Attending to an object's color entails attending to its location: Support for

Perception

& Psychophysics

2000, 62 (5), 960-968

Attending to an object's color entails attending to its location: Support for location-special

views

of visual

l~

le~

attention

~;~:~.

fects.Ts YEHOSHUA Tel Aviv Van der Heijden,

Kurvink,

TSAL and DOMINIQUE LAMY University, Tel Aviv, Israel

de Lange, de Leeuw,

and van der Geest (1996) argued

that the results

Experim letterwa Inare (1996) (

sup-

porting the location-special view obtained by Thal and Lavie (1988) were due to uncontrollable shifts of fixation, rather than reflecting the properties of the attentional system. In the present study, we present an improved variation of the Tsal and Lavie (1988) paradigm and reassert our claim that location is a special dimension. Subjects were presented with circular arrays of six letters of different colors. Three of the letters were enclosed by (Experiment 1) or superimposed on (Experiments 2, 3, and 4) different colored shapes. The subjects were instructed to report the (target) shape with a given color (e.g., report whether the re~ shape was a square, ~ circ.le, or a trian~le) and then either freel~ report letters from the array (Expenments 1, 2, and 4) or Identify a prespecified target letter (Expenment 3). In all four experiments, performance was substantially better for the letter that appeared in the location of the to-be-reported

shape (location

clude that attending

letter)

to the stimulus

color

than for the letter entails

directing

that shared attention

its color

(color

letter).

deed prG results (! f;v~te th j rep leu;rs. J der l( ~n

d tl

orce . In the

We con-

t~ated tl

to its location.

dJen et I onlyshf then re~

The special

status

of stimulus

location

in visual

selec-

(e.g., Baylis

& Driver,

.1992, 1993; Duncan,

1984; Harms

exactly

tive attention has been extensively debated in recent years. As van der Heijden, Kurvink, de Lange, de Leeuw, and van der Geest (1996) have suggested, "a brief look at cur-

& Bundesen, 1983; Humphreys, 1981). For example, using the Eriksen flanker paradigm, Baylis and Driver (1992) reported that distant incompatible distractors grouped

o~her ~~ s ape to ~ppe~

rent ~eorizing c~ .make ~is cl~ar. There are two gro~p's of theones: the 'posltlon-not-speclal' ones and the 'posltIon-

w~th the t~et b~ ~olo~ or by good con~inuation.interfered with target IdentIfIcatIon more than dId closer mcompat-

~i~::s ~ .

special' ones" (p. 1224). Over the years, there has been a wide range of findings that provided support for the unique role of location in visual selection (e.g., Cave & Pashler, 1995; Hoffman &

ible distractors that were not otherwise grouped with the target. Recently, a controversy arose concerning the results obtained under a particular paradigm introdl.1ced by Tsal

t

Nelson, 1981; Kim & Cave, 1995; Luck, Fan, & Hillyard, 1993; Posner, Snyder, & Davidson, 1980; Theeuwes, 1989; Tsal & Lavie, 1988, 1993;Vecera, 1994). For exampIe, Tsal and Lavie (1993, Experiment 4) presented a cuing

and Lavie (1988) that supported the location-special view. The uniqueness of this paradigm was that it assessed the effects of attending to location when location was completely irrelevant to the task. Van der Heijden et al. (1996) ~

: I

display consisting of two peripheral disks, one black and one colored (either pink or blue), followed by a probe

showed that these results were due to uncontrollable fixation shifts and, as such, did not reflect the properties of

display containing a target letter. Subjects were told to respond to the target letter only if the colored disk was

the attentional system. The present study is an improvement on our original paradigm. It shows that even under

pink. Although the location of the disk was entirely task irrelevant, the probe was detected faster when it appeared in the location previously occupied by the colored disk than when it appeared in the location of the black disk. In contrast to the above studies, a large number of findings have provided support for the notion that location is not different in principle from other selection dimensions

and two anonymous revIewers for theIr helpful comments on an earlter

proper fixation conditions, attempting to attend to any aspect of a stimulus entails attending to its location. Tsal and Lavie (1988, Experiment I) presented a circular array containing three red, three green, and three brown letters. The subjects were instructed to report first one letter of a given color and then any other letters they could identify. The letters reported additionally were more often letters adjacent to the first reported letter (location letters) than letters with the same color as the first reported letter (color letters). Tsal and Lavie (1988) concluded that the selective processing of a target specified by its 1 . I.

