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Coding processes in verbal learning
~OURNAL OF VERBAL LEARNING A~rDVERBAL BEHAVIOR 1, 250-257
(1963)
Coding Processes in Verbal Learning BENTON J . UNDERWOOD AND GEOFFREY
KEPPEL
Northwestern University, Evanston, lllinois 1
and Q. At recall, this unit is emitted exactly as carried in memory. A less extreme position would suggest that there is a transformation process so that the unit of memory is not isomorphic to the unit presented. These transformations may be of several levels of complexity. If the trigram is a word or an easily pronounceable unit, the sound may be the memory unit. At a more complex level, so-called associational aids or mnemonic devices may be involved in the transformations. For the present paper, transformations at all levels of complexity will be spoken of as encoding. It is at once apparent that if S encodes, further habits must be carried to produce decoding; S must get from the encoded unit back to the unit presented him since E requires that he reproduce the item exactly. If encoding via a well-known sound unit occurs, decoding habits are readily available through past learning. But, if decoding requires much new learning or the use of already established habits but complexly interrelated, decoding may not easily "get back" the item presented. In anecdotes, at least, the failure of the decoding processes may be responsible for errors at recall. That the senior author is sometimes called Remington may be an illustration. I t would seem, then, that in considering the likelihood of whether or not coding will occur, both the simplicity of encoding and simplicity of decoding must be evaluated. If both steps can be accomplished by means of well-established habits, the encoding-decoding 1 This work was done under Contract Nonr-1228 (15), Project 154-057, between Northwestern ldni- sequence might well be expected to occur. If either part of the sequence requires much versity and the Office of Naval Research.
The method used in the present study is free learning or free recall. By this method a series of verbal units is presented for a study period followed by a test period during which S attempts to reproduce all the units he can remember. This may be followed by another study and test period, and so on. The S may recall the units in any order he wishes, but if, as in the present study, the units consist of trigrams not forming words, the three letters for each trigram must be ordered as presented. Thus, if Q K J is one of several trigrams in a list, in producing this item S must get the letters in the correct order. The present study is concerned only with the learning involved which allows S to order correctly the letters within a trigram. More particularly, an attempt will be made to study the association (or associations) which are acquired and which, in a manner of speaking, are stored on the study trial so that S can reproduce the letters in correct order at the time of recall. Just what associations S acquires which allow him to produce the correct ordering of the three letters in a trigram is quite a speculative matter. One extreme position would be that by whatever means learning occurs, S acquires a unit which in its representation in the memory system may be said to be identical to the unit presented him objectively. Thus, if the trigram is QKJ, S carries some direct representation of the trigram, with associations between Q and K, between K and J, and perhaps between the general situation
250
CODING PROCESSES
new learning, it would seem that the likelihood of coding would be reduced, and whether or not it occurred might be determined by the difficulty involved in learning without coding. The design of the present experiment grew out of a pilot study in which Ss were presented 10 trigrams. Rearrangement of the letters within each trigram would produce two common three-letter words. The Ss in one group were instructed that the trigrams could be recalled in any order and, furthermore, that the three letters within each trigram could be reproduced in any order. Thus each trigram could be encoded into a common three-letter word and, according to the laws of meaningfulness, this word should be more quickly learned than the trigram. The notion was that if encoding came "naturally," this would be a favorable situation for it since no decoding was required at recall. However, the results showed that about 50% of the Ss did encode and 50% did not. That is, 50% wrote down words at recall and 50% wrote down the letters in the order presented. The differences in amount learned by these two subgroups, when compared with another group that was required to write down the letters in the order given, showed that encoding facilitated learning. If encoding in the above situation facilitated learning, the question may be raised as to why all Ss did not encode. There are at least two possibilities. First, perhaps only half the Ss perceived that the rearrangement of the letters would produce words. Second, perhaps this was perceived by all Ss but 50% chose to ignore this in learning. To help choose between these two alternatives, an instructional variable has been included in the present study. Half the group were instructed before learning that rearrangement of the letters would make words, and half were not. If the 50-50 split noted in the pilot study was due to failure of S to perceive that the trigrams could be transformed into words, it would be expected that all instructed Ss would encode. Although the instructional variable proved
251
to be a highly relevant one, the critical purpose of the present study was to attempt to determine if S uses an encoding-decoding process when he is required to recall the letters within a trigram in the order presented. Does S encode to a word and then decode back to the trigram at recall? It was reasoned that if this were occurring the major difficulty would occur in decoding. If this were true, the removal of the necessity for decoding at some point in learning should be followed by a sudden increase in performance. METHOD
Materials. All Ss were presented the following 10 trigrams: TFA, BSU, U T B , A M D , DNO, M D I , INP, TPO, E T N , D W E . E a c h trigram can be t r a n s f o r m e d into two three-letter words b y rearrangement of the letters, e.g., U T B m a y become T U B or BUT. The list was presented for five s t u d y trials on a m e m o r y d r u m alternating with five written recall trials. T h e rate of presentation was 2 sec. per item with 40 sec. allowed for S to write down the responses on the recall trials. All Ss were instructed that they could recall the items in a n y order they wished a n d t h a t the order of presentation of items on each s t u d y trial would vary. T h e five orders of presentation were r a n d o m , subject to the restriction that no item occurred more t h a n once in a given position. Conditions. Eight groups of Ss were employed. F o u r of these groups will be referred to as Instructed Groups (I Groups) a n d four as N o t - I n s t r u c t e d Groups ( N I Groups). T h e I Groups, in addition to being instructed concerning the learning requirements, were told prior to the first s t u d y trial t h a t : "I should point out t h a t if the letters of each trigram are rearranged, t h a t is, if the order of the letters is changed, a c o m m o n three-letter word will be formed. Thus, if a trigram were EJO, for example, y o u can see t h a t if the letters are rearranged they will spell J O E . " T h e N I Groups did not have this information included in the instructions. Within each of the two instructional conditions there were four subgroups. To u n d e r s t a n d the difference a m o n g these subgroups it is first necessary to explain two types of correct-response requirements. There is first the traditional requirement t h a t the three letters of the trigram be given at recall in the same order as presented. T h a t is, S is told t h a t to be counted correct the three letters m u s t be written d o w n in the same order as the order s h o w n on the s t u d y trial. T h e second type of correctresponse requirement used d e m a n d e d only that the
