Novel popout with nonsense strings: Effects of predictability of string length and spatial location

Transcription

1 Perceptin & Psychphysics 1994, 55 (3), 26/-268 Nvel pput with nnsense strings: Effects f predictability f string length and spatial lcatin KEVIN J. HAWLEY, WILLIAM A. JOHNSTON, and JAMES M. FARNHAM University f Utah, Salt Lake City, Utah Recent studies have shwn that when ne f fur expected wrds is replaced by a single unexpected wrd, the unexpected wrd may capture attentin. In three experiments, we explred the generality fthis effect. In each experiment, bservers viewed arrays cmpsed ffur cmputergenerated "nnsense" strings. Accuracy f string lcalizatin was assessed after each array. Sme strings, called familiar, appeared in many arrays, whereas thers, called nvel, appeared in nly ne. In each experiment, nvel strings in arrays cmpsed f ne nvel and three familiar strings were lcalized mre accurately than were nvel strings in arrays cmpsed entirely f nvel strings, and familiar strings in these arrays were lcalized less accurately than were familiar strings in arrays cmpsed entirely f familiar strings. These tw effects, termed nvel pput and familiar sink-in, respectively, were bserved even when nvel and familiar strings were rendered less discriminable by hlding their lengths cnstant (Experiment 2) and when familiar strings always appeared in the same spatial lcatins (Experiment 3). The data suggest that nvel bjects can capture attentin even when the bjects lack any clear linguistic referent, when they are superficially similar t the familiar bjects that surrund them, and when the spatial lcatins f familiar bjects are cmpletely predictable. When navigating thrugh a familiar envirnment, rganisms are faced with the dual challenge f identifying bth the regular r expected features fthat envirnment as well as any unexpected r nvel intrusins. Tw prcesses seem t aid in the identificatin f familiar r expected stimuli. First, the perceptin f familiar r previusly perceived stimuli may be enhanced via perceptual priming (e.g., Feustal, Shiffrin, & Salas, 1983; Jacby & Dallas, 1981; Meyers, Schvaneveldt, & Ruddy, 1975). Secnd, extensive familiarity with an envirnment may allw fr the develpment fperceptual schemata that encde the regularities f that envirnment (e.g., Biederman, 1972; Friedman, 1979; Mandler, 1984; Rumelhart, Smlensky, McClelland, & Hintn, 1986). Tgether, these prcesses allw an rganism t rapidly and accurately identify the stable features f its envirnment. Hwever, because these prcesses tend t bias perceptin tward what is familiar r expected, the rganism can becme relatively insensitive t envirnmental changes. Frtunately, this tendency appears t be cunteracted by This research was supprted in part by a University f Utah Graduate Research Fellwship and by a 1991 APA Dissertatin Research Award t the first authr. Additinal supprt was prvided by Air Frce Office fscientific Research Grant t WA.J. All fthe experiments described in this paper were cmpleted by the first authr in partial fulfillment f the requirements fr the dctral degree at the University f Utah. We wuld like t thank Charles Flk, Tram Neill, and an annymus reviewer fr their helpful cmments and suggestins regarding an earlier draft f this manuscript. Requests fr reprints shuld be directed t K. J. Hawley. wh is nw at the Department f Psychlgy, 210 McAlester Hall, University f Missuri-Clumbia, Clumbia, MO anther phenmenn, called nvel pput. Nvel pput refers t the tendency fr nvel r unexpected stimuli in an array r scene t capture attentin. By ensuring a degree fvigilance t envirnmental change, nvel pput may prvide a mechanism fr the apprpriate updating r revisin f perceptual schemata. Althugh a cnsiderable amunt f research has been directed tward an understanding f priming and schematic perceptin, the mechanisms underlying nvel pput have nly recently been addressed (e.g., Jhnstn, Hawley, & Farnham, 1993; Jhnstn, Hawley, Plewe, Ellitt, & DeWitt, 1990). In a typical experiment (e.g., Jhnstn et al., 1990, Experiment 4) bservers receive 200-msec glimpses f backward-masked fur-wrd arrays. Familiar wrds appear many times acrss the series f arrays, whereas nvel wrds appear nly nce. Three different cmbinatins f nvel and familiar wrds are emplyed. Ali-familiar arrays cntain nly familiar wrds, ali-nvel arrays cntain nly nvel wrds, and ne-nvel arrays cntain ne nvel wrd and three familiar wrds. The lcatins fbth nvel and familiar wrds vary randmly acrss arrays and, therefre, cannt be predicted in advance. Nvel pput, assessed via accuracy f wrd lcalizatin fllwing each array, manifests itself as tw particular effects. First, lcalizatin accuracies fr nvel wrds in ne-nvel arrays are higher than fr thse in all-nvel arrays, defining nvel pput. Secnd, accuracies fr familiar wrds in ne-nvel arrays tend t be lwer than fr thse in all-familiar arrays, defining familiar sink-in. Tgether, these findings suggest that attentin is shifted away frm familiar wrds and 261 Cpyright 1994 Psychnmic Sciety, Inc.

