Age-related Impairments in Long-Term Retention of Verbal Material: A Problem of Accelerated Forgetting or a Deficit in Acquisition?

Abstract

Several diverging theories exist as to whether young adults share the same analogous difficulties as healthy older adults on tests of verbal acquisition and retention of novel stimuli. Research suggests older adults may incur higher processing demands when instructed to remember lists containing unrelated words, compared to semantically categorised word lists, and over retention intervals. Through manipulation of learning criterion and list information, the current study attempted to delineate the contribution of age-related deficits to long-term forgetting. This longitudinal study assessed performance on four word lists each comprised of fifteen nouns, modified from the CVLT and RAVLT. Recall scores were measured over delay-intervals of 30minutes, 24hours and 7days, to test for reliable heterogeneity and critical periods in forgetting rates between young (18-25 years, n=20) and old adults (60-80 years, n=20). By matching subjects on acquisition for half the lists, this test aimed to decompose whether ageing reflects an encoding or consolidation deficit. Our findings indicate that: (a) older adults incur significantly more rapid forgetting of novel stimuli over time, providing evidence of reliable variability in forgetting slopes across the life span, (b) older adults incur greater difficulty in acquiring novel words, and (c) young and old adults do not differ in the benefit experienced from semantic relatedness of word lists. These results support Huppert & Kopelman’s (1989) findings of a mild acquisition deficit but a more robust impairment in subsequent retention processes and are consistent with a consolidation account of forgetting.