252
UNDERWOOD AND K E P P E L
correct three letters be given. The S was told that to be counted correct the correct three letters had to be given but that the order in which they were given was irrelevant. The four subgroups within each instructional condition differed in terms of the point in learning at which the traditional correct-response requirement was removed or lifted and the more lenient type substituted. Group 0 was instructed before the first learning trial that the letters could be written in any order, and these requirements held for all five trials. Group 1 was instructed initially that the order of the letters must be recalled in the order presented to be counted correct. However, after the first recall trial these Ss were instructed that on all subsequent trials the letters could be written in any order. For Group 3 the instructions to write the letters as presented held until after the third recall trial at which time the restriction was lifted so that the letters could be written in any order. The Ss in Group 5 were required to write the letters presented on all recall trials; that is, the traditional correct-response requirement held for these Ss on all trials. The symbols for the eight conditions can be formed by the appropriate combination of the two variables, instructions (I and NI) and point of change in correct-response requirements (0, 1, 3, and 5). Thus, the Ss in Group I-3 were instructed initially that the letters of the trigrams could be rearranged to form words and that the letters must be written in the order presented, but after the third recall trial were told that the letters could be written in any order on subsequent trials. Design and Subjects. Each of the eight groups contained 30 Ss. A schedule of 30 blocks of eight conditions each was constructed. Within each block each condition was represented once but the order in each block was random. The Ss were assigned to the schedule in order of their appearance at the laboratory. Most of the Ss had served in previous verballearning studies, but none of the previous experiments involved conditions similar to the present ones. RESULTS Since different criteria as to what may be counted correct prevail across some of the conditions, the results will be most meaningfully presented as a series of two-condition comparisions, the N I ( N o t - I n s t r u c t e d ) Group being compared with the I (Instructed) Group for each pair of subgroups. 5-Groups. The condition for these groups was the traditional one in which S is required to reproduce the three letters within the
trigram in the order they are presented on the study trials. Under these conditions the performance of the I Group was inferior to that of the N I Group, and this was true for all five trials. For the N I Group the mean total correct responses across the five trials was 28.07; for the I Group, 22.70. The difference, 5.37 --+ 2.34, gives a t of 2.29, significant beyond the 5 3 level. W h a t could produce this difference? T h e nature of the overt errors strongly suggests that the Ss in the I Group were more likely to try learning b y a n encoding-decoding process than were Ss in the N I Group. Apparently the instructions which informed Ss that each trigram could be transformed into a word increased the likelihood that S would try to use this knowledge in learning even though it proved deleterious to learning. T h e errors indicate that interference was produced in the decoding process. A n error in which the appropriate three letters were given, b u t in the wrong sequence, would be indicative of difficulty in decoding. T h e I Group produced a mean of 5.03 such errors across the five trials while the N I Group produced a mean of only .90 such errors. Not a single error made by the I Group constituted a word, so it is clear that the greater number of errors is not a consequence of S failing to attempt to decode. The difference in learning between the two groups as reported above, while significant b y statistical standards, is not great in a n absolute sense. However, the comparison made probably does not represent the full effect of the interference which may result from attempts to learn b y the encodingdecoding method. Perhaps some Ss in the I Group did not code, and perhaps some of the Ss in the N I Group did. However, as a working assumption, we will proceed as if few, if any, Ss in the N I Group did code. Among the 30 Ss in this group, one made seven "good" errors (errors indicating coding attempts since the proper letters were given in the wrong sequence), b u t no other S made more than three such errors and 17 made none. Thus,
CODING :PROCESSES
coding attempts oppear to be minimal in the N I Group; therefore, attention may be directed to the I Group where more Ss appear to be trying to learn by encoding to words. This group was broken into two subgroups such that one of these subgroups had approximately the same good-error frequency as the 30 Ss in the N I Group. The 15 Ss of the I Group with 4 or fewer errors constituted one of these subgroups. The mean number of errors was 1.33, which is a little higher than the mean for the 30 Ss in the N I Group (.90). The remaining 15 Ss had 8.73 mean errors across the five trials. The learning scores for the three groups may now be compared. The 15 Ss in Group I whose error rate was relatively low and roughly comparable to that of the 30 Ss in the N I Group had 27.67 mean total correct responses. This compares favorably with the mean for the N I Group (28.07). However, the 15 Ss in Group I whose error rates strongly suggest coding had a mean of only 17.73 correct responses across the five trials. Two points are to be made by the above comparisions. First, the gross comparisons between the 30 N I Ss and the 30 I Ss underestimate the inhibitory effects of trying to learn by encoding to words. When the learning of only those Ss who have high gooderror rates is examined, it is quite apparent that learning is occurring very slowly. The second point inferred from the data is that whether or not S attempts to learn by encoding to words is unrelated to his learning ability. This fact can be deduced from the finding that the 15 Ss in the I Group whose error frequencies indicated they were not trying to learn by encoding to words had about the same mean learning score as the 30 Ss in the N I Group, none of whom or few of whom, attempted to learn by encoding to words. This comparability would not obtain if any particular section of a distribution of learning ability was associated with Ss who attempted to learn by encoding to words. The results for the 5-Groups indicate that