2 262 HAWLEY, JOHNSTON, AND FARNHAM tward the nvel wrd in ne-nvel arrays. Occasinally, the effects f this shift can be great enugh s that lcalizatin accuracy fr the single nvel wrd actually exceeds that fr the familiar wrds that surrund it (an effect termed within-array nvel pput/jamiliar sink-in).' The previusly reprted findings f Jhnstn et al. (1990, 1993) discredit several ptential interpretatins f nvel pput. Fr example, nvel pput is nt attributable either t eye mvements r t an active search fr nvel items, because the effect has been bserved in displays expsed fr nly 33 msec. Nvel pput is nt easily attributable t familiarity-based figure-grund cntrast, because a cmplementary pput fr familiar wrds was nt bserved in displays cmpsed f ne familiar and three nvel wrds. In additin, nvel pput is unlikely t be the result feither perceptual satiatin r memrial cnfusin fr the familiar wrds, because lcalizatin accuracies fr all-familiar arrays are nrmally higher than thse fr all-nvel arrays. Finally, nvel pput is nt attributable t the perceptual fluency f individual familiar wrds, because nvel wrds d nt' 'pp ut" frm fields cmpsed f wrds that have been repeated many times but never tgether. Instead, a lne nvel wrd appears t capture attentin nly when it is imbedded in a field f wrds that have becme highly interassciated, r perceptually''unitized, " wing t their repeated presentatin tgether. Ntwithstanding previus effrts t identify the cnditins under which nvel pput ccurs, the verall generality f the effect remains unclear. In particular, three questins have ften been raised in respnse t prir reprts fnvel pput. First, becauseall fthe previusly reprted effects assciated with nvel pput have been btained with the use f wrds as stimuli, it is nt clear whether nvel pput reflects a general sensitivity t perceptually incngruent infrmatin r is limited t linguistic r therwise "meaningful" stimuli. Secnd, because nvel pput has been bserved in displays expsed fr as briefly as 33 msec, it is pssible that the effect ccurs principally with stimuli that happen t be cnspicuus in terms f sme simple feature r superficial physical characteristic, such as length. Finally, because all f the previusly reprted studies f nvel pput allwed the lcatins ffamiliar items t vary randmly, it is nt clear whether nvel pput generalizes t sirnatins in which the lcatins fexpected bjects are predictable, a situatin that characterizes the stable cnfiguratins fbjects fund in familiar envirnments. In the present research, we sught t extend the empirical fundatins upn which a thery f nvel pput wuld be based by addressing each f these questins. EXPERIMENT 1 In Experiment 1, we examined whether nvel-pput effects culd be btained with stimuli ther than wrds. This was achieved by emplying semirandm strings f graphics characters frm the ASCII extended character set as stimuli. The use f such "nnsense" strings prvides tw distinct advantages ver ther frms f nnverbal stimuli (e. g., nnwrds r pictures). First, because bservers have n previus experience with these bjects, perceptual prcesses can be examined in a cntext that is relatively free frm the influence f preexperimentally established schemata and expectancies. Instead, familiarity can be develped entirely within the experimental cntext. Secnd, because nnsense strings are nt subject t the phnlgical and grammatical rules that gvern the cnstructin flinguistic stimuli, the cnstructin fthese bjects can be tailred s that they share certain glbal characteristics, such as length. Aside frm the use f nnsense strings, the design f Experiment I was similar t that used by Jhnstn et al. (1990, Experiment 4). Observers viewed a lng series f all-familiar, all-nvel, and ne-nvel arrays. Familiarity with the familiar strings was established during a practice phase, and the relative perceptibility f familiar and nvel strings in the varius display cmpsitins was assessed in a subsequent test phase. If nvel pput represents a general tendency fr attentin t be captured by bjects thatare nt assciated with the field in which they appear, then the nvel-pput and familiar-sink-in effects bserved by Jhnstn et al. (1990, Experiment 4) shuld be replicated. Methd Observers and Design. The bservers were 36 undergraduate students frm an intrductry psychlgy curse at the University futah. They participated in the experiment in return fr extra credit tward a higher grade in their class. All reprted nrmal r crrected-t-nrmal visin. Array cmpsitin (all-familiar, nenvel, and all-nvel) was manipulated within bservers in the test phase. Object type (nvel vs. familiar) was an additinal factr nested within the ne-nvel arrays. Equipment and Stimuli. The bservers served individually in a small rm equipped with an ffim XT-cmpatible micrcmputer, a keybard, and a Sarnsung clr mnitr (Mdel MM-l464W) with a P22 phsphr. Each bserver wre headphnes ver which a lw level f white nise was cntinuusly bradcast in rder t minimize external distractins. They sat facing the mnitr frm an apprximate viewing distance f 60 cm. The mnitr prvided mst fthe light in the rm. The experiment was prepared and executed by