An interrupted stimulus can facilitate PA learning

JOURNAL OF VERBAL LEARNING AND VERBAL BEHAVIOR 8, 2 1 9 - 2 2 4

(1969)

An Interrupted Stimulus Can Facilitate PA Learning1 LEONARD M. HOROWITZAND WILLIAMNEWMAN2

Stanford University,Stanford, California94305 The S had to learn a PAlist containing CCC stimuli paired with common-wordresponses. Each pair was presented at a 4:l-sec rate. In the "continuous" condition, the stimulus appeared on the memory drum continuously throughout the A-sec stimulus interval. In the "interrupted" condition, the stimulus appeared for the first and last seconds of the 4-sec interval, and a blank screen appeared during the middle seconds. The interrupted stimulus facilitated learning in Exp. I. The effectwas particularly strong for female Ss. The experiment was replicated in Exp. III. Apparently, an interrupted stimulus is more effectivein stimulating S's associative processes. This interpretation was examined in Exp. II. First each S studied the PA list for 3 trials. Then S was given a test of free association; he was showneach trigramword pair and he had to think of some mediator (a word or a phrase) which connected the trigram to the word. The S's latency of response was measured. Those Ss who had observed the "interrupted" material responded faster in free association. trigram seems to be part of the larger mnemonic device. I f S is to learn a pair of associates, his mnemonic aid must meet two requirements: If he is to learn CGP-farm, CGP must elicit a verbal unit, usually a larger one, and that unit must elicit "farm ;" CGP, f o r example, might elicit "cows, goats, pigs" which in turn elicits "farm." Here, too, the trigram elicits some larger, easily remembered phrase. Some trigrams have a particularly weak tendency to elicit larger words and phrases. Trigrams of low association-value, for example, seem to require special instructions or encouragement from E before S will engage in whatever response activities generate the larger mediating words or phrases. Apparently, an uninstructed S is not predisposed to think of a mnemonic aid, to say, XIW. Thus, one reason trigrams of low association-value are harder to remember is perhaps that they do not predispose S to think of mnemonic aids. i This research was supported in part by Grant I f there were some way to present stimulus GB-4561 of the National Science Foundation. The material which did predispose S to generate authors thank Barbara E. Woodward and Richard C. mnemonic aids, that method would enhance Wise for their help in collecting and analyzing the P A learning. The present article reports data. one such method. The method was found 2 Now at Lehigh University. 219 In certain ways the effect of a "mnemonic device" resembles the effect of any Verbal label. Certain experiences are hard to remember unless the subject can translate the experience into a common, easily remembered verbal form which later helps him identify the earlier experience. Brown and Lenneberg (1954) and Lantz and Stefflre (1964) have shown that colors are better recognized if the color is easily labeled in the first place. Short, quickly emitted labels are apparently the most effective aids for remembering a color. Likewise, S can better remember a nonsense trigram if that trigram elicits some c o m m o n word or phrase which later allows him to reconstruct the trigram. Trigrams high in association-value elicit verbal units more readily, so S can remember those trigrams more easily. If XPO elicits "eXPOse," S's chances of remembering it are appreciably greater (Lindley, 1963; Schaub and Lindley, 1964; Lindley and Nedler, 1965). Usually, the

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unexpectedly when the authors were searching for a way to m a k e C C C trigrams m o r e available: The S l e a r n e d pairs of associates like " C G P - f a r m " a n d eventually was tested for b a c k w a r d recall. I n one experimental condition, the trigram was i n t e r r u p t e d during each exposure, so that S periodically h a d to view a b l a n k screen. D u r i n g this b l a n k period, it was hypothesized, S w o u l d generate the trigram as his own response, a n d the t r i g r a m w o u l d grow more available. C o n t r o l Ss studied the same material w i t h o u t the s t i m u l u s - i n t e r r u p t i o n . The results showed n o differences i n backward recall at all. However, t~e two groups did differ i n their speed of learning. W i t h o u t a n y specific instructions f r o m E, the interrupted stimulus, for some reason, stimulated S to t h i n k of mediating words or phrases, thereby speeding P A learning. The present article reports this research. ]~XPERIMENT I

