c h m a u d e r , & C l i f t o n , 1 9 8 9 ) a n d t h a tt h e v a r i a b i l i t y in t h e m e a s u r e s r e f l e c t s o n - l i n e p r o c e s s i n g . F o re x a m p l e , t h e r e i s n o w a b u f i d a n t e v i d e n c e t h a t t h e fr e q u e n c y o fa f i x a t e d w o r d i n f l u e n c e s h o w l o n g r e a d e r s l o o k a t t h e w o r d( I n h o f f 8~ R a y n e r , 1 9 8 6 ; R a y n e r & D u f f y , 1 9 8 6 ) . T h u s , p r o p e r -t i e s o f t h e f i x a te d w o r d m o d u l a t e t h e f i x a t i o n t i m e a n d r e s u l t i nv a r i a b i l i t y i n f i x a t i o n t im e s . T h e r e i s , o f c o u r s e , a p u r e l y m o t o r i cc o m p o n e n t t o t h is v a r i a b i l i t y ( K o w l e r & A n t o n , 1 9 8 7 ) , b e c a u s ew h e n s p a t i a l a n d t e m p o r a l u n c e r t a i n t y a b o u t w h e r e a n d w h e nt o m o v e t h e e y e s i s e l i m i n a t e d , t h e r e i s s t i l l v a r i a b i l i t y i n t h el a t e n c y o f e y e m o v e m e n t s ( R a y n e r , S l o w i a c z e k , e t a l . , 1 9 8 3;S a l t h o u s e & E l l i s , 1 9 8 0 ) . S i m i l a r l y , t h e r e i s v a r i a b i l i t y i n w h e r et h e e y e s l a n d o n a t a r g e t (C o ~ f f 6 & O ' R e g a n , 1 9 8 7 ; F i n d l a y ,1 9 8 2 ) . A l t h o u g h t h i s n o i s e o f m o t o r i c v a r i a b i l i t y m a k e s i t d i ff i -c u l t t o i n t e r p r e t th e c o g n i t i v e s i g n a l in t h e e y e m o v e m e n t r e c o r d ,i t i s c l e a r t h a t t h e s i g n a l i s t h e r e , a n d g r e a t s t r i d e s h a v e b e e nm a d e o v e r t h e p a s t 2 0 y e a r s i n u n d e r s t a n d i n g t h e r e l a t i o n s h i pb e t w e e n r e a d i n g a n d e y e m o v e m e n t s . O n e s i m p l e p o i n t c o n s i s -t e n t w i t h t h i s c l a i m i s t h a t , i n r e a d i n g , t h e r e i s n o c o r r e l a t i o nb e t w e e n f i x a t i o n d u r a t i o n a n d s a c c a d e l e n g t h ( R a y n e r &M c C o n k i e , 1 9 7 6 ) , w h e r e a s i n n o n r e a d i n g s i t u a ti o n s , i n w h i c ht h e n e c e s s i t y o f l i n g u i s t i c p r o c e s s i n g i s e l i m i n a t e d , t h e r e i s ac o r r e l a t i o n : t h e l o n g e r t h e s a c c a d e , t h e l o n g e r t h e n e x t f i x a t i o n( K a p o u l a , 1 9 8 3 ; N a t t k e m p e r & P r i n z , 1 9 8 6 ) . T h e d i f f e r e n c eb e t w e e n t h e s e t w o s i t u a t i o n s s u g g e s t s t h a t t h e d i f f ic u l t y o f o n -l i n e l a n g u a g e p r o c e s s i n g a s s o c i a t e d w i t h r e a d i n g w i p e s o u t a n ys i m p l e c o r r e l a t i o n . H o w e v e r , i t i s i m p o r t a n t t o n o t e t h a t a l t h o u g ht h e r e i s n o c o r r e l a t i o n b e t w e e n f i x a t i o n d u r a t i o n a n d s a c c a d el e n g t h a c r o s s e x t e n d e d t e x t , c o r r e l a t i o n s c a n b e o b t a i n e d l o c a l l yb e t w e e n a g i v e n fi x a t i o n d u r a t i o n a n d s a c c a d e l e n g t h ( P o l l a t s e k ,R a y n e r , & B a l o t a , 1 9 8 6 ) , i n d i c a t i n g t h a t p r o c e s s i n g d i f f i c u l t yi n f l u e n c e s b o t h e y e m o v e m e n t v a r i a b l e s .What Is the Best Measure of Processing Time?

A m a j o r i s s u e co n c e r n s h o w t o b e s t s u m m a r i z e t he e y e m o v e -m e n t r e c o r d t o u n d e r s t a n d c o g n i t i v e p r o c e s s i n g . T h i s i s s u e i sp a r t i c u l a r l y e l e v a n t t o th e q u e s t i o n o f h o w t o m e a s u r e t h e t e m -p o r a l p r o c e s s i n g a s s o c i a t e d w i t h a g i v e n r e g i o n o f t e x t . I f t h eu n i t o f a n a l y s i s i s l a r g e r t h a n a w o r d , t h e n t h e t o t a l f i r s t - p a s sf i x a t i o n t i m e o n t h a t u n i t i s g e n e r a l l y u s e d a s t h e p r i m a r y m e a -s u r e o f i n t e r e s t . I t i s i m p o r t a n t , w h e n a n a l y z i n g s u c h r e g i o n s ,t o d i s t i n g u i s h b e t w e e n f i r s t - p a s s ( i . e . , t h e i n i t i a l re a d i n g c o n -s i s t i n g o f a l l f o r w a r d f i x a t i o n s ) a n d s e c o n d - p a s s ( i . e . , r e r e a d i n g )r e a d i n g t i m e f o r t h e r e g i o n . T h e r e i s s o m e c o n t r o v e r s y a b o u th o w b e s t t o a n a l y z e a r e g i o n w h e n r e a d e r s m a k e r e g r e s s i o n s ( s e eA l t m a n n , 1 9 9 4 ; R a y n e r & S e r e n o , 1 9 9 4 b, 1 9 9 4 c ) . F o r e x a m p l e ,


6/51

EYE MOVEMENTS IN READING 37 7R a y n e r a n d S e r e n o ( 1 9 9 4 c ) n o t e d t h a t , w h e n r e a d e r s e n t e r ar e g i o n a n d t h e n q u i c k l y m a k e a r e g r e s s i o n o u t o f t h a t r e g i o n ,t h e f i r s t -p a s s ti m e i s v e r y s h o r t i n c o m p a r i s o n t o w h e n t h er e a d e r d o e s n o t r e g r e s s . H o w b e s t t o a n a l y z e s u c h r e g r e s s i o n si s u n c e r t a i n . S o m e r e s e a r c h e r s s i m p l y r e c o r d f i r s t - p a s s r e a d i n gt i m e a n d t h e n e x a m i n e t h e p a t t e r n o f r e g r e s s i o n s o u t o f t h et a r g e t r e g i o n . O t h e r s h a v e a r g u e d f o r r e g r e s s i o n - p a t h d u r a t i o n sa n a l y s e s ( K o n i e c z n y , H e m f o r t h , S c h e e p e r s , & S t r u b e , 1 9 9 7 ) o rc u m u l a t iv e r e g i o n r e a d i n g t i m e a n a l y s e s ( B r y s b a e r t & M i t c h e l l,1 9 9 6 ) . W i t h t h e s e a n a l y s e s , r e a d i n g t i m e r e p r e s e n t s t h e s u m o fa l l f i x a t io n s s t a r t i n g w i t h t h e f i r st f i x a t io n i n a r e g i o n a n d e n d i n gw i t h t h e f i r s t f o r w a r d s a c c a d e p a s t t h e r e g i o n u n d e r c o n s i d e r -a t i o n 3 ( s e e L i v e r s e d g e , P a t e r s o n , & P i c k e r i n g , 1 9 9 8 , f o r f u r t h e rd i s c u s s i o n o f t h e s e i s s u e s ) .