253
the attempt to learn by encoding to words produces interference in learning when S must recall the sequence of letters as given to him on the study trials. I t would be expected, however, that if S is not required to decode, performance would be facilitated by encoding. The results for the 0-Groups, to which attention is now directed, show exactly this. O-Groups. The Ss in these groups were told that to be counted correct the three appropriate letters must be given but that the order of these three letters was unimportant. Three categories of correct responses are possible for these Ss. First, the three letters may be given in the order presented. Second, a word may be given, and third, the three proper letters may be given but in one of the three orders remaining after exclusion of the first two categories. The mean number correct on each trial, and the mean totals for each of the three categories are given in Table 1 for the I and N I Groups. Table 1 shows that in the I Group almost all of the correct responses were obtained by responding with words, while for the N I Group only about 5 5 ~ of the correct responses were given as words. Furthermore, the I Group gave more total correct responses of all kinds than did the N I Group. The difference in mean total correct between the two groups is 4.67 ___ 1.61, which gives a t of 2.90. Clearly, the instructions which informed the Ss that each trigram could be made into a word facilitated the learning by causing more Ss in this group to learn via words. The difference in learning produced by encoding is probably again underestimated by the gross comparison between the I and N I Groups, for some Ss in the N I Group also used this procedure. As in the pilot study there was a fairly clear break between those who did not respond with words and those who did. Across all five trials, 14 Ss in the N I Group responded with words for 82% or more of the time; 12 Ss responded 1 6 ~ or less of the time. The remaining four Ss had
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U N D E R W O O D AND K E P P E L
TABLE 1 M E A N CORRECT RESPONSES BY TRIALS ~'OR DIEFERENT CATEGORIES OF CORRECT I~ESPONSES IN TIlE CONDITIONS IN WI-IICI~I S CO,ULD GIVE TIIE LETTERS IN ANY ORDERa
Instructed As Presented Words Other Order Totals
1
2
3
4
5
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.10 5.53 .07 5.70
.13 7.67 .07 7.87
.07 7.90 .17 8.14
.20 8.10 .13 8.43
.27 8.37 .13 8.77
.77 37.57 .57 38.91
1
2
3
4
5
Total
2.03 2.00 .30 4.33
2.57 3.10 .53 6.20
2.80 3.93 .57 7.30
3.07 4.70 .37 8.14
2.80 5.17 .30 8.27
13.27 18.90 2.07 34.24
Not Instructed As Presented Words Other Order Totals
a As Presented indicates the letters were given in the order presented; Words indicates the subject responded with one of the two orders constituting a word; Other Order indicates any other order of the three letters.
percentages of 57, 61, 43, and 59, and because of the a m b i g u i t y in classifying them under such circumstances, these four will not be considered further. T h e 14 coding Ss h a d a mean total correct of 36.63, the 12 noncoding Ss a mean of 32.17. While the difference between these means is not significant statistically (t ~-- 1.47), the direction of the difference is as expected. T h e over-all d a t a for the 0-Groups j u s t i f y the conclusion t h a t if S is told or perceives t h a t the trigrams can be transformed into words, and if he uses this transformation in learning, performance is facilitated if decoding is not required. Groups 1 and 3. T h e Ss in the N I - 1 a n d I-1 Groups were required to respond with the trigram as presented on the first recall trial b u t this restriction was removed on all following trials. T h e procedure was the same for the N I - 3 a n d I-3 Groups except t h a t the restriction was not lifted until after the third recall trial. I t was reasoned t h a t if the Ss were a t t e m p t i n g to learn b y an encoding-decoding process before the restriction was lifted, m a r k e d improvement would result on the trial following the lifting of the restriction, since decoding would no longer be required. T h e
initial comparisons will again be made between the N I and I Groups as indicating gross differences in Ss who are not likely to code ( N I ) a n d those who are ( I ) . Performance curves are plotted in Fig. 1. F o r the scores before the lifting of the restriction only those items were counted as correct in which the sequence was the same as the sequence given on the s t u d y trials. After lifting of the restrictions, all sequences were counted as correct if the a p p r o p r i a t e three letters were given. Looking first at the left section of Fig. 1, it can be seen t h a t after lifting the response restriction, the I-1 Group's performance became superior to that of the N I - 1 Group's on T r i a l 2 and remained so on all subsequent trials. T h e difference in total correct responses for Trials 2-5 is 5.20 -+ 1.22, which gives a t of 4.26. T h e right section of Fig. 1 shows the same effect after the response restriction was removed following T r i a l 3. T h e performance of Ss in Group I-3 exceeds t h a t of Group N I - 3 on Trials 4 and 5. T h e mean difference is 2.43 ± .74, with a t of 3.28. T h e fact t h a t a t both levels of learning the performance of the I Groups becomes superior to t h a t of the
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Fio. 1. Acquisition curves for the I (Instructed) and NI (Not-Instructed) Groups. For the groups on which the left figure is based the letters of the trigrams could be written in any order after the first trial. For the right figure the letters of the trigram could be first written in any order after the third trial. Responses were counted correct only if they conformed to the instructions prevailing on a given trial. N I Groups when the response restriction is removed indicates that more Ss in the I than in the N I Groups were attempting to learn by encoding to words and decoding to trigrams when they were required to produce the trigram as presented. Removal of the necessity to decode resulted in a marked improvement in performance. The differences between the I and N I Groups following lifting of the response restriction again do not reflect the full positive effect to be expected if S had been attempting to learn by coding to words before the restriction was lifted. This is because all Ss in the I Groups did not in fact use an encoding-decoding process initially. This may be demonstrated by further analysis of Group 1-3. It was indicated earlier that the number of good errors (right letters in wrong sequence) was a reasonable index for separating coders from noncoders. The records for the 30 Ss in Group I-3 were examined for good errors on the first three trials. The group was divided into two subgroups, those Ss having three or more good errors being called coders (N ~-~ 14) and those with two or fewer good errors being called noncoders (N ~ 16). The mean total correct responses on Trials 1-3 was 11.71 for the coders and 14.44 for tile noncoders. On Trials 4-5, the mean total correct
