From an object-superiority effect to an object-inferiority effect with movement of the fixation point

Transcription

1 Perceptin & Psychphysics 1980,28 (4), Frm an bject-superirity effect t an bject-inferirity effect with mvement f the fixatin pint BRUCE EARHARD and ROSEANNE ARMITAGE Dalhusie University, Halifax, Nva Sctia B3H 4J1, Canada The bject-superirity effect (OSE) refers t the fact that target lines can be mre accurately discerned when part f a cube-like, three-dimensinal bject cntext than when part f a flat, uncnnected line cntext (Weisstein & Harris, 1974). Explanatins f the OSE have been based n the assumptin that it is the cnfiguratinal prperties f the bject frm, such as its three dimensinality, and cherence that are respnsible fr the effect. It is demnstrated that the OSE prduced by stimuli such as thse used by Weisstein and Harris des nt depend exclusively n cnfiguratinal variables. Evidence is presented that fixatin-pint lcatin and the amunt f line detail abut the pint f fixatin are crucial. Fr a perid f time it was believed that it might be pssible t accunt fr frm perceptin in terms f a hierarchical, feature-analyzer system alng lines suggested by Selfridge (1959). Physilgical studies prvided clear evidence f neurns in the visual system capable f respnding t the presence f simple trigger features in the envirnment such as lines and edges in apprpriate rientatin, and there was reasn t believe that these neurns were part f a larger, cnvergent-hierarchical, neural structure capable f cumulatively integrating lwer rder infrmatin abut lines, edges, rientatin, etc., int the mre cmplex realities f cnventinal experience (Barlw, 1972; Hubel & Wiesel, 1962, 1965). Such a "datadriven" r "bttm-up" view f frm perceptin has nt weathered well. Subsequent analyses have affrded little supprt fr rigidly serial neural hierarchies (e.g., Sekular, 1974), and there is very strng behaviral evidence t suggest that "tp-dwn" r "cnceptually guided" behavir is imprtant (Lindsay & Nrman, 1977). The strngest evidence f "tp-dwn" prcessing is prvided by cntext effects in speech and visual perceptin. In the area f visual perceptin, fr example, Williams and Weisstein (1978) have demnstrated what they term an "bject-line effect," that is, that line cmpnents can be detected mre accurately when they are part f a cherent, three-dimensinal, cube-like bject frm than when they are presented alne. If the higher rder cnfiguratinal character f the frm is dependent upn the prir detectin f lwer rder line elements, then it is difficult t see hw, This research was supprted by grants frm the Natural Sciences and Engineering Research Cuncil f Canada. We are grateful t 1. Barresi, R. Klein, P. 1usczyk, and M. Ozier fr their encuragement and advice. Requests fr reprints shuld be addressed t B. Earhard, Department f Psychlgy, Dalhusie University, Halifax, Nva Sctia B3H 411, Canada. in terms f a simple cnvergent hierarchical mdel, higher rder cnfiguratinal variables can influence discriminatin f lwer rder line cmpnents. At the very least, sme srt f feedback mechanism has t be incrprated int the system t allw higher rder structures t influence the attentin directed tward lwer rder cmpnents in the analytic prcess as, fr example, in the mdel fmilner (1974). It is bvius that cntext effects can play a very imprtant rle in shaping thery frmatin, and because f this, much interest has centered n specifying the mechanism underlying cntext effects. One apprach has been t try t determine if prvisin f a cntext effectively serves t reduce an abslute judgment task t a relative judgment task and thereby facilitate anchring a stimulus in space r, mre generally, t reduce the uncertainty assciated with respnding. While appealingly simple, such an apprach has received little experimental supprt. Schendel and Shaw (1976) did find that they culd eliminate a cntext effect invlving detectin f tw line elements by prviding a subject with the tw-alternative chices prir t presentatin-a finding which suggests that the functin f cntext may indeed be t reduce uncertainty and that the effect may be verridden by prviding subjects with the pssible alternatives prir t presentatin. Mre recent experimentatin has shwn, hwever, that a prnunced cntext effect can be readily btained in experiments invlving a chice between tw line elements in which alternatives are prvided prir t presentatin (Earhard, 1980; Williams & Weisstein, 1978). As far as spatial anchring is cncerned, Williams and Weisstein (1978) tk steps t largely eliminate the benefit cntext culd prvide with respect t anchring, and a prnunced cntext effect remained evident (see als Pmerantz, Sager, & Stever, 1977). What has emerged as the mst likely underlying Cpyright 1980 Psychnmic Sciety, Inc /80/ $01.05/0

