Some effects of epistemological structure on memory*

Transcription

1 Memry & Cgnitin 1974, Vl. 2 (4), Sme effets f epistemlgial struture n memry* JAMES D. HOLLANt Clarksn Cllegef Tehnlgy, Ptsdam, New Yrk Graph theretial mdels f the epistemlgial struture impsed upn a set f mathematial nepts by Ss' definitins f them were nstruted. Three graphial harateristis f the mdels were manipulated in a series f experiments t assess their effets n reall. Experiment I shwed that reall and nfidene f reall were highest fr nept pairs nneted by shrt paths, next highest fr thse nneted by lng paths, and lwest fr thse nt nneted by paths. Experiment II repliated the result f Experiment I that reall and nfidene f reall were greater fr nept pairs nneted by paths than fr thse nt nneted by paths and revealed n differenes in reall between nept pairs nneted by many paths and thse nneted by a few paths. Experiment III fund n differenes in reall f abstrat and nrete nepts. The abstratness f a nept was quantified by the mean path length frm the nept t primitive (undefined) nepts. The apprah f building a mdel f eah S's epistemlgial struture was supprted by the finding that, while a given S's definitins f the nepts remained relatively nstant, there were nsiderable differenes in definitins f the nepts between Ss. Currently there is a burgening interest in semanti relatinships and their imprtane t memry. Muh f this interest an be traed t the wrk f Quillian (1966) n semanti memry, and mst experimental studies in this area have fllwed the paradigm set frth by Cllins and Quillian (1969). This paper is nerned with the semanti relatin f definitin and with the effets n memry f varius aspets f the epistemlgial struture impsed upn a set f nepts by this relatin. The present experiments ntrast with previus wrk in semanti memry by mputing, rather than assuming, the partiular epistemlgial struturing f the set f stimulus nepts fr eah S and by emplying reall rather than reatin time tasks. THE EPISTEMOLOGICAL STRUCTURE A nept's definitin states the essential harateristis f the nept's referent and thus serves epistemlgially t distinguish the referent frm everything else. A nept is lgially dependent upn the nepts whih mprise its definitin, and these nepts are, in turn, dependent upn the nepts whih mprise their defmitins, et. Thus, inherent in any set f nepts is a dependeny struture impsed upn the nepts by their defmitins. This epistemlgial struture an be graphially represented by a digraph in whih a pint f the graph is assiated with eah nept and a direted edge frm ne pint t anther pint exists just in ase the nept *This paper is based n a dissertatin submitted t the Department f Psyhlgy, University f Flrida, in partial fulfillment f the requirements fr the PhD degree. The authr expresses his appreiatin t his dissertatin mmittee and t R. E. Osteen fr allwing his mputer prgram, PROJECT_X, t be adapted t the requirements f this study. trequests fr reprints shuld be sent t the authr at the Department f Sial Sienes, Clarksn Cllege f Tehnlgy, Ptsdam, New Yrk assiated with the first pint is defined in terms f the nept assiated with the send pint. Beause f the mplexity that an arise in the epistemlgial struture assiated with even a few nepts, a mputer prgram was used t nstrut the epistemlgial strutures f the Ss in the present experiments and t asertain the many harateristis f these strutures made pssible by the graphial frmalizatin. The input t the prgram emplyed is a set f nepts, the definitins f the nepts, and key nepts frm the defmitins. The prgram frms the epistemlgial struture impsed upn the set f nepts by the relatin f definitin and utputs the fllwing infrmatin: all the paths (Harary, 1969) frm eah nept t primitive (undefined) nepts, an alphabetial list f the nepts whih inludes eah nept's fathers and sns (Le., the nepts whih this nept is defined in terms f and the nepts whih are defined in terms f this nept), and all paths that exist between every pair f nepts with their length. OVERVIEW OF THEEXPERIMENTS By frmalizing, in graph thereti terms, the epistemlgial struture impsed upn a set f nepts by their defmitins, it bemes pssible t asertain many strutural harateristis f this epistemlgial struture. One these harateristis ha ve been identified, it is then pssible t experimentally investigate their effet upn perfrmane in psyhlgial tasks in whih suh epistemlgial infrmatin is thught t be imprtant. The general strategy f the experiments reprted here is t identify the strutural harateristis f as's epistemlgial struturing f a set f nepts and then t vary the nepts presented in memry tasks in suh a way that the effet upn memry reall f these 670