was 17.36 for the coders and 15.69 for the noncoders. The coders show an increase of 5.65 correct responses, the noncoders an increase of only .25 correct responses. The difference in the increase, 5.39 ---+ 1.11, gives a t of 4.86. In considering the differences between performance of the 1-5 and NI-5 Groups in an earlier section, it was stated that the performance of the NI-5 Group exceeded that of the I-5 Group on all five trials. Under exactly the same conditions it can be seen in Fig. 1 that the NI-1 and I-1 Groups are equivalent on the first trial, but that the NI-3 Group is superior to the 1-3 Group. Thus, it appears that the differences between N I and I are not great when S must respond with the trigram as presented. However, across all three conditions the difference is significant statistically. The 90 1 Ss and the 90 N I Ss were compared on the first trial of the three conditions (1, 3, 5) where S was required to respond with the trigram as presented. The N I Ss showed a mean of 3.27, the I Ss a mean of 2.78, with the difference .49 ----- .21 producing a t of 2.33. Finally, the question may be asked as to whether the Ss in Group I-1 and I-3 ever attained the level of performance shown for Group I - 0 - - t h e group that could always
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FIG. 2. Acquisition curves for all I Groups. Group 0 could write the letters in any order on all trials, Group 1 only after the first trial, Group 3 only after the third trial, and Group 5 was always required to write the letters in the order presented. Responses were counted correct only if they conformed to the instructions prevailing on a given trial. respond with words. The answer to the question is shown in Fig. 2 where the performance curves for all of the four I Groups are plotted. Except for the second trial, the performance of the I-1 Group is essentially equivalent to that of the I-0 Group, and the performance of the I-3 Group on Trials 4-5 is only slightly less than that of the I-0 Group. On the fifth trial all groups are far ahead of the I-5 Group, the group which was required to produce the response terms as presented on all trials. DISCUSSION The present study has indicated that it is possible to exercise some experimental control over coding processes. At least for the Ss in the instructed groups, performance followed the course that would be anticipated if trigrams were being encoded into words and then decoded back to the trigrams at recall. Not all Ss in the instructed groups did this, and at best only few in the noninstructed groups attempted it. Instructing the Ss that the trigrams could be transformed into words probably had an effect over and above merely supplying transformation information. A secondary effect appeared to be that perhaps
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half the Ss also inferred that such a transformation would facilitate learning even when the trigram response was required. In any event, the evidence indicated that about half the Ss used an encoding-decoding procedure although it resulted in inferior performance. Only when the transformed words as such could be used as the written response was performance facilitated. I t is not surprising that the use of coding processes with these materials inhibited performance. Encoding was simple, but for each encoded word a decoding rule had to be learned. For example, if T F A was encoded to FAT, the decoding rule had to be something like: "put last letter first." No single decoding rule would apply to all trigrams, and there would be numerous possibilities for interference among decoding rules. The number of different decoding rules required would clearly be a variable determining performance. The present study was designed to evaluate only one particular coding sequence. I t is not to be inferred that the Ss not using this sequence did not use other coding procedures. Some of the trigrams would not be difficult to pronounce (e.g., I N P ) and this simple coding procedure may have been used. Some trigrams may have been encoded to sequential words (DNO to "don't know"), in which case decoding would be relatively simple. The present study did not gather evidence on such processes. In any event, it seems apparent that materials and procedures can be devised which will bias S toward a particular type of coding process. I t should, therefore, be possible to manipulate systematically and independently the ease of encoding and the ease of decoding and thereby determine the relevant variables for associative processes of this nature. S Uh/£1Vf A R Y
In a free learning situation Ss were presented I0 trigrams for five alternate study and recall trials. Each trigram could be transformed into either of two words by re-
CODING :PROCESSES
arranging the letters. Parallel groups were either instructed or not instructed concerning the transformation possibilities. Within these parallel groups, subgroups of 30 Ss each were differentiated on the basis of the nature of the correct response allowed. If Ss were allowed to write the letters of each trigram in any order they wished, performance was facilitated if the trigrams were encoded to words. This facilitation was more apparent in the instructed group than in the noninstructed
257
group simply because more Ss encoded in the former group. If S was required to write down the trigram as presented, encoding to words and decoding to trigrams inhibited performance, but if during learning the rules were changed so that S could write the letters in any order (eliminating decoding) performance rose sharply and to a higher level than that shown by Ss not using an encodingdecoding sequence. (Received July 30, 1962)
(1963)
Coding Processes in Verbal Learning BENTON J . UNDERWOOD AND GEOFFREY
KEPPEL
Northwestern University, Evanston, lllinois 1
and Q. At recall, this unit is emitted exactly as carried in memory. A less extreme position would suggest that there is a transformation process so that the unit of memory is not isomorphic to the unit presented. These transformations may be of several levels of complexity. If the trigram is a word or an easily pronounceable unit, the sound may be the memory unit. At a more complex level, so-called associational aids or mnemonic devices may be involved in the transformations. For the present paper, transformations at all levels of complexity will be spoken of as encoding. It is at once apparent that if S encodes, further habits must be carried to produce decoding; S must get from the encoded unit back to the unit presented him since E requires that he reproduce the item exactly. If encoding via a well-known sound unit occurs, decoding habits are readily available through past learning. But, if decoding requires much new learning or the use of already established habits but complexly interrelated, decoding may not easily "get back" the item presented. In anecdotes, at least, the failure of the decoding processes may be responsible for errors at recall. That the senior author is sometimes called Remington may be an illustration. I t would seem, then, that in considering the likelihood of whether or not coding will occur, both the simplicity of encoding and simplicity of decoding must be evaluated. If both steps can be accomplished by means of well-established habits, the encoding-decoding 1 This work was done under Contract Nonr-1228 (15), Project 154-057, between Northwestern ldni- sequence might well be expected to occur. If either part of the sequence requires much versity and the Office of Naval Research.