2 370 EARHARD AND ARMITAGE determinant f the cntext effect in perceptin is the cnfiguratinal character f the cntext. Weisstein and her assciates have emphasized, in particular, the imprtance f such glbal cnfiguratinal variables as three dimensinality, cnnectedness, and cherence in cnsideratins f the cntext effect (e.g., Weisstein & Maguire, 1980; Williams & Weisstein, Nte 1). T supprt this perspective, they cite the well-established bject-superirity effect (OSE), which shws that a target line can be discerned mre readily if it is part f a cherent, cnnected, and three-dimensinal bject cntext than if it is part f a flat, uncnnected line cntext (Weisstein & Harris, 1974). They cite als the fact that, in the case f the bject-line effect, the target line is discriminated mre accurately within a cntext than when alne if it is cntained within a cnnected, threedimensinal bject cntext, but nt if it is cntained within a flat, uncnnected line cntext. Other investigatrs have illustrated the imprtance f Gestalt cnfiguratinal factrs as determinants f whether cntexts facilitate r impair discriminatin f cmpnent elements (e.g., Banks & Prinzmetal, 1976; Pmerantz, Sager, & Stever, 1977; Prinzmetal & Banks, 1977). The present paper fcuses n the bject-superirity effect. It represents an attempt t determine whether an exclusively cnfiguratinal interpretatin f the OSE, generated with Weisstein and Harris' type f frms, is pssible. Previus research n the bjectline cntext effect with these frms suggests that cntext effectiveness depends crucially n the lcatin and the amunt f line detail f the fixatin pint. Earhard (1980) has shwn (1) that Williams and Weisstein's (1978) finding that line elements can be mre accurately discerned when part f a threedimensinal cntext than when alne can be ttally reversed by a small mvement f the fixatin pint, and (2) that, if the fixatin pint is psitined at lcatins cntaining substantial amunts f visual detail, nrmally effective cntexts can cease t be effective and even impair target-line discriminatin. T btain similar results in the case f the OSE wuld strengthen the cntentin that fixatin-pint lcatin and the amunt f visual detail at the fixatin pint are mre imprtant in the study f cntext effectiveness than has been assumed, and cnfirm that the OSE demnstrated with frms f the Weisstein and Harris type is nt determined slely by cnfiguratinal variatins amng the frms. EXPERIMENT 1 Experiment 1 was a preliminary study that cmpared the best three-dimensinal bject cntext used by Weisstein and Harris (1974) in their demnstratin f the bject-superirity effect with their least effective, flat, uncnnected line cntext with respect t their capacity t facilitate discriminatin f a cnstituent line element. The bject f interest was t determine whether the well-established superirity f the bject cntext wuld be evident, nt nly when the fixatin pint was lcated in the nrmal psitin shwn in Figure la, which is free f line detail, but als when the fixatin pint rested at the pint where there is a cncentratin f line detail as shwn in Figure 2a. If ur assumptins abut the negative effects f line detail at and abut the fixatin pint are crrect, the shift in fixatin pint t the new lcatin shuld very substantially reduce the effectiveness f the bject cntext. Methd Stimuli. The fur different variants f the best and prest f Weisstein and Harris' frms shwn in Figures la and Ib and Figures 2a and 2b, respectively, were selected fr tw reasns. First, these frms prvided an pprtunity t sample the capacity f subjects t discriminate target lines that fell alng all fur diagnals, and secnd, this assembly f frms prvided an arrangement such that it wuld be pssible in subsequent experiments t systematically alter the amunt f visual detail n and a b c /11ft /0 SET A / 0"- SET d /~ 10 ~ ~" ~ 01 e ~cl ~d lb~ ~~ f r;~ P/ 1ill ~~ ~='l1 Figure 1. Rws la, Ib, and Ic shw, respectively, the bject cntext, regular line cntext, and target-line elements used in Part A f Experiment I and in all parts f Experiment 3. Rws Id, Ie, and If shw, respectively, the mdificatins f the regular line cntext emplyed in Parts A, B, and C f Experiment 3. Clsed circles were nt part f the stimulus cnfiguratins; they are included nly t clarify lcatin f the fixatin pint, which was identical t that used by Weisstein and Harris (1974). B -,

3 OBJECT SUPERIORITY 371 a b c d e /fill ~III SET A SET B Till III\" 11'f Figure 2. Rws 2a, 2b, and 2c shw, respectively, the bject cntext, the regular line cntext, and targel-iine elements with the fixatin-pint lcatin used in Part B f Experiment I and in Experiment 2. Rws 2d and 2e shw, respectively, the utline and altered line cntexts used in Experiment 2. Clsed circles were nt part f stimulus cnfiguratins. They are included nly t clarify lcatin f the fixatin pint. them t detect, and reprt by pinting at a display card during an expsure, which f the tw target line elements assciated with a given type f cntext had been presented. The display card cntained the tw target line elements frm Set A r Set B in apprpriate lcatin with respect t the fixatin pint as shwn in Figures Ic and 2c. The level f illuminatin f the expsure field was fixed at 3.38 cd/rrr'. The level f illuminatin f the preexpsure field was adjusted fr every subject s as t ensure an verall perfrmance level f 706,10-806,10 crrect respnding. The mean level f illuminatin f the preexpsure field was 6.83 cd/rnin Part A and 6.54 cd/rn! in Part B. Tw blcks f 32 practice presentatins were given t familiarize the subjects with the prcedures and t adjust the level f illuminatin f the preexpsure fields s as t ensure that the requisite