Test of the total-time hypothesis in free-recall learning.

Abstract

A test of the total-time hypothesis in free-recall learning is reported. The hypothesis asserts that the amount recalled is determined by the total presentation time (TPT), regardless of list length (LL) and rate of presentation (RP). The purpose of the experiment was to verify the validity of this principle and to examine some potential limitations on its operation. With TPT held constant at 60 sec., there were three conditions of presentation: (a) LL 20 and 3-sec. RP; (b) LL 30 and 2-sec. RP; (c) LL 60 and 1-sec. RP. A first test of recall was given either immediately after a single presentation of the list or after an interval of 20 min. The first test was followed by two additional study-test cycles. In accord with the hypothesis, the amount recalled on the first test was invariant across conditions after both retention intervals, i.e., the operation of the principle was found to be independent of delay. After the first test, gains as a function of practice were related directly to LL. The longer the list the more new items were added on each test, although intertrial retention was essentially invariant under the different treatments. The divergence of the learning curves is attributed to the covariation of LL and the amount of semantic and associative overlap among individual items. This study is concerned with the totaltime hypothesis in free-recall learning. The hypothesis asserts that the amount recalled is determined by the total presentation time (TPT), independently of the length of the list (LL) and the rate of presentation (RP) for individual items. As long as the product LL X RP is held constant, the number of items recalled is expected to be the same. This expectation was fully supported in an experiment by Murdock (1960) in which LL and RP were varied concomitantly while TPT remained unchanged. There were four combinations of LL and RP which yielded closely similar recall scores: 20-3 (a 20-word list presented at a rate of 3 sec. per item), 30-2, 40-1.5, and 60-1. In addition to the principle of recall invariance illustrated by these findings, Murdock (1960) advanced the hypothesis that the amount of recall is a linear function of TPT. We shall not consider further the latter hypothesis, which has been called into question by the results of subsequent investigations (Roberts, 1972; Waugh, 1967). Rather attention will be 1 This research was supported by Grant MH-12006