2 EPISTEMOLOGICAL STRUCTURE AND MEMORY 671 strutural harateristis an be assessed. I hse t use mathematiians as Ss in this study. This hie was ditated primarily by the fat that it allwed the use f mathematial nepts as the stimulus materials in the experiments. The mtivatin t use mathematial nepts was that these nepts are, in general, muh mre preisely frmulated than nepts frm ther areas and are, thus, ideally suited t the nstrutin f their assiated epistemlgial struture. The hie f mathematiians as Ss als allwed the restritin f the set f nepts used in the experiments t a rather limited set, namely, thse f naive set thery (Halms, 1960), with the assurane that sine mst mathematiians are well aquainted with set thery, the familiarity f the Ss with the set f nepts used was reasnably unifrm. Fifty nepts were hsen frm a text n set thery (Halms, 1960), and eah S was asked t define these nepts. The epistemlgial struture impsed n the set f nepts by a S's definitins f them was nstruted by use f the mputer prgram mentined earlier. Thus, eah S's partiular epistemlgial struturing f the set f nepts was knwn alng with the strutural harateristis assiated with eah nept as determined by the graphial frmulatin f the struture. In eah f three experiments, ne harateristi f a S's epistemlgial struture was manipulated, by apprpriate seletin f the nepts presented t the S, and its effet upn memry reall was assessed. The partiular harateristis studied were the number f paths between pairs f nepts, the lengths f suh paths, and the abstratness f the nepts. Fr purpses f this study, the abstratness f a nept was defined t be the mean path length f the nept frm the primitive nepts. A paired-assiate paradigm was emplyed t investigate the number and length f paths between nept pairs, while a free reall paradigm was used in the investigatin f the abstratness f the nepts. EXPERIMENT I Methd Subjets. Ten graduate students and faulty members f the University f Flrida Department f Mathematis partiipated in the experiment. Eah S was paid fr his partiipatin in this and the fllwing experiments. Design. Fr eah S, 21 pairs f nepts were frmed based upn his nstruted epistemlgial struture. A given pair f nepts was nneted in the graphial representatin f as's epistemlgial struture by a shrt path (mean length f 1.06 and standard deviatin f 0.23), a lng path (mean length f 3.86 and standard deviatin f 0.69), r was nt nneted by any path. A within-s design was emplyed rssing distane between nepts with trials. Predure. Fr eah S, five randm mixed-list rders f the S's 21 pairs f nepts (7 f eah type) were nstruted with the restritin that a prprtinate number f the three types f pairings urred in eah quarter f an rdering. The 21 pairs f nepts were presented tahistspially t a S at the rate f 1 pair every 8 se with a pair visible fr 2 se. After expsure t the 21 pairs f nepts, a S partiipated in a deding task fr 2 min t prelude reall frm shrt-term memry. A S was then given a sheet f paper ntaining all f the left-hand members f the pairs f nepts and asked t write next t eah nept the assiated right-hand member and t give an assessment f his nfidene f rret reall n a 4-pint sale. Fur suh study-test trials were mpleted in an experimental sessin. After a perid f 24 h, eah S returned and was given a test trial fllwed by a study-test trial. Results Analysis f Mean Perentage Crret Reall. The mean perentage rret reall f the respnse terms (MPCRT) fr eah distane nditin was mputed fr eah S n eah trial. A tw-fatr repeated measures analysis f variane perfrmed n this measure revealed that the verall effets f distane, f trials, and f the interatin between distane and trials were signifiant (p <.00 I). Figure I depits the MPCRT n the six trials fr eah distane nditin. Beause f the signifiant interatin between distane and trials and beause the distane variable was f primary interest in this experiment, Tukey's HSD test was used t mpare the differenes between the means f eah level f the distane variable n eah trial. This analysis revealed that n the first tw trials, the MPCRT f nept pairs nneted by shrt, lng, r n paths were signifiantly (p <.01) different frm eah ther with reall highest fr shrt pairs, next highest fr lng pairs, and lwest fr unnneted pairs; that MPCRT f shrt pairings were signifiantly (p <.05) larger than thse fr lng pairings n s 3 and 5; and that the MPCRT fr shrt pairs were signifiantly (p <.01) greater than fr pairs nt nneted by a path n 3. Analysis f Mean Cnfidene Rating. Fr eah trial, eah S's mean nfidene rating fr reall f the respnse terms in eah distane nditin was mputed. As with the analysis f MPCRT, the effets f distane, f trials, and f their interatin were all signifiant (p <.001). Figure 2 shws the mean nfidene rating n the six trials fr eah type f nept pairing. Tukey's HSD test was used t make all pairwise mparisns between the means f eah level f the distane variable n eah trial. The results f the HSD test almst exatly parallel thse f the MPCRT analysis. On s 1 and 2, Ss were signifiantly (p <.01 and p <.05, respetively) mre nfident f their reall f respnse terms f nept pairs nneted by shrt paths than thse nt nneted by any paths r thse nneted by lng paths, and the nfidene freall f respnse terms f lng pairings was signifiantly (p <.01) higher than that f thse nt nneted by paths. Other signifiant (p <.01) differenes were fund n s 3 and 5 with nfidene f reall fr the shrt pairings greater than that fr lng pairings n 5 and fr thse pairings nt nneted by any paths n 3.