Method Materials. The experimental material consisted of 12 pairs of associates. The stimuli were CCC trigrams selected from Witmer's (1935) list to have association values of 13 ~. Each stimulus was paired with a common word as response. The words all had AA ratings in the Thorndike-Lorge (1944) word-count. The following pairs were formed: BPJ-talk, CGP-farm, FQC-vote, GCZ-year, HKM-door, JZH-girl, KXQcity, LHJ-salt, MFH-rain, TJW-ball, WBF-page, ZKG-lake. Letter-duplicationwas minimizedthroughout the pairs. PA Learning.First Slearned the paired-associate (PA) list which was presented on a Lafayaette memory drum revolving at a 1-sec rate. For one group each stimulus appeared four times in succession with each exposure lasting 1 sec. Then a 1-sec blank space appeared, and finally the response word appeared for 1 sec. A 1-sec interval separated this pair of associates from the next pair. Beginning with Trial 2, S tried to anticipate the response before it appeared. He was allowed to say the response as soon as the stimulus first appeared; therefore, he had a total of 5 sec to make his response. Four different orders of presentation were adopted, and the order was systematically changed from trial to trial. This group is called Group C since each stimulus appeared continuously for four 1-sec exposures. A second group is called Group I because each stimulus was interruptedduring the stimulus presenta-

tion. A stimulus trigram appeared on the memory drum for 1 sec, then a blank space appeared for 1 sec, then another blank space for 1 sec, and finally the trigram reappeared for 1 sec. (In other words, the trigram appeared during the first and last seconds of a 4-sec interval.) Then a 1-sec blank space separated stimulus and response, and finally the response word appeared for 1 sec. This group's task was identical to Group C's, except for the interruption of each stimulus. These Ss, too, were allowed to anticipate the response from the moment the stimulus first appeared. The Ss were assigned to the above two conditions randomly. When the results revealed a significant difference between them, a third group was added for comparison. This group, Group M, studied the material of Group C, but in addition, the instructions urged them to think of mediators connecting stimuli and responses. They were advised that their task would be easier if they thought of some word or phrase which integrated each stimulus and response. All Ss worked on the PA task to a criterion of one perfect trial. Other Tasks.After PA learning, each S was tested on three self-paced tests of R-S retention: backward recall and two multiple choice tests of backward recognition. Since the groups did not differ on these measures at all, they will not be discussed further. Subjects. The Ss were 60 students from the class in introductory psychology at Stanford University.

Results and Discussion G r o u p C, o n the average, reached a criterion of one perfect trial in 11.20 trials (SD = 3.41). G r o u p I required a m e a n of 8.00 trials (SD = 2.47), a n d G r o u p M, a m e a n of 9.70 trials (SD= 3.55). A n analysis of variance showed t h a t the c o n d i t i o n s differed significantly; F(2, 5 7 ) = 4 . 8 1 , p < . 0 5 . The only simple difference between m e a n s that reached significance was the difference between G r o u p C a n d G r o u p I ; t = 3.40, p < .01. N o other t was significant. G r o u p learning curves showed that G r o u p C was inferior t o t h e other groups f r o m Trial 3 on. G r o u p M was intermediate f r o m Trial 6 on. These differences are n o t due merely to a few particular items. The difference between G r o u p C a n d G r o u p I was further e x a m i n e d t h r o u g h individual learning curves for each item. The m e a n n u m b e r of correct responses over the first 20 trials was examined for each

