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Psychological ReviewJ Copyrigh t 1977 \ J by the A m e r i c a n Psycho log ica l Associa t ion , Inc.

V O L U M E 8 4 N U M B E R 2 M A R C H 1 9 7 7

Controlled and Automatic Human Information Processing:II. Perceptual Learning, Automatic Attending,a n d a General TheoryRichard M. Shi f f r in

Indiana Universi tyWalter Schneider

Univers i ty of Cal i forn ia , Berke leyThe two-process theory of detect ion, search, a n d a t t e n t i o n p r e s e n t e d bySchneider and Shiffrin is tested and extended in a ser ies of experiments . Thestudies demonstrate the quali tat ive difference b e t w e e n tw o modes of i n f o r m a -tion processing: automatic detect ion an d controlled search. They trace th ecourse of the l earn ing of au t o m a t i c de t e c t i o n , of ca tegor ies , and of au t o m a t i c -a t ten t ion responses . They show the dependence of au tomat ic de tec t ion on a t -tending responses a n d de m o ns t r a t e h o w such responses in te r rup t con t ro l ledprocessing a n d in te r fe re wi th th e focus ing o f at tent ion. T he learning of cat-egories is s h o w n to improve con t ro l led search per formance . A g e ne r a l f r am e -work fo r h u m an i n fo r m a t i o n p r o ce s s i ng is p r o p o s e d ; th e f r a m e w o r k emphasizesth e roles of a u t o m a t i c a n d control led processing. The theory is co m p ar e d to andcont ras ted wi th ex tan t models of search and a t ten t ion .

I. IntroductionIn Part I of this paper (Schneider &

Shif f r in , 1977) w e reported th e results o fseveral experiments on search and attentionthat led us to formulate a theory of i n f o r m a -tion processing based on two fundamentalprocessing modes: controlled and automatic.In the context of search studies, these modestook the form of controlled search and auto-matic detection. Controlled search is highlydemanding of attentional capacity, is usually

The research and theory reported here were sup-ported by PHS Grant 12717 and a GuggenheimFellowship to the first author, G r an t MH23878 tothe Rockefeller University, and a Miller Fellowshipat University of California at Berkeley to the secondauthor. This report represents equal and shared con-tributions of both authors .Requests for reprints should be sent to RichardM . S h i f f r i n , D e p ar t m e n t of Psychology, IndianaUniversity, Bloom ington, Indiana 47401. '

serial in nature with a limited comparisonrate, is easily established, altered, and evenreversed by the subject, and is strongly de-pendent on load. Automatic detection is rela-tively well learned in long-term memory, isdemanding of attention only when a targetis presented, is parallel in nature, is diff icul tto alter, to ignore, or to suppress once learned,and is virtually unaffec ted by load.

In the present article we shall reportseveral studies to elucidate fu r t h e r the proper-ties of automatic and controlled processingand their interrelations, to demonstrate thequalitative difference between these processingmodes, to study the development of automaticdetection and the role of the type and natureof practice in such development, to studyth e effects o f categorization, and to examinethe development of automatic attending andi ts effec t s . Af te r th e presentation of thestudies we shall present a general theory ofinformation processing, with emphasis on the

1 2 7


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12 8 R I C H A R D M . SHIFFRIN A N D W A L T E R SCHNEIDER

CM -

TRIAL I

TR I AL 2 rs63

TR I AL 3

TRIAL 4

VM -

TRIAL I

TRIAL 2 C J K

TRIAL 3

TRIAL 4Figure 1. Exa m ples of t r ia ls in the m ul t ip le- f ra m e search paradigm of Exper imen t 1 , Part I . In allcases , memory-set size = 4 a n d f r a m e size = 2 . Four va r i ed -ma pp ing ( V M ) t r i a l s a n d f o u r con-s i s t en t -ma pp ing ( CM ) trials a re depicted. T he m e m o r y set is presented in a d v a n c e of each tr ia l ,then the fixation dot goes on for .5 s ec w hen the s ub jec t starts the tr ia l , and then 20 f rames a represented at a fixed t ime per f r a m e . Either 0 or 1 m e m b e r of th e m e m o r y set is presented duringeach tr ia l . Frame time, memory - s e t size, an d f r a m e size a re varied across conditions.

roles of a u t o m a t i c an d con t ro l led processing .Our theory will then be compared an d con-t ras ted wi th extan t theor ies o f search a n da t t e n t i o n .A . Review of Paradigms and Results FromPart I

The paradigm fo r mos t of the s tudies ofP a r t I ( and P a r t II also) is depicted inF i gure 1. Four e lements a re presen ted s imul -t aneous ly in a s qua re ; a n d their joint presen-ta t ion for a brief period of t i m e is t e rme d a

frame. Each t r ia l consis ts of the presentat ionof 2 0 f r a m e s in immediate success ion. Thee lements presented are characters ( i .e . , digi tsor consonant s ) or random dot masks . In ad-vance o f each t r ia l th e subject is presen tedwith several i tems, called th e memory set, an dis then requi red to detect a n y m e m o r y - s e ti t ems tha t appear in the subsequent f rames .T he f r a m e t ime is kept constant across the20 f rames of each t r ia l , and the basic depen-dent var i ab le i s the psychomet r i c func t ionre l a t ing accuracy to f r a m e t i m e fo r eachcondi t ion .


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P E R C E PT U A L L E A R N I N G A N D A U TO M A T IC A T T E N D I N G 129Three bas ic independen t var iab les werem a n i p u l a t e d in Part I / E x p e r i m e n t 1. T h en u m b e r o f charac te r s in each f r a m e ( thef r a m e size, F) w a s varied from 1 to 4 (bu tw a s co n s t an t for all f r a m e s o f a given trial).

The n u m b e r of characters presented in ad-vance o f a t r i a l ( the memory - se t s ize , M )var ied f rom 1 to 4 . The p roduct o f M an d Fis t e r m e d th e load. A m e m o r y - s e t i t e m thatappear s in a f r a m e is called a target; a nitem in a f r a m e that is not in the m e m o r yset is called a distractor. O n e half of the tr ialscontained one target, and one half containedn o target . Final ly , a n d m o s t im p o r t an t , th ena tu re o f the t r a in ing p rocedure ac ross trialsand the relat ion of the m e m o r y - s e t i t e m s toth e dis tractors were var ied. In the consistentmapping (C M ) p rocedure , across all trials,memory - se t i t ems were never d is t r ac to r s ( andvice v e r s a ) . I n addi t ion , memory - se t i t emswere f rom one category (e .g . , dig i ts) anddis tractors from an other category (e .g . , con-sonants). In the varied mapping ( V M )procedure , memory - se t i t ems a n d dis tractorswere randomly in termixed over trials andwere a ll f rom on e category (e .g . , c o n s o n a n t s ) .Figu re 1 g ives exam ples o f trials in botht h e VM a n d C M condit ions . Depicted a refour consecutive t r ia ls f rom a C M b lo ck an dfour from a VM block in each of whichM = 4 and F = 2 . Table 1 gives the m e m o r yset, distractor, and target (if present) foreach tr ia l in Figure 1 . Note that m e m o r y - s e ti t e m s a n d dis tr ac to r s in te rm ix across t r ia l sin the VM con di tion bu t do no t in te rm ix overtr ials i n the CM condit ion .

The most important results are shown inFigu re 2 . These results showed that t he VMcondi t ions were s trongly affected by load a n dwere qu i te difficult ; the CM condi t ions werev i r tua l ly unaf fec t ed by load a n d were a lleasier than even th e easiest V M condi t ion .It was suggested that a controlled, serialsearch was operating in the VM conditionsa n d that a qual i t a t ive ly different process,au to m a t i c d e t e c t i o n , w a s operat ing in theC M condi t ions .T h e resu l ts o f Part I / E x p e r i m e n t 1 wereanalyzed on the bas is of the accuracy of thedetect ion responses . Part I / E x p e r i m e n t 2utilized comparable conditions but presented

T a b l e 1Examples of CM and VM Trials fo rFour Successive Trials

Tr ia lM e m o r yset Dis t rac torset Target

C o n s i s t e n t m a p p i n g ( C M )1234

1234

74812 5 8 317396S82Var ied

M J D GC J K HG M C HJ L K F

K G J C MC H F L DK G F D MC M J K Dm a p p i n g ( V M )

C F H K LL G D F MD L F K JC D G H M

4n o n e78

Dn o n en o n eL

on ly a single f r a m e o n each trial; accu r acywas high and the results were analyzed onthe bas is of the react ion t ime of the responses .T he resu l ts conf i rmed those of Part I/Experi-m e n t 1, and a quan t i t a t ive model was fi t tothe VM resul ts of both exper iments . Thismodel assumed that controlled search wasa serial, t e rmina t ing compar i son p rocess inwhich one first compared all f r a m e itemsaga in s t on e memory - se t i t em before switch ingto the nex t memory - se t i t e m . E ach co m p a r i -son and each swi tch was assumed to r equ i r esome t ime to be execu ted . T he success of themodel in fitting the results of both experi-men ts sugges ts that the same sear ch mech -an isms under l ie sear ch exper imen ts that uti-lize b o th a ccu r acy a n d r eac t ion t ime mea-sures, and suggests that the same searchm e ch an i s m s u n d e r l i e p e r f o r m an ce in bothdivided-at ten t ion a n d search paradigms.

The vast differences between results of theC M a n d VM condit ions provided a basis fo rreorgan iz ing and classifying the results ofprevious search an d detect ion s tudies . Thesestudies fell in to a relat ively s imple organ iza-tion, and many perp lexing and seeminglycontradictory resu l ts became explicable .Part I/Experiment 3 utilized a multiple-

t a rge t , m u l t ip le - f r am e p rocedure . T h e studyw as s imi la r to Part I / E x p e r i m e n t 1, but thesub jec t was presen ted ei ther zero , one, or twotarge ts p er t r ia l a n d w a s r equ i r ed to r epo r tthe n u m b e r of detected targets. The condi-


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130 R I C H A R D M. SHIFFRIN A N D W A L T E R S C H N E I D E R

c /)HIr-L U

100

80

60

CONSISTENTMAPPINGS

40

4,2) .(4,1)(4 ,4)

A " (1,4)

O)

LUOLJ

100

80

60

VARIEDMAPPINGS

40 80 120F R A M E TIME (msec)

120200 400 600 800F R A M E TIME (msec)