The method used in the present study is free learning or free recall. By this method a series of verbal units is presented for a study period followed by a test period during which S attempts to reproduce all the units he can remember. This may be followed by another study and test period, and so on. The S may recall the units in any order he wishes, but if, as in the present study, the units consist of trigrams not forming words, the three letters for each trigram must be ordered as presented. Thus, if Q K J is one of several trigrams in a list, in producing this item S must get the letters in the correct order. The present study is concerned only with the learning involved which allows S to order correctly the letters within a trigram. More particularly, an attempt will be made to study the association (or associations) which are acquired and which, in a manner of speaking, are stored on the study trial so that S can reproduce the letters in correct order at the time of recall. Just what associations S acquires which allow him to produce the correct ordering of the three letters in a trigram is quite a speculative matter. One extreme position would be that by whatever means learning occurs, S acquires a unit which in its representation in the memory system may be said to be identical to the unit presented him objectively. Thus, if the trigram is QKJ, S carries some direct representation of the trigram, with associations between Q and K, between K and J, and perhaps between the general situation
250
CODING PROCESSES
new learning, it would seem that the likelihood of coding would be reduced, and whether or not it occurred might be determined by the difficulty involved in learning without coding. The design of the present experiment grew out of a pilot study in which Ss were presented 10 trigrams. Rearrangement of the letters within each trigram would produce two common three-letter words. The Ss in one group were instructed that the trigrams could be recalled in any order and, furthermore, that the three letters within each trigram could be reproduced in any order. Thus each trigram could be encoded into a common three-letter word and, according to the laws of meaningfulness, this word should be more quickly learned than the trigram. The notion was that if encoding came "naturally," this would be a favorable situation for it since no decoding was required at recall. However, the results showed that about 50% of the Ss did encode and 50% did not. That is, 50% wrote down words at recall and 50% wrote down the letters in the order presented. The differences in amount learned by these two subgroups, when compared with another group that was required to write down the letters in the order given, showed that encoding facilitated learning. If encoding in the above situation facilitated learning, the question may be raised as to why all Ss did not encode. There are at least two possibilities. First, perhaps only half the Ss perceived that the rearrangement of the letters would produce words. Second, perhaps this was perceived by all Ss but 50% chose to ignore this in learning. To help choose between these two alternatives, an instructional variable has been included in the present study. Half the group were instructed before learning that rearrangement of the letters would make words, and half were not. If the 50-50 split noted in the pilot study was due to failure of S to perceive that the trigrams could be transformed into words, it would be expected that all instructed Ss would encode. Although the instructional variable proved
251
to be a highly relevant one, the critical purpose of the present study was to attempt to determine if S uses an encoding-decoding process when he is required to recall the letters within a trigram in the order presented. Does S encode to a word and then decode back to the trigram at recall? It was reasoned that if this were occurring the major difficulty would occur in decoding. If this were true, the removal of the necessity for decoding at some point in learning should be followed by a sudden increase in performance. METHOD
Materials. All Ss were presented the following 10 trigrams: TFA, BSU, U T B , A M D , DNO, M D I , INP, TPO, E T N , D W E . E a c h trigram can be t r a n s f o r m e d into two three-letter words b y rearrangement of the letters, e.g., U T B m a y become T U B or BUT. The list was presented for five s t u d y trials on a m e m o r y d r u m alternating with five written recall trials. T h e rate of presentation was 2 sec. per item with 40 sec. allowed for S to write down the responses on the recall trials. All Ss were instructed that they could recall the items in a n y order they wished a n d t h a t the order of presentation of items on each s t u d y trial would vary. T h e five orders of presentation were r a n d o m , subject to the restriction that no item occurred more t h a n once in a given position. Conditions. Eight groups of Ss were employed. F o u r of these groups will be referred to as Instructed Groups (I Groups) a n d four as N o t - I n s t r u c t e d Groups ( N I Groups). T h e I Groups, in addition to being instructed concerning the learning requirements, were told prior to the first s t u d y trial t h a t : "I should point out t h a t if the letters of each trigram are rearranged, t h a t is, if the order of the letters is changed, a c o m m o n three-letter word will be formed. Thus, if a trigram were EJO, for example, y o u can see t h a t if the letters are rearranged they will spell J O E . " T h e N I Groups did not have this information included in the instructions. Within each of the two instructional conditions there were four subgroups. To u n d e r s t a n d the difference a m o n g these subgroups it is first necessary to explain two types of correct-response requirements. There is first the traditional requirement t h a t the three letters of the trigram be given at recall in the same order as presented. T h a t is, S is told t h a t to be counted correct the three letters m u s t be written d o w n in the same order as the order s h o w n on the s t u d y trial. T h e second type of correctresponse requirement used d e m a n d e d only that the
252
UNDERWOOD AND K E P P E L