level f crrect respnding was btained. This was fllwed by 12 blcks f test presentatins. Object and line cntexts were presented in separate, alternating, 32-item presentatin blcks. The rder f items within a presentatin blck was randm, with the restrictin that n mre than fur presentatins f the same target-line-cntext cmbinatin culd ccur in immediate successin. After each presentatin blck there was a pause lng enugh fr the experimenter t tally the number f crrect respnses. Any adjustment t illuminatin level f the preexpsure field was made, if necessary, nly after bth bject and line cntexts had been presented equally ften. Twenty undergraduates, wh received curse credit fr participating, served as subjects. All subjects were between 17 and 28 years f age, and all were naive with respect t the purpse f the study. There were fur females and fur males in Part A and seven females and five males in Part B. Half the subjects in bth parts f the study were presented with cntexts frm Set A, and the ther half with cntexts frm Set B. The subjects were given n feedback abut their perfrmance levels. arund the fixatin pint and target line. Stimuli were separated int Sets A and B fr presentatin purpses. This was necessary because, as inspectin f Figures I and 2 will shw. cntexts in Set B are mirrr images f cntexts in Set A. T cmbine all fur frms in a single presentatin sequence wuld allw subjects the pprtunity t use mirrr-image differences in cntexts as a basis fr reducing uncertainty as t which f the fur target lines had been presented. Accrdingly, a given subject was presented with stimuli frm Set A r Set B, but nt bth. A Kh-l-nr Rapidmatic pen with a.25-mm nib was used t draw stimulus cntext n white bristl bard. Target lines were 5.8 mm in length. The verall width f the bject and line cntexts shwn in Figures I and 2 was 12 mm. The height f the bject cntext was 12 mm, and, as in the Weisstein and Harris study, the line cntext was slightly higher at 14 mm. At a viewing distance f 60 em, target lines subtended a visual angle f.56 deg. The bject and line cntexts in verall width subtended a visual angle f 1.14 deg. In height, the bject and line frms subtended visual angles f 1.14 and 1.34 deg, respectively. Prcedure. There were tw parts t the experiment. In Part A, subjects were presented with the Weisstein and Harris frms with the cnventinal fixatin-pint lcatin shwn in Figures la and Ib; in Part B, the same frms were presented with the new, mre central, fixatin-pint lcatin shwn in Figures 2a and 2b. A Gerbrands tw-field tachistscpe was used t present stimuli t the subjects. The subjects fixated n a faint pencil dt abut.35 mm in diameter and, when instructed t prceed by the experimenter, pressed a buttn which resulted in the remval f the preexpsure held and a 2U-msec presentatin f the expsure field cntaining stimulus material (but n fixatin pint), fllwed by the immediate reappearance f the preexpsure field. Befre the start f the presentatin sequence, subjects were presented with examples f cntexts frm either Set A r Set B. They were infrmed that the bject f the experiment was fr Results The typically bserved superirity f the bject cntext ver the line cntext was evident in Part A. Target lines within the bject cntext were identified crrectly n 80.7f11 f the presentatins, but within the line cntext n nly 73.1% f the presentatins. A very different pattern was evident in Part B. The subjects detected target lines n 78.4% f the presentatins in the case f the line cntext, but n nly 73.4% f the presentatins in the case f the bject cntext. An verall analysis f variance perfrmed n the number f crrect respnses cnfirmed that there was a very prnunced interactin, reflecting the different effect f cntext n perfrmance in Parts A and B [F(I,18) = 11.34, P <.01]. There was n verall difference in accuracy level in the tw parts f the experiment [F(l,18) = 1.45, p <.10]. This was nt unexpected, hwever, since a fixed level f perfrmance was maintained by adjusting luminance levelsf the preexpsure fields. The results f the study cnfirm the imprtance f fixatin-pint lcatin. A relatively small mvement f the fixatin-pint lcatin effectively eliminated the bject-superirity effect. The interesting questin, f curse, is hw the simple mvement f the pint f fixatin can eliminate the nrmal facilitating effect f a gd cntext. Our cntentin, as indicated in the intrductin, is that it is the amunt f line detail