draft.

c.o

This researchwas supportedby Grant 06 10710551from the israel ScienceFoundation.We.aregrateful t«:,Kyle Cave,Lex van derHeijd~n, Correspondence

concerning

this

article

should

be

addressed

h

to

Y. Tsal, Departmentof Psychology,Tel Aviv University, RamatAviv, Tel Aviv 69978,Israel (e-mail: [email protected]).

Copyright

2000 Psychonomic

Society, Inc.

or

IS

accomp

IS

d

e

b

d

.y

atten

.

.mg

h

to

t

.

IS

,

target

I

,

1

loca-

s

d

tIon. They noted that this expenment may have suffere from a methodological difficulty: "Since three of the letters

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SUPPORTFOR LOCATION-SPECIAL VIEWS OF ATTENTION

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portin~ additi?nal red letters may ha~e~eflectedeffects oft.he i?struCtionsratherthan the p~rSiStinge.ffectsof the ?ctivationof redness.In co~trast,smcelocation wastask irrelevant, effects of location could not have stemmed f~omtop-down ef!ectsof i~structio~sand c.oul~only in~icatethat atte~dmgto an item entaIledacti~at!nga sp~tial representation.In the presentstudy,we el1mmated this

Experiments 2.a~d 3, b?t in these experiments, t~e target letter was specif~ed by itS s~ape, rather than b~.its color. In a recent senes of expenments, van der HeiJden et al.

proble.m, since the color letter used.to ~ssessthe.effects of attendmg to color was not a potential Item for first-target report.

;~C ;?I~ 84. Harm ;', : :1 ie, usins,, i" v~r (199211 s groupedilc, interfered,l[:,,

(1996) de.monstratedthat improper fixation. could indeedprovidethe bestaccountfor Tsal and Lavie's(1988) results(Experiment I). They showedthat whenforced to fixatethe centerof the display,the additional letterss~bjectsreportedweremore often color lettersthan location letters.An advantagefor location letters wasfound only underlow-contrast conditions when subjects were not forcedto fi~ate the fix~tion point. . In the senesof expenmentspresentedbelow,we el1minatedthe fixation problem investigatedby van der Heidjenet al. (1996). Subjectshad to report the form of the only shapein a circular array that had a given color, and thenreport letters from the array. One of the letters had exactlythe samecolor asthe shape(color letter), andanother letter.occupied exactly the same location a~ the shape(Ioc~tionletter):The targetshapewasequallyI1kely to appearm any location. The letters,:",ereall o~differe~t colorsand were randomly presentedm the vanousPOSi-

The secondpro~l~mwith thi~ paradigmwasthat.it may not havebeensufficiently sensitivefor demonstrating10cationeffects,becauseit wasclearly dimensionallyasyrnmetrical.Indeed,the lettersincludedin.the color category wereexactlyof the samecolor asthe first reportedletter, whereasletters included in the location categorydid not occupy precisely the samelocation as the first letter reporte.d,but only positions adjacentt? .it. Thus, ?btainin.g location responsesunder thesecondItionsrequIresadditional assumptionsaboutthe shapeand size of the attentional spotlight. In the presentstudy,we eliminated this bias,s~ncethe loc.ationlett~rsused.toassessthe effect~of attendmgto locationoccupiedpreciselythe samelocation as the target item. -, Notethattheabov.ei~provementsonlyf~cilitateth~as- '-" sessment~f the pers~stingeffects0: attendm.gto locat~on. ~he paradig~ remamsstrongly biasedagamstlocation, smcethe subjecthasto attendto the color of the shapeand

f ;c' incompat" :d with thec~'

tions. T~?s, there ,:-,asno ben~fit in shifting :ixatio~ to any position or regio.1}?fthe circular a~ray pn?r to stim-

the locations o!the shapesand letters are totally irrelevant to the tas~. Still, t.he n~w results ~resented here ~upport

I-

S ~n ,. f-

"rfi" ',i'"

were alwaysrele,,:~nt,su?jects~ay haveshifted.fixation to any arra~ ~osition p~ior to.stimulu~ onset, smce any randomposition w~s hIghly li~ely to i~clude a le~t~rof the relevant color m that or m an adjacent pOSition" .17).Thus,.theresults m.ayhavereflected sen~orydifWrencesin visual ~rocessmgr~t~er.than a.ttentionale!fects.Tsal and LaVie (1988) miD1mizedthISproblem m

~

; 1'"' :" ,.

