Neural activity reveals effects of aging on inhibitory processes during word retrieval

摘要

Word retrieval difficulties are one of the most frustrating problems in older adults. Poorer access to phonological (speech sound) representation of the target word has been postulated as the underlying deficit, supported by findings of improvement in word retrieval after phonological priming. But the great variability in naming performance among older adults may reflect cognitive scaffolding or compensatory neurophysiological processes related to maintenance or decline of naming abilities. In order better understand aging effects in the underlying neurophysiological changes associated with phonological retrieval, the present study examined electrophysiological correlates of phonological priming and word retrieval in adults across the lifespan. Young, middle-aged, and older adults viewed pictures (targets) that were preceded by pseudo words (primes) that either shared phonemes with or were unrelated to the picture’s name. Participants used a button press to indicate whether the prime pseudo word and target picture shared the same initial sound. Behavioral and event-related-potential correlates of phonological priming and word retrieval were recorded. All age groups benefited from phonological priming, as evidenced by faster phonological judgment response times and increased ease of word retrieval for primed pictures, indexed by the mean amplitudes of the N400. The peak latency of the N2, however, showed a linear increase with age. The high correlation between the N2 peak latency and clinical measures of inhibition suggested that the N2 indexed inhibition of primed lexical competitors. Taken together, our results indicated intact access to phonological representation of the picture’s name, but age-related deficits in the cognitive ability to inhibit incompatible lexical competitors. Interestingly, our findings revealed that the delays in inhibiting lexical competitors may begin as early as middle age, highlighting the importance of including multiple age groups to better represent the trajectory of age-related cognitive processing. Our findings have important implications for understanding domain-specific changes in cognitive processing even within the same task. The present study lays the foundation for studying word retrieval in individuals with atypical word retrieval difficulties.