4 372 EARHARD AND ARMITAGE lcated n and abut the fixatin pint and the target line that is the crucial factr. Such a cntentin certainly cnfrms with the cnsequences f fixatinpint mvement in the present study. Inspectin f Figures 1a and 1b will shw that, in the bject cntext, the fixatin pint rests n a central area free f visual detail but that in the line cntext it falls upn the middle f a vertical line, with ther line elements interpsed between the fixatin pint and the t-be-detected target line. The shift in fixatin shwn in Figures 2a and 2b reversed the imbalance f line detail lcated at the pint f fixatin. In this instance, it is in the bject cntext that the fixatin pint falls upn the junctin pint f target and cntext lines; in the line cntext, fixatin rests n nly ne end f the target line and adjacent lines d nt intersect with the target line at the pint f fixatin. While the interpretatin ffered is cmpatible with the findings, it culd be much strengthened if it culd be shwn that systematically altering the amunt f line detail n r abut the fixatin pint and target line radically changed the effectiveness f a given cntext. Experiment 2 was directed tward this bjective. EXPERIMENT 2 Experiment 2 had three specific bjectives. The first was t determine whether the effectiveness f a cntext culd be enhanced by remving line detail frm n and arund the fixatin pint and target line. The secnd was t determine whether the effectiveness f a cntext culd be impaired by causing a small amunt f line detail t cnverge upn the fixatin pint. The third was t prvide a replicatin f the finding in Experiment 1 that the nrmally greater effectiveness f the bject cntext reprted by Weisstein and Harris (1974) can be eliminated by simply mving the fixatin pint t the lcatin shwn in Figure 2. There were tw parts t the study. The cntexts used in Part A cnsisted f regular line and bject cntexts frm Experiment 1 with the fixatin pint lcated at ne end f the target line (Figures 2a and 2b) and an additinal, utline, cntext as shwn in Figure 2d. The additinal frm pssessed the same number f line elements as the bject and line cntexts, but these line elements were mved as far as pssible frm the target line withut ding fatal injury t the general utline f the cntext. If ur assumptins were crrect, the absence f line detail abut the fixatin pint and the target line wuld make detectin f target-line elements easiest in the utline cntext, even thugh it lacked three dimensinality and cnnectedness, fllwed by the regular line cntext and, finally, the bject cntext, in which perfrmance wuld be prest, as in Experiment 1, because cntext and target lines cnverged at the fixatin pint. The cntexts used in Part B cnsisted f the bject and utline cntexts frm Part A (Figures 2a and 2d, respectively) and a slightly altered versin f the regular line cntext shwn in Figure 2e. Cmparisn f the altered line cntext with the regular line cntext shwn in Figure 2b will cnfirm that the nly change in the altered versin is that the tw shrtest line elements, usually remved 2 mm frm the target line, were nw jined with the target line. Given these three cntexts, the expectatin was again that the lack f line detail abut the fixatin pint and the target line wuld make the utline cntext mst effective in facilitating target-line detectin, but that the alteratin t the line cntext prduced by jining target and cntext lines at the pint f fixatin wuld impair very substantially the effectiveness f the altered line cntext and make perfrmance n the altered line cntext at least as pr as that evident in the bject cntext. Methd Stimuli. The bject and line cntexts were thse used in Part B f Experiment 1. The new utline frm shwn in Figure 2d was identical t the bject and line frms in height, but was 1.5 mm greater in width, subtending a visual angle f 1.29 deg. As in Experiment I, all frms were drawn n bristl bard with a.25-mmnib. Subjects and Prcedure. Sixteen subjects were recruited. They were between the ages f 17 and 28 and were naive with respect t the bjective f the experiment. There were fur males and fur females in Part A and five males and three females in Part B. Except fr ne male in Part A and ne female in Part B, wh were graduate vlunteers, subjects were undergraduate vlunteers, wh received curse credit pints fr participating. The prcedures were, in the main, similar t thse in Experiment 1. Half f the subjects in each part f the study were presented cntexts frm Set A and half with cntexts frm Set B. In bth Part A and Part B, the three different cntexts were presented in separate 32-item presentatin blcks. Within each presentatin blck, items were randmly arranged, with the restrictin that n mre than fur presentatins f the same target-line-cntext cmbinatin culd ccur in immediate successin within a blck. A ttal f 18 different blcks f test presentatins were given ver three sessins. Each type f cntext was presented equally ften. The rder f presentatin was randm, except fr the restrictin that a new presentatin blck cntaining examples f a given cntext culd nt be presented until all cntexts had been presented equally ften. The same 20-msec-expsure duratin used in Experiment J was emplyed in Experiment 2, and the subjects were required t indicate their respnses after each presentatin by pinting at a display with the tw apprpriate alternative target lines drawn frm either Set A r Set B. Each sessin was preceded by three practice blcks t familiarize, r refamiliarize, the subjects with the prcedures and t allw the level f illuminatin t be adjusted if necessary t ensure that an verall perfrmance level f crrect respnding be maintained. The level f illuminatin f the expsure field was the same as in Experiment I, and the mean level f illuminatin f the preexpsure field was 5.15 cd/m' in Part A and 4.85 cd/m' in Part B. If any adjustments in illuminatin level were required during the curse f test presentatins, they were carried ut nly after all cntexts had been presented equally ften.