I s s u e s h a v e a l s o a r i s e n c o n c e r n i n g t h e f a c t t h a t c o m p a r i s o n so f t e n a r e m a d e b e t w e e n r e g i o n s o f t e x t th a t c o n t a i n d i f f e r e n tw o r d s , w i t h s o m e r e g i o n s b e i n g l o n g e r t h a n o t h e r s . O n e p r o c e -d u r e i s t o d i v i d e t h e r e a d i n g t i m e ( f i r s t p a s s o r o t h e r w i s e ) b yt h e n u m b e r o f l e t t e r s i n t h e r e g i o n t o y i e l d a m i l l i s e c o n d -p e r - c h a r a c t e r r e a d i n g t i m e . H o w e v e r , t h i s p r o c e d u r e h a s b e e nd e m o n s t r a t e d t o y i e l d a n o n l i n e a r f u nc t i o n o f w o r d l e n g t h o nr e a d i n g t i m e , e s p e c i a l l y i n s h o r t r e g i o n s ( T r u e s w e l l , T a ne n -h a n s , & G a r n s e y , 1 9 9 4 ) . T h u s , w h e n t h e l e n g t h o f a r e g i o nd i f f e r s , a m o r e a p p r o p r i a t e p r o c e d u r e i s t o a n a l y z e t h e d e v i a t i o n sf r o m e x p e c t e d r e a d i n g t i m e s a s d e t e r m i n e d b y t h e b e s t l i n e a rf i t f o r t h e r e a d i n g t i m e a s a f u n c t i o n o f t h e n u m b e r o f l e t te r s i nt h e r e g i o n ( F e r r e i r a & C l i f t o n , 1 9 8 6 ; T r u e s w e l l e t a l ., 1 9 9 4 ) .

W h e n a w o r d i s t h e u n i t o f a n a l y s i s , t h e n t h e a p p r o p r i a t em e a s u r e t o u s e i s a l s o c o n t r o v e r s i a l ( I n h o f f & R a d a c h , 1 9 9 8 ) .I f r e a d e r s a l w a y s w e r e t o m a k e o n e a n d o n l y o n e f i x a t i o n o n aw o r d , t h e n t h e r e w o u l d b e l i t t le p r o b l e m : T h e f i x a t i o n d u r a t i o no n t h e w o r d w o u l d b e t h e m e a s u r e o f p r o c e s s in g t i m e . H o w e ve r ,w o r d s a r e S o m e t i m e s f i x a t e d m o r e t h a n o n c e , a n d s o m e t i m e st h e y a r e s k i p p e d . T h e p r o b l e m o f m u l t i p l e f i x a t i o n s h a s l e d t od i f f e r e n t s o l u ti o n s . U s i n g t h e m e a n f i x a t io n d u r a t i o n o n a w o r di s c l e a r l y in a d e q u a t e , b e c a u s e i t u n d e r e s t i m a t e s t h e t i m e t h e e y e sa r e a c t u a l l y o n t h e w o r d ( i . e . , a 2 0 0 - m s f i x a t i o n a n d a 1 5 0 - m sf i x a t i o n o n t h e s a m e w o r d w o u l d y i e l d a m e a n f i x a t i o n d u r a t i o no n t h e w o r d o f 1 7 5 m s ) . L i k e w i s e , th e s t r a t e g y o f i n c l u d i n go n l y w o r d s t h a t a r e f i x a t e d o n c e ( s i n g l e fi x a t i o n d u r a t i o n ) isp r o b l e m a t i c , b e c a u s e s o m e w o r d s a r e f i x a te d m o r e t h a n o n c e ,a n d s o m e a r e s k i p p e d a l t o g e t h e r ; s u c h a s t r a t e g y m a y r e s u l t i nt h e e l i m i n a t i o n o f t o o m u c h d a t a . T h u s , t h e t w o m o s t f r e q u e n t l yu s e d m e a s u r e s a r e t h e f i r s t f i x a t i o n d u r a t i o n a n d t h e g a z e d u r a -t ion o n a w o r d . G a z e d u r a t i o n r e p r e s e n t s t h e s u m o f a l l f i x a t i o n sm a d e o n a w o r d p r i o r t o a s a c c a d e t o a n o t h e r w o r d . F i r s t f ix a t i o nd u r a t i o n i s t h e d u r a t i o n o f t h e f ir s t f i x a t i o n o n a w o r d r e g a r d l e s so f w h e t h e r i t is t h e o n l y f i x a ff o n o n a w o r d o r t h e f i r s t o f m u l t i p l ef i x a t i o n s o n a w o r d .

T h e a r g u m e n t o v e r w h i c h m e a s u r e i s b e s t to u s e a s a n i n d e xo f p r o c e s s i n g t im e p a r t l y d e p e n d s o n w h a t i s b e i n g e x a m i n e d .I n h o f f ( 1 9 8 4 ) a r g u e d t h a t f i r s t f i x a t i o n d u r a t i o n a n d g a z e d u r a -t i o n m e a s u r e d i f f e r e n t p r o c e s s e s . I n h i s d a t a , f i r st f ix a t i o n d u r a -t i o n a n d g a z e d u r a t i o n b o t h w e r e a f f e c t e d b y w o r d f r e q u e n c y ,b u t o n l y g a z e d u r a t i o n w a s a f f e c t e d b y t h e p r e d i c t a b i l i t y o f t h ew o r d i n t h e c o n t e x t . H e t h u s p o s i t e d t h a t f i r s t f i x a t i o n i s am e a s u r e o f l e x i c a l a c c e s s , w h e r e a s g a z e d u r a t i o n r e f l e c t s t e x ti n t e g r a t i o n p r o c e s s e s a s w e l l . H o w e v e r , i t n o w a p p e a r s t h a t t h i sd i s t i n c t i o n d o e s n o t h o l d u p i n g e n e r a l a n d t h a t f o r m u c h o f

t h e t i m e , a l t h o u g h n o t a l w a y s , f i r s t f i x a t i o n d u r a t i o n a n d g a z ed u r a t i o n y i e l d s i m i l a r r e s u l t s : R a y n e r a n d P o l l a t s e k ( 1 9 8 7 ) a r -g u e d t h a t t h e d a t a s u g g e s t t h a t i f a c o g n i t i v e o p e r a t i o n i s v e r yf a s t i t a f f e c t s f i rs t f ix a t i o n d u r a t i o n , a n d i f i t i s a b i t s l o w e r i tm a y a f f e c t g a z e d u r a t i o n . A s s u m i n g t h a t t h e g a z e v e r s u s f i r s tf i x a t i o n d u r a t io n p r o b l e m w e r e s o l v e d , t h e r e is s t i l l t h e p r o b l e mo f t r y i n g t o a s s e s s t h e a v e r a g e t i m e s p e n t p r o c e s s i n g a w o r d .T h e p r o b l e m i s t h a t w o r d s a r e p r o c e s s e d w h e n t h e y a r e n o tf i x a te d . F i s h e r a n d S h e b i l s k e ( 1 9 8 5 ) s h o w e d t h i s b y h a v i n gr e a d e r s r e a d t e x t a s t h e i r e y e m o v e m e n t s w e r e m o n i t o r e d . T h e yt h e n h a d a n o t h e r g r o u p r e a d t h e s a m e t e x t a f t e r d e l e t i n g t h ew o r d s t h a t t h e f i r s t g r o u p s k i p p e d o v e r ( f u n c t i o n w o r d s a n do t h e r s h o r t w o r d s ) . T h e s e c o n d g r o u p h a d a d i f f i c u l t t i m e u n d e r -s tand ing the t ex t .

