Acta Psychologica 58 (1985) 63-74

North-Holland

63

RETROACTIVE INHIBITION WITHOUT INTENTIONAL NEW LEARNING: SUPPORT FOR A STIMULUS-ENCODING THEORY

John YANG *

Stare University of Utrecht, The Netherlands

Accepted April 1984

The present studies provide additional results concerning an interesting effect discussed in a

previous paper (Yang 1981) using a design in which retroactive inhibition (RI) was introduced

without the interpolation of a new PA list. The recurrence of the A terms of previously learned

PAS during a non-intentional learning interpolation task (NILIT) turned out to be a sufficient

condition to give rise to RI. The present experiment 1 provides for a design in which the B terms of

original learning (OL) are repeated during NILIT. In spite of the similarity relation between the

material used during OL and NILIT, no RI is obtained. The previous and present results suggest

that the detrimental effect of similarity on retention only becomes manifest when the common

items function as retrieval cues. This suggestion is in line with a stimulus-encoding interpretation

of the RI ‘phenomenon. Experiment 2 was executed as a further test of the stimulus-encoding

hypothesis. In this investigation the retention of OL is assessed by means of a backward recall

procedure. Since under this condition the B terms function as retrieval cues, the stimulus-encoding

theory predicts that RI will only be found in the group confronted with the B terms during NILIT,

whereas the recall of a group working with the A terms of the PA list will not differ from that of a

control group working with a set of new words during NILIT. These predictions are borne out by

the results. A further analysis shows that the results discredit two other explanations of RI, viz.,

the Response-set Interference theory and the Unlearning hypothesis.

The classical theory of interference is almost exclusively founded on results obtained in the study of paired-associate learning (PAL) accord- ing to the A-B/A-C paradigm. The notation refers to the fact that the two successive lists of PAS share the same stimulus terms. Under these circumstances it can be demonstrated that the cued recall of the

* I am indebted to Prof. dr. A.J.W.M. Thomassen and dr. J.G.W. Raaijmakers for their remarks on the first draft of this paper. I also wish to express my gratitude to drs. Ineke Verheul and Carla

Fenijn who assisted in the collection of the data.

Requests of reprints should be sent to John Yang, Psychologisch Laboratorium, Varkenmarkt

2, 3511 Bi! Utrecht, The Netherlands.

OOOl-6918/85/$3.30 0 1985, Elsevier Science Publishers B.V. (North-Holland)

64 J. Yang / Retroactive inhibition

first-list responses falls significantly below that of a group submitted to an A-B/C-D paradigm, in which the stimuli as well as the responses of both lists differ. This loss in retention of original learning (OL) after interpolated learning (IL) is called retroactive inhibition (RI).

It has long been recognized that similarity between OL and IL is an important factor in the occurrence and magnitude of RI (McGeoch 1932; Robinson 1927). The systematic variation of this parameter gave rise to further permutations of the A-B/A-C design (cf. second lists of the type C-B, A-B or A-B). It was shown that the degree of RI changed in function with the similarity relation between the two successive PA lists. The transfer- and the retroaction surfaces of Osgood (1949) and Martin (1965) provide for a succinct description of these relationships.

Hence, in the traditional RI paradigms forgetting is always induced by means of the interpolation of a second newly learned PA list, which suggests that the memorization of this new list is a prerequisite in the origination of RI, the magnitude of which is further determined by the similarity relation between the successively learned material. From this perspective one might think that “the very act of learning itself con- stitutes an ironic source of forgetting” (Houston 1976: 242). This notion is further strengthened by the fact that some interference theo- rists speak of “unlearning” when referring to RI (Keppel 1968; Post- man 1961; Postman and Underwood 1973). Indeed, the A-B/A-C paradigm can be conceived of as a “counterconditioning” design (Barnes and Underwood 1959) during which the original B responses have to be substituted by specific new alternatives (Postman and Gray 1977). The point to be made here is that one remains in doubt as to the role of memorization as a contributor to RI since the learning factor and the similarity factor are completely confounded in the traditional RI stud- ies.

In an effort to partial out the learning- from the similarity factor, Yang (1981) conducted a study in which the A terms of a previously learned PA list recurred during an interpolated activity that required no intentional new learning. During this interpolated stage the subjects carried out a series of simple assignments with respect to the stimulus terms (experiment l), or rated these terms on a number of dimensions of the semantic differential (experiment 2). The results on a subsequent test of recall clearly demonstrated a higher loss of response terms in the groups that worked with the A terms than the groups confronted with a set of new words during the non-intentional learning interpolation task

J. Yang / Retroactive inhibition 65

(NILIT). Thus, intentional learning is no prerequisite in the induction of RI.