.,

~

~ f ~-

~: ~ ~

j,

'"

ulusonset.Moreover,m the last expenment,m order to

the location-special view and remforce our claim that

the results' ed by Tsal ~ ,ecialview.'f

furtherensurethat the subjectswould not shift their eyes, whenattendingto the color of a given item, subjectscanwe followed the methodology used by v.ander Heij~en not avoid attendingto its location. ~tal. to control for e.yemovements.We m.clu~eda sign 'sessedthe 'J" m thecenterof the display,the form of which mstructed EXPERIMENT 1 , was com-; :;,subject.s whetherto r~~pondor withhold.their responses. .. tal. (1996}.;,1." >liablefix- ::: 0 ertiesof : n~m rove-; evenPunder' :i to anyas"" l' tion. ':" 'nted a cir-", , and three' ~

Followingvan d~r HeiJdenet al.'s~easoD1ng, we assu~ed ,thatthe ce~tra.1item would re~uu.efoveal processmg, thusnecessitatingcentral eye fixation. . . In addition to the ~act.th~t the present.study.was designedto overcomethis fixation problem,It alsoIncluded a numberof improvementsover Tsal and Lavie's (1988) parad!g~. The origin?1 rationale was that the loc~t~on supenonty the targetwas specified by its color effect and itsobtamed locationwhen was completely irrelevant to

.In the.present~xpenme";t,t~e subjectswerepr~sented with a cucular display of SiXdifferent lettersof diff~rent colors. Threeof the letterswere enclosedby threedifferent colored shapes(seeFigure I )'. The subjectswere instructedto report the shapeof a given color (e.g., report whetherthe red shapewasa square,a circle, or a triangle) and then asmany letters as they could. One of the le!ters had the same colorThe as the target shape defmed asthe color letter. letter enclosed byand thewas target shape

the task demonstrated that a.tt~n?ingto location is a I" m~ndator,>! proces~.However,it IS I~portant to ~~te.that theY:' .le~ers weremore thIS~ar~dlgmalsomvol.vedseve!albiasesthat mmi~ized ~r(location r !heI1k~l1hood of observmglo,cation~esponses e~en1fsubrst reported",; , Jectsdid attendto the tar~et~ location. S~chbiasesmay concluded,ic acc.~unt for the color supenontyeffectobtamedby vander ified by its' HelJdenet al. (1996). r et's loca-' " The first bias concernedthe fact that the color letters v~ suffered :,: ~erepotential targetsfor first-letter report. For instance, )fthe letters;;';, ~mcethere.were three re~ letters in the array,when sub; i;"c,,;Jects were mstructedto fust report a red letter, all three , ::,;;red letterswere potential targetsand were thus likely to

wasdefinedasthe location letter. Thecritical comparison conc~rnedthe fre9ue~cyof repo~ of c?lor letters and of location I~tters.Fmdmg that subjectsmdeedtend to report location letters more fre9uently than color letters wou!d dem~nstrate~hatattendmg.to the colo: of a.shape entails that itS loc~tion, altho~gh ~rrelevant,is activated, and more so than itS color, which IStask relevant.Sucha finding would strongly support the idea that location is a specialdimension.As in the studiesof Tsal and Lavie (.1988) andVander H~ijden et al. (1996),the subjectsinitially attendedto a given color and then freely reported any letters they could. Unlike thesetwo former studies,

~e ort first!

~~:ave undergonesomelevel.ofprocessing.As a result,re-

~ ~

the location letter-namely, the letter usedto assessthe

. -_.~

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1

962

TSAL AND LAMY

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X

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had to report correctly any letters of the array, and as many as possible. Thus: the letters reported could be, but d!d not need to be, the

;'~j"

lettersshanngthetargetshape'scolor or locatIon.