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item of Group C and Group I. Eleven of the 12 relevant associates so S can generate better differences favored Group I. mediators to connect stimulus and response. Each item was also scored to tell how often (We know that Group C could have benefited an item that was once correct remained correct from better mediators since Group M did on subsequent trials; i.e., the number of "one- learn faster. However, Group M's pertrial" masteries. Averaging across all 12 items, formance still remained below Group I's. the mean number of Ss in Group I who Therefore, instructions to mediate may only obtained a one-trial mastery was 14.58; for be of limited use, given the hindering effects of Group C, 12.08; and for Group M, 12.92. continuous stimuli.) With the item as the sampling unit, the means Sex Difference. Unexpectedly, the data also differed significantly; F(2, 22) = 4.94, p < .05. showed a sex difference. The difference Thus, an interrupted stimulus seems to between the interrupted and continuous increase the chances of a one-trial mastery. conditions was greater for female Ss than it The interrupted stimulus clearly facilitated was for male Ss. Table 1 shows the mean PA learning. TABLE 1 Condition C contained an extremely long stimulus duration (four successive 1-sec MEAN NUMBER OF TRIALS TO CRITERION ]]Y a s IN EACH EXPERIMENTAL CONDITION repetitions); for some reason an interruption was facilitating. Different explanations could Continuous Interrupted Mediation be offered for this effect: perhaps the absolute 10.80 8.56 9.80 amount of stimulus exposure is critical; M a l e (n = 15) (n = 9) (n = 10) perhaps the ratio of stimulus exposure to 12.40 7.55 9.60 response exposure is important. Such explana- Female (n = 5) (n = 11) (n = 10) tions would seem unlikely, though, since the total amount of learning time was constant, the amount of response anticipation time was number of trials needed to reach a criterion of constant, and the response duration was one perfect trial by the Ss of each sex. Because of unequal n's, it was not possible to test the constant. The authors therefore attach particular significance of the interaction directly. Instead, significance to the interruption per se. A a separate analysis of variance was performed continuously repeated stimulus is boring and on the data of each sex. For males, the may dampen S's associative processes. An difference among the means did not reach interruption may reduce this boredom and significance; F(2, 31) = 1.32. For females, on help S better generate potentially useful the other hand, F(2, 23) = 3.69,p < .05. Thus, associates., Two separate aspects of an the experimental treatment seems to have interruption can be noted. For one thing, interacted with S's sex. It is not clear why this interaction occurred. interruption implies change; the change itself may be facilitating (though certain kinds of Two Es have independently observed that changes would surely be distracting and female Ss in Group C generally remained ineffective). Second, the appearance of the attentive to each repetition of the stimulus, but blank screen during the stimulus exposure male Ss did not. Apparently, male Ss are apt may be helpful; every teacher knows the to turn away impatiently from a continuously repeated stimulus. Male Ss in Group C may advantage of a judiciously placed silence. Either view of the interruption suggests that have interrupted the stimuli by their own the S o f G r o u p I could generate associates more bodily movements. Subtle measurements readily. According to this explanation, an would be needed to test the validity of this interrupted stimulus encourages more task- interpretation.

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The difference between G r o u p s I and C m a y reside in S ' s use of mediators. The Ss o f G r o u p C were either less p r o n e or less able to use mediators. F o r one thing, they learned m o r e slowly. Second, they were more apt to miss an item they had once gotten correct. Third, specific instructions to mediate did improve G r o u p M ' s performance. I f the difference between G r o u p s I and C lies in their abilities to generate mediators, it should be possible to demonstrate the difference directly. Experiment I I served this purpose. The Ss studied the material o f the continuous or the interrupted conditions. Then they were asked to supply mediators to connect each stimulus and response. As the results below show, the two groups differed in their latencies.

Method Two groups of Ss were tested. Group C' saw the material that had been shown to Group C in Exp. I; Group I' saw the material of the earlier Group I. The

material was presented as three study trials of a PA task. The procedure was exactly like that of Exp. I, except that S did not actually respond out 10ud. After the third study trial, the S's task was changed to one of free-association. The E said, "Now I am going to show you a list containing the pairs you've seen. For every pair, I'd like you to think of some word or phrase that connects the two parts of each pair. Your connector can be anything--something personal, something logical, or anything at all. For example, suppose the pair was 'ABC-soup.' The connector could be C for 'chowder,' or B for 'Beef noodle soup.' Another way to connect these would be 'ABC-alphabet-soup.' Or you could use a phrase: 'Always Buy Campbell'sSoup.'"