5 OBJECT SUPERIORITY 373 Results Our first bjective was t determine whether remving line detail frm n and abut the fixatin pint and target line wuld facilitate detectin f the target line. As may be seen in Figure 3, the answer is that it des. The subjects were much mre accurate in discerning a target line when it was cntained within the utline cntext, where line detail had been mved frm the fixatin pint and target line, than when it was cntained in bject r line cntext. The mean advantage f the utline cntext ver the bject cntext was 19.3"10 in Part A and 16.0% in Part B. This pattern was evident in the data f all subjects and reliable in bth Part A [t(7) = 10.69, p <.01) and Part B [t(7) = 7.72, p <.01]. Similarly, cmparisns f the utline cntext with the line cntext shwed a mean advantage favring the utline cntext ver the regular line cntext f 8.0% in Part A; ver the altered line cntext in Part B (which was expected t impair perfrmance), the advantage was even mre prnunced-28.2%. The advantage was evident in the data f all subjects in Part Band f all but ne subject in Part A. Mean differences are significant in bth Part A [t(7) = 4.02, p <.01) and Part B [t(7) = 20.39, p <.01]. The marked superirity f the utline cntext cnfirms that mving line detail frm n and abut the fixatin pint and target line can facilitate cntext effectiveness. The remaining bjectives were t determine (l) whether the finding f Experiment I-that, with the fixatin pint lcatin used, the nrmally greater effectiveness f the bject cntext ver the line cntext is eliminated-culd be replicated, and (2) whether mving line detail s that it cnverged upn the fixatin pint, as in the altered line cntext f Part B, wuld impair cntext effectiveness. It can be seen in Figure 3 that bth bjectives were met. In Part A, as in Experiment 1, the subjects were mre accurate in specifying the target line when it was cntained within the regular line cntext than when it was in the bject cntext, but in Part B, in which the tw small line elementswere mved s that they jined the target line and pint f fixatin, the directin f the difference was reversed, and the effectiveness f the altered line cntext was impaired t such a degree that it was inferirt the bject cntext. This pattern was apparent in the data f all subjects. The 11.3% advantage f the regular line cntext ver the bject cntext was reliable in Part A [t(7) = 4.90, P <.01), as was the very substantial 12.2% disadvantage f the altered line cntext vis avis the bject cntext in Part B [t(7) = 7.29, P <.01]. While we had expected that the altered line cntext wuld impair detectin f target-line elements, we had nt anticipated such a large effect and can nly speculate abut its cause. One pssibility is that, in the case f the altered line cntext, there may be an.9 ~ U w.8 ~ ~ u z.7 ~ a.::.6 Q. a.:: a..5 PART _ A OBJECT CONTEXT REGULAR LINE CONTEXT EEl ALTERED LINE CONTEXT OUTLINE CONTEXT Figure 3. The mean prprtin f crrect target-line designatins made by subjects In Parts A and 8 f Experiment 2. Cntexts and fixatin-pint lcatin are as shwn In Figure 2. EXPERIMENT 3 PART B additinal detrimental interactin between the lcal structure prduced by jining the tw shrt cntext lines with the target line and nearby line elements that is absent in the bject cntext. Sme justificatin fr such an interpretatin is affrded by the results f the line manipulatins undertaken in Experiment 3. Experiment 2 thus cnfirms the finding f Experiment 1 that a shift in the fixatin pint can effectively eliminate the bject superirity effect. It prvides, in additin, cnsiderable supprt fr ur cntentin that line detail n and abut the fixatin pint can reduce the effectiveness with which a cntext can facilitate detectin f target-line elements. Remving line detail frm n and abut the fixatinpint and target line greatly facilitated the effectiveness f a cntext, and mving line details that it cnverged upn the fixatin pint and target line prfundly impaired target-line detectin. Experiment 3 sught t explre further the effects f fixatin lcatin and the amunt f line detail n and abut the fixatin pint. The Weisstein and Harris frms have been typically emplyed with the

6 374 EARBAROAND ARMITAGE fixatin pint lcated in the psitin shwn in Figures la and lb. Under such circumstances, it has been repeatedly fund that target lines are much mre accurately detected when they are part f the bject cntext than when they are part f the line cntext (e.g., Klein, 1978; McClelland, 1978; Wmersley, 1977; this study, Experiment 1). The argument advanced earlier in the paper t explain the advantage f the bject frm ver the regular line cntext was that, in the case f the bject frm, the fixatin pint rests n an area free f visual detail, whereas, in the case f the line cntext, nt nly des it rest n the middle f a vertical line, but als ther lines are interpsed between the fixatin pint and surrund the target line. Given such an argument, we shuld be able t demnstrate that, with the regular fixatin-pint lcatin (as shwn in Figure I, the systematic mvements f line detail away