correct three letters be given. The S was told that to be counted correct the correct three letters had to be given but that the order in which they were given was irrelevant. The four subgroups within each instructional condition differed in terms of the point in learning at which the traditional correct-response requirement was removed or lifted and the more lenient type substituted. Group 0 was instructed before the first learning trial that the letters could be written in any order, and these requirements held for all five trials. Group 1 was instructed initially that the order of the letters must be recalled in the order presented to be counted correct. However, after the first recall trial these Ss were instructed that on all subsequent trials the letters could be written in any order. For Group 3 the instructions to write the letters as presented held until after the third recall trial at which time the restriction was lifted so that the letters could be written in any order. The Ss in Group 5 were required to write the letters presented on all recall trials; that is, the traditional correct-response requirement held for these Ss on all trials. The symbols for the eight conditions can be formed by the appropriate combination of the two variables, instructions (I and NI) and point of change in correct-response requirements (0, 1, 3, and 5). Thus, the Ss in Group I-3 were instructed initially that the letters of the trigrams could be rearranged to form words and that the letters must be written in the order presented, but after the third recall trial were told that the letters could be written in any order on subsequent trials. Design and Subjects. Each of the eight groups contained 30 Ss. A schedule of 30 blocks of eight conditions each was constructed. Within each block each condition was represented once but the order in each block was random. The Ss were assigned to the schedule in order of their appearance at the laboratory. Most of the Ss had served in previous verballearning studies, but none of the previous experiments involved conditions similar to the present ones. RESULTS Since different criteria as to what may be counted correct prevail across some of the conditions, the results will be most meaningfully presented as a series of two-condition comparisions, the N I ( N o t - I n s t r u c t e d ) Group being compared with the I (Instructed) Group for each pair of subgroups. 5-Groups. The condition for these groups was the traditional one in which S is required to reproduce the three letters within the
trigram in the order they are presented on the study trials. Under these conditions the performance of the I Group was inferior to that of the N I Group, and this was true for all five trials. For the N I Group the mean total correct responses across the five trials was 28.07; for the I Group, 22.70. The difference, 5.37 --+ 2.34, gives a t of 2.29, significant beyond the 5 3 level. W h a t could produce this difference? T h e nature of the overt errors strongly suggests that the Ss in the I Group were more likely to try learning b y a n encoding-decoding process than were Ss in the N I Group. Apparently the instructions which informed Ss that each trigram could be transformed into a word increased the likelihood that S would try to use this knowledge in learning even though it proved deleterious to learning. T h e errors indicate that interference was produced in the decoding process. A n error in which the appropriate three letters were given, b u t in the wrong sequence, would be indicative of difficulty in decoding. T h e I Group produced a mean of 5.03 such errors across the five trials while the N I Group produced a mean of only .90 such errors. Not a single error made by the I Group constituted a word, so it is clear that the greater number of errors is not a consequence of S failing to attempt to decode. The difference in learning between the two groups as reported above, while significant b y statistical standards, is not great in a n absolute sense. However, the comparison made probably does not represent the full effect of the interference which may result from attempts to learn b y the encodingdecoding method. Perhaps some Ss in the I Group did not code, and perhaps some of the Ss in the N I Group did. However, as a working assumption, we will proceed as if few, if any, Ss in the N I Group did code. Among the 30 Ss in this group, one made seven "good" errors (errors indicating coding attempts since the proper letters were given in the wrong sequence), b u t no other S made more than three such errors and 17 made none. Thus,
CODING :PROCESSES
coding attempts oppear to be minimal in the N I Group; therefore, attention may be directed to the I Group where more Ss appear to be trying to learn by encoding to words. This group was broken into two subgroups such that one of these subgroups had approximately the same good-error frequency as the 30 Ss in the N I Group. The 15 Ss of the I Group with 4 or fewer errors constituted one of these subgroups. The mean number of errors was 1.33, which is a little higher than the mean for the 30 Ss in the N I Group (.90). The remaining 15 Ss had 8.73 mean errors across the five trials. The learning scores for the three groups may now be compared. The 15 Ss in Group I whose error rate was relatively low and roughly comparable to that of the 30 Ss in the N I Group had 27.67 mean total correct responses. This compares favorably with the mean for the N I Group (28.07). However, the 15 Ss in Group I whose error rates strongly suggest coding had a mean of only 17.73 correct responses across the five trials. Two points are to be made by the above comparisions. First, the gross comparisons between the 30 N I Ss and the 30 I Ss underestimate the inhibitory effects of trying to learn by encoding to words. When the learning of only those Ss who have high gooderror rates is examined, it is quite apparent that learning is occurring very slowly. The second point inferred from the data is that whether or not S attempts to learn by encoding to words is unrelated to his learning ability. This fact can be deduced from the finding that the 15 Ss in the I Group whose error frequencies indicated they were not trying to learn by encoding to words had about the same mean learning score as the 30 Ss in the N I Group, none of whom or few of whom, attempted to learn by encoding to words. This comparability would not obtain if any particular section of a distribution of learning ability was associated with Ss who attempted to learn by encoding to words. The results for the 5-Groups indicate that