J u s t a n d C a r p e n t e r ( 1 9 8 0 ) a s s i g n e d a v a l u e o f 0 m s t o w o r d st h a t w e r e n o t f i x a t e d i n t h e i r g a z e d u r a t i o n a n a l y s i s . H o w e v e r ,t h is p r o c e d u r e r e a l l y d o e s n o t s o l v e t h e p r o b l e m , b e c a u s e w o r d st h a t a r e n o t f i x a t e d a r e c le a r l y p r o c e s s e d b y t h e r e a d e r ( g e n e r a l l yo n t h e f i x a t i o n p r i o r t o t h e s k i p ) . S u b s e q u e n t l y , a s a m e a n s o fd e a l i n g w i th w o r d s k i p p i n g , C a r p e n t e r a n d J u s t ( 1 9 8 3 ) p r o p o s e da c o n d i t i o n a l i z e d g a z e d u r a t i o n , w h i c h i s t h e m e a n g a z e d u r a -t i o n , g i v e n t h a t t h e w o r d h a s b e e n f i x a t e d f o r a t l e a s t 5 0 m s .T h e p r o b l e m w i t h t h i s m e a s u r e i s t h a t i t i g n o r e s t h e t i m e s p e n ti n a f i x a t i o n p r o c e s s i n g w o r d s t o t h e r i g h t o f t h e f i x a t e d w o r d .A s d i s c u s s e d i n d e t a i l l a t e r i n t h i s r e v i e w , w h e n t h e w o r d t ot h e r i g h t o f f i x a t io n i s n o t i d e n t i f ie d , s o m e i n i t i a l p a r a f o v e a lp r o c e s s i n g o c c u r s . R a y n e r a n d P o l l a t s e k ( 1 9 8 7 ) s u g g e s t e d t h a tc o n d i t i o n a li z e d g a z e d u r a t i o n w o u l d b e b e t t er i f c o n d i t i o n a l i z e do n f i x a t i n g t h e w o r d f o r 5 0 m s a n d n o t s k i p p i n g th e n e x t w o r d .A s e c o n d s o l u t i o n t o th e p r o b l e m i s t h e r e a d t o t h e r i g h t o f g a z e( R R G ) a l g o r i th m ( B l a n c h a rd , 1 9 8 5; H o g a b o a m & M c C o n k i e ,1 9 8 1 ) . T h e R R G m e a s u r e s u m s f i x a t i o n s o n w o r d s r e c e i v i n gm o r e t h a n o n e f i x a t i o n ; w h e n w o r d s a r e s k i p p e d , t h e f i x a t i o nt i m e i s e q u a l l y d i s t r i b u t e d b e t w e e n t h e l a s t w o r d f i x a t e d a n d t h ew o r d t h a t w a s s k i p p e d . B o t h t h e c o n d i t i o n a l i z e d g a z e a n d t h eR R G m e a s u r e s a s s u m e t h a t ( e x c e p t f o r s k i p p i n g ) a w o r d i sp r o c e s s e d o n l y w h e n i t i s f i x a t e d . H o w e v e r , a s j u s t n o t e d , p a r a f o -v e a l i n f o r m a t i o n i s e x t r a c t e d f r o m a w o r d o n m o s t f i x a t i o n s a n df a c i l i t a t e s i d e n t i f i c a ti o n o n t h e s u b s e q u e n t f i x a t i o n . R a y n e r a n dP o l l a t s e k ( 1 9 8 7 ) s u g g e s te d t h a t p e rh a p s t h i s p r e v i e w b e n e f i ts h o u l d b e a d d e d t o t h e f ix a t i o n t i m e o n t h e w o r d a n d s h o u l d b es u b t r a c t e d f r o m t h e t i m e s p e n t o n t h e p r i o r w o r d . A l l o f t h i sa s s u m e s t h a t t h e s e p r o c e s s e s c a n b e p r e c i s e l y i d e n t i f i e d a n d t h a tw o r d s a r e p r o c e s s e d i n s e r i e s . I f s o m e p r o c e s s e s o v e r l a p , t h e nt h e c a l c u l a t io n o f p r o c e s s in g t i m e s w o u l d b e e v e n m o r e c o m -p l e x . I n a d d i t i o n , t h e r e i s t h e p r o b l e m t h a t t h e p r o c e s s i n g o f aw o r d i s . n o t a l w a y s c o m p l e t e d b y t h e t i m e t h e e y e s m o v e , a sthe re a re s p i U o v e r e f f e c t s : T i m e p r o c e s s in g a w o r d c a n " s p i l l

o v e r " o n t o t h e n e x t w o r d ( R a y n e r & D u f f y , 1 9 8 6 ; R a y n e r ,S e r e n o , e t a l . , 1 9 8 9 ) . T o t h e e x t e n t t h a t t h e p r o c e s s i n g o f aw o r d s p i l l s o v e r o n t o s u b s e q u e n t f i x a ti o n s ( M c C o n k i e , Z o l a , &B l a n c h a r d , 1 9 8 4 ; R a y n e r, S e r e n o , e t a l. , 1 9 8 9 ) , t h e s e m e a s u r e sa re in e r ro r .

I t t h u s a p p e a r s t h a t a n y s i n g l e m e a s u r e o f p r o c e s s i n g t i m e p e rw o r d i s a p a l e r e f l e c t i o n o f t h e r e a l i t y o f c o g n i t i v e p r o c e s s i n g .

3 Rayner and Duffy (1986) and Duffy, Morris, and Rayner (198 8)used a virtually identical procedure to establish the time needed tounderstand the information in a region.