using the PsyExper sftware system (Hawley, 1991). The stimuli were 484 bjects cmpsed f nnalphanumeric characters frm the ASCII extended character set. Each character, etched in white against a blue backgrund, subtended visual angles f vertically and hrizntally. A ttal f 60 different characters was used, with each character assigned t ne r mre f three grups. Characters in Grup 1 were always used as the first character f each string, thse in Grup 2 cmprised the middle characters f each string, and thse in Grup 3 were always the last character. Characters were assigned t each grup n the basis f ur judgment f the extent t which they frmed gd cntinuity with characters frm the ther tw grups. Fr any given string, a single character was chsen at randm frm bth Grup I and Grup 3, and tw t five characters were chsen at randm frm Grup 2. Thus, the individual strings varied frm fur t seven characters in length, with each character cnnected t the characters adjacent t it. Prcedure. An experimental sessin cmprised a series f 384 trials. During each trial, an array f fur rectangular bxes, hereafter referred t as lcatins, was centered n the mnitr at all

3 NOVEL POPOUT 263 times. The entire array subtended apprximate visual angles f vertically and 6.30 hrizntally. A character string culd appear, centrally adjusted, in any f the fur lcatins. As Figure I illustrates, each trial was cmpsed fa sequence f fur arrays: attentin, mask, prbe, and feedback. In an attentin array, each fthe fur lcatins cntained a different string. These strings were displayed fr 183 msec and were fllwed, 17 msec later, by a masking array. This prcedure yielded a virtual expsure f200 msec fr each attentin array. The masking array was displayed fr 100 msec and was fllwed, 500 msec later, by a prbe array. In the prbe array, ne f the strings frm the attentin array was displayed in all fur lcatins. The bserver's task was t indicate the particular lcatin in which the prbe string had appeared in the preceding attentin array. This indicatin was made by pressing the apprpriate key ut f fur n the numeric keypad f the keybard. The spatial cnfiguratin f these keys matched that f the fur array lcatins. The bservers were instructed t be as accurate as pssible in respnding. The speed and accuracy f each respnse was scred by the cmputer. A respnse terminated a prbe array and was fllwed, 17 msec later, by a feedback array in which the prbe string reappeared fr I sec in its crrect lcatin. The next trial cmmenced 500 msec after the ffset f the feedback array. After every blck f 30 trials, the percentage f crrect lcalizatins fr that blck was displayed fr 5 sec. At the end f the experiment, the bservers answered a shrt questinnaire designed t measure their awareness f the differences in array cmpsitin. The bservers were then debriefed and dismissed. 1. Attentin Array (183 ms) 2. Mask Array (100 ms) 3. Prbe Array (until respnse) 4. Feedback Array (1 s) (17 ms) (500 ms) (17 ms) Figure 1. Sequence and timing f the fur types f arrays in Experiment 1. Of the 384 trials, the first 64 served bth as practice and t prefamiliarize the bservers with the repeated strings. The duratin f expsure f the attentin arrays n these trials was gradually reduced frm I sec n the 1st trial t 200 msec by the 16th trial. On all remaining trials, the attentin arrays were presented fr 200 msec. Only the all-familiar arrays were presented n the prefamiliarizatin trials. The remaining 320trials, deemed test trials, cntained a randm rdering f 80 all-familiar, 80 all-nvel, and 160 ne-nvel arrays. Thrughut the experiment, the presentatin f familiar strings was cnstrained s that they were bth displayed and prbed fr with apprximately equal frequency. Additinally, nvel and familiar strings were randmly assigned t array lcatins with the restrictin thateach type fstring appear in, and be prbed frm, each array lcatin equally ften. Over all, the relative frequency with which nvel and farniliar strings wereprbed matched their relative frequencies f presentatin. Thus, nvel strings were prbed fr 25 % f the time in ne-nvel arrays, and 100% f the time in all-nvel arrays. Three independent cnstructins f the experiment were made, entailing different randm assignments fstrings t cnditins and cnditins t trials. Each cnstructin was administered t 12 bservers. Freach cnstructin, fur randmly chsen strings served as familiar bjects. Results and Discussin Thrughut the study, a respnse was excluded frm analysis if its latency was less than 250 msec r greater than 6,000 msec. Apprximately 1% f the data were drpped as a result fthis criterin. All effects were cnsidered statistically reliable at p <.05. In each f the present experiments, accuracy and latency flcalizatin tended t inversely cvary acrss the array cnditins. Hwever, wing t bth the instructinal emphasis n accuracy and the prvisin f accuracy feedback, respnse accuracy was mre sensitive t the experimental manipulatins than was respnse latency. Cnsequently, nly the accuracy data are reprted here. Further, because analyses assessing the impact f such auxiliary variables as prbed lcatin, particular string prbed, and