3 672 HOLLAN Disussin The effet upn reall f three different levels f semanti relatedness f nept pairs was experimentally investigated, using a new apprah whih was designed t make pssible greater ntrl f this variable. In a paired-assiate task, pairs f nepts whih were nneted by lng paths, shrt paths, r were nt nneted by any paths were emplyed. Semanti distane, as quantified by mean path length between pairs f nepts in the graphial representatin f the epistemlgial struture that a S impsed n a set f nepts by his definitin f them, was fund t be a ptent variable affeting memry. The results were in ardane with a straightfrward extraplatin frm reatin time studies f semanti memry: reall and nfidene f reall were highest fr respnse terms f nept pairs nneted by shrt paths, next highest fr thse f nept pairs nneted by lng paths, and lwest fr respnse terms f nept pairs nt nneted by any paths. Althugh this rdering f reall was fund nly n the initial trials, parallel results were btained frm the analysis f the tw dependent variables: mean perentage rret reall and mean nfidene rating. While there were n signifiant differenes between either reall r nfidene f reall fr respnse terms f nept pairs nt nneted by paths and thse f nept pairs nneted by lng paths subsequent t the send trial, it is interesting t nte that as late as the fifth trial, i.e., the first delayed trial, there was a signifiant differene fr reall and nfidene f reall <\l U Q) a: 60 Q) Q) Ol 40 Cll Q) Q.. 20 L T RI A L :, Shrt Lng Nne Fig. 1. Mean perentage rret reall n eah trial fr the three distane nditins. OJ 3.00 u; (l) (l) 2.00 "Q C t1l (l) T R I A L (:; Shrt Lng Nne Fig. 2. Mean nfidene rating n eah trial fr the three distane nditins. fr respnse terms f nept pairs nneted by shrt paths and thse f nept pairs nneted by lng paths. One an reasnably pstulate, if retrieval strategies make use f the strutural aspets f the epistemlgial struture, that Ss adpt different strategies. fr reall f respnse terms f nept pairs nneted by paths and thse nt nneted by paths. Based n this assumptin, the results indiate that the strategy fr pairs nneted by paths was, in ardane with reatin time studies, mre effetive, even as late as the fifth trial, fr thse pairs nneted by shrt paths, while the strategy fr unnneted pairs was, subsequent t the third trial, an equally effetive reall strategy. It an, n the ther hand, be argued that the failure f a ntinuatin f the lear distintin between reall fr the three different types f pairings, fllwing the send trial, was due t nthing mre than a eiling effet f apprahing perfet reall.e In any ase, the results f the analyses f reall and nfidene f reall fr respnse terms f nept pairs nneted by paths are in agreement with Quillian's (1969) mdel f semanti memry and ntribute evidene fr semanti distane being a variable f imprtane in memry tasks invlving nepts. In regard t any nlusins nerning the relative effetiveness f the retrieval strategy used with nepts nneted by paths and the strategy used with nepts nt nneted by paths, if ne aepts the assumptin f different strategies, ne pint shuld be made lear. The frmer strategy, beause f its dependene n the meanings, i.e., the definitins, f the nepts, is ne that wuld readily be adpted by a S, sine it is the meaning f nepts whih the S nrmally deals with. If this is, in fat, the ase, the inferirity f reall n the initial trials fr respnse terms f nept pairs nt nneted by paths uld be aunted fr by the S's initially attempting t adpt this type f strategy and, 5 6