~ii~

0

,;,;:"" ,

Results and Discussion

~

~

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X

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T

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Trialsin whichthe shapeof thedesignated colorwas

R fT'

n~medin.correctlywereexcludedfrom analysis(6% of the tnals). Smcethe color letter and the .locationletter were

~

enclosed byshapes, weanalyzed theresponses onlyfor

Figure 1. Examplesof the stimuli usedin Experiment 1.

i!~:~ f"i;

'

-

the neutralletterthat wasalsoenclosedby a shape,in

~

order to make the three relevant response categories di-

"!:.'~'.' p,., .'

rectlycomparable. Thus,in eachdisplaytherewereone color

letter,

one

location

letter,

and .

one

relevant

~g;;;!k,'.'

neutral .

;:~:.'~ ",",c,'

. " letter. The latter servedas a baselmefor measunngany;':""'" e.ffectsof attendmg.tolocatlon-occupled the sameloca~ facilitation resultingfrom sharingthe locationor the color (JlI t~onas~e shape.with the target color, ratherthan a loca of the target shape.Table I showsthe mean number of i!¥:,:.' tlon adjacent to It.

letters reported per trial in each category. On average, the

Method

subj,ectsreported 1.29relevantlettersper trial (excluding the Irrelevantneutral lettersnot enclosedby a shape).An ..

.

' t 8 d d t fi TIA . Su bJect 5, The sub~ec s were un ergra ua es rom e VIV University,Threewerepaid subjects,and5 participatedaspart of a courserequirement. All hadnormalor corrected-to-normal vision. Stimuli and Procedure. Stimuluspresentation anddatacollection werecontrolledby an IBM PC/ATwith a VGA graphicdisplay. A h' d b' l ' . ' d' 43

c

mrest

was

use

to

sta

I

Ize

vIewIng

Istance

at

:

andth ob,iJ ec1

overa~l analysIs of vanance (ANOYA) of letter cat~gory (location, color, or neutral) X color (red, blue, or white) X subjects revealed a highly significant effect for letter category [F(2,14) = 45.77,p < .0001]. Furthercomparisons

thesu' result; ing th " .

h

cm

so

t

at

elml!

indicated

that

location

letters

were

reported

more

fre-

,

~ cmonthedisplayco~res~ondedto 1.33~ofvisualangl~.Thesubjects werepresented WIthcIrcularletter dIsplays,EachdIsplaycon-. quentlythancolor letters[F(l ' 7).'= 37.51 p < .0005], sistedof six different letters of different colors.The letterswere This ~as.true for each of the 8 subjects (see Table 2). The randomlysampledfrom the entire alphabet.The colors were red supenonty of color letters over neutral letters was mar(RGB values,255/80/80;luminance,~I cd/m), blue (80/80/255; ginally significa?t [('(1,7) = 5.23,p = .056]. 21cd/m),green(0/160/0;32 cd/m),whIte(255/255/255;III cd/m), There was no significant effect of color [F(2,14) = 2.72], magenta (2,55/80/255; 37 cd/m),~d yellow(255/2.55/80,; ?8 cd/m). but there was a highly significant interaction effect beFor eachdIsplay,the letters,theIr colors,andtheIr posItIonswere tween color and letter category [F( 4 28) = 9 79 p > randomlypaired,Eachletter subtended1.33°in heightand0.93°in . . . . ' ., . width,andthecenter-to-center interletterdistance was5,32°of visual .000 ~], mdlcatmg that the difference between reporting

angle. The entire array subtended 9.31° of visual angle in diameter

location letters an? color letters ~as smaller when the tar-

white target shape, location letters were reported more:; frequently than color letters [F(I,7) = 7.07,p < .05] and:!: color letters were reported more often than neutral letters ~ ", [F(1,7) = 10.23,p < .05]. The above .mt~r~ctl°n.between::;;

stramtthata shape neverenclosed a letterof thesamecolor.The color and letter c.ategorywas also signIficant m all the ;~ shapeswerealwaysseparatedby one interveningletter,In half of