7/51

378 RAYNERT h e r e f o r e , t h e s t r a t e g y o f a n a l y z i n g l a r g e a m o u n t s o f t e x t w i t ha s i n g l e m e a s u r e o f p r o c e s s i n g i s l i k e l y t o b e o f l i m i t e d v a l u ei n m e a s u r i n g o n - l i n e p r o c e s s i n g . J u s t a n d C a r p e n t e r ( 1 9 8 0 )a d o p t e d s u c h a s t r a t e g y w h e n t h e y u s e d m u l t i p l e r e g r e s s i o nt e c h n i q u e s t o a n a l y z e e y e m o v e m e n t s o v e r l a r g e a m o u n t s o f t e x t.T h e i r p r o c e d u r e h a s b e e n c r i t ic i z e d b y a n u m b e r o f r e s e a r ch e r s( F i s h e r & S h e b i l s k e , 1 9 85 ; H o g a b o a m & M c C o n k i e , 1 9 8 1 ;K l i e g l , O l s o n , & D a v i d s o n , 1 9 8 2 ; S l o w i a c z e k , 1 9 8 3 ) . T h o s ec r i ti c i s m s a r e n o t r e p e a t e d h e re , b u t m a n y o f t h e m f o l lo w b e -

c a u s e a n y s u c h p r o c e d u r e m u s t m a k e u n j u s t if i a b le s im p l i f y i n ga s s u m p t i o n s a b o u t t h e r e l a t i o n s h i p b e t w e e n t h e m e a s u r e b e i n gu s e d ( i n t h i s c a s e , g a z e d u r a t i o n ) a n d c o g n i t i v e p r o c e s s i n g d u r -i n g r e a d i n g . A n a l t e r n a ti v e s t r a te g y t h a t m a n y r e s e a r c h e r s h a v ea d o p t e d i s t o s e l e c t t a r g e t lo c a t i o n s i n t e x t s f o r c a r e f u l a n a l y s i s( u s u a l l y o n t h e b a s i s o f t h e o r e t i c a l c o n s i d e r a t i o n s ) a n d e x a m i n em a n y d i f f e r e n t m e a s u r e s ( s u c h a s f i r s t f i x a t i o n d u r a t i o n , s i n g l ef i x a t i o n d u r a t i o n , g a z e d u r a t i o n , p r o b a b i l i t y o f f i x a t i n g a t a r g e tw o r d , n u m b e r o f f i x a t i o n s o n t h e t a r g e t w o r d , s a c c a d e l e n g t h t oa n d f r o m t h e t a r g e t w o r d , a n d s p i l l o v e r e f f e c t s ) . B y d o i n g s o ,i t is p o s s i b l e to d r a w s o m e r e a s o n a b l e i n f e r e n c e s a b o u t r e a d i n gp r o c e s s e s ( R a y n e r , S e r e n o , e t a l ., 1 9 8 9 ; S c h m a u d e r , 1 9 9 2 ) .

Saccade Durat ions and Gaze Du rat ionA r e c e n t c o n t r o v e r s i a l i s s u e c o n c e r n s w h e t h e r o r n o t s a c c a d e

d u r a t i o n s s h o u l d b e i n c l u d e d i n t h e c o m p u t a t i o n o f g a z e d u r a -t i o n . M o s t r e s e a r c h e r s h a v e f o l l o w e d t h e l e a d o f J u s t a n d C a r -p e n t e r ( 1 9 8 0 ) a n d h a v e u s e d o n l y f i x a t i o n d u r a t i o n v a l u e s i nc o m p u t i n g g a z e d u r a t i o n s . H o w e v e r , I r w i n ( 1 9 9 8 ) r e c e n t l y a r -g u e d t h a t l e x i c a l p r o c e s s i n g c o n t i n u e s d u r i n g s a c c a d e s a n d t h a ts a c c a d e d u r a t i o n s h o u l d b e a d d e d i n t o t h e g a z e c o m p u t a t i o n( s e e a l s o I n h o f f & R a d a c h , 1 9 9 8 ) . T h i s i s a r e a s o n a b l e s u g g e s -t i o n . O n t h e o t h e r h a n d , b e c a u s e i n t r a w o r d s a c c a d e d u r a t i o n sa r e q u i t e b r i e f a n d b e c a u s e t h e f r e q u e n c y o f r e f i x a t in g a w o r db e f o r e m o v i n g t o a n o t h e r w o r d i s r e l a t i v e l y l o w , a n y e f f e c t o fa d d i n g s a c c a d e d u r a t i o n i n t o th e g a z e d u r a t i o n m e a s u r e i s q u i t em i n i m a l . F o r e x a m p l e , a s n o t e d p r e v i o u s l y , r e a d e r s ' g a z e d u r a -t i o n s a r e lo n g e r o n l o w - f r e q u e n c y w o r d s t h a n o n h i g h - f r e q u e n c yw o r d s . W h e n s a c c a d e d u r a t i o n i s a d d e d i n t o t h e g a z e m e a s u r e ,t h e s i z e o f th e e f f e c t ( w h i c h i s t y p i c a l l y a r o u n d 5 0 m s ) i n c r e a s e sb y r o u g h l y 3 - 8 m s . I n a d d i t i o n , i f s a c c a de d u r a t io n s a r e t o b ea d d e d t o g a z e d u r a t i o n s , i t is u n c l e a r w h a t s h o u l d b e d o n e w i t hs a c c a d e d u r a t i o n s f o r i n t e r w o r d s a c c a d e s . S h o u l d t h e y b e a d d e dt o t h e w o r d j u s t f i x a t e d o r t h e w o r d t h a t i s t h e t a rg e t o f t h e n e x ts a c c a d e ? T h u s , t h e r e a r e u n r e s o l v e d i s s u e s r e g a r d i n g w h a t t od o w i t h s a c c a d e d u r a t i o n s . F o r g a z e d u r a t i o n s o n s i n g l e t a r g e tw o r d s , r e s e a r c h e r s w o u l d b e w i s e t o d e t e r m i n e i f a d d i n g s a c c a d ed u r a t i o n h a s a n e f f e c t i n a g i v e n s tu d y . A t t h i s p o i n t , i t a p p e a r st h a t i t t y p i c a l l y d o e s n o t . O n t h e o t h e r h a n d , w h e n r e g i o n s l a r g e rt h a n a s i n g l e w o r d r e p r e s e n t t h e u n i t o f a n a l y s i s , e f f e c t s o fs a c c a d e d u r a t i o n a r e l a r g e r a n d h e n c e a r e m o r e l i k e l y to a i d i nr e v e a l i n g d i f f e r e n c e s b e t w e e n c o n d i t i o n s .

E y e M o v e m e n t s a n d P e r c e p t u a l P r o c e s s e s in R e a d i n gThe Acquis i tion o f In format ion During R eading

W i t h r e s p e c t t o th e s e q u e n c e o f s a c c a d e s a n d f i x a t i o n s , w h e ni s i n f o r m a t i o n a c q u i r e d f r o m t h e t e x t d u r i n g r e a d i n g ? W o l v e r t o n

a n d Z o l a ( 1 9 8 3 ) u s e d t h e e y e - c o n t i n g e n t d i s p l a y c h a n g e t e c h -n i q u e t o r e p l a c e a n e n t i r e l i n e o f t e x t w i t h ( a ) a n o t h e r l i n e o ft e x t , ( b ) r a n d o m l e t te r s , o r ( c ) a r o w o f X s f o r a 2 0 - m s p e r i o dd u r i n g e i t h e r a s a c c a d e o r a f i x a t i o n . A f t e r t h e 2 0 - m s p e r i o d ,t h e n o r m a l t e x t re a p p e a r e d . I f t h e te x t w a s a l t e r e d a t a n y p o i n td u r i n g t h e f i x a t i o n ( i n c l u d i n g t h e f i r s t 2 0 m s o f t h e f i x a t i o n ) ,t h e c h a n g e w a s n o t i c e d a n d d i s r u p t e d r e a d i n g . H o w e v e r , i f t h ec h a n g e t o o k p l a c e d u r i n g t h e s a c c a d e , i t w a s n o t n o t i c e d a n dd i d n o t d i s r u p t r e a d i n g ( s e e a l s o I s h i d a & I k e d a , 1 9 8 9 ) . T h u s ,n e w i n f o r m a t i o n i s a c q u i r e d f r o m t h e t e x t o n l y d u r i n g f i x a t io n s .