Figure 2. Data from Experiment 1, Part I. Hits a s a funct ion of f r a m e time fo r each of the 12condi t ions . Three f r a m e t i me s we re util ized fo r each con di t i on . The f i r s t number i n pa re n t he se sindica tes t he m e m ory-se t si ze an d t he se con d n um be r in pa re n t he s is i n d ica t e s t he f r a m e size.dons of grea test in terest were those in whichtw o t a rgets per trial were p resen ted . In thesecases th e spacing between the two t a rge t sva r i ed from 0 to 4 (0 spacing indica tes s imul-t a n e o u s pre s e n t a t i on ; spacings of 1, 2, and 4indica te the n u m b e r of i n t e r v e n i n g f r a m eplus 1). Target similari ty also var ied, thetw o targets being e i ther physica l ly ident ica l( I I ) o r different (NI).T h e results fo r Part I / E x p e r i m e n t 3showed marked ly different p a t t e r n s for theV M and C M condi t ions. Consider ta rgets imi l a r i ty f i rs t . In the VM cond i t ions de-tec t ion of ident ica l ta rgets (II) was supe r io rto detec t ion of different t a rge t s (NI). H o w -ever, in the CM condit ions, the reversewa s t r u e : NI detect ion was supe r io r to IIdetect ion. Consider target spac ing nex t . Int h e VM c o n d i t i o n s p e r f o r m a n c e wa s l o we s twhen the targets occurred in successive f r a m e s(spacing 1 ) . Ho we v e r , i n the CM cond i t ionsp e r f o r m a n c e wa s lowes t when the targets we r es imul t aneous ( spac ing 0 ). These resul tshe lped emphas ize the q u a l i t a t i v e differencebetween th e au tomat i c de tec t ion p rocess ingm o d e p r e s u m e d to be ut i l ized in the CMcondi t ions , and the cont rol led search modepresum ed to be u t il ized in the V M con d i tions .In ce r t a in of the studies in th i s pape r , w eshal l u t i l ize th is mul t iple- target , mul t iple-

f r a m e procedure a n d will in fe r th e presenceof au tomat i c de tec t ion or cont rol led searchfrom the n a t u r e of the spac ing effect and thet a rge t - s imi l a r i ty effect .B . Rationale for the Experiments

We a r g u e d in Part I that the cause of thedifference b e t we e n t h e C M a n d VM r e su l t swas the cons i s t ency of the m a p p i n g ( o v e rt r i a l s ) o f the memory-se t i t ems and d i s -t r ac to r s to responses. W e a r g u e d that c o n -s i s t en t mapping l eads to the deve lopment ofau tomat i c de tec t ion , which enab les au to -ma t i c -a t t en t ion re sponses to b e c o m e a t t a c h e dto the memory-set items. The automatic-at-t en t ion re sponses enab le the ser ia l , cont rol ledsearch to be bypassed by a parallel detectionprocess unaf fec t ed by load . However , t heseh y p o t h e se s m u s t be f u r t h e r tested for thefollowing reasons. First, the f a c t that m e m -ory-se t i t ems were ca t egor i ca l ly d i s t i nc tfrom the dist rac tors w a s confounded w i t h th econs i s t ency of the mapping . These fac to r swill be separated in Part I I / E x p e r i m e n t s 1,2, and 3 . Second, th e course of d e v e l o p m e n tof th e hypothes ized au tom a t i c de tec t ionprocess was not studied in Part I. The courseof l e a rn ing will be t raced in Part II/Experi-m e n t s 1 a n d 3 . T h i r d , t h e re wa s n o de m o n -


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PERCEPTUAL LEARNING AND AUTOMATIC ATTENDING 131s t ra t ion in P a r t I t h a t a n au t oma t i c - a t t e n -t ion response is l ea rned i n CM paradigms .Such a fact wi l l be suggested by Part II /Expe r i me n t s 1 to 3 and d e mons t r a t e d inP a r t I I /E x p e r i m e n t 4 . Fina l ly , a l though thesegoals provide an in i t i a l j us t i f i ca t ion for thepresent experiments , these s tudies will servea n e ve n more i mpor t an t pu rpos e in elu-c ida t ing the character is t ics a n d deve lopmentof au t om a t i c p roce s si ng and in dif ferent ia t ingau t oma t i c from control led process ing.I I . The D e v e l o p m e n t of Automat i c Process ing:P e r ce p t ua l Le a rn i ngA . Perceptual Learning and Unlearning in aC M Task Using Letters Only

Ex per im ent 1 of the present series is s implein concept ion. With the use of the same bas icm u l t i p l e - f r am e paradigm used in Part I/Expe r i me n t 1 (seeF i g u r e 1 ) , p e r f o rm a n c e isexamined as a func t ion of the a m o u n t oft r a in ing under cons i s ten t -mapping condi t ions .O n e c h a n g e is mad e , how e ve r : B o t h the dis-t rac to r set and the me mory e ns e mb l e cons i s tof cons onan t s . This procedure enables us tos tudy the acquis i t ion of au tomat i c i ty whenthe two sets a re no t already-learned cate-gor ies . Fur thermore , i t had been observedinformal ly that the use of digits an d con-sonant s ( in the CM condi t ions o f Part I/E x p e r i m e n t 1) led to a re la t ively rapidacquis i t ion of automat i c de tec t ion . I t wasfelt t h a t the use of le t ters only to make upthe two sets wou ld s low down ac quis i tion .Values of M and F were chosen so as tomake cont ro l l ed process ing difficult (M = 4 ,F 2 ) , a n d a f r a m e t i me ( / ) o f 20 0 msecwas chosen so as to m ake pe r form an ce lowwhen control led process ing was being ut i l ized.(These choices a re justif ied by the data inF i gure 2 .) T h u s i t was expected that per-f o r m an ce would be qui te poor a t the s t a r t oft ra in ing , when automat i c de tec t ion had no tbeen learned and control led search had to beused , but would improve markedly as au to-mat ic detect ion developed.I . Method

The CM presen ta t ion p rocedure of Par t I /Exper i -m ent 1 was u t i l ized (seeFigure 1) . The f r ame size

w as a lways equa l to 2 and the m em ory-se t size w asalways equal to 4 . Two disjoint character sets wereused for the m e m o r y e n s e m b l e and the distractorset. O ne consisted of the following n i n e c o n s o n a n t s :B , C, D, F, G, H, J , K , an d L; the o ther con-sisted of the fol lowing n ine consonan ts : Q, R, S,T, V, W, X, Y, a nd Z.There were f our new subjects, two of each sex,a ll naive to our tasks.1 Tw o subjects began t r a in ingwith th e c o n s o n a n t s from th e second half of thea lphabe t 'as th e memory ensemble , and two subjectsbegan with th e c o n s o n a n t s from the first half ofthe a lpha be t as the m em ory ensem ble . There werefive blocks of trials per session, each contain ing60 test trials. There were no practice trials. Subjectswere i n fo rme d at the s tar t of the experiment con-cerning th e na tu re of the s tudy and the composi-t ion of the m e m o r y e n s e m b le and the distractor set.E a c h trial began w i t h th e presentat ion of a m e m o r yset (M = 4) se lected randomly from t h e m e m o r yensemble.Dur ing the first 1,500 trials of the experimentfo r each subject , th e f r a m e t ime was 200 m s e c ;during th e fol lowing 60 0 trials, 120 m s e c . Afterthese 2,100 trials th e m e m o r y e n s e m b l e and thedistractor se t were swi tched fo r each subjec t an dth e f r a m e t ime was set back to 200 msec . Thisreversal 'Condition w as then run at the frame t imeo f 200 msec for a to ta l of 2,400 addit ion al t ria ls. Thesubjects were i n f o r m e d of the reversal at the t imeo f th e switch .T he subjects respon ded wh enever a target wasdetected, or gave a negat ive response at the end ofth e trial. The accu racy of the response and thereaction t ime fo r hits were both recorded. Sub-jects heard a t o n e signifying an error after eachincorrect response.2 . Results and Discussion

T h e resul ts a re presen ted in F i gure 3 . Re-sul ts fo r each block, averaged across sub-jects, a re graphed consecut ive ly . T h u s , thegraphed poin t s in each in te rva l a re based on12 0 observa t ions .In the i n i t i a l group of 1,500 trials , the hi tra te rose from jus t over 5 0% to abou t 90%,while the false a larm rate dropped froma b o u t 12 % to a b o u t 3 % (and th e react ion

1Since the experiments a re no t repor ted in theirchronological order, w e list here th e e x p e r i m e n t s intheir original order a n d indicate th e subjects thatwere used in e a c h . E x p e r i m e n t 1 was run wi th n ewsubjects. E x p e r i m e n t 4 was run n e x t ) using thesubjects w ho took p a r t in Exper imen t 3 of P a r t I.E x p e r i m e n t 2 was then run on three of the fou rsubjects in Exper imen t 4 . Exper imen t 3 was runlast , on new subjects.


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13 2 R I C H A R D M. SHIFFRIN AND W A L T E R SCHNEIDER

100

EC/)o800:=60

HO:22 60

co*-u0>luac< uowa >a.73a >oE

II NIo& M = 2C a t e g o r i c a l , V M

i i100

oo O

a> O

-> O

roO M i x e d , V M0 1 0 1 2 4

i S p a c i n g o f t wo t a r g e t s |N u m b e r o f t a r g e t sFigure 6. Data f rom Experiment 3 . Estimated percentage o f detection a s a f u n c t i o n of number,spacing, and similarity of targets for VM Sessions 19-23 fo r all conditions. (VM = varied mapping;M = memory-set s ize; II = identical targets; NI = nonidentical targets.)


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14 0 R I C H A R D M. SHIFFRIN AND WALTER SCHNEIDERth e results of the M 2 an d M = 4 condi-t ions converge ( indica t ing ca tegory l ea rn ingand the use of a categorical search s t r a t e gy) .In the mixed condi t ion per formance in theM = 4 condi t ion remains much lower than inth e M = 2 condi t ion , but per formance inboth of these is worse than in e i ther cate-gorical condi t ion (suggest ing t h a t the pres-ence of well-known categories reduces th eeffect ive memory-se t s i ze to 1).To ascerta in whether control led search w asbeing ut i l ized in these various V M condi t ionsand to d e t e rmi ne th e n a t u r e o f t h a t search, itis necessary to consider th e spacing funct ionsshown in Figure 6. This f igure gives thespac ing func t ions fo r Sessions 19-23 , whenp e r f o r m an ce had s tabi l ized, averaged acrosssub jec t s . F or both M = 2 a n d M = 4 con-di t ions , the mixed condi t ion shows the pat-tern w e have come to expect fo r control ledsearch , w i th per form an ce worse a t spac ing 1a n d worse fo r different targets ( N I ) .Pe r f o r m a n c e in the categorical condi t ionw as e qu i va l e n t w he n M = 2 and M 4 .T h e us ua l pe rf o rma nce i mpa i rm e n t a t spacing1 occu r s fo r iden t i ca l t a rge t s ( I I ) , bu t w h e nt he two targets d i f f e r ( N I ) , p e r f o r m a n c e inth e spacing 0 condi t ion is grea t ly impai red ,a result no t seen in previou s VM con di tions .F u r t h e rmo re , the II and NI conditions showonly a smal l difference except a t spacing 0.

