DONALD F. DANSEREAU Texas Christian University, Fort Worth, Texas and. BILL R. BROWN University of Louisville, Louisville, Kentucky 40208

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1 Memry & Cgnitin Vl. 2. N. la The attribute selectin prcess in pattern perceptin: The effect f cnstraint redundancy and stimulus expsure time n the classificatin f spatially represented Markv patterns* DONALD F. DANSEREAU Texas Christian University, Frt Wrth, Texas and BILL R. BROWN University f Luisville, Luisville, Kentucky A transfer paradigm was used t study the effect f cnstraint redundancy (Re) and stimulus expsure time (ET) n the "same-different" classificatins f pairs f spatially represented Markv patterns (Vargus 7 stimuli; Evans & Mueller, 1966). In the training phase, each S classified, withut feedback, pairs f Vargus 7 stimuli generated as deviatins frm three prttypes (i.e., mst prbable sequences). Each S received stimuli genera ted at ne f three levels f Re and expsed fr ne f three duratins. In the test phase, all Ss classified different deviatins frm the same three prttypes at a single Re level and a single ET level. Unsupervised classificatin perfrmance was abve chance in bth training and transfer and increased slightly ver trials. Significant Re and ET effects were fund. These results supprted tw mdels f attribute selectin and utiliatin; discussins f these mdels and their relatinships t the findings were directed tward the analysis f the "scherna plus crrectin" hypthesis. A number f researchers cncerned with the encding f patterned stimuli have suggested that families f visual patterns (i.e., instances that are related t ne anther by a number f cmmn attributes) are stred in a structure that relates each individual stimulus t a representatin f the cmmunalities ccurring within the entire family. Fr example, a particular dg may be stred as a set f deviatins frm the attributes which are cmmn t all dgs. Such terms as schema plus crrectin (Wdwrth, 1938; Oldfield, 54), ideal plus transfrmatin (Bregman, 1968), and central tendency (r prttype) plus distrtin (psner, 1968) have been used t describe this hypthesied strage cnfiguratin. Encding f schematic characteristics plus the deviatins f individual stimuli frm the schema represents an effective prcess fr reducing memry strage (Oldfield, 1954; Attneave, 1957). The natural envirnment, hwever, seidm prvides an intact, undistrted prttype r schema. T cmplicate matters, the members f several different but clsely related schema families generally ccur tgether. Such strage cnfiguratins as schema plus crrectin are thus relevant t rdinary human pattern perceptin and strage nly if: (1) Ss are able t select the apprpriate set f attributes that are critical fr family membership (attribute selectin), (2) Ss are able t encde the *This research was supprted by the Department f Defense, Prject THEMIS Cntract (DAAD05-68-e-0176), under the Department f Army t the Institute fr the Study f Cgnitive Systems thrugh the TCU Research Fundatin. Further reprductin is authried t satisfy necds f the U.S. Gvernment. attribute values that define the prttype (prttype abstractin), and (3) Ss are able t use the stred prttypes t c1assify and encde new distrtins and t recgnie and recall previusly stred instances (prttype utiliatin). A number f experiments have attempted t deal directly with prttype abstractin and utiliatin. Psner and Keele (1968, 1970) have shwn that the prttype can be classified mre efficiently than ther instances f the same family after training n nnprttype family members. Studies by Hinsey (1963), Vinikr (1968), and Nrcrss (1968) have shwn that c1assificatin f distrted stimuli is enhanced by previus expsure t the prttype frm which these peripheral instances are derived. There are, hwever, tw factrs that limit the generaliability f these studies t real wrld pattern perceptin: (1) the presence f feedback, and (2) the simplicity f the distrtins used t prduce schema families. Generally, feedback (knwledge f results) is prvided t Ss in these studies t guide their abstractin and/r utiliatin prcesses. In the ne case feedback was nt emplyed, the Es, Psner and Keele (1970), btained results which did nt cnfrm t previus findings. Anther imprtant factr, affecting generaliability, is that the schema families used experimentally have been prduced primarily by apply i ng simple, independent manipulatins f prttype pints, r by simple rtatin. These cnditins d nt adequately simulate the natural envirnment in which feedback is usually nt prvided, and the available stimuli are distrted in a mre cmplex fashin. Experiments dealing with attribute selectin are based 75