frm the fixatin-pint and target-line lcatins will eliminate the nrmally bserved superirity f the three-dimensinal bject cntext ver the flat, uncnnected line cntext. Methd Stimuli. The three different mdified line cntexts used are shwn in Figures Id, Ie, and If. In the first mdificatin (Figure Id), line detail was mved, as shwn, away frm the fixatin pint lcatin; in the secnd mdificatin (Figure l e), visual detail was remved frm the upper part f the line cntext abve the target line; and in the third mdificatin (Figure 10, the remaining shrt vertical and hrizntal lines were mved away frm the target line t prduce the same utline cntext used in Experiment 2. The bject and regular line cntexts were identical t thse used in the preceding studies. All mdificatins f the line frm were the same height as the regular line and bject frms but were, as in Experiment 2, 1.5 mm wider and subtended a visual angle f 1.29 deg. Subjects and Prcedure. There were three parts t the study. In each part a different mdified line cntext was cmpared with the bject cntext and the regular line cntext shwn in Figures la and lb. In Part A, the mdified line cntext shwn in Figure Id was cmpared with bject and regular line cntexts; in Part B, the cmparisn invlved the mdified line cntext shwn in Figure Ie; and in Part C, it invlved the mdified cntext shwn in Figure If. A different grup f eight subjects served in each part f the experiment. All subjects were undergraduates, between the ages f 17 and 28, wh received curse credit fr their participatin. There were equal numbers f female and male subjects in Parts A and C and five female and three male subjects in Part B. All subjects were naive with respect t the bjectives f the study. Half the subjects received cntexts frm Set A, and half received them frm Set B. The number f presentatins, presentatin prcedure, and expsure parameters in each f the three parts f the experiment were identical t thse used in Experiment 2. As in the preceding studies, the level f illuminatin f the preexpsure field was adjusted s as t ensure an verall perfrmance level f between and crrect respnding. The mean level f illuminatin f the preexpsure field was 5.65 cd/m' in Part A cd/m' in Part B, and 5.13 cd1m' in Part C. ti.9 1&.1 GIl: GIl: 0.8 U Z.7 ọ.. GIl: 0.6 A. GIl: A..5 OBJECT CONTEXT REGULAR LINE CONTEXT MODIFIED LINE CONTEXT PART A PART B PART C Figure 4. The mean prprtin f crrect target-line designatins made by subjects in Parts A, D, and C f Experiment 3. Cntexts and fixatin-pint lcatin are as shwn in Figure 1. The mdified line cntexts shwn in Parts A, D, and C represent perfrmance n cntext mdificatins shwn, respectively, in Rws ld, Ie, and Iff Figure 1. Results Figure 4 shws the prprtin f crrect targetline detectin when target lines were part f the bject cntext, the regular line cntext, and the different mdified line cntexts used in the three parts f the study. There are three bservatins wrth making. First, the typically bserved superirity f the bject cntext ver the regular line cntext was evident. Secnd, remval f even a small amunt f visual detail frm the fixatin pint area f the mdified line cntext in Part A made it a mre effective cntext than the regular line cntext. Third, and mst imprtant, the remval f a substantial amunt f visual detail frm the fixatin-pint and targetline areas in Part C rendered the mdified (utline) line cntext superir t the bject cntext, as in Experiment 2. The advantage f the bject cntext ver the regular line cntext was evident in the data f all individual subjects in all three parts f the study. The mean advantage f the bject cntext ver the regular line cntext was in Part A, 25.4% in Part B, and 13.5% in Part C. Separate t tests shwed the advantage f the bject ver the line cntext t be reliable in Part A [t(7) = 21.31, P <.01], Part B [t(7) = 18.88, p <.01], and Part C [t(7) = 5.60, p <.01J. It is difficult t specify the reasn fr the reductin in magnitude f the difference between the bject and line cntexts in Part C. It may, in part, reflect individual differences. Indeed, in Part A f Experiment I, the magnitude f the difference was nly 7.6%. A mre likely cntributing factr is, hwever, that the design f the study required perfrmance t be maintained within the 70%-80% range f crrect respnding, that the increase in the, effectiveness f the mdified (utline) cntext in Part C had t be cmpensated fr by a reductin, in the level f perfrmance f ther cntexts t main-