The results from the mixed condi t ion con-form to the pa t te rn expec ted fo r control ledsearch in three respec t s ; When M = 4 per -f o r m a n c e is worse than when M 2; thereis a p e r f o r m an ce reduc t ion a t spac ing 1; an dp e r f o r m an ce is worse fo r NI than II con-di t ions.The resul ts f rom the categorical condi t ionwere unexpec ted in some respects but areexpl icable in terms of an hypothes is thatcategories were learned a n d ut i l ized in con-trolled search. Let us assume tha t the pres-ence of a kn ow n ca tegory a l lows one to c o m -pare the category of the memory set to thecategory of any given display item in a single

opera t ion . Then the M = 2 condi t ions shouldn ot d i f f e r from th e M 4 condi t ions , and inf ac t both con di tions should show perform an celevels equivalent to those expected for amemory-set s ize of 1 in a normal mixed con-

di t ion. This reasoning explains why the cate-gorical condi t ions a re both superior to thebes t mixed condi t ion , which uses a memory-se t size of 2 .T he category hypothes is , how ever, sug-gests that target s imilar i ty should n o t m a t t e r ,so that the I I and NI func t ions should beident ical . To explain th e spacing 0 resultswithout abandoning th e category model, w esuggest th e following hypothesis. Supposethat when a subject locates a target category,he or she briefly switches to an i tem mode,perhaps to check that th e i n p u t is t ru ly acategory me mbe r . If the second item in thef r a m e is identical , then i t will be found i n ani t e m-compa r i s on mod e , but if nonident i ca l , itwill be located only if the subject revertsquick ly enough to a categorical -comparisonmode . By the ne x t f r a m e , th e reversion to acategorical mode is complete , so the variousfunc t ions tend to converge. Why would sub-jects tend to switch to an i t e m m o d e ? T hecategories were constructed so as to be ex-t r eme ly confusab le wi th each o ther . Perhapscategory encoding is learned under these cir-cums tances but remains somewhat e r rorprone . Then it would be logical to check an yt a rge t ca tegory by us ing an i t em mode .Whatever the explanat ion for the detai ls ofthe spacing func t ion , th e data a s a wholem a k e a s t rong case that categories have beenlearned in the categorical condi t ion duringV M t r a in ing , and that the presence of cate-gories in a VM si tuat ion al lows the subjectto ad op t a s impler a n d m o r e efficient form ofcontrol led search.

T h e a r g u m e n t that controlled search isopera t ing in these condi t ions would be sub-s t an t i a ted if it could be d e mons t r a t e d thatp e r f o r m an ce improves when the subjectsswitched to CM t rain ing. W e turn next tot he C M proce d ure .3 . Method

Fol lowing the 24 th sess ion of VM tra in ing , a CMprocedure w a s initia ted. In the categorical condi-t ion , one of the ca tegor ies was f ixed thencefor thas the memory ens emble , and the other ca tegorywas f ixed t he r ea f t e r as the distractor set. In them ixe d condi t ion , a se t of 4 was chosen and wasfixed t he r ea f t e r a s the memory ens emblethe r e -ma in ing 4 items were fixed thereaf ter as the dis-


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PERCEPTUAL LEARNING AND AUTOMATIC ATTENDING 141tractor set. The two sets of 4 used in the mixedcondition were those indica ted by the posit ion ofth e c o m m a in the listing of the two sets of eightconsonan t s : {GMFP, C N H D } an d ( R V JZ , BWTX}.In other words , these were th e same sets tha t hadbeen used as categories in the categorical condi t ionsfor other subjects. This C M t ra ining procedure wasidentical fo r both conditions a n d followed in otherrespects th e procedures used in the preceding V Mcondi t ions. Each subject w as given at least 10sessions of VM t ra ining. The f r a me t ime after C MSession 4 (Session 24 overall) was reduced to 160msec and after CM Session 11 (Session 35 overall)was .reduced again to 120 ms ec (at the t ime of thiswriting this study had not been comple t ed) .4 . Results and Discussion o f the CM

Condit ionsThe changes over sessions following theswitch t o CM t r a i n i n g a re depicted in F ig u r e5. Consider first the resu l ts of Sessions 2 5th rough 2 8 , w h i ch im m e d ia t e ly followed th eswitch t o CM t r a in ing . Qu i te c lea r ly , a veryrapid a n d dramat ic r i se in p e r f o r m an ce t o o kp lace , and fu r th erm ore , the r esu l ts o f themixed and categorical conditions tend toconverge . By Sess ion 28 the per fo rmancelevel in the mixed condi t ion ha d risen to over

90% and in the categor ical condit ion h a dr isen to over 95%. Since th e subjec ts wereclearly approaching ceiling, the f r am e t im ew as then r educed to 160 m sec and CM t r a in -ing continued for six additional sessions.N o te that p e r f o r m a n c e w a s s t i l l improvinga n d that th e m ix e d a n d categor ical , a n d M= 2 a n d M = 4 , condi t ions effectively con -verged.

It is interesting to note that dur ing VMt r a i n i n g , 20-25 sess ions w ere n ecessary beforethe M = 2 and M = 4 p e r f o r m a n ce l ev e ls be-cam e e q u a l in the ca tego r ica l condi t ion . Thuso n e m ig h t t e n t a t i v e ly co n c lu d e that categoryencoding in the presen t exper imen ta l con tex tr equ i r ed 20-25 sess ions to develop . Thuscategory encoding would be unlikely to de-velop for the mixe d condi t ion in j u s t f o u rC M sessions. Y et a f t e r on ly four sessions ofCM t r a in in g , the per fo rm an ce leve l in themixed condi t ion ro se dramat ica l ly and ap-proached that of the categorical condition. Thisresu l t suggests that au tomatic detect ion de-veloped in the mixed condition in the absenceof a w el l- lea rned ca tego ry ( a t least d u r in g

the first four sess ions of CM train ing) . Ino ther words , th e l e a r n in g of a ca tego ry isapparently not a necessary prerequisite forth e d e v e l o p m e n t o f au tomat ic de tec t ion .

F igu re 7 shows th e spacing func t ions forthe six sessions (30-35) of CM t r a in ing runat a 160-msec f r a m e t im e . The results areaveraged over subjects and sessions. In ad-dition th e M 2 an d M = 4 condit ions a relumped together since they did not differ.S o m e w h a t t o our su rp r i se th e p a t t e r n is al-most iden t ica l to that seen for the categor icalcondi t ion du r ing the latter s tages of VMt r a i n i n g , except that th e p e r f o r m an ce l e v e lis much h igher . The comparable pattern fromt h e C M co n d i t io n s o f Part I / E x p e r i m e n t 3w as q u i t e different : D e te c t i o n w as ab o u te q u a l in al l condit ions except for a depresseddetec t ion rate w h e n s p ac in g w as 0 an d w h e nth e t a rge ts were iden t ica l . A t spac ing 0 thepresen t da ta c lea r ly show per fo rm an ce to behigher when the targets were identical.

Disregard ing the shape of the spac ingfunc t ions , th e l a rg e i m p r o v e m e n t in p e r f o r m -an ce w h e n C M t r a i n i n g co m m e n ce d do es s u g-gest that th e subjec ts were lea rn ing au to -mat ic de tec t ion . A n hypothesis that reconcilesthese facts suggests that th e subjec ts wereusing automatic detection to locate the firstt a rge t , a n d were then r ever t ing to controlledsearch to check th e accu racy of the t a rge tde tec t ion . Some t ime may be lost befo re thesubjects rever t to au to m a t i c d e t e c t i o n . Thusthe advantage of II at spacing 0 would bedu e to the t e m p o r a r y use of a contro l ledsearch. This hypothesis is similar to thatused to explain th e categorical results in theV M co n d i t i o n s ( F ig u r e 6). In both cases, at endency to recheck the first detected itemm a y h a v e led to an al terat ion in searchstrategy. The reason may be the same in bothcases: Rechecking of located targets m ayhave been induced by the s t imu lus sets,which were chosen so that th e m e m o r y seta n d dis tractor se t were max imal ly v isua l lyconfusable . Thus, both a u t o m a t i c detectionand c a tego ry encoding m ay hav e been some-what error prone, thereby requiring recheck-in g i n an i t e m m o d e . W e a r e c u r r e n t ly e x -plorin g this hypothesis.In s u m m a r y , a n u m b e r of conclusions c a n


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N um be r o f t a r g e t sFigure 7. Data from E x p e r i m e n t 3 . Est imated percentage of detection as a f un c t ion o f n u m b e r ,spacing, an d s imilar i ty of targets for CM Sessions 30-35, averaged over m e m o r y - s e t size (whichhad no effect) fo r a ll condit ions . (C M consis tent m a p p i n g ; f = f r a me t ime ; I I = iden t i ca l targets ;N I =nonident ica l targets.)

be d r a w n from the resul ts of E x p e r i m e n t 3 .First, arbi t rary col lec t ions of charac ters canbe l e a rned a s categories. F or th is learning too ccu r , i t is necessary that the categories re-main consistent ly denned across t r ia ls , bu tnot necessary that the same ca t egory re -m a i n the t a rge t se t across tr ials. Second, thel e a r n i n g of a ca t egory i n a VM sea rch pa ra -digm enables th e sub jec t to adopt a m o r eefficient cont rol led search, one in which thecategory of the m e m o r y se t may be c o m -pared in a single operation to the categoryof a disp l ay i t em , thus e l im ina t i ng the effectsof var ia t ions in memory-se t s ize . Third , aswi tch t o a C M t r a in ing p rocedure re su l t sin fa i r ly rapid acquisi t ion of a u t o m a t i c de -t e c t i o n , w i t h a c o n c o m i t a n t i m p r o v e m e n t i np e r f o r m a n c e fo r both th e categor ica l a n d n o n -ca tegor ica l s t imul i . These conclusions sup-port those suggested by the results of Ex-p e r i m e n t 2 in al l impor t an t r e spec t s .

D . What is a Category? A Discussion andSelective Review1. Some Hypotheses C oncerning C ategories

E x p e r i m e n t s 2 and 3 showed how searchbenefits from th e learning of a categoricaldis t in c t ion b e t we e n m e m o r y e n se m b l e a n ddistractor set . B u t w h a t is a ca tegory? Mostgenera l ly , w e m a y define a n y ob jec t in m e m -o ry that re fe rs to (s tands for , consists o f)a n y t wo o r m o r e o b je c t s i n m e m o r y a s a

ca tegory. Verbal labels a re one c o m m o n classof categories, but other types of categor iesm i g h t also exist . F or example , a vi sua l symbolmight represent severa l objec ts . Of course , aca tegory in genera l need not exist in a formsimi lar to any of the sensory modal i t ies . Acomple te ly abs t r ac t node cou ld represen t twoo r more ob jec t s in m e m o r y .Wi th re spec t to search tasks, th e i m p o r t -a n c e of categor ies is c lea r . When all of them e m b e r s o f a m e m o r y set are m e m b e r s ofthe same category and no distractors are inthat ca tegory , t hen a controlled search c a nbypass th e i n d i v i d u a l m e m o r y - se t i t e m s a n dut i l ize compar i sons that i n v o lv e m a t c h i n g th esingle ca tegory against the ca tegory of eachdisplay i tem . Fo r ca tegory search to be ut i -lized effect ively, however , the c a t e g o r y m u s tbe learned wel l enough that each displayedelement wil l be encoded automatically andcon sistent ly acco rding to i ts c a tegory. O fcourse other fea tures, such as the element 'sname and shape , wi l l a l so be encoded, butonly the ca tegory f e a t u r e is necessary for aca tegory search. W e suggest that th e categorycoding m u s t be a u t o m a t i c , b e c a u se if it we r eno t , a sea rch of long- t e rm memory wouldhave to be carried out to identify the cate-gory ; the t ime t aken fo r such a long- t e rmsearch wo uld a lm ost cer ta in ly w ipe ou t anygains that are due to the reduct ion in n u m -ber of comparisons a l lowed by the ca tegorysearch (at least fo r sma l l memory-se t s izes ) .