253
the attempt to learn by encoding to words produces interference in learning when S must recall the sequence of letters as given to him on the study trials. I t would be expected, however, that if S is not required to decode, performance would be facilitated by encoding. The results for the 0-Groups, to which attention is now directed, show exactly this. O-Groups. The Ss in these groups were told that to be counted correct the three appropriate letters must be given but that the order of these three letters was unimportant. Three categories of correct responses are possible for these Ss. First, the three letters may be given in the order presented. Second, a word may be given, and third, the three proper letters may be given but in one of the three orders remaining after exclusion of the first two categories. The mean number correct on each trial, and the mean totals for each of the three categories are given in Table 1 for the I and N I Groups. Table 1 shows that in the I Group almost all of the correct responses were obtained by responding with words, while for the N I Group only about 5 5 ~ of the correct responses were given as words. Furthermore, the I Group gave more total correct responses of all kinds than did the N I Group. The difference in mean total correct between the two groups is 4.67 ___ 1.61, which gives a t of 2.90. Clearly, the instructions which informed the Ss that each trigram could be made into a word facilitated the learning by causing more Ss in this group to learn via words. The difference in learning produced by encoding is probably again underestimated by the gross comparison between the I and N I Groups, for some Ss in the N I Group also used this procedure. As in the pilot study there was a fairly clear break between those who did not respond with words and those who did. Across all five trials, 14 Ss in the N I Group responded with words for 82% or more of the time; 12 Ss responded 1 6 ~ or less of the time. The remaining four Ss had
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U N D E R W O O D AND K E P P E L
TABLE 1 M E A N CORRECT RESPONSES BY TRIALS ~'OR DIEFERENT CATEGORIES OF CORRECT I~ESPONSES IN TIlE CONDITIONS IN WI-IICI~I S CO,ULD GIVE TIIE LETTERS IN ANY ORDERa
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.10 5.53 .07 5.70
.13 7.67 .07 7.87
.07 7.90 .17 8.14
.20 8.10 .13 8.43
.27 8.37 .13 8.77
.77 37.57 .57 38.91
1
2
3
4
5
Total
2.03 2.00 .30 4.33
2.57 3.10 .53 6.20
2.80 3.93 .57 7.30
3.07 4.70 .37 8.14
2.80 5.17 .30 8.27
13.27 18.90 2.07 34.24
Not Instructed As Presented Words Other Order Totals
a As Presented indicates the letters were given in the order presented; Words indicates the subject responded with one of the two orders constituting a word; Other Order indicates any other order of the three letters.
percentages of 57, 61, 43, and 59, and because of the a m b i g u i t y in classifying them under such circumstances, these four will not be considered further. T h e 14 coding Ss h a d a mean total correct of 36.63, the 12 noncoding Ss a mean of 32.17. While the difference between these means is not significant statistically (t ~-- 1.47), the direction of the difference is as expected. T h e over-all d a t a for the 0-Groups j u s t i f y the conclusion t h a t if S is told or perceives t h a t the trigrams can be transformed into words, and if he uses this transformation in learning, performance is facilitated if decoding is not required. Groups 1 and 3. T h e Ss in the N I - 1 a n d I-1 Groups were required to respond with the trigram as presented on the first recall trial b u t this restriction was removed on all following trials. T h e procedure was the same for the N I - 3 a n d I-3 Groups except t h a t the restriction was not lifted until after the third recall trial. I t was reasoned t h a t if the Ss were a t t e m p t i n g to learn b y an encoding-decoding process before the restriction was lifted, m a r k e d improvement would result on the trial following the lifting of the restriction, since decoding would no longer be required. T h e
initial comparisons will again be made between the N I and I Groups as indicating gross differences in Ss who are not likely to code ( N I ) a n d those who are ( I ) . Performance curves are plotted in Fig. 1. F o r the scores before the lifting of the restriction only those items were counted as correct in which the sequence was the same as the sequence given on the s t u d y trials. After lifting of the restrictions, all sequences were counted as correct if the a p p r o p r i a t e three letters were given. Looking first at the left section of Fig. 1, it can be seen t h a t after lifting the response restriction, the I-1 Group's performance became superior to that of the N I - 1 Group's on T r i a l 2 and remained so on all subsequent trials. T h e difference in total correct responses for Trials 2-5 is 5.20 -+ 1.22, which gives a t of 4.26. T h e right section of Fig. 1 shows the same effect after the response restriction was removed following T r i a l 3. T h e performance of Ss in Group I-3 exceeds t h a t of Group N I - 3 on Trials 4 and 5. T h e mean difference is 2.43 ± .74, with a t of 3.28. T h e fact t h a t a t both levels of learning the performance of the I Groups becomes superior to t h a t of the
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Fio. 1. Acquisition curves for the I (Instructed) and NI (Not-Instructed) Groups. For the groups on which the left figure is based the letters of the trigrams could be written in any order after the first trial. For the right figure the letters of the trigram could be first written in any order after the third trial. Responses were counted correct only if they conformed to the instructions prevailing on a given trial. N I Groups when the response restriction is removed indicates that more Ss in the I than in the N I Groups were attempting to learn by encoding to words and decoding to trigrams when they were required to produce the trigram as presented. Removal of the necessity to decode resulted in a marked improvement in performance. The differences between the I and N I Groups following lifting of the response restriction again do not reflect the full positive effect to be expected if S had been attempting to learn by coding to words before the restriction was lifted. This is because all Ss in the I Groups did not in fact use an encoding-decoding process initially. This may be demonstrated by further analysis of Group 1-3. It was indicated earlier that the number of good errors (right letters in wrong sequence) was a reasonable index for separating coders from noncoders. The records for the 30 Ss in Group I-3 were examined for good errors on the first three trials. The group was divided into two subgroups, those Ss having three or more good errors being called coders (N ~-~ 14) and those with two or fewer good errors being called noncoders (N ~ 16). The mean total correct responses on Trials 1-3 was 11.71 for the coders and 14.44 for tile noncoders. On Trials 4-5, the mean total correct
