Paired-associate learning with compound responses

~[OURNAL OF VERBAL LEARNING AND VERBAL BEHAVIOR 1, 6 6 - 7 0

(1962)

Paired-Associate Learning with Compound ResponsesI E. J. C~OTHERS Indiana University, Bloomington, Indiana ~

The all-or-none learning model (Bower, 1960; Estes, 1959) has been extensively studied in simple paired-associate situations (Bower, 1961; Estes, 1960, 1961; Estes, Hopkins, and Crothers, 1960; Suppes and Ginsberg, 1961). In each of these experiments, S was required to associate a single digit or familiar word with a given stimulus item. Since the response was a well-integrated unit, the question of separate conditioning of response components to the same paired stimulus did not arise. The success of the model in the simple situations led to the present comparison of alternative ways of extending the model to cover the case where two response components are learned concurrently to the same stimulus item (e.g., the response "green triangle" to the stimulus BYC). One may record S's response components separately and ask whether all-or-none learning applies to the response compound considered as a unit or to the individual components. If the response is associated as a unit to the stimulus, the model requires that the probability of a correct response component, conditional on an incorrect response on the other component of that compound, should be chance. This is because an incorrect response component is assumed to imply that the association of the unit is not learned. Then S can

respond correctly on the other component only by a fortuitous guess. Alternatively, if the response components are associated to the stimulus independently of each other, the probability of a correct response component should be independent of the correctness of the other response component to the same stimulus. The third hypothesis to be examined is that the components are conditioned separately but not independently (i.e., that the rate of conditioning of one component of a response compound depends on whether the other component of that compound has been conditioned). Prior analyses of response-component learning processes were performed by Peterson and Peterson (1959, 1960) in their studies of short-term retention of individual nonsense syllables. T h e y identified the response components with the individual letters of the syllables. Two independently manipulable learning processes were found: unconditional learning of the response components; and an increase in the conditional probability that a letter was recalled correctly, given that the preceding letter of that syllable was correct. If the present pairedassociate task also involves learning to integrate response components, one might expect a trend toward associating the response as a unit to the stimulus as training progresses. In addition to studying the response-component conditioning processes at two levels of learning, the present study compared learning under three different schedules of practice and test trials.

1 This paper is based on a dissertation submitted in partial fulfillment of the requirements for the Ph.D. degree at Indiana University while the author was a University Fellow in 1961. The author expresses deep gratitude to W. K. Estes for his advice and guidance. He is also indebted to L. R. Peterson and I. Gormezano for suggestions and criticisms. 2 Now at the Institute for Mathematical Studies in the Social Sciences, Stanford University.

MET:-IOD Subjects and Apparatus. The Ss were 60 students

from an introductory psychology class at Indiana 66

P A I R E D ASSOCIATES WITI-I C O M P O U N D R E S P O N S E S

University who served as part of a course requirement. The paired-associate exposure apparatus appeared to S as an 18 X 18-in. panel containing two windows, one for displaying the stimulus member and the other for displaying the response member of each pair. The apparatus has been described in detail previously (Estes et al., 1960). The materials presented for paired-associate learning were six lists of six stimulus-response pairs each. The stimulus member of each pair was a nonsense trigram composed of a random seleotion of letters not used in any other syllable in the list. Each syllable was typed on the left side of a 5 X 8-in. white card. The response member randomly assigned to a given syllable consisted of two components: an adjective naming the color (red, green, or blue) of the geometrical form drawn on the right side of the card; and a noun identifying the form (circle or triangle). Each of the six compounds of one of the three color components and one of the two form components was assigned to one stimulus in each list. No two lists contained the same syllable. Procedure. We shall use R to denote a reinforced (practice) trial and T to denote a test trial. An R trial consists of the simultaneous presentation of the stimulus and response members of a pair and ends when each pair has been presented once. On a T trial, only the stimulus member of the pair appears, and S is to say the response member. Each S received one of his first three lists under each of the schedules RTT, RRTT, and RTRT. Order of schedule presentation was counterbalanced across Ss. Then three new lists were presented, the schedules occurring in the same order as before. Ten Ss were assigned to each of the six possible orders of schedule presentation. At the start of a session, S was seated facing the presentation panel and instructed to the effect that: (a) on each practice trial, a typed syllable would appear in the left window and a colored plane figure would appear in the righl window simultaneously; (b) he was to say the color and figure aloud; (c) occasionally, there would be test trials on which only the syllable was shown, and his task was to state the color and figure from memory; (d) if he was not sure of the correct color or figure on a test trial, he was to guess. On a reinforced trial, both windows of the appar.atus were illuminated and the pair appeared for 4 sec., followed by a 4-sec. interpair interval. A 10sec. pause followed the first test on each list. A new random order of item presentation was used on each trial. A 45-sec. pause separated lists.