4 EPISTEMOLOGICAL STRUCTURE AND MEMORY (J) :::; '" Small Number f Paths a Large Number f Paths N Paths O-'---,-----,-----, r T R I A L Fig. 3. Mean perentage rret reall n eah trial fr the three levels f the path nditin. beause f the lak f suh relatinships between the nepts, as evidened by the graphial representatin, finding it unsuessful, turning t sme ther reall strategy based n ther aspets f the nepts. Whether r nt different reall strategies were emplyed by Ss in dealing with the different types f pairs, it seems lear that the graphial representatin f the epistemlgial struture a S impses n a set f nepts by his definitins f them has led t the quantitative identifiatin f a relatinship between nepts, semanti distane, whih is an imprtant variable in the type f memry tasks used in this experiment. pairs f nepts were presented tahistspially t a S at the rate f 1 pair every 8 se with a pair visible fr 2 se. After expsure t the 21 pairs f nepts, a S partiipated in a deding task fr 2 min t prelude reall frm shrt-term memry. A S was then given a sheet f paper ntaining all f the left-hand members f the pairs f nepts and asked t write next t eah nept the assiated right-hand member f the pair and t give an assessment f his nfidene n a 4-pint sale. Fur suh study-test trials were mpleted in the experimental sessin. Results Analysis f Mean Perentage Crret Reall. The MPCRT fr eah level f the number f paths variable was mputed fr eah S n eah trial. A tw-fatr repeated measures analysis f variane revealed a signifiant (p <.01) verall effet f number f paths, trials, and a signifiant (p <.05) interatin between trials and number f paths. Figure 3 depits the MPCRT fr the fur trials fr eah type f nept pairing. As in the first experiment, Tukey's HSD test was emplyed t make all pairwise mparisns between the MPCRT fr eah number f paths n eah trial. It was fund that there was n signifiant (p >.05) differene, either verall r n any trial, between MPCRT fr nept pairs nneted by a small number f paths and thse nneted by a large number f paths. It was als fund that, bth verall and n the first three trials, the MPCRT fr pairs f nepts nt nneted by paths was signifiantly (p <.05) less than thse nneted by paths. Analysis f Mean Cnfidene Rating. Fr eah trial, a S's mean nfidene rating fr reall f the respnse terms f the three types f nept pairings was mputed. Figure 4 shws the mean nfidene ratings n the fur trials fr eah type f nept pairing. The results f an analysis f variane perfrmed n these mean nfidene ratings, as in the first experiment, paralleled thse f the MPCRT analysis. The effets f EXPERIMENT II Methd Subjets. The same 10 graduate students and faulty members f the Department f Mathematis served as Ss in this experiment. Design. Fr eah S, 21 pairs f nepts were frmed based n his nstruted epistemlgial struture. A given pair f nepts was nneted in the graphial representatin f as's epistemlgial struture by a small number f paths (mean f 1.12 and standard deviatin f 0.33), by a large number f paths (mean 6.97 and standard deviatin f 3.95), r by n paths. The set f nepts did nt interset with the set used in Experiment I, and an attempt was made t hld the distane between nepts nneted by paths nstant. A within-s design was emplyed rssing the tw fatrs: number f paths between nepts and trials. Predure. Fr eah S, fur randm mixed-list rders f the S's 21 pairs f nepts (7 pairs frm eah nditin) were nstruted with the restritin that a prprtinate number f the three types urred in eah quarter f an rdering. The 21 (J) 2.00 "0 C U 1.00 (J) :2 '" Small Number f Paths Large Number f Paths N Paths OO-'---r ,r , T R I A L Fig. 4. Mean nfidene rating n eah trial fr the three levelsf the path nditin.