It is a well established fact that the execution of certain tasks with respect to verbal material results in incidental learning of this material. Postman, who conducted a series of investigations on this subject (cf. Postman and Adams 1960; Postman et al. 1955), concludes: “There is little or no reason to maintain a conceptual distinction between inten- tional and incidental learning. What is learned depends on the response elicited by the stimuli in the experimental situation” (1964: 193). So far, the functional effects of incidental learning have been studied with respect to the retention of the incidentally learned material itself. On the basis of the NILIT studies, Postman’s statement can be expanded as follows: Incidental learning of item X can also affect the retention of a different item Y.

One of the drawbacks of classical theory of interference is that it analyzes forgetting in a confined, artificial setting which raises the question whether these findings apply to real-life situations. It should be noted that the NILIT paradigm widens the scope of the study of forgetting by demonstrating that the induction of retention loss is not tied to a specific procedure such as the learning of new PAS. In this sense our earlier results bring the phenomenon of forgetting somewhat closer to real-life situations, where (interfering) information is probably predominantly acquired in a non-intentional way.

Let us now elucidate the rationale of the experiments to be reported below. Since the NILIT condition is an uncommon interference design, further exploration of the role of similarity within this experimental framework is needed. Our previous studies demonstrated that similarity alone is a sufficient factor to decrease the recall performance of OL. The investigated similarity relation concerned the repeated occurrence of the A terms of OL in the interpolated task. Similarity can also be induced, however, if the B terms of the pairs would recur during NILIT. Because the earlier studies did not provide for such a situation, experiment 1 was run in order to augment the previous findings as to the effect of the similarity factor in the NILIT paradigm. So, one purpose of experiment 1 is to see whether or not recall of OL is affected when the response terms instead of the stimuli are part of the NILIT material.

The aims of experiment 1, however, extend beyond the mere purpose of completing the picture of the role of similarity in the NILIT

66 f. Yang / Rerroacrive inhibition

paradigm. The investigation also allows for a test of the Stimulus-en- coding theory proposed by Martin (1968, 1971, 1973). On this view, RI (in the traditional A-B/A-C paradigm) is accounted for in the follow- ing way. The encoding of the nominal A term during IL is assumed to be different from the encoding of this term during OL. Since OL recall is requested immediately after IL, retrieval may falter because the original OL encoding of the nominal stimulus fails to be correctly reinstated.

From this perspective one arrives at the prediction that the manipu- lation of the B terms during NILIT will not result in RI. Although the encoding of these terms is supposed to be changed, recall of OL remains unhampered because the B terms do nof function as retrieval cues in the final recall stage. Since the A terms are charged with the initiation of the retrieval process, there is no need for making an appeal to B-term encoding. Hence, one may expect that the recall performance of subjects for whom the B terms recurred during interpolation will be equal to that of subjects submitted to the control condition in which there is no overlap between the OL- and NILIT materia1.

Previously (Yang 1981) we proposed that RI could be accounted for by the so-called Evocative Disuse hypothesis. According to this hy- pothesis, RI is caused by the fact that the subject has repeatedly refrained from retrieving the OL responses during interpolation, in spite of the presence of the former retrieval cues (the A terms). This aspect of the processing mechanism was supposed to affect the evoca- tive value of these terms as evidenced on a subsequent test for recall. We now think, however, that this hypothesis should be abandoned since it is open to the objection that it is merely a description of the situation under which RI is obtained. It is obvious that the subject ceases to emit the former B responses during the interpolated stage and, in our opinion, this fact cannot be offered as an explanation.

Experiment 1

Method

Design Two groups of Ss learned the same list of eight paired-associates. After attainment

of the criterion, Ss were required to judge a set of words on ten dimensions of a

J. Yang / Retroactive inhibition 67

semantic differential (the interpolated stage). In Group B this set consisted of the eight B terms of the previously learned PA list, whereas Group N was presented with eight new words which were not in that list. Subsequently, the Ss were submitted to a paced cued recall test to assess the retention of the word pairs.

Material The list of eight paired-associates was composed of one-syllable 3-letter nouns with

a frequency varying from 1 to 6 on list Al of a Dutch frequency count (Uit den Boogaard 1975). The list was presented by means of a memory drum. Care was taken to minimize formal and acoustic similarity between each stimulus and its response. There were four presentation orders of the list.