Then the first pair appeared on an MTA Scholar teaching machine, and a timer started. As soon as S thought of a mediator, he pressed a button which stopped the timer. Then he wrote his mediator. The E recorded S's latency in seconds. This latency measured the amount of time between the stimulus presentation and S's signal; it did not include S's writing time. This procedure was repeated for all items. Finally, S returned to the memory drum for three more trials of PA learning by the anticipation method. The procedure was exactly like that of Exp. I. After he completed these trials, he was given a list of the

response words, and he was asked to supply the stimulus for each. Fifteen Ss were tested in each condition. These Ss were all students from the introductory psychology class.

Results and Discussion Each S supplied 12 mediators, and the 12 latencies were s u m m e d to give a total score. The totals for Cond. C ranged f r o m 72.3 to 447.4, and their m e a n was 170.7 see. F o r Cond. I the totals ranged f r o m 18.4 to 141.9, with a mean o f 68.9 sec. The difference between the groups was highly significant: F ( I , 28) -15.71, p < .001. A separate analysis was also performed on the m e a n latencies of each item for each condition. Each m e a n value favored G r o u p I', and 7 o f the 12 F ' s reached the .05 level of significance or better. The n u m b e r of words that S used in each mediator was also scored. The subject o f Cond. C' produced a m e a n o f 55.47 words t h r o u g h o u t his twelve mediators. The corresponding value for the Ss of Cond. I ' was 29.67. This difference was significant, F(1, 28) = 4.64, p < .05. Thus, the S o f Cond. I' was n o t only faster in supplying mediators, but he was also more succinct. The superiority o f Cond. I ' also appeared on the three learning trials which followed the test for mediators. The m e a n n u m b e r o f correct anticipations for Cond. C ' on these three trials were: 7.47, 8.67, and 9.20. The corresponding values for Cond. I ' were: 9.93, 10.87, and 11.67. On each trial the difference between the two groups was significant: AII F's(1, 28) were significant at p < .05. The F ' s for each trial were: 7.49, 5.55, and 9.02. Finally the two groups did n o t differ in the final test o f stimulus recall; F(1, 28) = 0.67, p > .05. A n interrupted stimulus therefore se~ms to stimulate S ' s associative processes so he can think o f a mediator m o r e readily. If, instead, a trigram appears over and over, S is less prone or less able to associate to it. There is still one problem o f interpretation, though. W h y should an interrupted stimulus alone affect the S-R mediation? In Exp. II S generated his

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mnemonic aid as he observed the stimulus and response together. In the learning task of Exp. I, though, the stimulus and response did not co-appear; the facilitating interruption occurred in the midst of the stimulus presentation. What happens as S views an interrupted stimulus to allow him ultimately to generate more effective S,R mediators ? What happens as he views an interruption in H K M to help him connect H K M to " d o o r " ? If S thinks of " h o k u m " more readily to H K M , then somehow " h o k u m " facilitates the pair " H K M - d o o r . " Perhaps the advantage is due, not to the single response " h o k u m " , but to the associative meaning of " h o k u m " ; perhaps this associative meaning is present as the response " d o o r " appears, and the S imagines, say, a comedian-actor shouting "'Ho, Come through the door !" Possibly any easilyremembered associative meaning that S generated in the presence of H K M could facilitate the PA task. Sex Difference. Because of the sex difference that appeared in Exp. I, the data of Exp. I I were also analyzed separately for each sex. Since the sex variable had not been considered important when this experiment was planned, Ss were assigned to experimental conditions at random as they arrived at the laboratory. It so happened that 10 males and five females served in Cond. C', while six males and nine females served in Cond. I'. The data for the females yielded a very significant difference in mean latency of response: The mean of Cond. C' was 136.7 sec and that of Cond. I', 58.5 sec; F(1,12) = 14.86, p < .01. For males, the corresponding means were 187.8 sec and 84.6 sec. Although the absolute difference for the males was as large as that for the females, the larger variability made the difference insignificant: F(1, 14)= 2.04, p > .10. Thus, the sex difference of Exp. II was consistent with that of Exp. I. EXPERIMENTI I I The sex differences of Exps. I and I I were unexpected, so the following replication of

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Exp. I was performed. Also, the same E had performed both of the preceding experiments, and subtle experimenter biases might have influenced the experimental outcomes. Therefore, Exp. I I I was a replication of Cond. C and Cond. I of Exp. I, and it was conducted by two naive Es.