R a y n e r e t a l . ( 1 9 8 1 ; s e e I s h i d a & I k e d a , 1 9 89 ; S l o w i a c z e k &Rayner , 1987) p resen ted a mask ing pa t te rn a t va r ious po in t s in af ixa t ion and found tha t r ead ing p rocex~.ded qu i te sm ooth ly i f thet e x t w a s p r e s e n t e d f o r 5 0 m s o r m o r e p r i o r t o t h e o n s e t o f t h em a s k .4 O n t h e o t h e r h a n d , B l a n c h a r d , M c C o n k i e , Z o l a , a n d W o l v -e r t o n ( 1 9 8 4 ) a r g u e d t h a t v i s u a l i n f o r m a t i o n m a y b e a c q u i r e dw i t h i n t h e f i x a t e d r e g io n a t a n y p o i n t d u r i n g a f i x a ti o n a s n e e d e db y c o m p r e h e n s i o n p r o c e s s e s . T h e y r e p l a c e d a g i v e n t a rg e t w o r d( s u c h a s tombs) i n a s e n t e n c e w i t h a n o th e r w o r d ( s u c h a s bombs)a t v a r i o u s p o i n t s d u r i n g a f i x a t i o n a n d h a d r e a d e r s m a k e f o r c e d -c h o i c e d e c i s i o n s a b o u t w h e t h e r o r n o t t h e y h a d s e e n t h e s e w o r d s( a s w e l l a s f o i l s ) d u r i n g r e a d i n g . T h e i r b a s i c f i n d in g w a s t h a t t h el o n g e r th e w o r d w a s p r e s e n t i n t h e t e x t , t he h i g h e r t h e p r o b a b i l i t yo f i n d i c a t i n g th a t i t w a s p r e s e n t . H o w e v e r , w o r d s p r e s e n t e d f o ro n l y 5 0 m s ( a t e i t h e r t h e b e g i n n i n g o r e n d o f a f i x a t i o n ) w e r es o m e t i m e s r e s p o n d e d t o p o s i ti v e ly . B l a n c h a r d e t a l . a r g u e d t h a tv i s u al i n f or m a t io n i s a c q u ir e d w h e n e ve r n ~ d u r in g a f ix a ti o n.Ac tua l ly , the resu l t s o f these two se t s o f exper im ents a re rea l lyn o t s o c o n t r a d i c t o r y ; b o t h o f t h e m e m p h a s i z e t h e f l e x i b i l it y t h a tr e a d e r s h a v e i n d e a l i n g w i t h s i t u a t i o n s i n w h i c h m a s k s s u d d e n l ya p p e a r o r w o r d s s u d d e n l y c h a n g e d u r i n g a f i x a t io n . F o r th e s a k eo f p a r s i m o n y , i t s e e m s m o s t l i k e l y th a t r e a d e r s t y p i c a l l y a c q u i ret h e v i s u a l i n f o r m a t i o n n e c e s s a r y f o r r e a d i n g d u r i n g t h e f i r s t 5 0 -7 0 m s o f a f i x a t i o n , b u t w h e n o n e w o r d c h a n g e s t o a n o t h e r th e ya r e a w a r e o f i t . B o t h s t u d ie s a r e c o n s i s t e n t i n p r o v i d i n g e v i d e n c eaga ins t the no t ion tha t the re i s a se r ia l l e t t e r -by- le t t e r scan w i th ina f i x a t io n . T h e s a m e c o n c l u s i o n w a s r e a c h e d i n a s t u d y b y I n h o f f ,P o l l a ts e k , P os n e r, a n d R a y n e r ( 1 9 8 9 ) , i n w h i c h r e a d e r s r e a d t e x tt h a t w a s t r a n s f o r m e d i n s o m e w a y . B y r e q u i r i n g r e a d e r s to r e a dm i r r o r - i m a g e te x t ( o r r o t a t e d o r r e v e r s e d te x t ) a n d v a r y i n g ( a )t h e d i r e c t i o n o f l e t te r s w i t h i n w o r d s ( l e f t t o r i g h t v s . r i g h t t o l e f t )a n d ( b ) t h e d i r e c t i o n o f r e a d i n g ( l e f t to r i g h t v s . r i g h t t o l e f t ) ,I n h o f f e t a l . s h o w e d t h a t c o n g r u e n c y o f l e t t e r o r d e r a n d d i r e c t i o no f r e a d i n g i s n o t c r i t i c a l f o r r e a d i n g ( K o w l e r & A n t o n , 1 9 8 7 )and tha t a se r ia l scan o f l e t t e r s in fovea l v i s ion does no t occur .

The Perceptual Span in ReadingH o w m u c h u s e f u l i n f o r m a t i o n c a n a r e a d e r o b t a i n d u r i n g e y e

f i x a t i o n s ? M a n y d i f f e r e n t te c h n i q u e s h a v e b e e n u s e d t o e s t i m a t et h e s i z e o f t h e e f f e c t i v e v i s u a l f i e l d o r perceptual span i n r e a d -i n g . H o w e v e r , m o s t o f t h e m h a v e s e v e r e l i m i t a t i o n s t h a t a r en o t d i s c u s s e d h e r e ( s e e R a y n e r , 1 9 7 5 b, 1 9 7 8 b f o r d i s c u s s i o n ) .R a t h e r, t h e f o c u s i s o n s t u d i e s u s i n g e y e - c o n t i n g e n t d i s p l a y t e c h -

4 Ishida and Ikeda (1989) concluded that the visual sensitivity that issuppressed during a saccade recovers only partially during the initialpart of a fixation and that it is fully recovered approximately 70 msafter the beginning o f the fixation.


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E Y E M O V E M E N T S I N R E A D I N Gd u r i n g a s a c c a d e b e c a u s e t h e e y e s a r e m o v i n g s o N o r m a l T e x t

379

X X X X X X X X X X c a d e b e c a u s e t h e X X X X X X X XX X X X X X X

X X X X X X X X X X X X X X X X X X X s e t h e e y e s a r e m X X X X X X XM o v i n g W i n d o w

d u r i n g a s a c c a d e X X X X X X X t h e e y e s a r e m o v i n g s oF o v e a l M a s k

d u r i n g a s a c c a d e b e c a u s X X X X X X X y e s a r e m o v i n g s o*

d u r i n g a s a c c a d e b e c a u s e t h e d o g s a re m o v i n g s o*

d u r i n g a s a c c a d e b e c a u s e t h e e y e s a r e m o v i n g s oB o u n d a r y

Figure 2. Examples of the moving window, foveal mask, and boundary paradigms. The first line showsa normal line o f text with the fixation location marked by an asterisk. The next two lines show an exam pleof two successive fixations with a window o f 17 letter spaces (with other letters replaced with Xs and thespaces between words preserved). The next two lines show an example of two successive fixations with a7-letter mask. The bottom two lines show an example of the boundary paradigm. The first line shows thetext prior to a displa y change with fixation locations marked by asterisks. When the reade r's eye movementcrosses an invisible boundary location (the letter e in the), an initially displayed word (dogs) is replacedby the target word (eyes). The change occurs during the saccade so that the reader is not aware of thechange.

n i q u es ( s e e F i g u r e 2 ) d e v e l o p e d b y M c C o n k i e a n d R a y n e r( 1 9 7 5 ) a n d R a y n e r ( 1 9 7 5 b ) . T h i s r e s e ar c h h a s p r o v i d e d th em o s t d e f i n i t iv e in f o r m a t i o n c o n c e r n i n g t h e p e r c e p t u a l s p a n .