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P E R C E P T U A L L E A R N I N G A N D A U T O M A T I C A T T E N D I N G 143Note that au tomat ic ca tego ry encoding isn o t th e s a m e a s au to m a t i c d e t e c t i o n . A u to -m a t i c detection refers to the case when as t im u lu s gives r ise to an au to m a t i c - a t t e n t i o nresponse that bypasses the need for a serialsearch th rough e i ther m em ory o r the d isp lay .A u t o m a t i c ca tego ry encoding refers to thecase when th e s t imulus g ives r ise au to-m a t i c a l l y to a node r ep resen t ing th e ca tego ryof the s t imulus . However , without an at-t en t ion r esponse a t t ached to the s t im u lu snode o r the c a tego ry n ode , the p resence o fthe ca tego ry wou ld have to be deducedt h r o u g h a ser ial search of the disp layedelements .O ur s tudies have shown that a n a u t o m a t i ccategory encoding of arbitrary collections ofcharac te r s ( consonan ts , in the case of E x p e r i -m e n t 3 ) can develop . The cause of the learn-ing is no t yet c lear . Some subjects in ear lyvers ions of E x p e r i m e n t 3 never showed a n yevidence of categorical search (usually sub-jec t s w i th low levels o f p e r f o r m a n c e ) . I t m aybe that these subjec ts did not no t ice th eca tego r ica l n a tu re of the m e m o r y e n s e m b l ean d hence cou ld no t deve lop a wel l - lea rnedca tego ry node in m e m o r y . A l t e r n a t i v e l y ,these subjects could have developed a n a p -propriate category node but have fai led touse th is n ode to f ac i l i t a te the i r sear ch .

T h e r e a re several lines o f e v ide nce sug-gest ing that au to m a t i c d e t e c t i o n m a y developfas te r if a ca t e g o r i z a t i o n is ava i lab le at thestart o f co n s i s t e n t t r a i n i n g . For example , i tis easy to learn to search for a set of s t imulidefined by a simple physical feature (seeNeisser , 1963 , 1967 , an d studies in the n e x tsec t ion ) . The CM resu l t s in F igu re 5 show thatth e ca tego r ica l condi t ion r e ta in s some super i -o r i ty over the mixed condit ion fo r abou t e igh tsessions ( 2 5 - 3 2 ) but the m ag n i tu d e of thedifference is surpr is ing ly sma l l . It is possiblethat the high confusability between the twoca tego r ies o f Exper imen t 3 makes the ca te -gories and the au to m a t i c r e s p o n s e difficult tol ea rn . I f so , m ore t r a in in g p r io r to the C Mphase could possibly have led to a larger dif -ference in the rate of development for thetw o groups . A l te rna t ive ly (o r addi t ion a l ly )th e small size of these categories m ay haveal lowed au tomat ic r esponses to the ind iv idua l

m e m b e r s to develop so quickly that ad v an -tages due to a ca tego ry r esponse we re m in i -mized.It is co n ce p tu a l l y im p o r t an t to keep in

m i n d th e possibility that au tomat ic r esponsesm i g h t be a t t a ch e d to different s tages of en-coding of a s ing le s t imu lus . I n par t i cu la r ,w h e n an au to m a t i c - a t t e n t i o n r e s p o n s e d e -ve lops fo r a ca tego ry , o ther a t ten t ion r e -sponses may develop at a different rate forth e s t i m u l i m a k i n g u p that ca tego ry . Thus,i f a ca tego r iza t ion i s ava i lab le a t the start ofC M t r a i n i n g , th e a t ten t ion r esponses to theca tego ry migh t deve lop sooner than atten-t ion responses to s o m e or al l of the indiv iduals t imul i in the ca tego ry . This effect w o u ld beexpected since any one s t imulus would appearonly occas ional ly a s a target , whereas everyt a r g e t w ould be an in s tance o f the ca tego ry .On the o ther hand , in the cases in wh ich them e m o r y ensemble does no t form a ca tego ryat the start of CM t ra in ing , there m ig h t bea t l east some ind iv idu a l s t imu l i that c o m eto e l ic i t au tomat ic - a t ten t ion r esponses wh i lethe category is s t i l l being learned.

O n ce an au to m a t i c - a t t e n t i o n o r e n co d in gresponse develops , w e a s s u m e that i t is nolonger u n d e r co n t r o l of the s u b j e c t a n d willoccur whenever its corresponding s t imulus ispresen ted . Th is as sumpt ion wi l l be suppor tedb y E x p e r i m e n t 4 . H o w e v e r , w h e n a ca te -go r ia l encoding (bu t no t an a t ten t ion r e -sponse ) is l e a r n e d , it will n o t necessar i ly beutilized by the subjec t du r ing a controlledsear ch . W e suppose a ca tego ry r esponse willfacilitate controlled search only if the subjectboth not ices th e ca tego ry a n d also decides toal ter his search to c o m p a r e th e ca tego ryra ther than th e ind iv idua l s t imu l i . Theseconsiderat ions w ould n o longer apply if anautomatic-attention response were learned inresponse to the ca tegory; in such a case sub-ject strategy would not matter since attentionwould be direc ted to the ca tego ry i n a n yeven t .2 . Search Studies Using Categories

In a n u m b e r o f memory - sear ch s tud ies (inthese studies F = 1 and M varies), the m e m -ory set consis ts o f several categor ies , an d


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144 R I C H A R D M . SHIFFRIN A N D WA L TE R SC H N E ID E Rthe distractors might be drawn f rom thesesame categories o r f rom di f fe ren t (unknown)categories. The results of these studies alldemonstrate the use of some sort of con-t ro l led search, perhaps in conjunction withsimultaneous automatic detection, that isfacilitated by the presence of categories.

For example, Naus, Glucksberg, and Orn-stein ( 1 9 7 2 ) and Naus (1974) used memorysets consisting o f words from several cate-gories and a distractor set made up of wordsfrom these same categories. The resultsshowed linear memory-set-size f u n c t i o n s ,parallel for negative and positive displayitems. However, there was a slope reductionw h e n the number of categories increased. Theauthors suggested that categories were suc-cessively searched in random order, each inserial, exhaustive fashion, until the categoryof the displayed item was reached. When thesearch of this category was completed, aresponse was initiated. Homa (1973) pre-sented a related paradigm; his results sug-gested that a serial, exhaustive search ofcategories was followed by a serial, exhaustivesearch within th e category of the displayeditem. Williams ( 1 9 7 1 ) , who presented an-other related paradigm, also argued that aserial, exhaustive search of categories w a sfo l lowed by a serial search within the cate-gory. Okada and Burrows (1973) used mul-tiple categories in the memory set and some-times cued the subject as to the category ofthe displayed item in advance of the trial.Their results showed that the search couldbe restricted to the cued category. Cliftonand Gutschera ( 1 9 7 1 ) used memory sets con-sisting o f two-digit numbers a n d showed thaton some trials the subjects would first com-pare the 10s digits and then would comparethe Is digit only if a 10s digit match wasf o u n d . Lively a n d Sanford ( 1 9 7 2 ) used amemory set f rom one category and a dis-tractor se t consisting of some members ofthat category and other members outsidethat category. Negative items outside thecategory of the memory set showed a set-sizef u n c t i o n with reduced slope.

The various findings in these memory-search studies differ in many details that willnot be discussed here. They all tend to show

the use of some sort o f controlled search thatis facilitated by the presence of categories inthe memory set.3

The final studies to be considered are thosevisual search studies in which M = 1 and Fvaries, but in which the visually presenteditems fall in two or more categories, one ofw h i c h matches the category of the memory-

3 We shall not attempt at this t ime to explainw hy a particular controlled search strategy is adoptedin a particular paradigm. Procedural differencesa m o n g t h e studies would make such explanationspure guesswork. Another class o f studies usingcategories also deserves mention fo r completeness,but i s not discussed in the main text because of adifficulty in ascertaining whether th e effects f o u n din these studies w e r e due to automatic o r controlledprocess ing. These are visual search studies (M = 1,F varied) that have used memory ensembles a n ddi s t r ac to r sets from different categories. They haves how n either flat set-size functions or curvilinear set-size f u n c t i o n s with reduced slopes (e.g., Brand,1971; Ingling, 1972; Jonides & G l e i t m a n , 1972,1976). These studies have utilized CM designs withlo w practice levels; this makes it difficult to ascertainw h e t h e r the slope reductions are due to the presenceof automatic detection, to beneficial effects of cate-gor izat ion on controlled search, or to some combina-t ion of these fac to rs .N o t e that th e slope reductions fo r visual set-sizefu nc t i o ns normally should be taken a s evidence ofautomatic detection. That is , in a controlled searchon e would expect a serial comparison process tobe needed to compare the memorized categoryaga ins t th e category of each displayed item. How-ever, it was seen in our VM 'data f rom Part I/Experiment 2 that a reduction of slope occurredw h e n M w a s equal t o 1 an d F varied, a n d w e sug-gested that a "controlled parallel search" might berespons ib le for this result. A similar argument mightbe made to explain th e slope reductions in the abovevisua l search studies. W e d o n o t particularly f a v o rsuch a n explanation because it does n o t explainw hy normal set-size functions are f o u n d in visualsearch studies that do not use categories (e.g.,A t k i n s o n , Holmbren, & Juola, 1969).A finding related to those from studies usingcategor ies in visual search is that of De Rosa a n dMorin (1970) in a memory search study. Theyshowed that when the memory set consisted ofc o ns ec u t i v e digits, then both th e positive a n d nega-tive reaction times increased a s a func t ion of thenumer i c a l closeness of the displayed item to theboundaries of the consecutive memory set. T h e C Mproc edure w a s used with small amounts of practice,so it is again difficult to ascertain whether sucheffects were due to the action of automatic detectionor to some controlled search facilitation allowed bythe categorical character of the memory set.