subsequent expenments reported below. We will address-;,

thedisplays, th~y,occupied,the topcentralpositionandt~erightand this issueby presentingadditional analysesin the Gen-J'!; left bottomposItIons,and m the otherhalf, theyoccupIedthe bott~m centerpositionand the ri¥ht an~left top positions.T.h~se two dIsplaytypeswererandomlyIntermIxed.Thus,eachpositIonwas equallylikely to containthetargetshape,andtherewasthereforeno gain in shifting fixation to any position prior to stimulus onset, Eachstimuluswas presentedfor 100msecand was immediately preceded by a graycentralfixation crosspresented for I sec,Thesubjectswereinstructedto reporttheshape(thetargetshape)C?f a given colr;>r (e,g" reportwhetherthered shapewasa square,a t~angle,or a cIrcle)andthenasmany lettersasthey could,The subjectswere presentedwith three45-trial blocks,eachprecededby 15practice trials, Dependingon block, the designatedcolor for the targetwas red,blue,or white.Theorderof blockpresentation wasrandomized acrosssubjects, Thelocationletterwasdefinedastheletterenclosed by the targetshape,The color letter wasdefinedasthe lettersharing the color of the targetshape,It wasalwaysseparated from the locationletterby oneinterveningletterandwasalwaysenclosedby a nontargetshape.All the other lettersweredefinedas neutral,It wasemphasized to the subjectsbeforeeachblockof trials thatthey

eral Discussion section. ;;, The present findings provide strong support for thet!' . .. . . ., I ' locatl~n-speclal view of'!lsual attention. Not surp?smg y,~ attendmg to the shape With the relevant color entailed that;; color letters were reported more often than neutralletters.~ More interestingly, it also entailed that location letters) were reported more often than neutral letters and even,: more often than color letters. 11bl 1 Mean Numberof Le~e~ Reportedper Trial by Letter Categoryand Color Block in Experiment1 , M LetterCategory Red Blue WhIte e Location 0.75 0.81 0.59 0.7 Color 0.24 0.31 0.36 0.3 Neutral 0.30 0.26 0.25 0,2

m.atl slight! posed in the

shape Onthl

letter.. '

h

Int e entanJ cepto tifica1

,

andwascentered onthefixationpoint,In eachdisplay, threeof the get shapewas white than when It was red O[ blue. How- j1 letterswereenclosed by threedifferentcoloredshapes: a square ever, additional comparisonsshowedthat even for the;:

(s!de=-2,53°2,a circle(diameter= 2.66°~,a~danequilate~1triangle (sIde- 3.01 ). The letter wascenteredI~sldethe e~closmgshape, Oneofth,e~eshapeswasred,blue,or whIte(dependmg on block, as was specifIed below). The colorsof five the other shapes rando~ly sampled from the remaining lettertwo colors, withwere the con-

cOm

~",.,

,.teth Sub Univer course Stin asthe1 totheI perimp

R c'i esn As the d.. clude, respo; Posed with t cTnean On te a.. rs

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SUP FO LO VI O A 9 )s1It:~; Tab 2 pe loc let w r m f e r subje Loca Colo Neu twe the fre of re co le a n h l . k h d f . I . :utrali jc"~~ fec of co [F( = 6. < .0 T i b n g any~ ,;'~:"~ twe an let ca w s [F = i colo,i )c\::c EXP 2 ~~ c. ., . , l . g t th d n h 32 II P < ber o\:~f' . ... rep l.e fro th c w ~e, thez~ One migh argu that m the first exp the lett sm for the wh ta sh fo re a luding and the surro shap form a coh per tar sh Ind ad an o Ie). An~ };: objec (Trei Kah & Bur 198 He res to re s ltegor ;;:" supe perfo for loca lette ma hav can dif be re le fr th ore fre-i:i m~tio o~ a per~ obje m the sec exp by for the wh s~ ~o w w b a in .OO0 displ the shap so that ~he wer sup Ge DI se th re o t s h Has m~f,~ first expe the. spa ~rra of the per sh ~n ev ~t lo ~),: 2.7t# 'c On the contr It e?ha t~e salie of the enc lett On ma th co th lo effect ~;~: ~ette In with the spat arra pre sup eff wa m by sp a n ). 79, p..~lc m next subj had to effo dls by ob pr repor entan shap from lette bec glob per \en the~1 c.ept pote obje they form wou imp ide EX 3 }lue, H.~'~ ufica perfo of b?th the sha and the lett ,en for:!J Th thi ex wa de to fu c orted ~~,l': Meth . . the rel co dim an th ir l o < .05) ~!l ~Ubj .The subj we~ 9 und from Tel AvI dim un mo co co O m IocatlO .It le~? UnIv ~Ive were paid subj and 4 part as par of a '. . b f ~utr~ co~~ All had no~ or ~orr visi arg tha m the firs tw ex s ~ o \on. all"'t', Stimu and Proc Thl~ expe was exa t~e sam som ~e ha ad a s. st th ~ tnt, In di~~i: i!Sthe ~rst one, with one exce All the sha wer disp fav of th l~ ~ d e ~Ill adQ;f ~e~~ nght by 1.33 As a re.su I.eft ~ide of the sha was sumg the eff at pn o t c l h t c c. . i wit ide pr ta le Th . h d . d . .. b . surp~ fIrst expe trIal ~n whi of a p~ as of st ch o t a h IT entall colo ~as nam mc? wer exten sy W u th sa d a m s ) . We ana y z ed \':,oP y for the neut lette that was sup :tters ~jfJ ';.'i~,W in ?rde to mak them com /\ :~~ 1;g;~ c~of repo per trIal m eac cat G D ,r ~ r~.36'; 1ria~ ,,;c,,! Cion m fi orm re I atlv . to ?e eri~~ ,~:1~ ~~n prob be attri to the fac tha '~;;iC if~~fi Aga the ANO reve a hig T 0 'ii:'*~ ca~e [F(2 16) = 24. < Ind t d . h h f . y s es '~k3! '!fI:&. i