The dimensions of the semantic differential were cast in 7-point scales. At the extremes of the scales the poles pertaining to the dimension were printed (strong-weak, active-passive, etc.). Above each scale, a space was provided for the S to write down the word-to-be-rated. Ten such dimensions were used and because there was a set of eight words, the interpolated task entailed 80 scales. The scales with identical dimen- sions were grouped. Four sheets of paper each contained two such blocks.

The words-to-be-rated were typed on cards mounted on a turn-over device. A light metronome signaled the experimenter when to turn a card. Two separate decks of cards were used, one for each interpolation condition. Four different presentation orders were composed. The N group rated 3-letter nouns selected from the same frequency

range as the nouns employed in the PA list. The test for recall took place by means of a memory drum.

Procedure The PA list was learned by the anticipation method with a criterion of one errorless

trial. During 3 set the A term was shown followed by a dash, then the B term preceded by a dash was presented for another 3 sec. The dash appeared always on the same spot of the window. The terms had to be pronounced aloud; wrong anticipations had to be corrected. The intertrial interval was set at 3 sec.

The interpolation stage was announced as another experiment. Half the Ss judged the B terms, the other half the new words. Each word was shown for 5 sec. During that time the S wrote the word on top of the scale and marked one of the dimensional positions. All words of the set were rated on the first dimension (for each word there was a scale). Subsequently, the words were shown again, in a changed order, to be rated on the next dimension. Because 10 dimensions were used, the words were repeated ten times. Including the instruction this stage took about 10 min.

The recall procedure was identical to a presentation trial of the A term during learning, with the exception that the term was not followed by the B term. Ss had to anticipate the correct B term within the 3 set that the A term was exposed in the window of the memory drum.

Subjects Fourty-two Ss, all students in psychology at the University of Utrecht, participated

in this experiment. They were altematingly assigned to one of the two groups, so that each group comprised 21 Ss.

68 J. Yang / Retroactive inhibition

Results

Mean number of trials to reach the learning criterion was 13.04 trials (sd 4.47) in Group B and 12.52 trials (sd 4.44) in Group N. The difference in speed of learning between the two groups was not significant.

The mean number of forgotten items in both groups also failed to yield statistical significance. In Group B the mean number of forgotten B terms was 1.42 (sd 1.32) and in Group N it was 1.57 items (sd 0.97); t (40) = 0.39, p > 0.20.

The prediction of the Stimulus-encoding theory is corroborated. Although the encoding potency of the B term may have been affected during NILIT, the recall of the PA list does not suffer from more RI than the control group since retrieval is guided by the non-recurring A term.

Discussion

The results of this simple experiment do not necessitate a lengthy consideration. Sofar, the stimulus-encoding assumption provides an explanation for the present as well as for the previously obtained results. Resuming the findings of similarity manipulation in the NILIT paradigm, we see that RI is distributed over the three groups in the following manner: group A > group N = group B. This distribution is in accordance with our theoretical expectations. The detrimental effects of item overlap turn up only when the common item is used as a retrieval cue, which in this case is the A term.

At this moment an additional test of the stimulus-encoding assumption suggests itself. For, if the OL pairs would have been addressed by another retrieval cue during recall, then group A would have shown no signs of RI! Such an alternative cue could be the B terms of the pairs. Thus, in case OL retention is tested by means of a backward recall procedure (during which the B terms function as retrieval cues), the present theory predicts a change in the distribution of RI over the three earlier mentioned groups. Under this condition one may expect that the recall performance of group B will fall below that of the two other groups, whereas the difference between group A and group N should be zero (the latter comparison is analogous to the test executed in experiment 1 where a forward recall procedure has been used).

Experiment 2

Experiment 2 was designed in order to put the just advanced inference to test: If OL retention is tested by a backward recall procedure, the distribution of RI over the three groups will show the mirror image of the distribution obtained in the forward recall studies, viz., group B > group N = group A.

Method

Design, procedure and material In many respects the present investigation resembled the previous one. Ss learned

the same list of eight noun-noun pairs to a 7/8 learning criterion. The pairs were

J. Yang / Retroactive inhibition 69

presented by a memory drum. First the A term appeared during 3 sec. Subsequently the B term was shown for another 3 sec. The intertrial interval was set at 3 sec. When learning was completed the semantic differential task followed as interpolated activity (see experiment 1 for a description). The third stage of the experiment consisted of a backward, paced cued test for the recall of the originally learned PA list. The B terms were shown in the window of the memory drum during 3-set intervals. Ss had to provide the A terms within these intervals.

Three groups of Ss were run. They differed with respect to the treatment during the interpolated task. Group A rated the A terms of the PAS, group B did the same with respect to the B terms, whereas group N rated words that did not occur in the PA list.