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P E R C E P T U A L L E A R N I N G A N D A U T O M A T I C A T T E N D I N G 145se t i t em . Smi th ( 1 9 6 2 ) a n d Gr e e n a n d An d e r -son (1956) carr ied out similar studies in whicha field of co lored tw o-d ig i t nu m bers w as pre-sented and the subject was asked to searchfo r a par t i cu l a r two-d ig i t number in a par -ticular color. The results showed that searchr a t e depended much more on the n u m b e r ofitems in the designated color than on thetotal n u m b e r of i t ems p resen ted , though bo theffects were present. A VM procedure w asuti l ized in their studies so that a u t o m a t i cdetection could not have been used to restrictsearch to the i t ems of a par t icular color .Probably a two-phase controlled search wasuti l ized in th is s i tua t ion. First, a r a the r fa s tserial search was probably carried out tolocate the next i tem of the designated color ;then a slow comparison o f that two-digitn u m b e r wa s p robab ly m ade to de te rm inew h e th e r i t w as the t a rge t . This explanat ion issuppor t ed by the f a c t tha t searching took along t im e (up to 20 sec ) , so that a 30-40 msecsearch ra te fo r color could have accountedfo r the increases in response t ime as to ta lsize increased. These increases were smal lon ly i n compar i son wi th the l a rge r with in -category effects.T h e main conc lus ion to be d r a w n from th estudies reported in this section, based on re-peated findings, is that the presence of ca te-gories in search tasks can b e used to fac i l i ta te ,benefit , an d modi fy cont rol led search.

I I I . Exper imen t s on Focused At t en t ionIn part I we m a d e the case that the

processes utilized in attention experiments andthose uti l ized in search and detection experi-m e n t s a re often th e same . In fac t , in m a n ycases it is pure ly a rb i t r a ry whe the r a givenstudy is re fe rred t o a s an "attention,""search," or "detection" s tudy . Exper imen t 1in Part I could be described as a divided-a t t en t ion s tudy in which a t t en t ion had tobe divided among M memory-se t i t ems an dF f r a m e i tems dur ing each f r a m e . T he resultsshowed t r e m e n d o u s deficits in dividing a t-tent ion in the VM condi t ions, and vi r tua l lyn o deficit in dividing a t tent ion in the CMcondi t ions. The results of E x p e r i m e n t 2 ofPart I, and the fit of the quan t i t a t ive mode lto both studies, showed that divided-atten-

t ion deficits in these paradigms are due tothe limitations of controlled processes, inp a r t i c u l a r , to the l imi ted ra te of shor t - te rmsearch.

Thus , a l l our comment s and conc lus ionsconcerning search and detection apply equallywell t o a t t en t ion s tud ies . In pa r t i cu l a r , CMtraining should lead to the development ofau tomat i c de tec t ion that shoul ld bypassdivided-attention limitations, while VMt ra in ing should cause cont rol led search tha tshould severely l imit the ability to dividea t t en t ion .In discussing the development of automaticdetection w e have proposed that a n au to-matic-attention response is learned in re-sponse to the u n c h a n g i n g m e m b e r s of thememory ensemble . The present study willtest this hypothesis. The test ( E x p e r i m e n t4 d) will enta i l asking the sub jec t to igno recer ta in loca t ions and then inser t ing in thoselocat ions i tems that sub jec t s ha d been pre-viously t r a ined to re spond to a s CM ta rge t s( to see whe the r these t a rge t s a t t r ac t atten-t i o n ) .These studies will also answer the followingques t ion : T o wha t degree can the sub jec tfocus at tent ion on a specified subset of thei npu t s wi thou t d i s t r ac t ion f rom th e r e m a i n -in g ( i r re l evan t ) i npu t s . Such s tud ies a reusua l ly t e rmed focused-attention studies, incon t ra s t to the studies of Part I and Experi -m ents 1 to 3 of the present ar t ic le , studiesthat would be appropr i a t e ly t e rmed divided-

attention studies,A . Terminology

There is a problem of terminology in thestudies of this section that is best solved byth e introduction of the following definitions:1. A foil re fe r s t o any i npu t that appears in

a to-be- ignored display loca t ion, whereas adistractor refers to a non ta rge t that appearsin to-be-at tended display location.2 . A C M foil is a foil t h a t h as previouslybeen used in CM t ra in ing a s a memory-se ti t em .3 . A C M target foil is a CM foil that wouldhave been a t a rge t r equ i r i ng a posit ive re -sponse if i t had appea red in a to-be-at tended


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146 R I C H A R D M. SHIFFRIN A N D W A L T E R S C H N E I D E R100

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I SPAC ING OF 2 T A R G E T S |NUMBER OF TARGETS

Figure 8. D a ta f rom E x p e r i m e n t 4 a . Es t imated per -centage of detection as a func t ion of number an ds pa c ing o f ta rgets i n a V M proc edure w i th f r a m e t imeequa l to 200 ms ec . T he spac ing 0 points a re n o n -ide n t i ca l ta rgets , whi le th e spac ings of 1, 2 , and 4 areide n t i ca l ta rgets . (F = f r a m e size.)display locat ion (al though i t appears in f ac tin a to-be-ignored display l o c a t i o n ) . It is am e m b e r of the cu r r e n t me mory s e t .4 . A V M foil is a foil t ha t has previous lyserved as both a t a rge t and d i s t rac tor in VMcond i t ions .

5. A VM target foil i s a V M foil that wouldhave been a t a rge t r equ i r ing a posi t ive re-sponse if i t had appeared in a to-be-a t t endeddisplay locat ion. I t i s a member of the cur-r e n t m e m ory s e t.6. Valid posi t ions or cha r a c t e r s a re to-be-attended positions o r characters . Invalidposi t ions or characters are to-be-ignored posi-t ions or characters .7. FII denotes a t r ia l in w hi ch tw o ident i ca lmemory-se t i t ems appear , one in a to-be-a t -t ended display posi t ion, and one in a to-be-ignored display posi t ion.8 . FN I d e no t e s a t r ia l in which tw o d i f -fe re n t memory-se t i t ems appear , one in a to-be-at tended display posi t ion, and one in ato -be- ignored posi t ion.B . Focusing Attention in a V M Multiple-Frame TaskThe first s tudy in the present ser ies ofe x p e r i m e n t s is designed to show t h a t "con-trolled search" i s not a misnomer , that sub-jec t s can cont ro l the i r sea rch to the exten tt ha t V M foils can be igno red , and t h a t searchcan be carr ied out through the val id display

posi t ions without decrement caused by thefoils.1. M et hod

T h e pa r a d igm ut i l izes th e mult ip le- ta rget , mul t ip le-f r a m e V M procedure . T h e r e a re three m a i n c on-ditions: (a) M = 2, F = 2; (b) M = 2, F = 4; (c)M = 2, F =4, diagona l . Condi t ion (c ) , denoted"diagona l ," was des igned so t h a t one of the di-agona ls of the display w as always valid (to-be-a t t ended) , an d t he other d iagona l w a s a lways in -va l id ( to -be - igno red) . In this condi t ion four c h a r -ac ters were presented on each f rame, two valid,and two inva l id foils. We expec ted that this diagonalcon di t i on would e l ici t perfo rm an ce s im ila r to thatfo r th e M = 2, F = 2 c o n d i t i o n , a n d b e t t e r t h a nthat of the M = 2, F = 4 c ond i t ion .T h e f o u r subjects in this s tudy were the sameas those used as in E x p e r i m e n t 3 of Part I. Inth e diagona l condi t ion , only the upper- lef t andlow er - r igh t f r a m e pos i t ions ever conta ined a t arget .T he sub jec t s were fully ins t ruc ted regarding thisf ac t a n d were ins t ruc ted to ignore th e invaliddiagona l . For each subjec t , the blocks of t rialsu t i l i z ing th e dia gona l p roc edure w ere ru n a f t e r th eo the r c ond i t ions w ere c om ple ted . T h e M = 2, F = 2con di t i on had 14 bloc ks per s ubjec t ; th e M =2,F = 4 c ond i t ion ha d 11 b loc ks pe r s ub jec t ; thediagon a l con di t ion had 16 blocks per subjec t , the

first 4 of which were prac t ice blocks . There w e r e12 0 tes t t r ia ls per block , p lus an addi t iona l 30trials of prac t ice for the first block of a session a n d15 tr ia ls of pra c t i c e fo r each subsequent block ina session.The procedure used in th is s tudy differed some-w h a t from tha t of P a r t I /Exper im en t 3 a nd fromthe o ther mul t ip le- ta rget tasks repo r t ed in thisar t ic le . The p r i m a r y difference lay in the relat ionof t a rge t s imila r i ty to spac ing . The spac ing 0 con-di t ion u t i l ized NI targets only , and the spac ing 1 ,2 , an d 4 condi t ions u t i l ized II t argets on ly . Inaddi t ion , th e present exper iment a l lowed t argets toreoccur in the same f rame pos i t ions i f they were n o tin successive frames. Also, in the present study, th esubjects p u s h e d a s ingle response but ton each t imethey thought they detec ted th e ta rget . T h e responsesw ere to be ma de w hen the t a rge t s appeared r a the rt h a n at the tr ia l 's end.2 . Results and Discussion

O n a b o u t 1% of the t r ia ls in each condi t iona response w a s m a d e before the t a rge t a p-peared, an d these respon ses were not cou nted.T he resul ts a re presen ted in F i gure 8 . Theresul ts of the F = 2 and diagona l con dit ionsobviously do not differ, but results of bothcondi t ions are c lear ly superior to those of theF = 4 co ndi t ion . These resul t s were expec tedon the supposi t ion t h a t the subject should


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P E R C E P TU A L L E A R N I N G A N D A U T O M A T I C A T T E N D IN G 147have been able to cont rol h is processing inthe diagonal condi t ion so that compar i sonswould occur on ly for the cha rac t e r s on thevalid diagonal .The pecul iar re la t ionship of spacing totarget s imi lar i ty in th is s tudy caused th eshape of the spacing func t ions to appear todiffer f rom those in prev ious mul t ip l e - t a rge tstudies. In f ac t , however, the correspondingpoints from th e present s tudy a n d Part I/E x p e r i m e n t 3 a r e quite close in va lue . It isi n t e re s t i ng to no te the sub jec t ' s comment sa t t he end of the expe r im en t . They no t i ceda n e xc es s n u m b e r of II con di tions overa l l, bu tn o n e not iced that the I I pairs we r e n o t testeda t spac ing 0 , no r that th e NI pa i r s were n o ttested a t the longer spacings.Th e im pl ica t ion s of th is s tudy are s t ra ight -fo rw ard . Subjec t s c a n cont rol the i r search inV M situations at least to the degree thatcompar i sons can be l im i t ed to a specifieddiagonal . It is possible that cha rac t e r s on t heinva l id diagona l a re so m e tim e s c o m p a r e d , bu tn o t u n t i l th e val id diagonal is searched first(i f t i m e we r e t a k e n to c o m p a r e foils d u r i n gthe search of the val id diagonal , then per-f o r m a n c e wo u l d b e w o r s e ) . O f course, thiss tu d y d e m o n s t ra t es o n l y a m i n i m u m a m o u n tof sub jec t con t ro l . In f u t u r e studies i t wouldbe desirable to explore th is m at ter m orethoroughly. For example, we might ask:C a n search alternate between diagonals insuccessive f r a m e s ? C a n search order be cuedind iv idua l ly fo r each f r a m e ?