I n t h e moving window technique ( M c C o n k i e & R a y n e r ,1 9 7 5 ) , t h e t e x t i s p e r t u r b e d e x c e p t i n a n e x p e r i m e n t e r - d e f i n e dwindow r e g i o n a r o u n d t h e p o i n t o f f i x a t i o n . W h e r e v e r t h e r e a d e rl o o k s , t h e t e x t i s v i s i b l e , w h i l e o u t s i d e o f t h e w i n d o w a r e a t h et e x t i s p e r t u r b e d i n s o m e w a y . R e a d e r s a r e f r e e t o m o v e t h e i re y e s w h e n e v e r a n d w h e r e v e r t h e y w i s h , b u t t h e a m o u n t o f u s e f u li n f o r m a t i o n t h a t i s a v a i l a b l e o n e a c h f i x a t i o n i s c o n t r o l l e d b yt h e e x p e r im e n t e r . E a c h t i m e t h e e y e s m o v e , a n e w r e g i o n o f t e x ti s e x p o s e d w h i l e t h e r e g i o n p r e v i o u s l y f i x a t e d i s p e r t u r b e d . I ns o m e c a s e s , t h e w i n d o w i s d e f i n e d i n t e r m s o f l e t t e r s p a c e s ,w h e r e a s , i n o t h e r c a s e s , t h e w i n d o w c o i n c i d e s w i t h w o r d b o u n d -a r i e s . S o m e t i m e s t h e s p a c e s b e t w e e n w o r d s o u t s i d e o f th e w i n -d o w a r e p r e s e r v e d , a n d o t h e r t i m e s t h e y a r e f i l l e d i n , a n d s o m e -t i m e s t h e t e x t i s p e r t u r b e d o u t s i d e t h e w i n d o w o n l y o n s e l e c t e df i x a t i o n s . T h e a s s u m p t i o n w i t h t h i s t e c h n i q u e i s t h a t w h e n t h ew i n d o w i s a s l a r g e a s t h e r e g i o n f r o m w h i c h t h e r e a d e r c a no b t a i n i n f o r m a t i o n , t h e r e i s n o d i f f e r e n c e b e t w e e n r e a d i n g i nt h a t s i t u a t i o n a n d w h e n t h e r e i s n o w i n d o w .The m oving ma sk technique ( R a y n e r & B e r t e r a , 1 9 7 9 ) i s li k et h e m o v i n g w i n d o w t e c h n i q u e e x c e p t t h a t , w h e r e v e r t h e r e a d e rf i x a t e s, a m a s k o b s c u r e s t h e t e x t a r o u n d f i x a t i o n w h i l e t h e n o r -m a l t e x t i s p r e s e n t e d b e y o n d t h e m a s k r e g i o n . J u s t a s w i t h t h em o v i n g w i n d o w t e c h n i q u e , t h e s iz e o f t h e m a s k c a n b e v a r i e d .5In the boundary technique ( R a y n e r , 1 9 7 5 b ) , a s i n g l e c r i ti c a l

t a r g e t w o r d i s i n i t i a l l y r e p l a c e d b y a n o t h e r w o r d o r b y a n o n -w o r d . W h e n t h e r e a d e r ' s s a c c a d e c r o s s e s o v e r a n in v i s i b l e p r e -s p e c i f i e d b o u n d a r y l o c a t i o n i n t h e t e x t , t h e i n i t i a l l y d i s p l a y e ds t i m u l u s is r e p l a c e d b y t h e t a r g e t w o r d . T h e a s s u m p t i o n w i t ht h i s t e c h n i q u e i s th a t i f a r e a d e r o b t a i n s i n f o r m a t i o n f r o m t h ei n i t i a l l y p r e s e n t e d s t i m u l u s , a n y i n c o n s i s t e n c y b e t w e e n w h a t i sa v a i l a b l e o n t h e f i x a t i o n a f t e r c r o s s i n g t h e b o u n d a r y a n d w i t hw h a t w a s p r o c e s s e d o n t h e p r i o r f i x a t i o n ( w h e n i n f o r m a t i o na b o u t t h e i n i t i a l s t i m u l u s w a s p r o c e s s e d ) i s r e g i s t e r e d i n t h ef i x a t i o n t i m e o n t h e t a r g e t w o r d . I n a r e l a t e d te c h n i q u e ( M c C o n -k i e & Z o l a , 1 9 7 9 ) , a s i n g l e w o r d i n a g i v e n t a r g e t l o c a t i o na l t e rn a t e s b e t w e e n t w o d i f f e r e n t w o r d s w i t h e a c h s a c c a d e . F i -n a l l y , i n a n o t h e r v a r i a t i o n o f t h e b o u n d a r y t e c h n i q u e ( M c C 0 n -k i e & H o g a b o a m , 1 9 8 5 ), t e x t i s m a s k e d ( o r s i m p l y r e m o v e d )f o l l o w i n g a s a c c a d e a n d t h e r e a d e r m u s t r e p o r t t h e l a s t w o r dt h a t w a s r e a d .

S t u d i e s u s i n g t h e s e t e c h n i q u e s ( D e n B u u r m a n , B o e r s m a , &G e r r i s s e n , 1 9 8 1 ; I k e d a & S a i d a , 1 9 78 ; M c C o n k i e & H o g a b o a m ,1 9 8 5 ; M c C o n k i e & R a y n e r , 1 9 7 5 ; O ' R e g a n , 1 9 7 9 , 1 9 8 0 ; P o l l a t -sek e t a l . , 1986 ; Rayner , 1975b , 1986 ; Ray ner & Ber te ra , 1979 ;R a y n e r e t a l ., 1 9 8 1 ; R a y n e t ; W e l l , P o l l a t s e k , & B e r t e r a , 1 9 8 2 ;N . R . U n d e r w o o d & M c C o n k i e , 1 9 8 5 ; N . R . U n d e r w o o d &

This situation creates an artificial foveal scotoma and e ye movem entbehavior if the situation is quite similar to the ey e movement behaviorof patients with real scotomas (Whittak~, Cumm ings, & Swieson, 1991;Zihl, 1995).


