Encoding processes, memory strength and the Korsakoff amnesic syndrome

Abstract

Korsakoff amnesic subjects were compared with matched and unmatched control subjects on a free recall test for words learnt under one of three encoding conditions: (a) nonsemantic; detecting the presence or absence of the letter "e" in a word; (b) semantic; deciding whether or not a word fits in a particular sentence; (c) no instructions; words were to be remembered. The control subjects were tested, either at the same no delay retention interval as the Korsakoff amnesic subjects, or at 10 or 24 hour delayed retention intervals. The differential testing equated the Korsakoff and control groups for memory strength to distinguish between quantitative and qualitative differences in patterns of performance. There was no difference in recall for Korsakoff amnesic subjects and matched control subjects between semantic and no encoding instructions, which is inconsistent with the semantic encoding deficit hypothesis. Matched control subjects were more impaired as retention delay increased and their similar pattern of performance to Korsakoff amnesic subjects, indicated a quantitative difference in performance when both are tested at the same retention interval. The unmatched student control subjects displayed a different pattern of performance and different effects of delay to the Korsakoff amnesic subjects and matched control subjects. This appeared to be related to differences in strategies for remembering the words. The results indicate equating memory strength between groups is subject to the influence of many factors not yet adequately controlled.