Subjects Eighty-four freshmen in psychology of the University of Utrecht participated in the

experiment, 28 in each of the three groups. The Ss were all naive as to verbal learning studies.

Results

The mean number of trials needed to reach the 7/8 learning criterion in group A was 10.64 (sd 4.89); in group B it was 11.00 (sd 4.45) and in group N it was 10.96 (sd 4.65) trials. No difference between the groups was evident on this variable.

Performance on the recall test is expressed in loss scores defined as the difference between the number of correct anticipations on the criterion trial (7 or 8 pairs) and the number of correct reproductions on the cued backward recall test. The mean loss scores in the groups was as follows: group A 3.21 (sd 1.79), group B 4.43 (sd 1.57) and group N 3.50 (sd 1.48) items. The prediction of a specific pattern of RI distribution over the groups, viz., B > A = N, indicated the use of a test for Planned Comparison (Hayes 1976) by means of which can be assessed whether or not RI is higher in group B than in groups N and A (contrast 1) and whether the recall performance of groups N and A are equal (contrast 2).

The test of contrast 1 confirmed the prediction that the mean loss score of group B surpasses the average of the means of group A and group N; t (81) = 2.86, p < 0.01. Contrast 2 revealed, as predicted, that there is no difference between group A and group N, t (81) = - 0.66, p > 0.25.

A further analysis of the data reveals an individual feature of the Ss learning performance. Although the phenomenon falls outside the scope of the present topic, it is of sufficient interest to be reported here. Observing the behavior of the Ss in the previous experiment 1, we got the impression that Ss who tended to emit incorrect responses (emission faults) during their anticipation efforts in the learning stage, needed more trials to reach the learning criterion than those who remained silent during an anticipation failure (omission fault). In the present experiment we therefore noted on the protocols whether an incorrect anticipation during learning was due to an emission or omission fault. Since the absolute number of emission faults depends on the total number of incorrect anticipations, we measured the “emission proneness” of each S by calculating the fraction of emission faults over the total number of

70 J. Yang / Retroactiue inhibition

committed errors during the learning stage according to the formula, emissions/(emis- sions + omissions). Subsequently, the emission fraction and number of trials to reach the learning criterion of all Ss has been submitted to a Pearson correlation test. It turned out that there existed a significant positive correlation between “emission proneness” and number of learning trials; r = +0.36, p = 0.001. The relationship revealed here is of obvious relevance for the study of individual differences in learning.

General discussion

Let us resume the present results and those obtained earlier: When the A terms of OL function as retrieval cues (forward recall), RI is distributed over the three groups in the following manner: Group A > group N = group B. However, if, as in experiment 2, a backward recall procedure is applied, the picture changes drastically into another distribution: Group B > group N = group A.

The predicted results confirm the Stimulus-encoding theory. In this framework the change in the distributions is perfectly feasible since they show that RI depends solely on whether the cue through which memory is addressed has been part of the interpolated task. If so, troubles arise as to the proper encoding of the retrieval cue and actualization is hampered.

It should be noted that the present theoretical context provides for a specification of the relationship between task similarity and RI. Al- though similarity, or item overlap, is an important precondition, the presence of intertask similarity does not necessitate the rise of RI. Let us now confront the present findings with other interpretations that have been advanced within the context of the classical theory of interference.

Whereas the Stimulus-encoding theory locates the cause of RI at the side of the stimulus, the Response-set theory (Postman et al. 1968) assumes that the complete class of the to-be-emitted OL responses is suppressed by the dominance of the IL response repertory. The results reported above are not easy to assimilate into the latter theoretical context. In experiment 2 the to-be-emitted responses (A terms) were shown repeatedly (ten times) during the interpolated task. Hence, one would expect that these items remain highly available. Nevertheless group A does not perform any better than control group N (see experiment 1 for an analogous situation and outcome). It should be

J. Yang / Reiroacfive inhibition 71

noted that the lack of difference is not due to a ceiling effect, since group A is, on the average, still 3.21 items away from optimal recall. Furthermore, the fact that RI is exclusively located in group B is unexplainable in terms of the Response-set theory since it is not conceivable why the A terms (the to-be-emitted responses) should be more suppressed in group B than in group N.