was 17.36 for the coders and 15.69 for the noncoders. The coders show an increase of 5.65 correct responses, the noncoders an increase of only .25 correct responses. The difference in the increase, 5.39 ---+ 1.11, gives a t of 4.86. In considering the differences between performance of the 1-5 and NI-5 Groups in an earlier section, it was stated that the performance of the NI-5 Group exceeded that of the I-5 Group on all five trials. Under exactly the same conditions it can be seen in Fig. 1 that the NI-1 and I-1 Groups are equivalent on the first trial, but that the NI-3 Group is superior to the 1-3 Group. Thus, it appears that the differences between N I and I are not great when S must respond with the trigram as presented. However, across all three conditions the difference is significant statistically. The 90 1 Ss and the 90 N I Ss were compared on the first trial of the three conditions (1, 3, 5) where S was required to respond with the trigram as presented. The N I Ss showed a mean of 3.27, the I Ss a mean of 2.78, with the difference .49 ----- .21 producing a t of 2.33. Finally, the question may be asked as to whether the Ss in Group I-1 and I-3 ever attained the level of performance shown for Group I - 0 - - t h e group that could always
256
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FIG. 2. Acquisition curves for all I Groups. Group 0 could write the letters in any order on all trials, Group 1 only after the first trial, Group 3 only after the third trial, and Group 5 was always required to write the letters in the order presented. Responses were counted correct only if they conformed to the instructions prevailing on a given trial. respond with words. The answer to the question is shown in Fig. 2 where the performance curves for all of the four I Groups are plotted. Except for the second trial, the performance of the I-1 Group is essentially equivalent to that of the I-0 Group, and the performance of the I-3 Group on Trials 4-5 is only slightly less than that of the I-0 Group. On the fifth trial all groups are far ahead of the I-5 Group, the group which was required to produce the response terms as presented on all trials. DISCUSSION The present study has indicated that it is possible to exercise some experimental control over coding processes. At least for the Ss in the instructed groups, performance followed the course that would be anticipated if trigrams were being encoded into words and then decoded back to the trigrams at recall. Not all Ss in the instructed groups did this, and at best only few in the noninstructed groups attempted it. Instructing the Ss that the trigrams could be transformed into words probably had an effect over and above merely supplying transformation information. A secondary effect appeared to be that perhaps
AND
KEPPEL
half the Ss also inferred that such a transformation would facilitate learning even when the trigram response was required. In any event, the evidence indicated that about half the Ss used an encoding-decoding procedure although it resulted in inferior performance. Only when the transformed words as such could be used as the written response was performance facilitated. I t is not surprising that the use of coding processes with these materials inhibited performance. Encoding was simple, but for each encoded word a decoding rule had to be learned. For example, if T F A was encoded to FAT, the decoding rule had to be something like: "put last letter first." No single decoding rule would apply to all trigrams, and there would be numerous possibilities for interference among decoding rules. The number of different decoding rules required would clearly be a variable determining performance. The present study was designed to evaluate only one particular coding sequence. I t is not to be inferred that the Ss not using this sequence did not use other coding procedures. Some of the trigrams would not be difficult to pronounce (e.g., I N P ) and this simple coding procedure may have been used. Some trigrams may have been encoded to sequential words (DNO to "don't know"), in which case decoding would be relatively simple. The present study did not gather evidence on such processes. In any event, it seems apparent that materials and procedures can be devised which will bias S toward a particular type of coding process. I t should, therefore, be possible to manipulate systematically and independently the ease of encoding and the ease of decoding and thereby determine the relevant variables for associative processes of this nature. S Uh/£1Vf A R Y
In a free learning situation Ss were presented I0 trigrams for five alternate study and recall trials. Each trigram could be transformed into either of two words by re-
CODING :PROCESSES
arranging the letters. Parallel groups were either instructed or not instructed concerning the transformation possibilities. Within these parallel groups, subgroups of 30 Ss each were differentiated on the basis of the nature of the correct response allowed. If Ss were allowed to write the letters of each trigram in any order they wished, performance was facilitated if the trigrams were encoded to words. This facilitation was more apparent in the instructed group than in the noninstructed
257
group simply because more Ss encoded in the former group. If S was required to write down the trigram as presented, encoding to words and decoding to trigrams inhibited performance, but if during learning the rules were changed so that S could write the letters in any order (eliminating decoding) performance rose sharply and to a higher level than that shown by Ss not using an encodingdecoding sequence. (Received July 30, 1962)