RESPONSE PROBABILITIES IN VERBAL RECALL

Ten Ss were allowed 15 min to name all the U.S. Presidents they could remember. Twenty-five other Ss were allowed 25 min to name nations. The probability of occurrence per unit time, i.e., probability density, of each name was estimated from the distribution of latencies for that name. The probabilities in each category were then ranked in order of decreasing magnitude, and log probability density was plotted against log rank. In both cases most of the points fell on a straight line, with a slope of -1.14 for Presidents and -.87 for nations. These results indicate that the distribution of recall probabilities for words in a category can be described by an equation similar to one applied by Zipf to the relative frequencies of words in general usage. © 1969 Academic Press Inc. All rights reserved.