38 Vulnerability to Semantic and Phonemic Interference in Normal Aging and Amnestic Mild Cognitive Impairment (aMCI)

Abstract

Objective:

Studies on vulnerability to interference have shown promise in distinguishing between normal and pathological aging, such as the early stage of Alzheimer’s disease (AD) or amnestic Mild Cognitive Impairment (aMCI). However, these studies did not include a non-semantic condition essential in distinguishing between what is attributable specifically to semantic memory impairments and more generalized vulnerability to interference. The present study aimed to determine whether the increased vulnerability to semantic interference previously observed in individuals at increased risk of AD (aMCI) is specifically associated with the semantic nature of the material, or if it also affects other types of material, suggesting more generalized executive and inhibitory impairment.

Participants and Methods:

Seventy-two participants (N = 72) divided into two groups (33 aMCI and 39 NC) matched for age and education were included in the study. They underwent a comprehensive neuropsychological examination, and took the adapted French version of the LASSI-L (semantic interference test), as well as a homologous experimental phonemic test, the TIP-A. Independent sample t-tests, mixed ANOVA and ANCOVA on memory and vulnerability to interference scores with the Group (NC, aMCI) as between-group factor and the Type of material (semantic, phonemic) as within-subject factor were conducted to compare memory and interference in both contexts for both groups.

Results:

For all memory scores, results revealed a significant main effect of group (NC > aMCI), a significant main effect of the type of material (semantic > phonemic) and a significant Group x Type interaction (disproportionately poorer performance in a semantic context for aMCI compared to NC). Word recognition was equivalent in both contexts for aMCI, whereas NC were better in a semantic context. aMCI also committed more phonemic false recognition errors, were disproportionately more vulnerable to retroactive semantic interference and showed a disproportionately higher percentage of intrusion errors associated with proactive semantic interference than NC.

Conclusions:

To our knowledge, this is the first study to meticulously compare aMCI and elderly control vulnerability to inter-list interference and its impact on memory processes in two very similarly designed conditions using different types of material (semantic vs. phonemic). Indeed, many studies on interference focused solely on intra-list buildup of interference or on semantic material. Taken together, our results suggest that aMCI patients present generalized difficulties in source memory and inhibition, but that their inability to benefit normally from the depth of processing of semantic material results in even more semantic intrusion errors during proactive interference. This superficial semantic processing also significantly impacts the ability of aMCI to show good recall after being exposed to an interference list and the passage of time, resulting in a greater vulnerability to semantic retroactive interference than controls. In summary, our results suggest that impairment of semantic memory, and, more precisely, the loss of benefit from the depth of semantic processing, represents the cornerstone of their memory and vulnerability to interference patterns. The classical level of processing theory therefore constitutes an ideal, simple framework to predict aMCI patients’ performance when facing interference, a parallel too rarely addressed in the literature.