Perceptual strength influences lexical decision in Alzheimer's disease

The multimodal approach where cognition is embodied in language, perceptual, motor, and emotional systems is a widely agreed theoretical framework for conceptual representations. However, the lack of work supporting this view of cognition in healthy and pathological aging stands in stark contrast with the ongoing need to understand the factors that uncover semantic degradation in brain pathologies. The aim of this study is to explore the impact of perceptual strength (PS) - i.e., the extent to which a word can be experienced by multiple sensory modalities in visual word recognition in Alzheimer's disease (AD). Thirty-six healthy participants, 22 participants in the mild stage of AD (AD1) and 20 in the moderate stage (AD2) took part in a lexical decision task with two conditions: words with high vs low PS words. Results showed an interaction effect only between healthy controls and AD1 individuals, revealing that the latter were faster in processing high PS words in contrast to low PS words, while this was not the case for healthy individuals. Furthermore, it was specifically the ratings of the neuropsychological executive and lexical-semantic assessments that predicted these results. However, no results were observed for AD2 participants, suggesting that lexical-semantic degradation was too severe to reveal a PS effect. This study demonstrates the importance of considering the perceptual dimension when examining the conceptual system and opens up new avenues in the exploration of semantic impairment in AD.