7 OBJECT SUPERIORITY 375 tain this verall perfrmance level, and that this, t sme degree, depressed the range f allwable differences. Whatever the reasn, a substantial and reliable difference remained evident. The mdified line cntexts were fund t be mre effective than the regular line cntext by all subjects in all three parts f the study. The mean difference favring the mdified line cntext was in Part A, 18.5% in Part B, and 22.6% in Part C. Separate t tests indicated that differences in Part A [t(7) = 12.25, p <.01], Part B [t(7) = 13.31, P <.01], and Part C [t(7) = 10.89, p <.01] were reliable. The data cnfirm that mving line detail frm the fixatin pint and the target line can greatly facilitate the effectiveness f a line cntext. While the mdified line cntexts were cnsistently mre effective than regular line cntexts in all three parts f the study, the mdificatins intrduced in Parts A and B were nt sufficient t make either f the mdified cntexts invlved mre effective than the bject cntext. In fact, all subjects were significantly mre accurate when target lines were cntained in the bject cntext than when they were in the mdified line cntext [Part A, t(7) = 8.89, p <.01; Part B, t(7) = 4.73, p <.01]. The mean advantage f the bject cntext ver the mdified line cntext in Part A was 9.4%; in Part B, it was 6.9%. It was nt until Part C, when all line detail was remved frm n and abut the fixatin pint and target line f the mdified line cntext t prduce the same utline cntext used in Experiment 2, that there was a substantial advantage in favr f the mdified (utline) cntext ver the bject cntext. All subjects were mre accurate in detecting the target line in the utline cntext, and the verall advantage f 9.1% was reliable [t(7) = 12.72, P <.01]. The results btained in Part C with the utline cntext are similar t thse btained in Experiment 2, and they demnstrate again that, if the fixatin pint is apprpriately lcated and if it and the target line are suitably free f visual detail, a flat frm lacking cnnectedness and unity can be a mre effective cntext than a cherent, cnnected, and unified three-dimensinal frm. DISCUSSION It seems unlikely that the OSE prduced with Weisstein and Harris' type f frms can be accunted fr exclusively by cnfiguratinal variables. Fixatinpint lcatin must be taken int cnsideratin. The widely bserved superirity f the three-dimensinal cherent and cnnected bject frm was readily demnstrated in Experiment 2 with the standard fixatin-pint lcatin, but a small shift in fixatinpint lcatin eliminated the effect, and a flat line cntext, lacking in cherence and cnnectedness, was shwn t be the mre effective cntext. Mvement f the fixatin pint des nt reverse the very bvius differences in three-dimensinality, cherence, and cnnectedness between bject and line cntexts, but it des reverse the relative effectiveness f the tw frms. What is respnsible fr the reversal f the OSE? Experiments 2 and 3 lend supprt t the view that the crucial factr is the amunt f line detail n, r abut, the fixatin pint. Mvement f line detail tward the pint f fixatin in Experiment 2 impaired cntext effectiveness, and mvement f line detail away frm the pint ffixatin in Experiments 2 and 3 facilitated cntext effectiveness. In fact, when all line detail was mved a sufficient distance away frm bth the fixatin pint and the target line, the resulting flat, uncnnected utline cntext prved t be the mst effective cntext. Hw general is the fixatin lcatin effect described? In the study f the OSE reprted, the frms used were either identical t thse used by Weisstein and Harris r were variants f thse frms. Althugh these frms have been used very extensively in the literature (e.g., Klein, 1978; McClelland, 1978; Wrnersley, 1977), it must be cnceded that they cnstitute a limited range f stimulus cnfiguratins, and it can be argued that this must cnstrain the generality f the findings. Althugh, as has been nted, an analysis n the bject-line effect with a substantially brader set f frms has prduced fixatin lcatin effects which clsely parallel thse reprted (Earhard, 1980), a degree f cautin is necessary. One questin, in particular, t which the answer is nt clear is whether these findings can be generalized t stimulus cnfiguratins that are very large and in which individual elements in the frm are separated frm ne anther by a sufficient distance t prevent lateral masking interactins (e.g., Banks & Prinzmetal, 1976). The frms used in the research described are very small. All subtend a visual angle f less than 2 deg, and the ptential fr lateral masking interactins is large. The reslutin f this questin must await future research.. With respect t the questin f why the amunt f line detail at the fixatin pint shuld be imprtant, ur preference (which is elabrated mre fully in Earhard, 1980) is t accept the arguments f Bradbent (1977) and Navn (1977) that perceptin invlves bth glbal and lcal prcessing peratins. The glbal system is cnsidered t have a shrter latency than the lcal system, and the lw-level reslutin f the visual terrain prduced prvides a fundatin fr the peratin f the lcal analytic system that is respnsible fr mre detailed, finegrain elabratin fthe visual stimulus. The fixatinlcatin effect is judged t be a cnsequence f the way in which the lcal analytic system perates. Tw assumptins are made: (1) that there are preferred ways t carry ut the lcal analytic prcess, and (2) that the lcal analytic system begins autmatically