67

p o n e n t , c o n d i t i o n a l on a correct or on an i n c o r r e c t response on the o t h e r c o m p o n e n t of t h a t item. T h e four i n t r a - p a i r c o n d i t i o n a l p r o b a b i l i t i e s a r e : P(C[F) a n d P(CIF), the p r o b a b i l i t y t h a t the color c o m p o n e n t was correct, given t h a t the f o r m response c o m p o n e n t was correct or incorrect, r e s p e c t i v e l y , a n d P(FIC ) and P(FIC), the p r o b a b i l i t y t h a t the f o r m response c o m p o n e n t was correct, g i v e n t h a t the color c o m p o n e n t was c o r r e c t or incorrect, respectively. T h e s e p r o p o r t i o n s , c o m p u t e d s e p a r a t e l y for e a c h r e i n f o r c e m e n t t e s t schedule, b o t h for t h e original set of t h r e e lists a n d for t h e replication, a p p e a r in T a b l e 1. E a c h p r o p o r t i o n was c o m p u t e d f r o m the f r e q u e n c y d a t a a g g r e g a t e d over all Ss. Assuming independent observations, the m a x i m u m SEp is .04. Since (a) each of the 12 p r o p o r t i o n s in t h e P(C[F) c o l u m n is at least .07 greater t h a n the c o r r e s p o n d i n g P(CIF ) e n t r y , a n d (b) each P(F[C) e n t r y is at least .06 g r e a t e r t h a n the c o r r e s p o n d i n g P(FICi entry, it seems clear, first of all, t h a t the p r o b a b i l i t y of a correct c o m p o n e n t response is h i g h e r w h e n the o t h e r response c o m p o n e n t is c o r r e c t t h a n w h e n the l a t t e r is incorrect. T h i s finding m a y be i n t e r p r e t e d as c o n t r a d i c t o r y to the a s s u m p t i o n t h a t the response c o m p o n e n t s are c o n d i t i o n e d i n d e p e n d e n t l y of each other. W e also n o t e t h a t each P(CIF ) o b s e r v a t i o n exceeds .33, the e x p e c t e d p r o p o r t i o n correct b y guessing in a t h r e e - a l t e r n a t i v e task. Likewise, e a c h P(FIC ) o b s e r v a t i o n exceeds the .50 p r o b a b i l i t y of a c o r r e c t f o r m guess. T h e r e fore, there m a y h a v e been l e a r n i n g on one c o m p o n e n t of an item, t h e o t h e r c o m p o n e n t of w h i c h is n o t learned. T h i s finding is inconsistent w i t h the a s s u m p t i o n t h a t the response c o m p o u n d is l e a r n e d as a unit. A t e n t a t i v e answer to the q u e s t i o n of w h e t h e r S tends to associate the response as a u n i t to the s t i m u l u s m o r e f r e q u e n t l y as training progresses m a y be o b t a i n e d b y c o m p a r i n g the c o n d i t i o n a l p r o p o r t i o n s on the first set of three lists w i t h those on the second set of three lists. O n e m a n i f e s t a t i o n of a t e n d e n c y t o w a r d u n i t c o n d i t i o n i n g w o u l d be an increase RESULTS AND DISCUSSION in the a m o u n t b y which P(C[F) exceeds P(C]F) f r o m t h e first set of three lists to the T h e d a t a w e r e first a n a l y z e d in t e r m s of the p r o b a b i l i t y of a correct response corn- second. B y a v e r a g i n g across tests (successive