2 76 DANSEREAU AND BROWN n the fact that stimuli presented fr classificatins ften vary alng a large number f attributes r dimensins, nly a subset f which determine family membership. The first step in learning a new schema family invlves the selectin f apprpriate attributes thrugh experience with the stimuli. This increased sensitivity t critical attributes is fllwed by the abstractin prcess, which invlves the strage f attribute values defining the schema r prttype. Prttype utiliatin then fllws directly. It shuld nt be assumed, f curse, that these prcesses necessarily ccur sequentially; the prcesses undubtedly verlap. Studies in the area f attribute selectin have been designed t explre the variables cntrlling the selectin prcess. T date, it has been shwn that: (1) Ss can becme increasingly sensitive t the attributes that define schema families withut the presence f external feedback (Hastings et al, 1969; Hastings, 1970; Harris et al, 1970; and Rankin & Evans, 1968). It shuld be nted, hwever, that the families used in these studies are frmed by prducing simple, attribute-independent (dependent nly n spatial lcatin f the attribute) deviatins frm the prttypes. (2) The amunt f deviatin strngly influences perfrmance n tasks requiring sensitivity t an apprpriate set f attributes (Brwn et al, 1968; Brwn & Dansereau, 1969). There are, hwever, still a number f issues relating t attribute selectin that must be reslved in rder t prvide the grundwrk fr further experimentatin n prttype abstractin and utiliatin: (1) Can Ss becme increasingly sensitive t an apprpriate set f attributes, withut external feedback, when the schema farnilies are prduced by cmplex distrtins frm a prttype? An example f such stimuli wuld be thse created by mapping the results f P. Markv prcess int the spatial dmain. Patterns f this type wuld be analgus t graphical representatins f time series data (e.g., EEG recrds). In additin, deviatins frm the mst prbable Markv sequence can represent cmplex rtatins f parts f a spatial pattern. Studies invlving spatially represented Markv stimuli have fund that Ss were influenced by the attributes (Brwn & Dansereau, 1969; Brwn & Evans, 1969), but have nt fund an imprvement in classificatin perfrmance ver trials. It is, therefre, nt clear that Ss can learn t refine their attribute selectins in the face f mre cmplex distrtin. (2) D Ss becme sensitive t the level and type f stimulus distrtin as well as t the relevant attributes fr schema discriminatin? This questin sterns frm Attneave's (1957) hypthesis that Ss learn the relative variability f the family members abut the prttype as weil as the schema r prttype itself. If this ntin is crrect, transferring Ss frm ne level f distrtin t anther shuld strngly affect certain aspects f their pattern classiflcatin perfrmance. Specifically, in a task requiring the S t say whether tw patterns belng t the same family r t different families, it might be expected that the threshld fr making "same" r "different" judgments wuld be altered fllwing training n stimuli at varius distrtin levels. (3) Des Ss' perfrmance vary systematically with stimulus expsure time? The relatinship f expsure time t perfrmance may depend heavily n the prcesses Ss emply in making classificatin judgments; therefre, specificatin f the relatinship may lead t mre detailed hyptheses abut attribute selectin. The present experiment was designed t explre the issues cited abve. Ss were required t classify spatially represented Markv patterns withut feedback (knwledge f results). In the training phase, amunt f distrtin hree levels) and expsure time hree levels) were treated as between-s variables. In the test phase, all Ss served under a single distrtin level and a single stimulus expsure time. Since the study invlved multiple independent variables and was primarily explratry in nature, detailed hyptheses were nt made. In general, it was expected that increasing the distrtin f the training stimuli frm the prttype wuld be deleterius t perfrmance in bth the training and test phases. The effect f increasing stimulus expsure time was expected t imprve perfrmance, but interactins f this variable with distrtin level were anticipated. METHOD Subjects The Ss cnsisted f 90 undergraduates enrlled in intrductry psychlgy curses at Texas Christian