Degree of Learning, Proactive Interference and Retention

Abstract

IT is well known that retention of verbal material declines with the number of lists learnt¹ if all lists are learnt to the same criterion. Underwood¹ concluded from this that the decline in retention is caused by proactive interference from the material previously learnt. This conclusion, however, has been questioned by Warr^2,3, who reports that the number of trials to reach a standard criterion decreases with successive lists (a finding also due to Deutsch and Mamakos⁴), and suggests therefore that the decline in retention is caused by the decline in degree of learning. In support of this argument he presents data showing that, when successive lists are practised, not to a criterion but for a constant number of trials, the usual decline in retention over successive lists fails to appear. If, however, degree of learning is the most important factor determining retention over successive lists, there should have been an actual increase in retention in Warr's experiment, for the degree of learning increases with successive lists when number of trials is held constant³. In the present experiment, we investigated retention over successive lists with degree of learning experimentally held constant.