experimental cnstructin revealed n interactins that cmprmised ur cnclusins, discussin is limited t the effects fthe main experimental variables. The data fr Experiment 1 are summarized in Figure 2. As in previus studies, lcalizatin accuracy was higher fr all-familiararrays than fr all-nvel arrays [F(l,35) = 21.89, MSe = ]. This finding replicates the usual perceptual advantage f familiar arrays and is attributable t the effects f priming and perceptual schemata. Hwever, when a single nvel string was intrduced int a field fthree familiar strings, lcalizatin accuracy fr the nvel string rse abve that fr all-nvel arrays [F(1,35) = 7.79, MS e = 88.23], and accuracy fr the familiar strings fell belw that fr all-familiar arrays [F(l,35) = 4.58, MS e = 93.89]. Lcalizatin accuracies fr nvel and familiar strings in the same array were statistically indistinguishable (F < 1.0). The results f Experiment 1 shw that bth the nvelpput and familiar-sink-in effects bserved by Jhnstn et al. (1990, 1993) are replicable with the use f nnsense strings as stimuli in lieu f wrds. Thus, these effects d nt appear t be restricted t linguistic stimuli. Bth the structure f the experimental trials and the pstexperimen-

4 264 HAWLEY, JOHNSTON, AND FARNHAM Familiar III c: E::l Nvel ca 50.!::! ca u 0...J 45 -U... Q) ~0 35 All-Familiar One-Nvel All-Nvel Array Cmpsitin Figure 2. Lcalizatin accuracy fr nvel and familiar bjects in Experiment 1 as a functin farray cmpsitin. (Vertical bars represent standard errrs.) tal questinnaire data discredit an interpretatin f these findings in tenns fan explicit attempt t search fr nvel strings. First, the arrays were displayed fr nly 200 msec, s these effects are nt attributable t eye fixatin mvements. Secnd, the nvel strings were prbed fr n nly 25 % f the ne-nvel trials, s there was n prbabilistic bias that might have fstered a search fr these strings. Finally, analysis f the questinnaire data revealed that althugh 92% fthe bservers were aware that sme stimuli were repeated during the experiment, nly 25 % prfessed any knwledge f the existence f ne-nvel arrays, and nne f these reprted any deliberate attempts t search fr nvel strings. EXPERIMENT 2 Because the stimuli used in Experiment 1 were generally unfamiliar t the bservers, it seems likely that the mechanisms that underlie nvel pput can perate n the physical representatins f stimuli alne. Further, because nvel pput has been bserved in arrays expsed fr as briefly as 33 msec (Jhnstn et al., 1993), it is pssible that the perceptual dynamics that give rise t nvel pput rely n sme relatively simple physical feature t distinguish between nvel and familiar strings. One bvius candidate fr such a feature is string length. Althugh previus investigatins f nvel pput have attempted t minimize the impact f distinctive perceptual features by randmly assigning wrds t serve as nvel and familiar stimuli, it is pssible that nvel pput ccurs principally within the small percentage ftrials in which nvel stimuli happen t be nticeably lnger r shrter than the familiar wrds that surrund them. In Experiment 2, we sught t test this pssibility. In Experiment 2, tw different sets f nnsense strings were emplyed. Strings in the first set varied randmly in tenns f their length, whereas thse in the secnd set were cnstant. Observers were randmly assigned t view ne fthese tw sets at the start fthe experiment. Thus, althugh sme f the bservers culd ccasinally use the simple featural cue f string length as an aid in identifying individual strings, thers culd nt. Additinally, the number f prefamiliarizatin trials was increased frm 64 t 122 fr all the bservers. Because previus studies have suggested that nvel pput varies as a functin f the interitem assciatins between familiar stimuli (Jhnstn et al., 1993), it was reasned that the strnger interitem assciatins between familiar strings prduced by this manipulatin wuld engender a crrespnding increase in the magnitude f nvel pput. Methd Observers and Design. A new sample f 72 bservers was recruited in the same manner described in Experiment I. Frmally, the design was a 2 x 3 (length variability x array cmpsitin) mixed factrial, with repeated measures nthe secndfactr. Stimulus type (nvel vs. familiar) was a third factr nested within the ne-nvel arrays. Equipment, Stimuli, and Prcedure. The equipment and sftware were identical t thse emplyed in Experiment I. At the start f the experimental sessin, each bserver was randmly assigned t ne f tw length variability grups. The strings viewed by the bservers in the variable-length grup were identical, in terms f their verall characteristics, t thse emplyed in Experiment 1. Fr the bservers in the cnstant-length grup, a crrespnding set f384 strings was assembled by using the sameprceduredescribed in Experiment I, but with the additinal restrictin that all the strings be limited t fur characters in length. Fr each grup, three independent cnstructins fthe experiment weregenerated, and each cnstructin was administered t 12 bservers. All ther prcedures were identical t thse emplyed in Experiment I, with the exceptin that an additinal 48 trials