C . Distraction Caused by "Targets"During VM SearchE x p e r i m e n t 4 a showed n o dist rac t ing effectof V M foils (on the i nva l id d i agona l ) . H ow-ever , n o n e of these foils was in f a c t iden t i ca l

to any m e m b e r of the memory se t . Thepresen t s tudy , then , is designed to d e t e r m i n ethe dis t r ac t i ng effect of VM t a rge t foi ls: T owh a t e x t e n t c an m e m b e r s of the m e m o r y se tbe igno red w hen they appea r in inva l id dis-play loca t ions?1. Method

The paradigm i s s imi lar in genera l out l ine tot ha t of the VM con di t i on s of P a r t I/Experiment 3 .

gHOUJHUJ01 UJc c\-\-UJo:UJ

IUU

90

80

70

en

-*v 0 Q 0

N. /V oo FIIFNI

i i i i-I + 1 +4NUMBER OF F RA MES F ROM T A R G E T

TO FOILFigure 9. D a t a from E x p e r i m e n t 4b. FII = t a rge tfoil ident ical to t a r g e t ; FNI = t a rge t foil noniden t ica lto t arge t. P ercen tage of ta rge t de tec t ion as a fun ct ionof th e spacing and the s imi lar i ty be tween th e targetand the t a rge t foil. Var i e d-mappi n g p roce dure s we reused, a n d f r a m e t ime w a s 200 mse c .The pecul iar i t i es of Exper iment 4a were e l iminated.T h e m u l t i p l e - f r a m e p r o c e d u r e w a s uti l ized withM = 2 a n d F = 4 . The upper- le f t , lower-r ightdiagon a l w a s valid, and the other diagonal w a sinval id. Ei ther zero or one targets appeared onthe valid diagonal , and an appropriate binary re-sponse w a s r e qu i re d . A V M task w a s uti l ized onth e valid diagonal , and the foils on the inval iddia gona l we re chose n from th e dist ractor set for theva l id diagonal . In addi t ion , there was on everytrial exact ly o n e V M t a rge t foil (i.e., a m e m b e r ofthe memory se t ) on the inval id diagonal .O n one- thi rd of the trials, only a V M target foila ppea red , a l ways on f r a mes 8-13. O n two- th i rds ofth e trials both a target foil a n d targe t appeared;on one-hal f of these trials the target and targe tfoil were identical (FII), and on one-hal f of theset r i a l s the t arge t and t arge t foil were different (FNI).Finally, th e t a rge t appeared on any o f f r am e s 8-13,and the target foil appeared eq ua l ly of ten on f r a m e s4, 1, +1, and +4 with respect to the targetf r am e . That i s , the spacing be tween the target a n dtarge t foil was systematical ly varied. Thus, theta rget- fo i l -only t rials occurred with a probabil i tyof J , a n d e ach of the other e ight condi t ions occurredwith a probability of 8 X i = A. All these trials werer a n d o m l y in te rmixed wi thin each block.Each block con ta ined 144 test trials preceded by15 pract i ce t r i a l s . Each subject ran t h r o u g h a totalof 12 or 13 blocks in f o u r sessions.2 . Results and Discussion

T he results a re shown in Figure 9 . Thef igure gives the percentage of hits a s a f u n c -t ion of the spacing between th e t a rge t a n d


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148 R I C H A R D M . S H I F F R I N A N D W A L T E R SC H N E I D E Rthe ta rge t foil , w h e n the t a r g e t foil is iden -t i ca l ( F I X ) an d n o n id e n t i c a l (FNI) to thet a r g e t . T h e co r r e c t r e j e c t i o n r a t e w h e n n ot a r g e t was p r e s e n t was 91%. The r esu l t s maybe s u m m a r i z e d br ief ly: T h e t a r g e t foil h a dn o effect on the h i t r a te excep t when i t wa sdifferent f rom th e t a r g e t (FNI) a n d p r e ce d e dthe t a rge t by 1 f r a m e , in wh ich case de tec-tion probability was decreased by .11.

In the p resen t s tudy a t a rge t foil r e d u ce dp e r f o r m a n c e w h e n i t p r e ce d e d , b u t n o t w h e nit followed, the t a rge t , Suppose that this re-duc t ion is due to the s a m e f a c t o r s that pro -duce decremen ts in multiple-target detectionin V M c o n d i t i o n s ( E x p e r i m e n t 3 , Part I ) .T h e n one t a rge t p robably inh ib i t s de tec t ionof a subseq uen t t a rge t , bu t no t o f an an teced-ent t a r g e t . That is, the r educed de tec t ion atspac ing 1 seen in the VM con di t ions o f PartI/Experiment 3 and a l so seen in F igu re 4and 6 of the presen t paper , cou ld have beencaused b y ei ther of the two targe ts ' r educ ingde tec t ion o f the o ther . The p resen t r esu l t sp rov ide some r eason to a r g u e that it is thefirst of two successive targets that reducesde tec t ion of the second.Let us a s s u m e that the d e c r e m e n t in per -ce n t ag e of detect ion of two t a rge ts i n V Mp a r a d i g m s is in f a c t a d e c r e m e n t in de tec t ionof the second target. Then it is possible toco m p a r e t h e m a g n i t u d e of the d e c r e m e n t s inthe m ul t ip le - ta rge t s tud ies ( e .g . , Exper i -m e n t 3, Part I) and the presen t s tudy . Inf a c t , t h e d e c r e m e n t s a r e m u ch l a r g e r i n t h eear l ier s tudies in w h ich a ll display locat ionsw e re valid. For example , the difference inde tec t ion be tween spac ing 1 and spac ing 4in Part I / E x p e r i m e n t 3 was 30% in the NIcondit ion and 8% in the II c o n d i t i o n ; theco m p a r ab l e d e c r e m e n t s i n the presen t s tudyare \\% and 0%. Thus a target foil r educesde tec t ion o f a t a rge t in the nex t f r a m e , b u tthe r educ t ion is m u ch s m a l l e r t h an thatcaused by an ac tu a l t a r g e t .

H ow can the p r e s e n t f indings be reconci ledwith those of Experiment 4a in which foilsdi d n o t i m p a i r p e r f o rm a n c e ? T h e p a t t e r n off indings would be explicable if the validdiagona l were a lways sear ched f i rs t and t h e n ,whenever that search finished ear ly , one orm o r e characters on the invalid diagonal were

in ad v e r t e n t l y ch e ck e d in ad d i t i o n . In thiseven t , t a rge t foils would occas iona l ly beno t i ced an d m ig h t h a r m s u b s e q u e n t d e t e c t i o nin a f ash ion s imi la r to that caused by t ruet a r g e t d e t e c t i o n . O f cou r se , th i s hypo thes isis s p e cu l a t i v e an d o th e r e x p l an a t i o n s a r eu n d o u b t e d l y ava i lab le .Whatever the exp lana t ions fo r the de ta i l sof the results, it is safe to s u m m ar i z e ther esu l t s o f E x p e r i m e n t s 4 a a n d 4 b a s fol lows:Subjec t s are ab le to con t ro l the i r sear ch inv a r i e d - m a p p i n g p a r a d i g m s . T h e d e g r e e o fthe i r con t ro l is suffic ient to e l im in a t e a n ydistracting effect of nontarget foils and toreduce the dis t r ac t ing effect of t a r g e t foilswell below the leve l caused by o ther t a rge ts .T h u s , a t t e n t i o n focus ing i s qu i te success fu l :V M foils h a v e , a t m o s t , a s m a l l d i s t r a c t i n geffect w h e n th e y ap p e a r in to -be- igno redloca t ions dur ing con t ro l led sear ch .

D . The Distracting E f f e c t of "Targets"During C M SearchE x p e r i m e n t s 4a and 4b e x a m i n e d the

ab i l i ty to focus a t t e n t i o n d u r i n g co n t r o ll e ds e a r ch . W e n e x t a s k : T o w h a t d e g r e e d oe sa t t e n t i o n focus ing affect au to m a t i c d e t e c -t i o n ? O u r p r e v io u s s tu d ie s h av e d e m o n s t r a t e dthat automatic detection is not affected byf r a m e s ize, so t h e r e w o u ld be no p o i n t incar ry ing o u t a C M c o u n t e r p a r t o f E x p e r i m e n t4a in wh ich the inva l id d iagona l wou ld con -ta in d is t r ac to r s on ly . We dec ided to ca r ry ou ta coun te rpar t to E x p e r im e n t 4b to find outw h e t h e r a C M t a r g e t foil w o u ld i n t e r f e r ew i th au to m a t i c t a r g e t d e t e c t i o n o n t h e v a l iddiagona l .M a n d F w e r e se t e q u a l to 2 . D u r in g e achf r a m e , e ach d i ag o n a l co n t a i n e d o n e m as k an don e ch a r ac t e r . O n e d i ag o n a l w as a lw ay sva l id , th e o ther inva l id . O n every t r i a l a C Mt a r g e t foil ap p e a r e d o n t h e inva l id d iagona lin exact ly o n e f r a m e . A C M t a rge t appearedon the val id d iagona l o n tw o - th i r d s of thetrials; on one-half of these trials the targetan d t a r g e t foil were iden t ica l (FII) an d o none -ha l f , n o n i d e n t i c a l (FNI). In each o fthese cases , the target foil o ccu r r e d e i t h e rfour f r ames be fo re , i n the s a m e f r a m e w i t h ,o r fou r f r ames a f te r the target (-J probability


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PERCEPTUAL L E A R N I N G AND A U T O M A T I C ATTENDING 149each). There w ere 162 tr ia ls per b lock an d 6blocks per each 1-hour session. Two sessionswere run with f r a m e t im e eq u a l to 60 msecand two sessions were then run with f r amet ime eq u a l to 30 m sec .T he resul ts a re shown in Table 2 . Theon ly s ign if ican t effect wa s a slight drop inp e r f o r m a n c e ( a b o u t 4%) i n the FII condit ionat / = 60 msec wi th s imul taneous t a rge t andfoil (0 = 4 . 4 5 , p < . Q O Q l ) ; p e r f o r m a n c edropped considerably when / dropped to3 0 msec , but all cond i t ions became roughlyequal .

