Geoffrey Keppel

Proactive inhibition in short-term retention of single items

Summary Three experiments were performed to determine the relationship between certain variables influencing proactive inhibition in long-term retention of lists of verbal items and the influence of these variables on short-term retention of single items. More particularly, retention of single items over 18 sec. should, if the laws of long-term retention are applied, decrease with number of previous items to which S has been exposed. In addition, amount of forgetting should be a direct joint function of number of previous items and length of the retention interval. In Exp. 1 each S was presented consonant syllables singly, with retention being measured after 3, 9, and 18 sec. Forgetting of the first item presented (T-1) was less than for the second (T-2) or third (T-3) item, but forgetting of the latter (T-2 vs. T-3) did not differ. On all three tests forgetting was directly related to length of retention interval, but no interaction was evident between number of previous items and length of retention interval. In Exp. 2 a higher degree of initial learning of the items was achieved. Forgetting increased directly as a function of number of previous items presented. The predicted interaction was indeterminate since retention was essentially 100% on T-1 for all retention intervals. Experiment 3 tested retention of six successive items over 3- and 18-sec. intervals. Retention after 3 sec. showed an initial drop and then a rise over the six tests, the rise suggesting a practice effect. Forgetting over 18 sec. increased directly from T-1 to T-6 and there was no indication that a constant amount of proactive interference had been reached. The interaction between length of retention interval and number of potential proactively interfering items was very evident. The results were interpreted to mean that proactive inhibition in short-term memory of single items follows the same laws as proactive inhibition in long-term memory of lists of items.

Coding processes in verbal learning

Summary In a free learning situation S s were presented 10 trigrams for five alternate study and recall trials. Each trigram could be transformed into either of two words by rearranging the letters. Parallel groups were either instructed or not instructed concerning the transformation possibilities. Within these parallel groups, subgroups of 30 S s each were differentiated on the basis of the nature of the correct response allowed. If S s 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 group simply because more S s 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 S s not using an encoding-decoding sequence.

Word value and verbal learning

Summary Two experiments evaluated the influence of rated goodness (G) of nonsense syllables and words on the rate of verbal learning. Exp. I investigated the independent effects of G and association value upon the learning of two lists containing digit-nonsense syllable pairs. Variation in association value was highly related to learning, while variation in G was only slightly related to learning. In addition, a breakdown of the relationship between association value and G occurred when the effect of pronunciability was controlled. In Exp. II, seven pairs of words, matched in frequency and meaningfulness but varying in G, were placed in a paired-associate list. No difference was obtained in the rate of learning between the two sets of words. The results of both experiments question the importance of G as a variable in verbal learning.

Perceptual conditions of association: A possible confounding

Summary Asch, Ceraso, and Heimer (1960) compared the free recall of two types of figures, unitary (U) and non-unitary (NU). The former consisted of a series of single figures drawn with distinctive outlines or modes, while the latter consisted of the same figures except that the shape or form was drawn in continuous line and the pattern of the outline displayed to the side of the figure. The joint recall of form and mode was superior for the U stimuli. The present experiment replicated the U and NU conditions, adding a control group which received the U stimuli and the pattern display to one side of the form. This was done to make the “twoness” of the U and UN stimuli the same. That “twoness” of the NU stimuli appears to be critical in producing the original “unitary effect” was shown by the fact that the U-NU difference disappeared when the control stimuli were recalled. These findings provide an alternative explanation of the findings of Asch et al.

LEARNING AND RETENTION OF LETTER PAIRS AS A FUNCTION OF ASSOCIATION STRENGTH

Three experiments on paired-associate learning and retention of letter pairs tested the Underwood-Postman hypothesis that extraexperimental associations interfere with learning and produce forgetting. As hypothesized, in experiments with seven- and ten-year-old children and with adults, highly associated (high-strength) letter pairs were learned faster and, on the whole, retained better over one week than low-strength pairs. The positive retention effects, not observed in previous studies, are partly attributed to the use of the correction procedure as a control for the overlearning of easy items in low-strength lists that is unavoidable with standard methods. This overlearn- ing is believed to reduce the probability of detecting any differential retention of high- and low-strength lists. Developmental differences in children were small for original learning and insignificant for forgetting. A single postcriterion trial, however, facilitated retention-test performance. Theoretical implications are discussed.