were added t the practice phase. Results and Discussin The results fr Experiment 2 are summarized in Figure 3. With ne exceptin, the same pattern f effects bserved in Experiment 1 was duplicated in bth f the grups f Experiment 2. As in Experiment 1, strings in all-familiar arrays were lcalized mre accurately than thse in all-nvel arrays [F(l,70) = 56.15, MS e = 44.60]. Mrever, nvel strings in ne-nvel arrays were lcalized mre accurately than thse in all-nvel arrays [F(I,70) = 6.37, MS e = 59.60], and familiar strings in ne-nvel arrays were lcalized less accurately than thse in all-familiar arrays [F(1,70) = 7.99, MS e = 18.42]. Nne fthese effects interacted with the factr f length variability (all Fs < 1.28). These results reinfrce the cnclusin fexperiment 1 that nvel pput is nt limited t linguistic r therwise meaningful stimuli. Further, because neither nvel pput nr familiar sink-in interacted with the factr flength variability, the mechanisms upn which nvel pput is based d nt appear t rely n the simple feature f string length as a cue fr discriminating between nvel and familiar strings. Hwever, unlike Experiment 1, nvel strings in the ne-nvel arrays f Experiment 2 were lcalized reliably less accurately than the familiar strings in thse same ar-

5 NOVEL POPOUT 265 III c::: -as.!::! as (,)...J -(,) Q) ~ ~ III c::: -as!::! as (,)...J -(,) Q) Cnstant All-Familiar Array length Grup One-Nvel Cmpsitin Variable length Grup Familiar ~ Nvel L '-_L.C..L.4...,....L.LL--, 50 ~ (; 40 :>l! All-Nvel Familiar 121 Nvel All-Familiar One-Nvel AII Nvel Array Cmpsitin Figure 3. Lcalizatin accuracy fr nvel and familiar bjects in Experiment 2 as a functin f array cmpsitin fr the cnstantand variable-length grups. (Vertical bars represent standard errrs.) rays [F(l,70) = 8.63, MS e = 39.38]. This effect als did nt interact with the factr flength variability [F(I,70) = 1.74, MS e = 39.38]. One pssible explanatin fr this finding is that the higher number f practice trials that were emplyed in an effrt t increase the magnitude f nvel pput had the unanticipated effect f increasing the perceptibility f familiar strings. As a result, althugh attentin was shifted tward the nvel string in ne-nvel arrays, the enhanced prcessing f the nvel string was nt enugh t vercme the perceptual advantage f the familiar strings in thse arrays. A cmparisn fthe lcalizatin accuracies fr all-nvel and all-familiar arrays in Experiments I and 2 tends t supprt this hypthesis. Althugh accuracies fr all-nvel arrays are statistically equivalent in bth experiments [t(70) = 1.54, SE = 1.13], all-familiar accuracies were smewhat higher in Experiment 2 [t(70) = 1.81, SE = 1.39]. Because all f the majr effects assciated with nvel pput were evident in the present study, this enhanced perceptibility f familiar strings did nt appear t alter the basic perceptual dynamics underlying nvel pput. Thus, the results f Experiment 2 generally demnstrate that nvel bjects can capture attentin even when they cannt be segregated frm their perceptual field n the basis f the simple feature f length. EXPERIMENT 3 The finding f significantly prer lcalizatin accuracies fr nvel stimuli in ne-nvel arrays in spite f an apparent shift f attentin tward thse bjects raises an interesting questin abut the relatinship between nvelpput and schematic perceptin. Specifically, the findings f Experiment 2 suggest that althugh attentin may be directed tward nvel r incngruent stimuli during scene perceptin, this bias may nt be enugh t vercme the tp-dwn perceptual advantage f familiar stimuli. Thus, althugh nvel pput may prduce a perceptual bst fr nvel stimuli, these stimuli may remain relatively imperceptible when briefly viewed in a highly familiar scene. In examining the perceptibility f bjects f varying cngruency with their surrundings, ther researchers have fund nvel r incngruent bjects t be less perceptible than the familiar r cngruent bjects with which they appear (e.g., Biederman, Mezzantte, & Rabinwitz, 1982). This finding has been mre prnunced when the nvel bjects appeared in sme highly familiar setting such as a street scene, as ppsed t a mre abstract setting such as randmly arranged bjects n a cmputer screen (e.g., Biederman, Blickle, Teitelbaum, & Klatsky, 1988). Because bjects in naturalistic scenes tend t be arranged in stable cnfiguratins, the lcatins f these bjects culd, t sme extent, be inferred, thus inflating the likelihd f their crrect lcalizatin. In additin t the tpdwn benefits prvided by priming and schematic perceptin, this predictability wuld tend t ensure the superir lcalizability f familiar bjects. Hwever, the Biederman et al. (1982) study did nt incrprate the equivalent f an all-nvel baseline cnditin, s the extent t which nvel bjects in this study nnetheless benefited frm a subtle shift f attentin is nt knwn. Thus, even thugh familiar bjects are substantially mre lcalizable than nvel nes in highly familiar scenes, a subtle shift fattentin tward nvel bjects in these settings may cntinue t ccur. In Experiment 3, we sught t determine whether the between-arrays effects indicative f nvel pput cntinue t ccur even when the lcatins f familiar bjects are cmpletely predictable. T achieve this, familiar strings were presented in ne ftw frmats. In randm arrays, familiar strings cntinued t be randmly assigned t array lcatins, but infixed arrays, each familiar string always appeared in the same lcatin. Observers were randmly assigned t view ne f these tw frmats at the