The reversibility of the RI effect strongly suggests that interpolation does not affect the strength of the internal representations of the stored pairs. The results can therefore also be viewed as evidence against the Unlearning hypothesis (Keppel 1968; Postman 1961; Postman and Underwood 1973). The Unlearning hypothesis predicts RI by means of an analysis of OL with respect to extinguished associations induced by A-B/A-C similarity relations (Keppel 1968; McGovern 1964). If one applies this analysis to experiment 2 it turns out that in group A (recurring A terms during NILIT) two associative relationships are subjected to extinction, viz., (1) the fonvuvd associations from the A term to the B term, since these first terms are followed during NILIT by different responses (ratings on the semantic differential) and (2) the contextual associations that are supposed to exist between the environ- mental cues and the B terms of the PA list, since a different set of responses (ratings) are connected to the same context. The latter type of extinction would account for the loss of responses per se. In the control group, however, there is just one associative relationship that suffers from extinction, namely, the contextual associations of the B terms.

A basic concomitant assumption of the component analysis dis- cussed here is “. . . that the unlearning of responses per se and of specific associations are in large measure independent processes whose effects summate to determine the level of first-list recall” (Postman and Underwood 1973: 22) (italics mine J.Y.). Hence, according to this “summation postulate” underlying the Unlearning hypothesis, group A should show more RI than group N because more associative relation- ships are extinguished. This prediction is clearly refuted by the results of experiment 2 which show that the recall of the two groups does not differ.

The present results could be interpreted in terms of independent action of forward and backward associative pathways. Evidence for such independency has earlier been reported in the framework of the classical interference literature by Houston (1964, 1966), Johnston (1967), Keppel et al. (1971), Keppel and Underwood (1962) and Petrich

12 J. Yang / Rerroaciive inhibition

(1970, 1971). None of these investigators seems to realize, however, that this finding of independency is directly at odds with the summation postulate on the basis of which the Unlearning theory explains RI in the several interference paradigms. Although Keppel and Underwood acknowledge some interpretative problems they rather prefer the collec- tion of more experimental data on the subject since, in their opinion, “it seems most apparent that the critical need at present time is not further assumptions” (1962: 404).

Thus, the Unlearning hypothesis runs into troubles by assuming that different associations summate in recall. We have seen that the empiri- cal data argue against this assumption. Moreover, the summation postulate can also be questioned on logical grounds. This assertion can be elucidated as follows.

Unlearning is based on an elicitation - extinction process (see Yang 1981 for a critical evaluation of this concept). This means that the hypothesis is solidly rooted in the context of S-R theory. As we see it, the latter theory implies a commitment to the position that retrieval is a stimulus (cue) dependent affair. Let us now pose the following ques- tion: What is the appropriate stimulus for the activation of a specific forward (A --) B) association? Shouldn’t that be the A term of the pair? Assume furthermore that a subject has learned a list of PAS and is subsequently tested for recall of these pairs in backward direction. The Unlearning hypothesis holds that the forward association assists in backward retrieval (similarly, the backward association is supposed to contribute to recall in forward direction). The logical problem that immediately raises pertains to the question how the A term can activate the forward A --) B association during a recall procedure in which this term is evidently the item-to-be retrieved. The endproduct of a certain mental process can never function as initiating euent for this same process (unless one adheres to the position that occurrences in the present are influenced by “retroaction of future events”).

Finally, there remains one explanation of RI that deserves considera- tion in the present context, namely, the second factor that constitutes the Two-Factor theory; competition (Keppell968; Postman and Under- wood 1973). Competition can be conceived of in two different ways. The Response-set theory assumes that competition, and thus RI, is engendered by the complete class of the second-list responses (see also Newton and Wickens 1956). This interpretation of competition is discredited by the present results.

J. Yang / Retroactiue inhibition 13

According to the original interpretation, however, competition is of a specific nature and refers “to a struggle between two available re- sponses elicited by the same stimulus” (Keppel 1968: 187). It was McGeoch and his coworkers who introduced this notion in the field of interference (cf. McGeoch et al. 1937; McGeoch 1942) under the name “reproductive inhibition”. Since competition pertains to a fight be- tween responses, preference has been given to the term “response competition”. This label is somewhat misleading because it detracts attention from the underlying assumption that the presence of a com- mon stimulus is responsible for the rise of competition. The point to be made is that, in as far as one presupposes that (response) competition is engendered by specific retrieval cues, the present results are also in accordance with a competition concept.

Modern formulations of the just discussed competition notion can be found in papers of Anderson (1983) and Raaijmakers and Shiffrin (1981), who explain RI in terms of the relative strength that exists between a presented stimulus’ linkage to the target response on the one hand and the cue’s connections to all potential responses on the other hand. It seems, therefore, that at present the explanation of RI should be sought along the pathways offered by the Stimulus-encoding and the Competition concept. This state of affairs requires a sharpening of the assumptions underlying each of these points of view so that it becomes possible to design better discriminative tests as to these alternative explanations of RI.

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