Method The two Es were undergraduate students at Stanford University who were majoring in psychology. One was male, the other was female, and neither E was told the purpose of the experiment. Each E ran half of the Ss in each condition. The experimental condition and the S's sex were assigned to E at random. (The data showed no systematic E-difference and no interactions involving E; all F's < 1. Therefore, E differences need not be discussed further.) The Ss were all students at Stanford University enrolled in the class in introductory psychology. The pool from which the Ss were drawn contained more males than females, so the sample contained 22 males and 10 females in each experimental condition, making 64 Ss altogether. The two experimental conditions are again designated C (continuous) and I (interrupted). The S was only tested on the PA task. Other tests, like the test of backward recall, were eliminated to allow enough time for S to continue the PA task to a more stringent criterion. The S continued to a criterion of two successive perfect trials. Otherwise, the details of PA learning and the instructions to S were identical to those described above.

Results and Discussion The mean number of trials needed to reach the first perfect trial was computed for each experimental condition. For female Ss, the means were 8.7 for Cond. I (SD = 2.8) and 13.6 for Cond. C (SD = 3.6). For male Ss, these means were 13.3 ( S D = 4 . 8 ) and 12.8 (SD = 5.3). A n analysis of variance showed that the sex difference fell short of significance at the .05 level, F(1, 6 0 ) = 3.07. The Sex-× Condition interaction was significant, F(1,60) = 6.09, p < .05. The mean trial on which S achieved the more stringent criterion showed a similar pattern. For the female Ss the means were 16.1 (Cond. C) and 10.9 (Cond. I). For male Ss the corresponding means were 14.6 and 15.8.

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The data of this experiment further show that female Ss are particularly sensitive to continued or interrupted stimuli. Apparently female Ss are more attentive to a continued stimulus when it is repeated on the memory drum, so they are more hindered by the material of Cond. C. Male Ss, on the other hand, seem to be less susceptible to these hindering effects. One puzzling feature of the data is that the performance of the male Ss resembles Cond. C of the female Ss, not Cond. I. Perhaps this result can be explained this way: Male Ss at Stanford University do not generally perform as well as female Ss on verbal tasks. In general, male Ss take longer to master a PA task. The present experiment contained a particularly monotonous, repetitive set of stimuli. Because of the monotony, male Ss may have moved a great deal and given themselves the advantage of an interrupted stimulus, no matter which condition they were in. This advantage may have brought the male S's performance up to the level of a female S in Cond. C. However, if the male S were denied the opportunity to

move around during the learning task of Cond. C, perhaps his performance would have been impaired even further. REFERENCES BROWN, R. W., AND LENNEBERG, E. H. A study in language and cognition, J. abn. soc. Pseyhol.,

1954, 49, 454-462. LANTZ,D., ANDSTEFFLRE,V. Language and cognition revisited. J. abn. soc. PsyehoL, 1964, 69, 472-481. LINDLEV,R. H. Effects of controlled coding cues in short-term memory. J. exp. Psyehol., 1963, 66, 580-587. LINDLEY, R. H., AND NEDLER, S. E. Supplementary report: Further effects of subject-generated recoding cues on short-term memory. J. exp. PsychoI., 1965, 69, 324-325. ScI~avB,G. R., ANDLrNDrEV,R. H. Effects of subjectgenerated recoding cues on short-term memory. J. exp. PsychoL, 1964, 68, 171-175. THORNDtKE,E. L., ANDLORGE,I. The Teacher's word book of 30,000 words. New York: Teachers College, Columbia University, Bureau of Publications, 1944. WITMER, L. R. The association value of three-place consonant syllables. J. genetic Psychol., 1935, 47, 337-359. (Received July 15, 1968)