6 266 HAWLEY, JOHNSTON, AND FARNHAM start f the experiment. Thus, althugh sme f the bserversculd inferthe lcatins ffamiliar strings, thers culd nt. Ifhigher levels f lcatin predictability merely inflate lcalizatin accuracies fr familiar bjects withut eliminating a capture f attentin by nvel stimuli, then bth nvel pput and familiar sink-in shuld be bserved, even fr fixed arrays. Methd Observers and Design. A new sample f 72 bservers was recruited frm the same pl used in Experiments 1 and 2. The design was a 2 x 3 (array frmat x array cmpsitin) mixed factrial, with repeated measures n the secnd factr. String type (nvel vs. familiar) cntinued t be a third factr nested within the ne-nvel arrays. Equipment, Stimuli, and Prcedure. The equipment and sftware were identical t thse emplyed in Experiments 1 and 2. A new sample f532 bjects, which varied frm fur t seven characters in length, was generated by using the same prceduredescribed in Experiment 1. At the start fthe experiment, the bservers were randmly assigned t ne f the tw array frmat grups. Fr the bservers in the randm-array grup. the familiar strings were assigned randmly t lcatins. Fr the bservers in the fixed-array grup. each familiar string always appeared in the same spatial 10 catin. Fr each grup, three independent cnstructins f the experiment, entailing different familiar strings and different rderings fprbed lcatin and array type, were made; each cnstructin was administered t 12 bservers. In all, there were 484 experimental trials, including 116 practice trials and 368 test trials. The frmer trials cnsisted f96 all-familiar and 20 all-nvel arrays, and the latter trials cnsisted f 160 allfamiliar arrays, 128 ne-nvel arrays, and 80 all-nvel arrays. All ther prcedures were identical t thse emplyed in Experiments I and 2. Results and Discussin The results fr Experiment 3 are summarized in Figure 4. Althugh lcalizatin accuracies fr all-familiar arrays were significantly higher than thse fr all-nvel arrays in bth f the grups [F(l,70) = , MS e = ], the strng interactin between this effect and the factr farray frmat cnfirmed what was expected and what is evident in Figure 4; namely, familiar bjects were much mre lcalizable when they appeared in fixed rather than in randm frmats [F(l,70) = , MS e = ]. Hwever, in spite f the near-perfect lcalizability f familiar strings in the fixed frmat, bth nvel pput and familiar sink-in achieved statistical reliability in bth f the grups. As Figure 4 shws, nvel strings were lcalized mre accurately when they appeared in ne-nvel as ppsed t all-nvel arrays [F(l,70) = 7.51, MS e = ], and familiar strings in these arrays were. lcalized less accurately than when they appeared in allfamiliar arrays [F(l,70) = 5.42,MS e = 57.18]. Neither fthese effects interacted with the factr farray frmat (bth Fs < 1.0). Mrever, althugh there was a significant main effect f string type within the ne-nvel arrays [F(1,70) = , MS e = ], this effect interacted strngly with the factr farray frmat [F(l,70) = , MS e = ]. Pst hc tests revealed that althugh familiar strings were much mre lcalizable than -as.!:! as u..j -U CD... til C -as.!:! as u..j -U CD Randm Frmat Grup Familiar f2i Nvel I-_1.-_...J._...L<~'l-.,..._...J~...:.L..., All-Familiar One-Nvel All-Nvel Array Cmpsitin All-Familiar Fixed Array Frmat Grup One-Nvel Cmpsitin Familiar E:l Nvel All-Nvel Figure 4. Lcalizatin accuracy fr nvel and familiar bjects in Experiment 3 as a functin farray cmpsitin fr bth array frmats. Nte that therdinateaxis fr thefixed-frmat grup has been brken t accmmdate the higherlcalizatinaccuracies fr fixed familiar strings. (Vertical bars represent standard errrs.) the accmpanying nvel string in fixed-frmat ne-nvel arrays [t(36) = 16.94, SE = 2.69], thse in randmfrmat arrays were apprximately equal t their nvel cunterparts [t(36) = 0.52, SE = 1.29] in lcalizability. Cllectively, these findings suggest that althugh lcalizatin accuracies fr familiar bjects are substantially enhanced by the lcatin predictability inherent in stable, naturalistic scenes, this enhancement des nt eliminate the shift f attentin tward nvel r unexpected bjects in thse scenes. These findings are particularly remarkable in light f the highly unfavrable cnditins fr btaining nvel pput in the fixed-array grup. Because the lcatins f