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380 RAYNERZ o l a , 1 9 8 6 ) h a v e b e e n v e r y c o n s i s t e n t i n i n d i c a t i n g t h a t t h es i z e o f t h e p e r c e p t u a l s p a n i s r e l a t i v e l y s m a l l ; f o r r e a d e r s o fa l p h a b e t i c a l o r th o g r a p h i e s ( e . g . , E n g l i s h , F r e n c h , a n d D u t c h )t h e s p a n e x t e n d s f r o m t h e b e g i n n i n g o f t h e c u r r e n t l y fi x a t e dw o r d b u t n o m o r e t h a n 3 - 4 l e t t e rs t o t h e l e f t o f f i x a t i o n 6( M c C o n k i e & R a y n e r , 1 9 7 6 a ; R a y n e r , W e l l , & P o l l a t s e k , 1 9 80 ;N . R . U n d e r w o o d & M c C o n k i e , 1 9 8 5 ) t o a b o u t 1 4 - 1 5 l e t t e rs p a c e s t o t h e r i g h t o f f i x a t i o n ( D e n B u u r m a n e t a l . , 1 9 8 1 ;M c C o n k i e & R a y n e r , 1 9 7 5 ; R a y n e r , 1 9 8 6 ; R a y n e r & B e r t e r a ,1 9 7 9 ; R a y n e r e t a l . , 1 9 8 1 ) . 7 T h u s , t h e s p a n i s a s y m m e t r i c t ot h e r i g h t f o r r e a d e r s o f E n g l i s h . H o w e v e r , f o r o r t h o g r a p h i e s ,s u c h a s H e b r e w , t h a t a r e p r i n t e d f r o m r i g h t t o l e f t , t h e s p a n i sa s y m m e t r i c t o t h e l e f t o f f i x a t i o n ( P o l l a t s e k , B o l o z k y , W e l l , &Rayner , 1981) .

C h a r a c t e r i s t i c s o f t h e w r i t i n g s y s t e m i n f l u e n c e n o t o n l y t h ea s y m m e t r y o f t he s p a n b u t a l s o t h e o v e r a l l s i z e o f th e p e r c e p t u a ls p a n . I k e d a a n d S a i d a ( 1 9 7 8 ) f o u n d t h a t t h e p e r c e p t u a l s p a nf o r r e a d e r s o f J a p a n e s e w a s a b o u t 1 3 c h a r a c t e r s p a c e s ( 6 c h a r a c -t e r s p a c e s t o t h e r i g h t o f f i x a t i o n ) , w h i c h i s c o n s i d e r a b l y s m a l l e rt h a n t h a t o f r e a d e r s o f E n g l i s h . O s a k a ( 1 9 87 , 1 9 9 2 ) f o u n d t h a tt h e s p a n w a s l a r g e r f o r t e x t c o n s i s t i n g o f a c o m b i n a t i o n o f k a n j i( a n i d e o g r a p h i c s c r i p t ) a n d k a n a ( a p h o n e t i c - b a s e d s c r i p t ) t h a nf o r t e x t c o n s i s t i n g o n l y o f k a n a c h a r a c t e r s . F o r t h e c o m b i n e dk a n a - k a n j i s c r i p t ( w h i c h i s t y p ic a l o f J a p a n e s e t e x t ) , t h e s p a ne x t e n d e d 7 c h a r a c t e r s p a c e s t o t h e r i g h t o f f i x a t i o n , w h e r e a s f o rt h e k a n a s c r i p t i t e x t e n d e d 5 c h a r a c t e r s p a c e s t o t h e r i g h t o ff i x a ti o n . T h e s e s t u d i e s i n v o l v e d h o r i z o n t a l r e a d i n g , b u t J a p a n e s ec a n a l s o b e p r i n t e d ( a n d r e a d ) v e r t i c a l l y . O s a k a a n d O d a ( 1 9 91 )f o u n d t h a t t h e s p a n w a s 5 - 6 c h a r a c t e r s p a c e s i n t h e v e r t i c a ld i r e c t i o n o f t h e e y e m o v e m e n t . S u b s e q u e n t e x p e r i m e n t s b yO s a k a ( 1 9 9 3 a ) r e v e a le d th a t t h e s p an w a s a s y m m e t r i c w h e nr e a d i n g h o r i z o n t a l l y a n d v e r ti c a l ly . O s a k a ( 1 9 9 3 b ) a l s o f o u n d( u s i n g t h e m o v i n g m a s k t e c h n i q u e ) t h a t r e a d e r s o f J a p a n e s e h a da g r e a t d e a l o f d i f f ic u l t y w h e n 4 o r 6 c h a r a c t e r s i n t h e c e n t e ro f v i s i o n w e r e m a s k e d ; t h i s r e s u l t is q u i t e c o n s i s t e n t w i t h r e s u l t sw i t h r e a d e r s o f E n g l i s h ( R a y n e r & B e r t e r a , 1 9 7 9 ) , e x c e p t th a tt h e m a s k n e e d e d t o b e l a r g e r f o r E n g l i s h t o c a u s e th e s a m e t y p eo f d i s r u p t i o n ( w h i c h i s c o n s i s t e n t w i t h t h e f i n d i n g t h a t m o r ec h a r a c t e r s a r e p r o c e s s e d p e r f i x a t i o n i n E n g l i s h t h a n i n J a p a -n e s e ) . R e c e n t l y , I n h o f f a n d L i u ( 1 9 9 8 ) f o u n d t h a t r e a d e r s o fC h i n e s e h a v e a n a s y m m e t r i c p e r c e p t u a l s p a n e x t e n d i n g f r o m Ic h a r a c t e r s p a c e l e f t o f f i x a t i o n t o 3 c h a r a c t e r s p a c e s t o t h er i g h t . I n a d d i t i o n t o t h e c h a r a c t e r i s t i c s o f t h e w r i t i n g s y s t e mi n f l u e n c i n g th e s i z e o f t h e p e r c e p t u a l s p a n , r e a d i n g s k i l l in f l u -e n c e s i t . R a y n e r ( 1 9 8 6 ) f o u n d t h a t b e g i n n i n g r e a d e r s h a d as m a l l e r s p a n ( a b o u t 1 2 l e t te r s p a c e s to t h e r i g h t o f f i x a t i o n )t h a n s k i l l e d r e a d e r s ( 1 4 - 1 5 l e t t e r s p a c e s ) b u t t h a t i t w a s a s y m -m e t r i c t o t h e r i g h t o f f i x a t i o n .

T h e r e s u l t s o f a n u m b e r o f s t u d i e s a r e q u i t e c o n s i s t e n t i ni n d i c a t i n g t h at , f o r s k i l l e d r e a d e r s o f a l p h a b e t i c w r i t i n g s y s t e m s ,t h e p e r c e p t u a l s p a n e x t e n d s a b o u t 1 4 - 1 5 c h a r a c t e r s p a c e s t ot h e r i g h t o f f i x a t i o n . H o w e v e r , t h i s d o e s n o t m e a n t h a t w o r d sc a n b e i d e n t i f i e d t h a t f a r f r o m f i x a t i o n ; in d e e d , w o r d l e n g t hi n f o r m a t i o n i s a c q u i r e d f u r t h e r t o t h e r i g h t o f f i x a t i o n t h a n i sl e t t e r i n f o r m a t i o n ( I k e d a & S a i d a , 1 9 7 8 ; M c C o n k i e & R a y n e r ,1975 ; Rayner , 1986) . The wor d i de n t if i ca t i on s pa n ( o r a r e a f r o mw h i c h w o r d s c a n b e i d e n t i f i e d o n a g i v e n f i x a t i o n ) i s s m a l l e rt h a n t h e to t a l p e r c e p t u a l s p a n ( R a y n e r e t a l ., 1 9 8 2 ; M c C o n k i e &

Z o l a , 1 9 8 7 ; N . R . U n d e r w o o d & M c C o n k i e , 1 9 8 5 ) a n d g e n e r a l l yd o e s n o t e x c e e d 7 - 8 l e t t e r s p a c e s t o t h e r i g h t o f f i x at i o n .