8 376 EARHARD AND ARMITAGE t prcess material at the pint f fixatin. The suggestin that there are preferred ways f carrying ut the prcess f lcal analysis des nt mean that a specific sequence r mde f analysis must be rigidly adhered t in prcessing a frm, but nly that general preferences may exist fr varius classes f frm, r even fr individual frms. These preferences will be determined in part by hardware-capacity cnstraints n the lcal system, that is, hw much and hw rapidly detail can be dealt with, and in part by the cnfiguratinal character f the frm presented, that is, hw line detail is rdered and cncentrated. This wuld mean that, in the case f tachistscpic studies using line stimuli such as thse reprted, the fixatin-pint lcatin will be extremely imprtant. Cntextual facilitatin will depend t a large degree n whether the experimenter has psitined the fixatin pint at a lcatin that cincides with the first step in the preferred prcessing sequence f a given frm. In view f the large number f pssible lcatins and the likelihd that prcessing preferences may vary with size (Kinchla & Wlfe, 1979), it is rather imprbable that this ideal state will always be achieved. If the fixatin pint falls n a nn preferred lcatin with a cncentratin f line detail, r there is a cncentratin f line detail between the fixatin pint and the t-be-specified target line, the results f Experiments 2 and 3 suggest that interference can be anticipated. The impairment can be reduced t sme degree by shifting the fixatin pint, if pssible, t a central lcatin where there is little, r n, detail. This wuld minimize the amunt f detail that wuld have t be dealt with at the initial pint befre pursuing an analytic sequence that adheres mre clsely t a preferred sequence. With respect t line detail n r abut the target line, little can be dne withut altering the frm. The data we have reprted suggest that it can nly serve t impair target-line detectin. Whether the interpretatin f the fixatin-lcatin effect described is accepted r nt, it seems t us that a mre detailed analyis f the fixatin-pint and the way in which it interacts with figural infrastructure will prve rewarding. One interesting cntrast already apparent is that between the emphasis placed n the imprtance f cmplex line intersectin in cmputer recgnitin mdels and ur finding that cmplex line intersectins seem t be anything but ideal sites fr fixatin-pint lcatin in tachistscpic studies. REFERENCE NOTE I. Williams, A., & Weisstein, N. The time curse f bjectsuperirity. Unpublished manuscript, REFERENCES BANKS, W. P., & PRINZMETAL, W. Cnfiguratinal effects in visual infrmatin prcessing. Perceptin & Psychphysics, 1976,19, BARLOW, H. B. Single units and sensatin: A neurn dctrine fr perceptual psychlgy? Perceptin, 1972, I, BROADBENT, D. E. The hidden preattentive prcesses. American Psychlgist, 1977,32, EARHARD, B. The line-in-bject superirity effect in perceptin: It depends n where yu fix yur eyes and what is lcated at the pint f fixatin. Perceptin & Psychphysics, 1980, 28, HUBEL, D. H., & WIESEL, T. N. Receptive fields, bincular interactin and functinal architecture in the eat's visual crtex. Jurnal fpsychlgy, 1962, 160, HUBEL, D. H., & WIESEL, T. N. Receptive fields and functinal architecture in tw nn-striate visual areas (18 and 19) f the cat. Jurnal fneurphysilgy, 1965,28, KINCHLA, R. A., & WOLFE, J. M. The rder f visual prcessing: "Tp-dwn," "bttm-up," r "middle-ut." Perceptin & Psychphysics, 1979,25, KLEIN, R. Visual detectin f line segments: Tw exceptins t the bject-superirity effect. Perceptin & Psychphysics, 1978, 24, LINDSAY, P. H., & NORMAN, D. A. Human infrmatin prcessing: An intrductin t psychlgy. New Yrk: Academic Press, MCCLELLAND, J. L. Perceptin and masking f whles and parts. Jurnal f Experimental Psychlgy: Human Perceptin & Perfrmance, 1978,4, MILNER, P. M. A mdel fr shape recgnitin. Psychlgical Review, 1974,81, NAVON, D. Frest befre trees: The precedence f glbal features in visual perceptin. Cgnitive Psychlgy, 1977,9, POMERANTZ, J. R., SAGER, L. C., & STOEVER, R. J. Perceptin f whles and f their cmpnent parts: Sme cnfigural effects. Jurnal f Experimental Psychlgy: Human Perceptin & Perfrmance, 1977,3, PRINZMETAL, W., & BANKS, W. P. Gd cntinuatin affects visual perceptin. Perceptin & Psychphysics, 1977, 21, SCHENDEL, J. D., & SHAW, P. A test f the generality f the wrd-cntext effect. Perceptin & Psychphysics, 1976, 19, SEKULAR, R. Spatial visin. In Annual review f psychlgy (Vl. 31). Pal Alt: Annual Reviews, SELFRIDGE, O. G. Pandemnium: A paradigm fr learning. In The mechanizatin f thught prcesses. Lndn: H. M. Statinery Office, WEISSTEIN, N., & HARRIS, C. S. Visual detectin f line segments: An bject-superirity effect. Science, 1974, 186, WEISSTEIN, N., & MAGUIRE, W. Cmputing the next step: Psychphysical measures f representatin and interpretatin. In E. M. Riseman & A. R. Hansn (Eds.), Cmputer visual systems. New Yrk: Academic Press, WILLIAMS, A., & WEISSTEIN, N. Line segments are perceived better in a cherent cntext than alne: An bject -line effect in visual perceptin. Memry & Cgnitin, 1978, 6, WOMERSLEY, M. A cntextual effect in feature detectin with applicatin f signal detectin methdlgy. Perceptin & Psychphysics, 1977, 21, (Received fr publicatin September 27, 1979; revisin accepted July 24, 1980.)