7 familiar strings in this grup are cmpletely predictable, there is relatively little incentive fr bservers t rely n a detailed bttm-up analysis f arrays. Indeed, a cmparisn f lcalizatin accuracies fr nvel strings in the fixed and randm grups revealed a significant drp in lcalizatin accuracy fr nvel strings in the fixed-frmat grup [F(l,70) = 6.74, MS e = ], suggesting that the bservers in this grup relied less n bttm-up prcessing fthe arrays than did thse in the randm-frmat grup. Because the detectin f perceptually incngruent infrmatin is presumably dependent n the bttm-up prcessing f an array r scene, the cntinued presence fnvel pput under cnditins in which bttm-up infrmatin is underutilized suggests that the mechanisms upn which nvel pput is based require relatively little bttm-up infrmatin. Finally, althugh the relative magnitudes fthe nvelpput effects depicted in Figure 4 are small in cmparisn with the effect f lcatin predictability, there are at least tw reasns why this shuld nt be cnsidered t trivialize the impact fnvel pput in scene perceptin. First, it is nt clear that the abslute magnitude f nvel pput in briefly expsed arrays directly crrespnds t its lng-term impact n perceptual prcessing. Althugh the perceptual enhancement resulting frm a shift in attentin tward nvel bjects in highly predictable scenes may nt be enugh t vercme the perceptual advantage ffamiliar bjects, the perceptualbstaccrded this bject may still be sufficient t bth enhance its subsequent perceptibility and t facilitate the frmatin f assciative links betweenthatbjectand the familiar bjectsthat surrund it. In turn, acrss multiple expsures tthe same scenes, these prcesses may be sufficient t allw a slw but cntinuus updating f perceptual schemata in respnse t envirnmental change. Secnd, althugh the present findings suggest that nvel bjects are substantially less perceptible than familiar nes when briefly viewed in highly predictable arrays, there is cnsiderable evidence that lnger viewing time f such arrays results in nvel stimuli's being bth recalled and recgnized mre accurately than theirfamiliar cunterparts (Bwer, Black, & Turner, 1979; Friedman, 1979; MiintyHi & Backman, 1992; Pezdek, Whetstne, Reynlds, Askari, & Dugherty, 1989). Thus, the relatively small nvel-pput effect bserved in Experiment 3 may in fact reflect the initial stages fa mre detailed level fperceptual prcessing wherein strng memrial traces fr stimuli that are incngruent with their surrundings are established. GENERAL DISCUSSION In the present research, we investigated sme fthe cnditins under which attentin is captured by nvel r unexpected stimuli. If, as suggested by Jhnstn et al. (1990), the capture fattentin by nvel stimuli cunteracts the biasing effects f schematic perceptin, then a brader understanding f the cnditins under which this effect perates is crucial t the develpment fmre cm- NOVEL POPOUT 267 plete theries fperceptual prcessing. The results fthe present experiments attest t the generality and rbustness f nvel pput. The present research extends the research n nvel pput in several ways. First, each fthe present experiments demnstrates that nvel pput can be btained with the use fnnsense strings as stimuli, in lieu fwrds. Nvel pput in these experiments was manifested bth as a higher accuracy f lcalizatin fr nvel strings in nenvel arrays versus thse in all-nvel arrays, and as lwer accuracies fr familiar strings in ne-nvel arrays versus thse in all-familiar arrays. These findings shw that nvel pput is nt limited t stimuli with well-established meanings, such as the wrds emplyed in ur previus studies (Jhnstn et al., 1990, 1993). Rather, they suggest that nvel pput is a relatively general perceptual phenmenn in which attentin is captured by any bject that is incngruent with the scene in which it appears. Mrever, because the stimuli used in the present experiments were generally unfamiliar t subjects, it seems likely that the mechanisms that underlie nvel pput can perate n the physical representatins f stimuli alne. A secnd finding that emerges frm the present study is the bservatin that nvel pput can ccur under cnditins that lessen reliance n bttm-up perceptual infrmatin (e.g., the fixed-array grup fexperiment 3). This fmding suggests that nvel pput hlds up ver a wide range f levels f bttm-up prcessing fr an array r scene. Further, because the lcatins f familiar strings in fixed arrays were cmpletely predictable, nvel pput des nt appear t be based n any perceptual r memrial cnfusin regarding the lcatins f familiar bjects. Finally, the bservatinthatthere is nvel pput when the length fnvel and familiar strings is held cnstant, thus remving the simple feature f string length as a cue fr discriminating between stimuli, suggests that nvel pput entails a mre detailed perceptual analysis f nvel and familiar strings than a simple discriminatin based n string length. Altgether, these findings generally reinfrce the view that nvel pput is a relatively basic and rbust perceptual phenmenn. As indicated by the results f Experiment 3, increases in the spatial predictability ffamiliar strings tend t prduce cncmitant increases in lcalizatin accuracy fr thse strings. One effect f this increase is that familiar strings are lcalized cnsiderably mre accurately when they appear in a predictable frmat than when they ap.pear in a randm frmat. This difference extends t arrays in which a single nvel string is intrduced, s that familiar strings in highly predictable arrays are lcalized mre accurately than the nvel string that appears in their midst. Hwever, in spite f this enhanced lcalizability f familiar ver nvel strings in highly predictable nenvel arrays, nvel strings in these arrays cntinue tbenefit frm a shift f attentin. This shift is manifest bth as lwerlcalizatin accuracies fr familiar strings in nenvel arrays versus thse in all-familiar arrays and as higher accuracies fr the nvel string in these arrays