I s t h e s i z e o f t h e p e r c e p t u a l s p a n b e t t e r t h o u g h t o f i n t e r m so f l e t t e rs o r w o r d s ? T h e a n s w e r a p p e a r s t o d i f f e r t o t h e l e f t a n dr i g h t o f f i x a t io n . R a y n e r , W e l l , a n d P o l l a t s e k ( 1 9 8 0 ) f o u n d t h a tt h e l e f t b o u n d a r y o f t h e s p a n w a s p r i m a r i l y d e fi n e d b y t h eb e g i n n i n g o f th e f i x a t e d w o r d ( t h o u g h i t d i d n o t e x t e n d m o r et h a n 4 l e t t e r s p a c e s t o t h e l e f t o f f i x a t i o n ) . I n c o n t r a s t, R a y n e re t a l . ( 1 9 8 2 ) f o u n d t h a t t h e r i g h t b o u n d a r y o f t h e s p a n w a sp r i m a r i l y d e f i n e d i n t e rm s o f l e t te r s . W h e n t h e y c o m p a r e d r e a d -i n g p e r f o r m a n c e w h e n t h e w i n d o w w a s d e f i n e d i n t e r m s o f t h en u m b e r o f l e t t e r s a v a i l a b l e t o t h e r i g h t o f f i x a t io n w i t h r e a d i n gp e r f o r m a n c e w h e n t h e w i n d o w w a s d e f i n e d b y t h e n u m b e r o fw o r d s t o t h e r i g h t o f f i x a t io n , th e r e w a s n o d i f f e r e n c e b e t w e e n" w o r d " a n d " l e t t e r w i n d o w s " w h e n th e y w e r e r o u g h l y e q u iv a -l e n t i n s i z e . M o r e c r i t ic a l l y , d e t a i l e d a n a l y s e s r e v e a l e d t h a t p e r -f o r m a n c e i n t h e w o r d w i n d o w c o n d i t i o n s (i n w h i c h w o r d i n te g -r i t y w a s m a i n t a i n e d ) c o u l d b e p r e d i c t e d v e ry a c c u r a te l y f r o mk n o w i n g t h e n u m b e r o f l e t t e r s a v a i l a b l e o n e a c h f i x a t io n ,w h e r e a s p e r f o r m a n c e i n t h e l e t t e r w i n d o w c o n d i t i o n s c o u l d n o tb e p r e d i c t e d f r o m k n o w i n g t h e n u m b e r o f w o r d s a v a i l a b l e o ne a c h f i x a t i o n . T h u s , t h e p e r c e p t u a l s p a n s h o u l d b e d e f i n e d i nt e r m s o f t h e n u m b e r o f l e t t e r s a v a i l a b l e t o t h e r i g h t o f f i x a t i o n .

A n o t h e r i n t e r e s t i n g i s s u e i s w h e t h e r o r n o t r e a d e r s a r e a b l et o a c q u i r e i n f o r m a t i o n f r o m b e l o w t h e l i n e th a t t h e y a r e r e a d i n g .I n h o f f a n d B r i i h l ( 1 9 9 1 ; I n h o f f & T o p o l s k i, 1 9 9 2 ) a d d r e s s e dt h i s i s s u e b y a s k i n g r e a d e r s t o r e a d a l i n e f r o m a t a r g e t p a s s a g ew h i l e i g n o r i n g a d i s t r a c t i n g l i n e ( f r o m a r e l a t e d p a s s a g e ) a st h e i r ey e m o v e m e n t s w e r e r e c o r d e d . W h e n r e a d e r s c o m p l e t e d al i n e , t h e y p u s h e d a b u t t o n , a n d t h e n e x t l i n e ( w i t h t h e c o r r e -s p o n d i n g d i s t r a c t i n g l i n e o f t e x t d i r e c t l y b e l o w t h e t a r g e t t e x t )w a s p r e s e n t e d . R e a d e r s ' a n s w e r s t o m u l t i p l e - c h o i c e q u e s t i o n ss u g g e s t e d t h a t th e y h a d o b t a i n e d i n f o r m a t i o n f r o m b o t h a t t e n d e da n d u n a t t e n d e d l i n e s . H o w e v e r , a d e t a i l e d e x a m i n a t i o n o f t h e i re y e m o v e m e n t s s h o w e d t h a t t h e y o c c a s i o n a l l y f i x a te d u n a t -t e n d e d t e x t . W h e n s u c h f i x a t i o n s w e r e e x c l u d e d , t h e r e w a s n oi n d i c a t i o n t h a t r e a d e r s o b t a i n e d u s e f u l s e m a n t i c i n f o r m a t i o nf r o m t h e u n a t t e n d e d t e x t. P o U a t s ek , R a n e y , L a G a s s e , a n d R a y n e r( 1 9 9 3 ) m o r e d i r e c t l y e x a m i n e d t h e is s u e b y u s i n g a m o v i n gw i n d o w t e c h n i q u e . T h e l i n e t h e r e a d e r w a s r e a d i n g a n d a l l l i n e sa b o v e i t w e r e n o r m a l , b u t t h e t e x t b e l o w t h e c u r r e n t l y f i x a t e dl i n e w a s a l t e r e d . T h e l i n e s b e l o w t h e c u r r e n t l y f i x a te d l i n e c o n -s i s t e d o f ( a ) t h e o r i g i n a l te x t , ( b ) l i n e s f r o m a n o t h e r p a s s a g e( a s e m a n t i c a l l y d i f f e r e n t c o n d i t i o n ) , ( c ) X s , ( d ) v i s u a l l y s i m i l a rl e t te r s , o r ( e ) d i s s i m i l a r l e t t e r s re p l a c i n g t h e l e t t e r s f r o m t h eo r i g i n a l t e x t . P o l l a t s e k e t a l . f o u n d t h a t t h e p a s s a g e s w e r e r e a dm o s t e a s i l y w h e n t h e n o r m a l t e x t w a s b e l o w t h e l i n e a n d w h e nt h e r e w e r e X s b e l o w t h e li n e . N o n e o f t h e o t h e r c o n d i t i o n s

6 Binder, Pollatsek, and Rayner (in press ) recently found that thereare some circumstances under which readers process more informationto the left of fixation. For example, when a word is skipped, attentionmay often b e directed to the left of the fixation following the skip.7 It is important to note that the m oving window technique yields amaximum span estimate rather than an absolute value for each fixation(Well, 1983). Thus, although the size of the perceptual span has beenestimated as being 14- 15 letter spaces to the right of fixation, there isvariability in the size of the actual perceptual span from fixation tofixation, as some studies reviewed in a later section have dem onstrated.


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EYE MOVEME

eye movements in reading and information processing: 20 years of research

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