The resul ts of th is s tudy demonstra te thata t a rge t foil hinders detec t ion of an iden t ica ls imul t aneous ta rget . T he m a g n i t u d e of theeffect is sma l l , but so is the m a g n i t u d e ofth e decremen t that occurs when tw o simul-taneous CM ta rgets a re p resen ted . In f ac tthese d ec r em en t s a re no t m u c h different a tthe e q u i v a l e n t f r a m e t im es (4% vs. &%).It seems reasonable to a s su m e that th e s a m eme chan i s m is caus ing bo th effects.4It is i n t e r e s t i n g to c o m p a r e t h ese f indingsto those of Eriksen and Eriksen ( 1 9 7 4 ) . Inour t e rmino logy , they used a s ingle- f rameC M task with M 2, F = 1, and they usedreac t ion t im e a s the depe nden t m easure .However , the distractor set and the m e m o r yensemble were bo th of size 2 and were con-sis tent ly mapped across t r ia ls , so th a t a nequal ly s trong but opposi te tendency to auto-matica l ly respond to the m e m b e r s of the twosets wa s prob ably learned. (In our CMstudies, only the m em o r y -se t it em s ca n c o m eto elicit automatic responses, because dis-t rac tors a re presented on every t r ia l . Theonly exception in our studies occurred whenF = 1 in the s ingle- f rame parad igm of Pa r t I ,an d even then the dis trac tor set was a lwaysla rger than the m em ory se t .) I n the Eriksena n d Eriksen s tudy, th e re levan t i t em a lwaysappeared directly above the fixation point,bu t th ree inva l id i tems were p laced on eachside of the r e levan t i t em. T he n a t u r e an ddistance of these inval id i tems were var ied.W h e n the dis tance to the nearest i tem reached1 of visual angle, th e inva l id cha rac ter s hadl i t t le effect on r eac t ion t ime. A t closer dis-tances, a ll reaction times were slowed, butf lank ing distrac tors produced th e greatest

Tab le 2E f f e c t of Distraction on A utomaticDetection: Experim ent 4c

V a r i a b l eSession 160-msec f r a m e timeFIIFNIFIIFNIFIIFNISession 260-msec f r a m e t i m eFIIFNIFII

FNIFIIFNISession 33 0 - ms e c f r a m e timeFI IFNIFI IFNIFIIFNISession 430-msec f r a m e t i m eFIIFNIFI IFN IFIIFNI

S p a c i n g( t a r g e tto foil)

-4-400+4+4

-4-4

00+4

+4

-4-4

00+4+4

-4-400+4+4

% h i t s

91.994 .289.495.696.195. 1

9 5 .493.590.793.892.895.6

7 5 . 779.174 .57 7 . 677.180.1

77 .378 .980.381.07 8 . 778.2

% c o r r e c tr e j e c t i o n s90.0

91.2

7 5 . 2

71.5

Note. FII = t r i a l in w h i c h two i d e n t i c a l m e m o r y - s e t itemsappear, one in a t o - b e - a t t e n d e d d i s p l a y p o s i t i o n , and one in at o - b e - i g n o r e d d i s p l a y p o s i t i o n . F N I = t r i a l i n which two di f -f e r e n t m e m o r y - s e t items a p p e a r , one in a to-be-attended posi-t i o n , and one in a t o - b e - i g n o r e d p o s i t i o n .slowing (s ince they au toma t ica l ly p roduced acompe t i ng r e s pons e ) ; f lank ing cha rac ter stha t were no t d is t r ac to r s o r memory-se ti tems produced a m o d er a t e slowing ( r ega rd-

4 T h e results in Table 2 give some indicat ionsthat the disrupting effect may change with practice.O v e r th e f o u r sessions, th e dif fe rences be tween F IIa n d FNI at spacing 0 was, respect ive ly, 6 .2%, 3 .1%,3.1%, and .7%. If this trend actually exists, it maybe caused by the development of a new automaticresponse that restr icts search to the valid diagon a l .That is , pos i ti on -spe c if ic i n f o r m a t ion m igh t gove rnth e au tom a t i c - a t t e n t i on r e spon se ; such a n auto-mat ic process could be learned because th e val iddiagonal never changes over t r ia l s . It w o u l d bein te res t ing in f u t u r e invest igat ions to com par e pe r -f o r m a n c e in th is condi t ion with p e r f o r m a n c e in acondi t ion that al te rnates th e valid diagon a l f romtrial to trial, since alternation should prevent thelong-term learning of posit ion-specific enc oding .


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15 0 R I C H A R D M . SHIFFRIN A N D W A L T E R S C H N E I D E R90

oLUr~ 80LUQ

cr

L UoO LLU0.

70

60

50

NO FOIL-

-I 0 + 1NUMBER OF FRAMES FROMT A R G E T TO FOIL

Figure 10. Data from E x p e r i m e n t 4 d. Percen tage oft a rge t detec t ion in a va r i ed-mapping procedure as afu nc t i o n of the spacing b e t w e e n th e ta rget and thet a rge t foil, when subjec ts ha d previous ly been t r a inedto respond to the foil a s a cons i s t en t -m apping t a rge t .F r a m e t i m e was 200 msec .less of their v isual s imilar i ty to e i ther set) ,and f l ank ing t a rge ts , whe ther iden t ica l o rnonidentical , p roduced the least slowing( s ince they au tomat ica l ly p roduced a c o m -pa t ib le r e s pons e ) .B o th th e Er iksen a n d Er iksen ( 1 9 7 4 )s tudy a n d o u r s tudy suggest that C M t a rge tfoils c a n n e i th e r be exc luded f rom process ingn o r p r e v e n t e d from affec t ing p e r f o r m a n c e . Inad d i t i o n , h o w e v e r , th e Er iksen a n d Er iksenresul t suggests that th e spatial con f igu ra t ionof t h e i n p u t s c an d e t e r m in e t h e m ag n i tu d eof these effects (see Footnote 4 for a discus-sion of loca t ion - spec i f ic au tomat ic d e t e c t i on ) .

E . The Distraction of Controlled Searchby Automatic DetectionCon tro l led sear ch depends o n a n a p p a r e n t l yserial process that should easily be dis tu rbedif an au to m a t i c - a t t e n t i o n r e s po n s e o ccu r sth a t d r aw s a t t e n t i o n to an inva l id loca t ion .Such a r a t iona le sugges ts a parad igm fo rour nex t s tudy in wh ich CM foils appear onth e inval id diagonal while a contro l led searcho ccu r s on the val id d iagona l .This s tu d y is probably th e m o s t i m p o r t a n tin this series (4a-4d) because it provides a

test of the hypothesis that a n au to m a t i c -at ten t ion response to consis ten t ly t ra inedta rge ts is l ea rned .1. Method

E a c h f rame conta ined 4 charac ters . The upper -left to lower - r igh t d i agona l w a s val id. Memory-setsize was 2, and the VM condi t ions were ut i l ized.Search on the val id diagonal was for consonan t sin c o n s o n a n t s (o r digits in digits fo r other sub-j e c t s ) . The foils on the inval id diagonal werechosen from th e dis t rac tor set used for the validdiagonal , excep t for the CM foil. W h e n a C M foilappeared it was chosen from the set tha t had servedas the CM memory ensemble in all previous studiesfo r tha t subjec t . Thus , if consonants were beingused on the val id diagonal , a C M foil w o u l d be adigit, an d vice versa.O n one-s ixth of the tr ials , neither a ta rget nor aC M foil appeared; on one-s ixth of the tr ials onlya t a rge t appea red; on one- s ix th of the tr ials onlya C M foil and no t a rge t appea red; on one-hal f ofth e t r ia ls both a t a rge t and a CM foil appea red ,with the spacing between them equal ly likely tobe 1 , 0, +1. Each block of trials conta ined 144test tr ials . The first block of each session had ISprac t ice t r ia ls and the o ther thre e blocks had 5pract i ce tr ials . T w o sessions were run for each ofth e fo u r subjec ts ( the same subjec ts a s those usedin E x p e r i m e n t s 4a-4c . ) The f r ame t ime was 200msec .2 . Results and Discussion

T he results a re shown in F ig u r e 10. Eachpercen tage is based on 7,68 observat ions .W h e n n o C M foil or targe t appea red thefalse a l a r m r a t e w a s 4%. W h e n o n ly a C Mfoil appeared the fajse a l a r m r a t e w as ag a in4%. T h u s , i n the absence of an ac tua l t a rge tthe presence of a CM foil caused no in creasein false alarms. Since the appearance of CMfoils was highly correlated with the ap-p e a r an ce of targets , on e might have supposedthat a bias or guessing s trategy would a r ise ,such that subjec ts wou ld more o f ten guessthat targets w ere presen t i f a CM foil w a sseen. The presen t data argue aga in s t such abias (as do the data discussed below).The h i t r a te when a t a rge t b u t n o C M foilw as presen t w a s 84%. T h e dis tract ion causedb y a C M foil m a y b e d e te r m in e d th r o u g hco m p a r i s o n w i th this p e r f o r m an ce l e v e l .W h e n t he CM foil preceded th e t a rge t b y o n ef r a m e the hi t r a te w a s & 2 < f c , n o t s ign i f ican t ly


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P E R C E P T U A L L E A R N I N G A N D A U TO M A T IC A T T E N D I N G 151lower than the 84% base r a te . When th eta rget and CM foil we re presented s im ul-taneously, the hit ra te dropped to 62%. A n dw he n the CM foil followed th e t a rge t by onef r a m e the hit rate rose to 7 7 % , a figure stillsignificantly lower s ta t ist ica l ly than the 8 4 %hit rate w h en n o C M foil w as presen t . Inshort, a CM foil provides little hindrance tothe detec t ion of a VM target presented inth e fo l lowing f rame, great ly hinders detec t ionof a VM ta rget p resen ted s im ul taneous ly , andeven reduces s l ight ly th e detec t ion of a VMta rget presented in the preced ing f r a m e .The simplest in terpreta t ion of these re-sul ts i s tha t a CM foil in ter rup ts the ongoingcontrol led search and causes a loss of process-in g t ime, thereby reducing ta rget detec t ion.The in ter rup t ion i s c aused by w ha t w e havet e rme d an au toma t ic - a t ten t ion r esponse tothe CM foil. W e have a rgued tha t sub jec tshave been t r a ined to r espond to CM ta rgetswith an au toma t ic - a t ten t ion r esponse . Evenwhen such a ta rget appears on a to-be- ignoreddisplay diagonal , it apparent ly causes an a t -tention response that i n ter rup t s processinga long the va l id diagonal and direc ts a t tent ionto the inval id diagonal . The t ime lost beforea t tent ion is returned to the va l id diagonaland the search is resumed causes a consider-ab le dec remen t in p e r f o r m a n c e if the ta rgetis in fact on the val id diagonal dur ing thatf r am e .Since ta rget detec t ion in a f r a m e followinga C M foil i s not hindered , the recovery fromth e distrac t ion caused by a C M foil m u s t bequi te r ap id ; t h a t is , r ecovery m us t t ake p lacein a t ime per iod under 200 msec . Fur ther -more , t h e a u to m a t i c - a t t en t i o n r e sp o n se m u s toccur fa i r ly rapidly, s ince a C M foil evenreduces detec t ion of a t a rge t in the preced ingf r ame . Perhaps th e processing of one f r a m eoccasionally overlaps the start of the nex t ;fo r example , a compar i son in i t i a ted bu t no tcomple ted before t e r m in a t i o n of a f r a m e m aybe completed before controlled processing ofthe nex t f r am e begins . Occa sionally , a ta rgetm i g h t be the cha rac ter u ndergo in g com pari -son w h en th e subsequen t f r a m e begins , an da C M foil in that n e x t f r a m e cou ld in ter rup tcompar ison of the t a rge t an d t h e reb y im p a i rp e r f o r m a n c e .