5 674 HOLLAN the number f paths, trials, and the interatin between number f paths and trials were signifiant (p <.01). Tukey's HSD test revealed that there was nt a signifiant (p <.05) differene, either verall r n any trial, between the mean nfidene rating fr reall f the respnse terms f nepts nneted by a small number f paths and thse f nepts nneted by a large number f paths. As with the MPCRT analysis, the mean nfidene ratings f Ss were signifiantly (p <.05) higher fr reall f respnse terms f nept pairs nneted by either a small r large number f paths than fr thse nt nneted by any paths, bth verall and n the first tw trials. Disussin In this experiment, n differenes were fund fr reall r nfidene f reall f respnse terms f nept pairs nneted by many paths and thse nneted by few paths. As in the first experiment, thugh, there was, n the initial trials, a signifiant superirity f reall and nfidene f reall fr respnse terms f nept pairs whih were nneted by paths ver that f pairs nt nneted by paths. The results f the analyses f the tw dependent variables again were parallel. The strength f assiative relatinships between wrd pairs has been shwn (see, fr example, Jenkins, Mink, & Russel, 1958) t be an imprtant variable affeting reall in paired-assiate tasks. One measure f strength f assiatin devised by Deese (1962) is simply t unt the number f assiates a pair f wrds have in mmn. There are sme grunds fr pstulating that nept pairs with many paths between them wuld have mre mmn assiates than thse with nly a few nneting paths. This assumptin wuld lead ne t expet that reall f respnse terms f pairs nneted by many paths wuld be superir t that f pairs nneted by a few paths. The results f this experiment are nt in ardane with this preditin. It shuld be pinted ut that the results f this experiment are in agreement with ne aspet f Quillian's thery f semanti memry. Qnllian (1969) ntends that searh predures dealing with semanti memry preed in parallel fanning ut frm a given nept in a "breadth-first" fashin. In tenus f the graphial representatin presented in this study, this type f searh predure wuld preed alng eah path jining a pair f nepts in parallel. Therefre, the number f paths between a pair f nepts wuld nt be a fatr influening reall. EXPERIMENT III Methd Subjets. The same 10 graduate students and faulty members f the Department f Mathematis served as Ss. Design. Fr eah S, based n his epistemlgial struturing f the set f nepts, tw nninterseting sets f 10 nepts eah ,,(J-.._--<> 4.00 =,.-'=:'_.-l;.. _ e (J r-- 0::, : (J Q tlt 40 Cnrete 2.00 a.. e ::>- ;) : (i Abstrat n.. (J AI a.. e : 20 \.00. e _ mean perentage rret --- mean nfidene rating Ot----"T---,-----,---r--tO.OO I Fig. 5. Mean perentage rret reall and mean nfidene rating n eah trial fr abstrat and nrete nepts. were identified suh that the differene in mean path length frm primitive nepts was maximized between the tw sets. Arss Ss, the mean f the mean path lengths frm primitive nepts fr ne set was 0.95 with standard deviatin f 0.36 and fr the ther the mean was 3.78 with standard deviatin f The frmer set f nepts will be termed "nrete," while the latter will be alled "abstrat." Examples, frm ne S's prtl, f nrete nepts are: singletn, rdered pair, and intersetin. Examples, frm the same S's prtl, f abstrat nepts are: mmutative, suessr, and equivalene lass. A free reall experiment emplying a within-s design was used t asertain the effets f abstratness and nreteness arss fur trials. Predure. Fr eah S, fur randm lists f eah S's 20 nepts were nstruted with the restritin that a prprtinate number f nrete and abstrat nepts urred in eah quarter f a list. On eah f fur trials, a S was allwed t view ne f his fur lists fr a perid f 11 se. Fllwing eah trial, a S partiipated in a deding task fr 2 min t prelude reall frm shrt-term memry. After the deding task n eah trial, a S was given a sheet f paper and asked t write all f the nepts whih had been presented and next t eah give an assessment f his nfidene f rret reall n a 4-pint sale. Results Fr eah S, the mean perentage f rret reall and mean nfidene ratings fr reall f abstrat and nrete nepts n eah trial were mputed. These means are depited in Fig. 5. A tw-fatr repeated measures analysis f variane, rssing the abstratness f the nepts with trials, was used t analyze the data. The an alyses revealed n signifiant (F < 1) differenes, fr either auray r nfidene f reall, between abstrat and nrete nepts. There was n signifiant interatin (F < 1) between the abstratness f the nepts and trials, but the usual signifiant (p <.01) trials effet was fund.