University. Stimuli The Vargus 7 cmputer prgram (Evans, 1967a) was used t generate Markv digit strings f 50%, 70%, and 100% enstraint redundancy (Re). The Re measure has been discussed in detail by Evans (l967b) and refers t the extent t which the stimuli adhere t a schema rule (i.e., the average degree f distrtin ver the entire family f patterns). The 100% Re strings are sirnply cyclic permutatins f ne anther (e.g., 1,2,3,4; 2,3, 4, 1; 3, 4, 1, 2 wuld an be 100% Re members f the same family). In a sense, these stimuli are examples f the Markv prttype (i.e., the mst prbable sequence). Strings prduced at the 70% Re level have the same cyclic permutatin prperties, but they als cntain deviatins frm the mst prbable sequenee ransitin prbabilities alng the mst prbable sequence are.88 in this case). At 50% Re the stimuli have an even higher prbability f being distrted (.79 is the prbability f a mst prbable sequence transitin). These sets f digit strings, prduced by the Vargus 7 prgram, were mapped int histfrm (histgram-like) patterns fr spatial presentatin. The instances were 24 clumns in length and were prduced frm a seven-element Markv prcess by cnverting the elements int clumn heights. The prgram selected clumn heights with transitinal prbabilities favring three different mst prbable sequences (MPSs). The stimulus ppulatins sampled in the present study can be fund in Bersted, Brwn, and Evans (l968a), and are identified as Schemata 2, 3, and 4. The manner in which the stimuli were generated assured that crrespnding instances f the three schema families had the same variance. This variance measure is the prprtin f schematic steps (POSS) fr each instance, and it describes the

3 ATTRIBUTE SELECTION PROCESS IN PATTERN PERCEPTION 77 adherence f each individual instance t the MPS. The POSS statistic has been discussed in detail by Bersted et al (l968a). The cmputed POSS values fr stimuli generated at 100% Re wuld, f curse, always be 1.00, althugh the first clumn in each f these instances culd crrespnd t any f the seven elements in the MPS. Training Task The Ss were given 60 trials with 50%, 70%, r 100% Vargus 7 patterns. On a typical trial, the Ss viewed tw stimuli and then judged them t be f the same family r f different families. The 60 trials cnsisted f 30 pairings f instances frm different schema families and 30 pairings frm the same family, A Kdak Carusel prjectr, impulsed by tapes that cntrlled the varius timing sequences, prjected each f the 60 stimulus pairs nt a 2 x 2 ft while rear prjectin screen. Fr each f the three Re cnditins, the fllwing duratins cnstituted the presentatin time variable: (1) 2 sec (100%-2, 70%-2, and 50%-2 grups); (2) 5 sec (100%-5, 70%-5, and 50%-5 grups); and (3) 8 sec (100%-8, 70%-8, and 50%-8 grups). The Ss were randmly assigned t the nine treatment cnditins (10 Ss per grup). Grups f tw Ss, seated 5 ft frm the screen, were given 7 sec t mark their judgments f each pair n an answer sheet. A variable intertrial interval was used t equate all Ss with respect t the ttal amunt f time spent in the task. N ne instance frm any f the three schemata was presented mre than nce during the 60 trials. The tw instances presented n each trial, whether they were frm the same r different schemata, were paired n the basis f their having equal POSS values. This prcedure assured that the instances f any given pair were equal in difficulty as far as abstractin f the schema rules was cncerned. In the case f the 100% Re stimuli, the patterns were paired n the basis f their first clumns being f different heights. Tw stimulus presentatin rders were used. These were randmly prduced under the cnstraint that each blck f 10 trials cntained an equal number f "same" and "different" pairings. Test Task Fllwing training, ali Ss received 60 trials f 70% Re patterns sampled frm the same three schema families used in the training task; hwever, n stimulus appeared in bth the training and test phase. A 5-sec presentatin time and 7-sec respnse time were used fr all Ss. As in training, 50% f the 60 trials invlved the pairing f instances frm different schema families; the remaining 50% f the trials cnsisted f pairs f instances sampled frm the same family. Instances frm the three schema families were represented nly nce in the task. Tw presentatin rders were btained, using exactly the same methd as used in the training phase. These rders were equally represented within the nine training cnditins. RESULTS In rder t evaluate the effects f the tw stimulus presentatin rders upn perfrmance, a three-factr analysis f variance (with Re, expsure time, and presentatin rder as variables) was cnducted separately fr the training and test task. Re and expsure time (ET) fr the test grups were the cnditins they were expsed t during training. The number f crrect same-different judgments made acrss 60 trials served as the dependent measure fr each f these analyses. The rder f stimulus presentatin, in bth the training and testing phases, was nt significant C)'Q B.e '" wvi.10 Z Q. '" ~.e~ > u w Q'..80 0: U Q..