8 268 HAWLEY, JOHNSTON, AND FARNHAM versus thse in all-nvel arrays. This suggests that nvel pput cntinues t perate in, and is relatively undiminished by, situatins in which the identities and lcatins ffamiliar bjects are highly predictable. Because lnger perids farray expsure are knwn t prduce a marked enhancement in bth recall and recgnitin fr nvel stimuli, it seems likely that this shift reflects the initial stages f a mre intensive prcessing f thse stimuli. In summary, the present studies reinfrce the view f nvel pput as a relatively basic, primitive, and rbust perceptual phenmenn in which bjects that are incngruent with their surrundings capture attentin. Given bth the generality f the effect and its agreement with studies demnstrating increased recall and recgnitin fr nvel versus familiar stimuli, it seems likely that nvel pput acts as a persistent and substantial cunterweight t the biasing effects fpriming and perceptual schemata. If the shift f attentin tward nvel stimuli fsters the integratin f thse stimuli within existing perceptual schemata, then nvel pput may substantially increase the survival ptential f rganisms by allwing them t cnstantly detect and adapt t changes in their envirnment. REFERENCES BIEDERMAN, I. (1972). Perceiving real-wrld scenes. Science, 177, BIEDERMAN, I., BUCKLE, T. W., TEITELBAUM, R. C., & KLATSKY, G. J. (1988). Object search in nnscene displays. Jurnal f Experimental Psyclwlgy: Learning, Memry, & Cgnitin, 14, BIEDERMAN, I., MEZZANOTTE, R. J., & RABINOWITZ, J. (1982). Scene perceptin: Detecting and judging bjects underging relatinal vilatins. Cgnitive Psychlgy, 14, BWER, G. H., BLACK, J. 8., & TURNER, T. J. (1979). Scripts in memry fr text. Cgnitive Psychlgy, 11, FEUSTAL, T. C., SHIFFRIN, R. M., & SALASOO, A. (1983). Episdic and lexical cntributins t the repetitin effect in wrd identificatin. Jurnal fexperimental Psychlgy: General, 112, FRIEDMAN, A. (1979). Framing pictures: The rle fknwledge in autmatized encding and memry fr gist. Jurnal fexperimental Psychlgy: General, 168, HAWLEY, K. J. (1991). PsyExper: Anther experimental generatin system fr the mm PC. Behavir Research Methds, Instruments, & Cmputers, 23, JACOBY, L. L., & DALLAS, M. (1981). On the relatinship between autbigraphical memry and perceptualleaming. Jurnal fexperimental Psychlgy: General, 3, JOHNSTON, W. A., HAWLEY, K. J., & FARNHAM,J. M. (1993). Nvel pput: Empirical bundaries and tentative thery. Jurnal f Experimental Psychlgy: Human Perceptin & Perfrmance, 19, JOHNSTON, W. A., HAWLEY, K. J., PLEWE, S. H., ELUOTT, 1. M. G., & DEWITT, M. J. (1990). Attentin capture by nvel stimuli. Jurnal fexperimental Psyclwlgy: General, 119, JONIDES, J., & YANTIS, S. (1988). Uniqueness f abrupt visual nset in capturing attentin. Perceptin & Psychphysics, 43, MANDLER, J. M. (1984). Stries, scripts, and scenes: Aspects fschema thery. Hillsdale, NJ: Erlbaum. MANTYLA, T., & BACKMAN, L. (1992). Aging and memry fr expected and unexpected bjects in real-wrld settings. Jurnal fexperimental Psychlgy: Learning, Memry, & Cgnitin, 18, MEYERS, D. E., ScHVANEVELDT, R. W., & RUDDY, M. G. (1975). Lci fcntextual effects n visual wrd recgnitin. In P. M. A. Rabbit & S. Drnic (Eds.), Anentin andperfnnance V(pp ). Lndn: Academic Press. PEZDEK, K., WHETSTONE, T., REYNOLDS, K., ASKARI, N., & DOUGH ERTY, T. (1989). Memry fr real-wrld scenes: The rle f cnstancy and expectatin. Jurnal fexperimental Psychlgy: learning, Memry, & Cgnitin, 15, RUMELHART, D. E., SMOLENSKY, P., MCCLELLAND, J. L., & HINTON, G. E. (1986). Schemata and sequential thught prcesses in PDP mdels. In J. L. McClelland & D. E. Rumelhart (Eds.), Parallel distributed prcessing (pp. 7-57). Cambridge: MIT Press. NOTE I. Our use f the phrase nvel pput may be misleading in light f the fact that nvel stimuli achieve abslute perceptual dminance ver familiar stimuli nly in the case f the within-array effect. As it was riginally used in Jhnstn et al. (1990), the term nvel pput was intended t dente the capture f attentin by any nvel r unexpected stimulus in an array f therwise familiar r expected stimuli. We recgnize that the term is smewhat cnfusing in that it is arguable ~at anentin capture and pput are nt synnymus terms (see Jmdes & Yantis, 1988). Hwever, in rder t avid generating a redundant vcabulary t describe the previusly reprted findings n nvel pput, we have chsen t emply the riginal descriptive terms develped by Jhnstn et al. (1990). Thus, thrughut this paper, the termnvel pput is used t dente a shift f attentin tward any nvel r unexpected stimulus within an array rscene as indexed by an increase in lcalizatin accuracy fr that stimulus relative t thernvel stimuli appearing in all-nvel arrays. (Manuscript received January 29, 1993; revisin accepted fr publicatin July 24, 1993.)