6 EPISTEMOLOGICAL STRUCTURE AND MEMORY 675 In rder t quantify the extent f lustering f nrete and abstrat nepts in the S's reall, the ARC index f lustering (Renker, Thmpsn, & Brwn, 1971) was mputed frm the reall f eah S n eah trial. The means f the ARC sres n s 14 were.372,.131,.123, and.197 with standard deviatins f.683,.515,.327, and.270, respetively. A single-fatr repeated measures analysis f variane revealed n signifiant (F < 1) lustering differenes between trials. Disussin In this experiment, abstrat and nrete nepts were presented in randmized lists using a free reall paradigm. N differenes were fund fr either reall r nfidene f reall between the tw types f nepts. The abstratness f a given nept was quantified by the mean path length between the nept and the primitive nepts t whih it was nneted in the graphial representatin f a S's epistemlgial struturing f the set f nepts. Thus, this quantifiatin f the abstratness f a nept is dependent upn the definitin f the nept. One an speulate that the reall strategies emplyed by the Ss attempting t reall the lists f wrds primarily made use f nndefining harateristis f the nepts. Sme verbal reprts f the Ss were in ardane with this speulatin. If this were the ase, ne wuld nt expet t bserve any differene between reall f abstrat and nrete nepts. Fllwing frm this speulatin, a mre fruitful paradigm fr assessing pssible differential effets f the abstratness variable wuld be ne whih fused the Ss' reall strategies n the meanings f the nepts. The ARC lustering sres were als in ardane with the abve speulatin abut reall strategy. If the strategies emplyed by the Ss were dependent upn the fatrs whih distinguished the tw types f nepts, ne wuld expet an inrease f lustering arss trials. This was nt the ase. CONSISTENCY OF EPISTEMOLOGICAL STRUCTURES Eah S defined the set f 50 set-thereti nepts n tw asins. The first asin was befre the start f the sequene f experiments and the send asin was abut 2 mnths later fllwing the nlusin f the final experiment. In an effrt t indiate the nsisteny f the Ss' epistemlgial struturings f the set f nepts, the perentage f agreement in defining the set f nepts was mputed. The mean perentage f agreement within Ss in defining the set f nepts n. the tw asins was with standard deviatin f The mean perentage between Ss was with standard deviatin f 3.10 fr the first asin and with standard deviatin f 4.26 fr the send asin. Nte therefre that while a given S's definitins f the set f nepts remained relatively nstant, there were nsiderable differenes in definitins between Ss. GENERAL DISCUSSION These investigatins have been based n a rather limited graph theretial mdel f epistemlgial struture: that impsed upn a set f nepts by their definitins. A mputer prgram made pssible the nstrutin f eah S's epistemlgial struturing f 50 nepts frm set thery and the identifiatin f many assiated strutural harateristis. A number f these graphial harateristis-the distane between pairs f nepts, the number f paths between nept pairs, and the abstratness f the nepts-were manipulated in rder t assess the effets f these harateristis n reall. The reasning behind the experiments was the idea that if the mdel aurately represents sme aspets f the epistemlgial infrmatin that a S might use in memry tasks, then the quantitative identifiatins made pssible by the mdel wuld allw ne t manipulate variables whih affet a S's perfrmane in suh memry tasks. The suitability f the mdel is rather straightfrward when variatins in graphial harateristis, by apprpriate seletin f stimulus materials, result in nmitant variatins in perfrmane, but rather diffiult t evaluate when there are n variatins in perfrmane. In this latter ase, it is a mt pint whether suh harateristis are invalid identifiatins r, while valid identifiatins, are nt f differential imprtane t perfrmane. The majr result f the studies reprted here was that semanti distane as quantified by mean path length between nepts in the graphial representatin f as's epistemlgial struture was a ptent variable affeting reall f nepts in a paired-assiate task. A rllary f this result was that reall fr respnse terms f nept pairs nneted by paths was deisively better than thse f nept pairs nt nneted by paths. Bth f these results lend weight t the auray f the mdel f epistemlgial struture presented here; but it is neessary t mentin that the present results uld be ammdated by a number f urrent mdels f semanti struture (e.g., Quillian, 1969; Rumelhart, Lindsay, & Nrman, 1972; Andersn & Bwer, 1973; Cllins & Lftus, 1973). As mentined earlier, the negative findings are muh mre diffiult t interpret. Fr example, it is usually pssible t pstulate a reall strategy based n the mdel whih uld aunt fr any partiular negative findings. Suh pstulatins and speulatins as ffered here are, f urse, nly njetures and shuld be subjeted t further experimental analysis. The psitive findings f these studies nt nly prvide evidene in supprt f the partiular mdel f epistemlgial struture presented here, but als fr the distintive apprah f these investigatins. This