- CHANCE a::.~ Q. 0: Q.. ' BLOCKS OF TEN TRIALS Fig. 1. Prprtin f crrect "same-different" respnses in training fr the three Re grups as a functin f blcks f trials. and did nt significantly interact with the Re r ET cnditins present in the training task. In rder t simplify the subsequent analyses, the tw presentatin rders were cmbined fr all treatment grups. Training Task A three-way analysis f variance with tw between-grup factrs (Re and ET) and ne within-grup factr (blcks f 10 trials) was perfrmed with the number f crrect same-different judgments made in the training task as the dependent variable. There was a significant blcks effect, F(5,405) = 7.84, p<.001, a significant Re main effect, F(2,81) = 13.61, p<.001, and a significant ET main effect, F(2,81) = 7.83, p<.01. Figure 1 shws that increasing the magnitude f Re n the training task facilitated perfrmance. Perfrmance als imprved as a functin f increasing the amunt f ET (see Fig. 2). The Re by ET interactin was als significant, F(4,81) = 4.77, P <.05; a highly significant prtin f the variance accunted fr by this interactin may be attributed t the simple main effect f ET at the 100% Re level, F(2,81) = , p<.001. Figure 3 shws that increasing ET facilitated perfrmance under the 100% Re cnditin, but prduced little effect n perfrmance under the 50% and 70% Rc cnditins. The simple effects f ET at these latter tw Re levels were nt significant. Test Task A three-way analysis f variance with tw between-grup faetrs (Re and ET training cnditins)

4 78 DANSEREAU AND BROWN.0..,..7. Z 0 0- ll) t- V "' lt 0V.6. u, 0 '? I- (!: lt.e. ~ I SECS.. 2 sees BLOCKS OF TEN TRIALS e. ~ Fig. 2. Prprtin f errect "same-different" respnses in training fr the three ET grups as a funetin f blcks f trials..ic ~.'~ Cl..IC '" ll:.7. _ 100'f!.C ' f!.c erreet judgments made in the test task by the 50% Re training grup (cllapsed aerss ET) t that exhibited in training under the 70% Re cnditin (cllapsed acrss ET). Cntrary t expectatin, the perfrmance mean fr the 70% Re grup in training was nt significantly different frm that f the 50% Re training grup in the test task. Training n 50% Re stimuli thus did nt facilitate perfrmance with 70% Re stimuli in cmparisn t a n-training cnditin. In rder t prvide mre detailed infrmatin abut the effects f shifts in Re magnitude n perfrmance, a three-way analysis f variance, with tw between-grup factrs (Re and ET) and ne within-grup factr raining task and test task), was cnducted using the ttal number f "different" judgrnents rials n which Ss judged the patterns t be frm different families) as the dependent variable. The Re by Task interactin was highly significant, F(2,81) = 26.10, p<.001. Table 1 shws that inereasing the magnitude f Re tended in tj.i.70 '" Z \Ü.1$ l V a: "',80 8 IOO"70!!C.1. "Z Q t- ':) a: Cl. -==::-::::::-:::::==---=:::::::::: '? I- er.'0 e lt.e. 0'----' ' ' 2 SEC.. 5(C'. Ire>. STIMULUS EXPOSURE TIME Fig. 3. Prprtin f crrect "same-different" respnses in training fr the grups serving under the varius Re-ET embinatins. and ne within-grup factr (blcks f five trials) was used t analye perfrmance in the test task. The number f crrect same-different judgrnents made in the testing phase cnstituted the dependent measure. As in training, the blcks effect was significant, F(5,405) = 3.40, P <.01. Mrever, the Re main effect was significant, F(2,81) = 4.98, p<.01. Inspectin f Fig. 4 shws that perfrmance in the test task was facilitated by increasing the magnitude f Re present in training. The abve analysis was accmpanied by attest fr independent grups in rder t cmpare the mean BLOCKS OF TEN TRIALS Fig. 4. Prprtin f errect "same-different" respnses in testing fr the three Re grups (in training) as a funetin f blcks f trials. Table 1 Ttal Number f "Different" Respnses: Crreet and Inerreet* _ Grups Training Transfer "There are 300 actual "different" trials fr each f the nine graups.

