Entropy and Choice Time: The Effect of Frequency Unbalance on Choice-Response

Abstract

A human subject making a sequence of choice-responses is considered as a channel transmitting information. Earlier work suggests that the rate of transmission is limited, and so that response time is proportional to the “entropy” of the source of signals. Entropy is reduced by unbalance in the relative frequency of the possible signals according to the formula, sum (p log p). Unbalance should therefore reduce average response time This prediction is tested in a card-sorting task. The subjects sorted playing-cards into classes in various ways; times taken were proportional to calculated entropy-per-card. Departures from the expected results occurred and were found to be due to differences in perceptual difficulty of discriminations. Some incidental results are mentioned.