7 676 HOLLAN apprah was based n the assumptin that eah S's partiular struturing f the set f nepts was f primary imprtane t his subsequent perfrmane in memry tasks invlving these nepts. Nte as supprtive evidene fr this apprah the high level f agreement fdefinitins within Ss but the mparatively lw level f agreement between Ss. This apprah ntrasts greatly with that f ther researhers in the area f semanti memry. A reent study (Rips, Shben, & Smith, 1973) has departed smewhat frm the typial apprah f assuming sme nrmative struture (e.g., ditinary definitins) t be an adequate mdel f eah S's epistemlgial struture. These investigatrs measured semanti distane by asking Ss t indiate the degree f relatedness, n a 4-pint sale, f pairs f wrds. They fund that rated distane and a derived distane, based upn a multidimensinal saling tehnique, were preditive, under ertain nditins, f reatin times in verifiatin f semanti relatinships invlving these wrds. In the Rips et al (1973) study, there is an attempt t diretly measure semanti distane, and this prvides greater ntrl f this variable. The apprah f the present experiments was hsen beause f the nsiderable experimental ntrl it affrded. It may be the ase that lak f suh ntrl might well have led t the present ntrversies (e.g., Wilkins, 1971; Cnrad, 1972) surrunding the reatin time studies disussed earlier. In any ase, when dealing with a phenmenn as mplex and intratable as human memry, any additinal ntrl ver the experimental situatin is f tremendus imprtane. The majr benefit f this mdel f epistemlgial struture was that it allwed the quantifiatin f numerus strutural harateristis by virtue f its graphial frmulatin. Suh quantifiatins made pssible the experimental investigatins whih mprise this wrk. There are numerus ther things whih a mdel f epistemlgial struture makes pssible. It allws ne t frmulate in expliit terms reall strategies whih a S might use in retrieving infrmatin frm semanti memry, e.g., Quillian's (1969) breadth-first searh. It allws the identifiatin f the many lgial dependenies whih are ntained in the epistemlgial struture. These dependenies, while imprtant in their wn right, might well be imprtant t gnitive ativities like memry, but suh imprtane is unlikely t be identified withut mdels f this struture and mputerized tehniques fr aessing strutural harateristis. In additin, a graphial mdel allws the use f the extensive literature f graph thery in identifying the strutural harateristis. Finally, and pssibly mst imprtantly, t the extent that the mdel is an aurate representatin f a S's epistemlgial struture, it allws an extensive analysis f the strutural harateristis f this struture- withut requiring the ntinual presene f the S, freeing the investigatr f many restritins usually assiated with human Ss, and thus might well make pssible muh better ntrlled and infrmative subsequent experiments. REFERENCES Andersn, J. R., & Bwer, G. H. Human assiative memry. Washingtn, D.C: Winstn, Cllins, A. M., & Lftus, E. F. A spreading ativatin thery f semanti pressing. Reprt N. 2711, Blt Beranek and Newman, In., Cllins, A. M., & Quillian, M. R. Retrieval time frm semanti memry. Jurnal f Verbal Learning & 'Verbal Behavir, 1969,8, Cnrad, C. Cgnitive enmy in semanti memry. Jurnal f Experimental Psyhlgy, 1972,92, Deese, J. On the struture f assiative memry. Psyhlgial Bulletin, 1962, 69, Halms, P. R. Naive set thery. Prinetn, N.J: Van Nstrand, 1960., Harary F. Graph thery, Reading, Mass: Addisn-Wesley, Jenki, J. J., Mink, W. D., & Russel, W. A. Assiative lustering as a funtin f verbal assiative strength. Psyhlgial Reprts, 1958, 4, Quillian, M. R. Semanti memry. PhD dissertatin, Carnegie Institute f Tehnlgy, Qilllian, M. R. The teahable language rnprehender. Cmmuniatins f the ACM, 1969, 12, Rips, L. J., Shben, E. J., & Smith. E. E. Semanti distane and the verifiatin f semanti relatins. Jurnal f Verbal Learning & Verbal Behavir, 1973, 12, Renker, D. L., Thmpsn, C. P., & Brwn, S. C. A mparisn f measures fr the estimatin f lustering in free reall. Psyhlgial Bulletin, 1971, 76, Rumelhart, D. E., Lindsay, P. H., & Nrman, D. A. A press mdel fr lng-term memry. In E. Tulving and W. Dnaldsn (Eds.), Organizatin and memry, New Yrk: Aademi Press, Wilkins, A. T. Cnjint frequeny," ategry size, and ategrizatin time. Jurnal f Verbal Learning & Verbal Behavir, 1971, 10, (Reeived fr publiatin January 19, 1974; revisin reeived April 2, 1974.)