" 7,ft:~r:

:he

.

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Mean Number of Letters Reported per. Trial by Subject and Letter Category in Experiment 1

-

first experiment, however,there was no difference be-

i;.,}c

LetterCategory

than color letters [F(I,8) = 26.28,p < .001].This wastrue for each of the 9 subjects (see Table 4). In contrast with the

NaS!

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';:cJI: ;~,!~~tjftf:

2 3

0.38

0.09

0.03

tralletters[F(I,8)=0.30].Inordertoaccountforthedis-

0.85 0.72

0.55 0.00

0.53 0.0 I

appearance of the color letter effect, it is reasonable to assume that the increased difficulty of the task reduced

ti ¥"!i{",c c ' ~r::I\! Ftlr,j~,Jic.:

4 5

0.71 0.85

0.48 0.43

0.38 0.46

t. e I e I 00

e, lRc; ,i~:?2\;c

6

0.60

0.09

0.06

tlon letter. As a result, floor effects may have masked the

s di-:,'~j'i;;;§~~\'c\!;;l~i;;

7

0.83

0.62

0.54

possiblesmalldifferencebetweencolor lettersandneutral

0.79

0.16

0.14

letters. The ANOVA

: one;~

:tit~t~~;b~~

etters m add Itlon .. to t h e Ioca-

0 reporting

also revealed a significant

main ef-

000 1] in dl.cat

hite) 1~ j;;c resultedfrom.o~ject-based pro~esse.s,rat~er than reflecttter cat~;;'c;;~..~.oing the superIorIty of the location dimension. In order to

categories [F(I,8) = 1.69, 1.96, and 3.03 for the differences between location and color, color and neutral, and

)ariso~!\'\c.oeliminatethis possibility,.we.disruptedthe pote~tial for-

locationandneutrallettercategories,respectively].Except

e 2). Th~,:icvo,posed onthe lettersratherthan en~losmgthem. Note that

experiment,in which the shapesand the letters were su-

\J

']c\l;,c:c shape andthelett~rwasnot likely to .dlsruptperformance. effectthan m ExpenmentI, m which the shapesenclosed

;,L."

>Ll

:.~~~,ij",nt""tl~r and location responses: T~ble 3 shows the

X

"LJ

:f:~. ;~,:'.' i,{~;~!ii~~'r~he ~ubJects ~eported only 0.64 relevantletcc~,~1al.ThI S redu t .

!.x~

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5 .

0.2 "

f,;' ;'l1i~~~P~ltlon

c.""

,,";".'C"~r.anal '!('!;;);'/~:in$:';:

of the shapes and the letters made the

Ica e

at, as m t e Irst ex-

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0

0

E

R

Figure2.Examples of thestimuliusedin Experiment 2.

'.-+0'

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e

res:,ci'"rqm the analysIs (7% of the trIals neutral,S,;' . ie 'J:':; jCr c... ponses I

d

d

provi

~n

las~s

strategic

minimize

us

t

0

met

In thepresentexperIment,the freereporttaskwasreplaced IS

.

..

