Memory in Parkinson's disease: A feature-processing analysis

Abstract

Memory for distinctive contextual features was investigated in 19 subjects with idiopathic Parkinson's Disease (PD) and 19 elderly control subjects. Subjects were administered a brief battery of neuropsychological tests, two word recognition tests, and a final free recall test. Forty-eight words, varying in Thomdike-Lorge frequency and presentation location, were presented visually at a rate of one word every five seconds. On the initial self-paced yes/no recognition test, both PD and control groups showed a significant recognition advantage for semantically or spatially distinctive words. PD subjects exhibited a frequency-dependent shift in strategy, being less cautious for high frequency words and more cautions for low frequency words. On the second recognition test, however, in which some of the distractor items from the prior test were repeated, the recognition advantage for semantically distinctive words disappeared in the PD group. The control group continued to maintain superior recognition accuracy for semantically distinctive words. PD subjects may have a diminished ability to recognize distinctive contextual features, which becomes apparent when a subtler temporal discrimination is required between targets and distractors.

On the final free recall test, PD subjects recalled fewer words than control subjects if the words were relatively accessible (repetitions, high frequency), but lacking explicitly-defined distinctive cues. Possibly, control subjects were more efficient in utilizing alternative sources of distinctive contextual information to improve recall performance. PD subjects also were less able to use distinctive spatial cues to improve recall of words which were relatively inaccessible (low frequency). Thus both recognition and recall tasks indicate that under certain conditions PD subjects exhibit a diminished ability to retain distinctive contextual features.

Neuropsychological test results indicated that PD subjects, relative to control subjects, achieved (a) higher depression scores, probably appropriate for medical outpatients, and unrelated to any measures of retention in the present study; (b) poorer paragraph recall, despite an equivalent rate of forgetting over time; and (c) poorer visual recall, even after accounting for visuoconstructional ability.