5 ATTRIBUTE SELECTION PROCESS IN PATTERN PERCEPTION 79 general t prduce a decrement in the number f "different" respnses in training. On the ther hand, the number f such respnses exhibited in testing became larger as a functin f increased magnitudes f Re present in the training phase. lt is imprtant t nte that in all cases, the percentages f "different respnses" were abve the ideal 50% level. Althugh it might be expected that classificatin perfrmance wuld imprve as the "different" percentage apprached 50%, the ppsite relatinship was fund in the test task. DlSCUSSION The results f the training phase shw that perfrmance n the "same-different" discriminatin task is abve chance and increases slightly ver blcks. These results clearly indicate that, even withut knwledge f results, Ss can select an apprpriate set f attributes upn which t base discriminatin judgments f spatially represented Markv stimuli. Since the Markv prcess generates stimuli cmpsed f "parts" (in this case, clumn heights) that depend nly n their immediate predecessrs and nt n spatial psitin, it is apparent that Ss can learn t attend t relatinships between stimulus "parts" independent f their spatial lcatins. With place-dependent stimuli, such as thse used in the majrity f abstractin and utiliatin studies (e.g., Vargus 9 stimuli, Evans & Mueller, 1966), "parts" f patterns are crrelated with bth the preceding "parts" and with their spatial psitin. lt is therefre nt pssible t determine which aspect f the pattern is critical t the Ss' judgments. The results f this experiment prvide an initial step in specifying the critical features f attribute selectin; it is apparent that Ss, at least under sme circumstances, can utilie infrmatin based n lcal (first-rder) relatinships between the "parts" f spatial patterns. lt remains t be determined t what extent this prperty is utilied when psitin infrmatin is als present. There are at least tw hyptheses abut hw Ss may be using the selected attributes in arriving at their "same-different" judgments. Upn presentatin f tw patterns t be judged same r different, the S may, in sme sense, "measure" the distance between the tw stimuli alng a set f attributes he has selected and then respnd accrding t the magnitude f this difference (i.e., if small differences, respnd "same"; if large differences, respnd "different"). These "measurements" culd be made withut any reference t a schema r prttype. A secnd pssibility is that each f the tw stimuli is cmpared with each f the stred prttypes. The stimulus is then cnsidered t be a distrtin f the clsest prttype. The stimuli are judged t be same if they are distrtins f the same prttype and different if they are distrtins f different prttypes. Bth f these hyptheses predict the results f the training task, including the apparent increase in the bias t say "different" as Re decreases (Table 1). The effect f decreasing Re, due t the distributinal prperties f the sample (stimuli at small distance frm the prttype ccur mre frequently than stimuli at large distances), is t increase the average distance alng an apprpriate set f attributes between stimuli f the same schema family and, by definitin, t increase the average distances f stimuli frm their prttype. These crrelated increases wuld bth result in a greater number f "different" respnses and ptentially prer perfrmance, depending n the threshlding peratin. The ET effect is als cmpatible with bth hyptheses. Increased ET at 100% Re allws Ss t develp mreaccurate "measures" whether between stimuli r between the stimuli and their prttypes. At lwer Re (50% and 70%), the increased distances between pairs f stimuli and between the stimuli and their prttypes prhibit greater accuracy with greater expsure time. The Re effect in the analysis f crrect judgments in the test task indicates that experience n the unsupervised discriminatin f 100% Re stimuli, which in effect are Markv prttypes, is mre effective than identical experience with distrtins f these prttypes, even when the level f distrtin in training is the same as with the test stimuli (70% t 70% cnditin). These results are in accrd with Attneave (1957) and Hinsey (1963), wh fund facilitatin f perfrmance n family members after expsure t the prttypes. The results als cnfirm the findings f Lawrence (1952), Baker and Osgd (1954), and Restle (1955). These investigatrs have shwn that, under certain circumstances, a difficult discriminatin may be learned mre easily if the Ss are trained n an easy discriminatin f the same type than if all training is given directly n the difficult discriminatin. The fact that prir familiariatin with the prttypes facilitated discriminatin f peripheral stimuli des illustrate what has been termed "prttype