68

CROTHERS

TABLE 1 OBSERVED PROPORTIONS Ol• CORRECT RESPONSES FOR: COLOR COI~fPONENT GIVEN F O R M C O M P O N E N T

CORRECT

(C[F), COLOR COWXPONENTGrVE~ FOR~ CO1VEPONENTINCORRECT (CIF), FORI~ COiVIPONENT GXVEN COLOR COMPONENT CORRECT (Fit), AND FORM COMPONENT GreEN COLOR COMPONENT INCORRECT ( F ~ , FOR T~E

Fn~sT SET OF T~REE L~STS (0) ann FOR T~E REPLICATION(R) Reinforcementtest schedule

Set of three lists

Ordinal number of test

P(CIF)

P(Clfi-)

P(F[C)

P(F[C')

RTT

0 0 R R

1 2 1 2

.55 .54 .61 .61

.42 .45 .46 .39

.66 .65 .74 .77

.53 .57 .61 .59

RRTT

0 0 R R

1 2 1 2

.69 .60 .76 .72

.46 .53 .56 .49

.76 .70 .80 .83

.55 .64 .61 .65

RTRT

0 0 R R

1 2 1 2

.55 .67 .66 .79

.45 .53 .49 .48

.61 .75 .73 .83

.51 .62 .59 .57

pairs of rows in T a b l e 1) it m a y be seen t h a t P(CIF ) minus P(C]F) increased across the two sets of three lists for each reinforcementtest schedule. A like increase obtained with P(FIC ) minus P(FIC ) for each schedule. T h e average increase was .075. Using these six averages, a t for p a i r e d scores was computed. E a c h of the three P(C[F) minus P(CIF ) averages obtained from the original lists was p a i r e d with the proportion obtained on the same schedule in the replication; the P(FIC ) minus P(F[C) proportions were treated likewise. W i t h 5 dJ, t --- 5.43, which is significant at the .01 level. Hence, the findings appear consistent with those reported b y Peterson and Peterson (1959) in a somewhat different situation. P e r h a p s association of the response as a unit to the stimulus might be even more pronounced if no two response compounds contained the same component. T h e possibility t h a t the results represented an average over two types of Ss, some conforming to the independent conditioning model and others to the unit conditioning model, was briefly examined. However, the conditional proportions for a given S varied a p p r e c i a b l y from list to list instead of consistently adhering to either model. A prediction (Estes et al., 1960) of the simple linear model, t h a t the p r o b a b i l i t y of a correct response should depend only on the

number of prior reinforcements and not on the prior responses to t h a t stimulus, was tested also. T h e p r o b a b i l i t y t h a t a response compound was correct on T e s t 2, given that it was correct on T e s t 1, was compared with the p r o b a b i l i t y of a correct T e s t 2 response compound, given t h a t the compound was incorrect on T e s t I. T h e T e s t 2 proportion correct conditional on a correct T e s t 1 response compound averaged .704 and .709 under R T T and R R T T , respectively, while the proportion of compounds correct on T e s t 2, conditional on being incorrect on T e s t 1, a v e r a g e d . 176 and .228 under the same schedules. Clearly, the simple linear model is refuted. However, the fact t h a t the proportions correct on T e s t 2 following incorrect on T e s t 1 exceeded chance (.167) and increased with the number of reinforcements is evidence against all three all-or-none models being considered. Of these three models, our main conclusion was that only the one which assumes t h a t the rate of conditioning of one response component depends on whether the other component is conditioned accounts for the intra-item response p a t t e r n s on a given test. Hence, this is the model which p r o b a b l y should be modified to accommodate the findings on the proportions correct on T e s t 2 following incorrect on T e s t 1.

