Episodic and semantic memory functioning in very old age: Explanations from executive functioning and processing speed theories

Abstract

Structural equation modeling was used to investigate whether age-related episodic and semantic memory impairments are better explained by decline in processing speed or executive functioning (or both), rather than directly in terms of memory components. The models tested were based on an extensive review of the literature on cognitive decline in normal aging, up to very old age. A computerized test battery, measuring episodic memory (free and cued recall; recognition), semantic memory (fluency; naming accuracy and latencies), processing speed and executive functioning, was administered to 234 elderly persons ranging from young-old to very old age (55–96 years). To avoid large variance in response times due to physical instead of cognitive limitations, no motor responses were required from participants. Age-related decline in episodic and semantic memory performance was found to be the consequence of declines in processing speed and executive functioning. Processing speed mainly mediated decline of semantic memory, whereas executive functioning mainly mediated episodic memory decline. The most parsimonious model showed that both processing speed and executive functioning attributed to memory decline but independent from one another. The results suggest that at very old age, the impact of executive dysfunctions on episodic memory performance exceeds the influence of cognitive slowing.

Keywords

• episodic memory
• semantic memory
• processing speed
• executive functioning
• very old age
• structural equation modeling