utiliatin." In this case, hwever, such a cnceptualiatin may be misleading in that the enhancement culd be prduced by an increase in sensitivity t the apprpriate attribute space, as weil as by the actual utiliatin f the stred prttypes. All that can be cncluded, therefre, is that sme infrmatin abut the apprpriate dimensins was stred during expsure t prttypical instances. The significant result f the t test cmparing S-D perfrmance n the 70% Re stimuli in training with perfrmance n the 70% Re stimuli in the test phase after 50% Re training shws that, apparently, training n 50% Re stimuli is nt f any psitive value t the Ss in perfrming 70% Re diseriminatins in the test task. This result is supprted by Bersted et al (1968b); they fund that training n50% Re task did nt, in general, imprve subsequent perfrmance n a reprductin task in emparisn with a grup pretrained n randm patterns. It is suggested that individuals in the 50% Re grup in training are nt attending t an apprpriate set f

6 80 DANSEREAU AND BROWN Table 2 Variances f the Ttal Scres Grups Training Transfer 1OD D D D D D attributes, since their perfrmance is nly slightly abve chance. Apparently the amunt f distrtin invlved in 50% Re stimuli severely interferred with the attribute selectin prcess. The analysis f the shift in "D" bias frm training t test shwed that the lwer the distrtins in training, the greater the "D" bias in the test task. Smewhat unexpectedly, this bias is negatively related t perfrmance in terms f S-D judgments. Hwever, the ntin f increased cnservatism in setting requirements fr class inclusin with training n increasing1y undistrted stimuli is nt withut supprt. Psner (1968), in reviewing a number f studies, prpsed that a majr functin f increased variability is in changing the criterin fr acceptance f a new pattern as a member f the same categry. He suggested that lw variability training (high Re) aids Ss in becming sensitive t the apprpriate attributes and in abstracting a prttype, but leads t a cnservative criterin fr dass inclusin. These results supprt Attneave's (1958) cntentin that Ss becme sensitive t the variability f dass members abut their prttype as weil as the apprpriate set f attributes which define the family. It is interesting t nte that the grup perfrmances in these types f tasks, as in mst learning experiments, may be misleading. The variances f the nine grups in the training and test phases are shwn in Table 2; these variances are significantly hetergeneus in bth tasks. The results f tw Cchran tests shw C(9,9) =.53, p <.01 in the training phase and C(9,9) =.31, P<.01 in the test phase. Variance appears t increase as Re increases and t a lesser extent as ET increases in training. This variance reflects individual differences in S-D perfrmance; in fact, at the high Re level Ss' perfrmance appears t be bimdal, while at the lwer levels perfrmance is cnsiderably mre hmgeneus. Mdels f this behavir shuld reflect these individual differences. In cnclusin, the results f this experiment have the fllwing implicatins fr the issues cited in the intrductin: (1) Ss can, withut feedback, select an apprpriate set f attributes upn which t base their discriminatin f stimuli prduced as relatively cmplex distrtins f varius prttypes. This finding is an imprtant prerequisite fr the extensin f the schema plus crrectin hypthesis t real-wrld pattern perceptin. (2) Ss apparently becme sensitive t the variability f family members abut their prttype (i.e., the average amunt f deviatin) and make use f this infrmatin in making classificatinjudgments. (3) Unsupervised training n Markv prttypes enhances subsequent classificatin perfrmance n distrted instances f the same schema families. This enhancement is greater than that which ccurs with training n patterns at the same level f distrtin as the test stimuli. (4) Increased stimulus expsure time at high Re (lw distrtin) tends t imprve perfrmance, presumably by allwing the Ss t respnd t and encde a larger subset f the attributes relevant t stimulus classificatin. At lw Re (high distrtin), the greater prprtin f nnschematic infrmatin available in the patterns apparently inhibits imprvement n the basis f increased viewing time. REFERENCES Attneave, F. Transfer f experience with a class-schema t identificatin-iearning f patterns and shapes. Jurnal f Experimental Psychlgy, 1957,54, Baker, R. A., & Osgd, C. W. Discriminatin transfer alng a pitch cntinuum. Jurnal f Experimental Psychlgy, 1954, 48, : Bersted, C. T., Brwn, B. R., & Evans, S. H. A standard set f Vargus 7 patterns at three levels f schematic redundancy. Psychnmic Mngraph Supplements, 1968a, 2, Bersted, C. T., Brwn, B. R., & Evans, S. H. 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