The pr imary f ind ing of the p resen t s tudyis the d em o n s t r a t i o n that the responses toC M targets a re both well l ea rned and au to-m a t ic . CM ta rgets canno t be ignored , evenwhen they a re known to be i r r e levan t andoccur in consistently invalid display loca-t ions and even when sub jec ts a re ins t ruc tedto ignore them.O ur resul ts , of course, do not establishthat it is impossible to control th e detectionprocesses t h a t w e have labeled "automatic."In f ac t , Sper l ing (Note 1 , N o t e 2) has re-por t e d some f indings that do tend to showthat a t l ea st some am oun t o f con t ro l oversome aspects of the search process i n CMm u l t i p l e - f r am e tasks is possible. However,th e degree of con t ro l over , and the abili ty toignore, s t im u l i t h a t subjec ts have beent r a ined to see a s t a rge ts in CM s i tua t ionsa re c lea r ly much less than in VM s i tua t ions .T h u s , for the process ing mode i n the CMcondi t ions of the present tasks, w e preferthe possibly s l ight ly inaccura te, but de-scriptive, term automatic to the logicallym o r e accurate, but less descriptive, termsystemic, w h ic h w a s used in Shiffrin ( 1 9 7 S a )to refer to the same type of processing.

F . Limitations on the Ability toFocus AttentionThe present series of studies (4a-4d) ex-amined the subjec ts ' abi l i ty to focus a t t en -t i o n . E x p er im en t 4 a showed t h a t a t tent iondur ing controlled search could be focused on

specified spa t ia l loca t ions . Exper imen t 4bshowed that th e focus ing is not complete,because cer ta in types of s t imul i in to-be-ignored loca t ions are sometimes processedan d when processed, can reduce ta rget detec-t i o n . E x p er im en t 4 c showed that a C Mt a rge t in a to-be-ignored location hindersau toma t ic dele t ion by a sma l l amoun t . Ex-p e r i m e n t 4 d showed t h a t a t ten t ion is grea t lydistrac ted from the relevant loca t ions whena C M ta rget appears in a to-be-ignored loca-t ion dur ing a VM sea rch task. This las t find-in g is par t icular ly in terest ing because thed is t r ac t ing s t imulus differs from the r e levan ts t imuli n o t only in spatial location but alsoin category.


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15 2 R I C H A R D M . SHIFFRIN A N D W A L T E R S C H N E I D E RThese findings are p a r t i c u l a r l y i m p o r t a n tb e cau s e p r e v io u s d e m o n s t r a t i o n s of difficul-t ies in f o cu s in g a t t e n t i o n h av e u s u a l ly u t i l iz e dincompat ib le r esponses . That is, a s t i m u l u sin response to w h i c h a s u b j e c t has been trained

to e m i t response x is presented in a to-be-i g n o r e d l o ca ti o n i n co n j u n c t i o n w i th a s t im u lu sr e q u i r i n g a response y that is i n co m p a t ib l ew i th x. In the Stroop Color-Word I n t e r -f e r ence Test ( 1 9 3 5 ) , fo r e x am p le , th e sub-jec t m us t r ead nam es o f co lo rs that a rep r in ted in ink co lo r s that do no t co r r espondto the names . Reading speed i s g rea t ly s lowedin th is case ( see Jensen & R o h w e r , 1 9 6 6 ) .Keele ( 1 9 7 2 ) showed that d e c r e m e n t s i np rocess ing s t imu l i r esu l ted when a s imi la rcolor-name i n c o m p a t i b i l i t y w a s p r e s e n t . T h eEr iksen a n d E r ik s e n ( 1 9 7 4 ) s tudy d iscussedabove also showed that r esponse t ime w a sd e p e n d e n t on the co m p a t ib i l i t y of responsesb e t w e e n s t imu l i to be a t tended to and thoseto be igno red .M an y o th e r e x am p le s o f this k ind can bef o u n d i n t h e l i t e r a tu r e , b u t o u r d e m o n s t r a -t ions differ i n o n e v e r y im p o r t an t r e s p e c t .N am e ly , t h e d i s t r a c t i n g s t im u lu s i n o u r s t u d -ies hurts per fo rmance even though subjectshave been t r a ined to r espond to i t in exac t lyth e s a m e wa y a s t o t h e target s t imu lus . Bo thtypes o f s tud ies demons t r a te that the to-be-ignored s t imu lus r ece ives p rocess ing , bu t thes tudies u t i l i z ing in compat ib le r esponses don o t demons t r a te any p rocess ing in te r ac t ions h o r t of the moto r r esponses themse lves . O nth e o t h e r h a n d , o u r s tudies suggest that th ef o c u s e d - a t t e n t i o n deficit r esu l t s f rom a di-vers ion o f a t t e n t i o n a n d a n a c c o m p a n y i n gloss of process ing t ime , s in ce there i s no re-s p o n s e i n co m p a t ib i l i t y .

O u r s tud ies have shown that f o cu s e d - a t -t e n t i o n defici ts c a n ar ise due to dis t r ac t ionb y e i t h e r C M o r V M i t e m s in ap p r o p r i a t ec o n t e x t s , though p robably due to r a ther d i f -f e r e n t m e ch a n i s m s i n th e tw o c a s es . In m an ys tud ies in the l i t e r a tu re that h av e s h o w nfocused-a t t en t ion defici ts , i t is no t c lear whichf a c t o r is responsible . F o r e x am p le , in s h ad o w -in g t asks th e l i s tener r epea ts a loud a desig-na ted message (usua l ly in one ear ) wh i leo t h e r dis t r ac t ing messages a re a lso p resen ted .T h e ear ly s tudies showed that dis t r ac t ing

m e ss age s b a r e ly h a r m s h ado w in g p e r f o r m an cew h e n they a re d is t ingu ishab le by an obv iousphys ica l cha r ac te r i s t ic ( such a s spatial o r i g i n ;see C h e r r y , 1 9 5 3 ; C h e r r y & T ay lo r , 1 9 5 4 ) .These s tud ies a r e p robably l ike ou r Exper i -m e n t 4a in which one diagonal is relevantd u r in g V M s e a r ch an d th e o th e r c an b eignored . A r e s u lt r e l a te d t o E x p e r im e n t 4 bc a n b e f o u n d in s tud ies by Tre isma n (1964 a ,1964c) in w h i c h i t e m s of some possiblere levance a re presen ted in the nonshadowedear ( s imi la r to ou r target fo i l s ) . F o r e x am p le ,if the dis t r ac t ing message i s in the s a m evoice, but in F r e n ch , a considerable dis trac-t ion occu r s . Many s tud ies have shown thatthe message in the n o n s h ad o w e d ear i s an -alyzed to som e con siderable depth (e .g .,Lewis , 1 9 7 0 ; T r e i s m a n , 1 9 60 , 1 9 64 b ) . Inthese s tudies i t is no t c lear wh ich typ e ofprocess ing causes th e analysis, but in o thers tud ies it is clear that au to m a t i c p r o ce s s i n gis responsible for the analysis that occu r s( C o r t e e n & W o o d , 1 9 7 2 ; V on W r i g h t, A n d e r-son , & S t e n m a n , 1 9 7 5 ) .F ur th er rev iews of such s tudies wil l no tbe u n d e r t ak e n h e r e b e cau s e of the difficultyin ascertaining whether focused-at ten t iondefici ts a re caused by con t ro lled p rocess ing o finva l id i t e m s or by au to m a t i c p r o ce s s i n g ofinva l id i t e m s . 5 I f no th ing else , our resu l tss trongly suggest that f u t u r e research onfocused a t te n t io n shou ld in c lude con t ro ls todi f fe ren t i a t e defici ts caused by contro l led a n dau to m a t i c p r o ce s s i n g .In s u m m a r y , w e have seen that subjec tsc a n d iv id e a t t e n t i o n a lm o s t w i th o u t defici tw h e n au to m a t i c d e t e c t i o n is u t i l ized (Part I/

6 C o n t r o l l e d process ing m i g h t be given to oc-cas ion a l i n p u t s in an i r r e l e van t e a r , be cause ear oforigin is a fa i r ly difficult cue to u t i l i z e ( c o m p a r e dw i t h spa t i a l l oca t i on in a vi sua l t a sk , fo r e x a m p l e ) .W h e t h e r a u t o m a t i c process ing or c o n t r o l l e d p r o c -essing is use d to r e s t r i c t an a l ys i s to the desired ear,occas ion a l fa i lures of select ion are to be e x p e c t e d ,fa i lures t h a t will cause occas ion a l i t e m s in the t o -be -ignored ear to be given con t ro l l e d process ing . Inaddi t ion , 'Control led proce ss i n g of i t e m s in the to-be-i gn or e d e a r m a y o c c u r on occas i on whe n p roce ss i n gof th e i t ems in the valid ea r is comple ted and abrief i n t e r v a l occur s before th e n e x t va l i d i n pu ta r r ive s ( an a rg um e n t s i mi l a r to t h i s i s used i n t hediscussion of E x p e r im e n t 4 b ) .


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P E R C E P T U A L L E A R N I N G A N D A U T O M A T IC A T T E N D I N G 15 3E x p e r im e n t s 1 and 2 , CM condit ions , seeFigu re 2 ) and can no t d iv ide a t ten t ion wi th -o u t defici t when contro l led search is u t i l ized(Part I /E x p e r im e n t s 1 an d 2 , V M co n d i ti o n s ,see F igu re 2 ) . Focused-a t ten t ion deficits a requ i te subs tan t ia l when caused by au tomat icresponses to to-be- ignored i tems (Exper i-m e n t 4d and F ig u r e 10) but are qu i te a bitsmal le r w h e n caused by contro l led process ingof to-be-ignored items, since the subjects'con t ro l i s u sua l ly adequa te to p reven t suchprocess ing (Exper imen ts 4a and 4b, andF ig u r e s 8 a n d 9 ) . O n e im p l i c a t i o n is the p r e -diction that the type of training procedures,V M o r C M , will dete rmine whether d iv ided-o r f o cu s e d - a t t e n t i o n defici ts wil l occu r .

G . The Nature of Automatic DetectionThe r eversa l s tudies , Ex per im en ts 1 and 2,

and the ca t e g o r y s tu d y , E x p e r im e n t 3, m a k eit c lear that long - te rm learn ing is responsiblefo r th e phenomenon of automatic detect ionthat is seen in the CM condi t ions . T h e l e n g th yt r a in ing per iod r equ i r ed fo r acqu is i t ion , a n dthe even longer t r a in ing per iods r equ i r edto al ter the detect ion process once learned,tes t i fy to the p e r m a n e n t n a t u r e of the l ea rn -i n g . F u r th e r m o r e , t h e p h e n o m e n o n i s p o w e r -fu l enou gh to t r an scend the l a bo ra to rycontext . Subjects g iven C M tr a in i n g ono n e group of letters as memory - se t i t ems wi thano ther g roup as dis tractors , as in Exper i-m e n t s 1 an d 3 , re p o r t effects o n r e ad in g o u t -side the laboratory . Despite the f a c t that allthe letters used in the exper iments werecapi tal ized, the subjec ts r epo r ted that them e m o r y - s e t i t e m s f rom t h e C M cond

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