Individual differences in memory

This paper has recounted some of the salient features of an investigation of individual differences in memory. One hundred forty-nine subjects (Ss), in individual sessions, learned and recalled and relearned four lists each, two of paired adjectives and two of paired picture-names. Significant correlations, ranging from .23 to .41, were obtained among the various recall scores. On the two paired adjectives lists, r's between trials to learn and words recalled (after 24 hours) were not significant. Significant r's of -.23 and -.25 were obtained between these variables on the two picture-names lists. Ss were divided into fifths upon the basis of trials to learn on each of the four lists. No significant differences were obtained among the recall scores of the various fifths on any of the lists. At best, the results of the various analyses suggest no more than a slight relationship between rate of learning and recall. The data have been analyzed with respect to differences in habit strength among Ss of varying rates of learning, all of whom attained a common trials-to-learn criterion. It was found that the mean number of reinforcements bore a fairly constant ratio to the number of item presentations (or number of trials) for the different levels of learning ability. The mean number of reinforcements accomplished by the slowest fifth of Ss was 3.6 times as great as that by the fastest fifth. Further analysis of specific items showed that the slowest fifth required five reinforcements to establish a probability of making a correct response on the succeeding trial equal to that established by the fastest fifth after one reinforcement. The important question of whether or not Ss who have learned to a common habit strength criterion differ significantly among themselves in retention is unanswered. The data are in accord with the proposition that significant differences in retention do exist among Ss who have achieved a common trials-to-learn criterion. Practice effects reduced the trials required to learn, but did not result in increased recall scores.