I~n

;As'tn'

.i~~\:;i!

m the:o\W~~ic",: ,:,:~~§e~on the letter, as ISshown In Figure 2. :: :i~j R:es rt fo~j1"i;;""!' u ts and DISCUSS'

ppo

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TSAL AND LAMY

3

gories

LetterCategory

Red

Biue

White

Mean

Location Color Neutral

0.51 0.09 0.09

0.52 0.09 0,09

0.22 0,17 0,13

0.42 0,12 0,10

performance

letter

(I.e.,

with

~hen

appeared

that

when

it

e

er

was

the

tar~et

a color

letter the

(i.e.,

y

d

'

I was

of

letter

'

compare

location

was

equa

d

vve

the

m was

ge

"'1

f

'

entl

a

re

,

'",

Jects and

t ' a Ive

I

0

er

t oca

fi

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.

Ion

m

I

e co

or

to to

the the

d or

tt

shared

the

Id

e

ers

t er

,',

location color rt

th

0 repo

t

sugges

of the dimension

,

I

e co

b

a

designated . or shift

I

-

su color to an-

tt

or

e

e

that

t

other

Results

th

an

d

up

e

k

any

,&4",

"

.

position

outside

the

.

.

en

(

Ion.

"

the

4

.

location

supenonty

effect

was

".,

not

.

contamInated

by eye movements. Note1988) agaInthat, unlikem our prevIous stu y sa avle m t h e th ree expenmen ts d

(T

I &

.

L

'

'

. " reported '

h .

above,

the

subjects

, could

' h

I

not

benefit

' ,

.

, from

shlft-

,

mg t elr eyesto anypenp era posItionprIor to stlmuIus onset,sincee~c~positionwa~equallylikely t~ in-

er.

Method Subjects,The subjectswere 10 undergraduates from Tel Aviv University,who participatedaspart of a courserequirement,Five subjectsalso participated in Experiment 2, All had normal or corrected-to-normal vision, Sti~uli and Procedure.The ~splayswer~identicalto thosein ~xpenment2, .exceptthat ea~hdIsplaycontalne~a targetletter,H In half of thedIsplaysandU In the otherThhalf, ThIs targetletter was, b Idf k I to appearIn . anyposItIon. .. equaIIy Iley e su ~ectswereto Irst to reportthe shapeof a givencolor andthento indicatewhichtar'

'

a

.

m

EXPERIMENT

target

t th

wou

tt

0

I

,

appearIng

f

ocus

;

I

th

0 .' attend switch

InitIally need to

th

t

\%!;~ Ne

shape)

.

I ers

",c

1-

shape'scolor). Supenorperformance for the location lett

target

a location

target

,;~

'

IS .

position.

, II

'

clude the target. Stll,l, I,tmay be poss~blethat some su?Je~ts adopted an eye-shifting strat~gy m order to m~xI~lze performance on part of the trIals, In order to elImInate this possibility, in the present experiment we adopted van der Heijden et al.'s (1996) method for minimizing eye movements by having subjects respond to a sign appear-

g men th '

m

ce

t

of

th

er

. cessmg.

d e

'

spl

I

d ayan

'

requi

r

.

g fiove

-

I pro

m

Results and Discussion

UnIversItywhopartIcIpated aspa.Tt,ofa courserequIrement. All had,

the

first

two

.

experIments,

'

'0

we

excluded

.

trIals

m

ported n p < .00]

normal orcorrected-to-normal :;c Sti.mu I.I and Procedure, ThVISIon, e st.ImuII' and procedure were,den-\!!~

F(4,40, orl ' ty of

'

~

of the trIals) and Included only responses for neutral let-

jects were presented with 60 trials in each block, Second, a gray

ters that were sup~rimposed on a shape. ~able~ ~ an? 6 show the proportions of correc,t target Identification when the target letter was a location letter, a color letter, and a neutral letter.

sjgn~as now presented.in the centerof the display..It waseithera~; ~Iussign (~O%of the tnals) or an X (20% ofth~ tnals), ~he sub-;~ Jectswer~Instructedt? respond?nly on thosetnals that !n.clude.d~; the plu~sIgn~ndto.wlthhol?the~rresponses on the remainingt~-":

The

AN.oV.A,

gory

was

,

significant

that

[F(2,

18)

the =

effect

19,40,

of P