69

PAIRED ASSOCIATES W I T H COMPOUND RESPONSES

The adjective-noun structure of the response compounds used in the present experiment suggests a possible simplification in our hypothesis concerning the interaction of the component conditioning processes. Since S always verbalizes the "color" adjective before the "form" noun, perhaps an assumption that the rate of conditioning of the form component depends on whether the color component is conditioned, but that the rate of conditioning of the color component is independent of the state of conditioning of the form component, will account for the data. Fortunately, an all-or-none model incorporating this assumption may be tested in a direct manner which does not require parameter estimation or calculation of theoretical proportions. According to all-or-none models, the occurrence of an incorrect response is assumed to imply that the stimulus-response association is not learned. Applying this implication to the present situation, an incorrect color response component presumably indicates

P(F2]CaC2) should

all be equal when no reinforcement intervenes between the first and second tests. Here neither forgetting nor learning is assumed to occur on test trials not separated by a reinforced trial. Table 2 presents the relevant data. The proportions were obtained by summing over the two lists under each schedule, yielding 81-250 cases. A separate X2 was computed for each of the two schedules by assuming 250 observations per cell and taking the theoretical proportion correct equal to the mean observed proportion correct under that schedule. The first assumption inflates X2, leading to a conservative estimate of the goodness-offit. Five of the six proportions from R T T data are approximately equal. The deviations from the mean proportion are not significant (Z2 _z 4.65, d / ~ 5; .50 < p < .25). With a few exceptions, the R R T T proportions also are nearly equal. Again the deviations from the mean proportion are not significant (X2 : 3.10, d/ -~- 5; .75 < p < .50). The surprisingly small differences between the

TABLE 2 OBSERVED PROPORTIONS OF FORM-RESPONSE COMPONENTS CORRECT CONDITIONAL ON EQUIVALENT COLOR-CoMPONENT RESPONSE SEQUENCES

Reinforcementtest schedule RTT RRTT

P(FIIC1C2) P(FII-C1C2) P(FIIC1C-'2) P(F21C1C2) P(F21C1C2) .61

.57

.58

.52

.59

P(F21C~C2) .58

.61

.59

.57

.60

.62

.64

that the color component of that item is not conditioned. Hence, by our simplified assumption concerning the interaction of the component conditioning processes, conditioning of the form component of that item proceeds at a rate which is equal to the rate for another form component whose color counterpart is also not conditioned. Using the subscripts "1" and "2" to refer to the test number, an occurrence of any of the response sequences CIC2, CIC2, or C1C2 (i.e., each consisting of an incorrect color response component on one or both tests) is assumed to imply the same probability that the form component is conditioned. Therefore, the conditional proportions P (F1 IC1C-2), P (F1 IC~C2), P(FIIC~C~), P(F21CI~), P(F2]C~C2), and

entries in the two rows seem to indicate that the second reinforcement in the R R T T condition had little effect on form-response component learning when the color component of the compound was not conditioned. That the TABLE 3 PROPORTION OF RESPONSE CO~VfPOUNDS CORRECT ON RACe[ TEST

Reinforcementtes* schedule RTT RRTT RTRT

Set of three lists 0 R 0 R 0 R

Test 1 .33 .43 .47 .58 .31 .46

Test 2 .33 .43 .4O .56 .47 .61

70

CROUPIERS

second reinforcement did, in general, produce learning is shown b y T a b l e 3, which gives the proportion of response compounds correct on each test. T h e table also reveals some forgetting across successive tests under the R R T T schedule, a finding at odds with the model under consideration. Possibly, this forgetting accounts for the fact t h a t the T e s t 2 proportions correct are slightly higher under R T R T than under R R T T .

SUMMARY T h r e e alternative hypotheses for extending Estes' and Bower's all-or-none learning model to cover the case where S learns two response components concurrently to a nonsense syllable stimulus were tested. Sixty college students each received two six-item lists under each of three schedules of one or two practice trials and two tests. I n each list, each of the six combinations of the color adjectives "red," "green," and " b l u e " and the form nouns "circle" and " t r i a n g l e " was r a n d o m l y designated as a " c o r r e c t " response compound for one syllable. T h e main analysis consisted in computing the p r o b a b i l i t y of a correct response component, conditional on an incorrect response on the other component of t h a t compound. Since these conditional probabilities were consistently above chance, conditioning of the compound as a unit was refuted. However, the finding that the p r o b a b i l i t y of a correct response component was higher when the other component of t h a t item was correct than when the latter was incorrect disp u t e d the hypothesis that the response components are conditioned independently of each other. T h e d a t a supported the hypothesis

t h a t the rate of conditioning of the noun component depends on whether the adjective component is conditioned. REFERENCES

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