Examining Neurophysiological Evidence of Age-Related Interactions of Sensory and Cognitive Processes During Speech Processing

The present study sought to examine the contribution of sensory and cognitive factors on speech processing as evidenced by ERP measures and to find support for the Sensory Cognitive Interaction Theory (SCIT) and the Effortfulness Hypothesis in that older adults. who experience sensory deficits with normal aging. must put forth increased effort during early sensory stages of speech processing that may compromise subsequent semantic performance and recall of information. In the present investigation. younger and older adults performed a sentence verification task at low and high presentation levels (PL). Accuracy and response time to sentence verifications were assessed along with event-related potential (ERP) components associated with sensory (NJ 00) and semantic (N400) stages of speech processing. It was predicted that increases in PL would at least partially offset typically observed age-related declines in speech processing ability and delayed Nl 00 responses. The low PL negatively impacted older participants. Increased RT and decreased accuracies were observed in the low PL condition for the older participants while older adults· performance mirrored that of young participants in the high PL condition and younger adults were not affected by the decreased PL. PL significantly impacted latencies of both the NI00 and N400 components. NI00 and N400 responses were delayed in the low relative to the high PL conditions for both young and old listeners. Irrespective of the PL conditions. older participants exhibited delayed NI 00 responses consistent with previous literature. Age-related delays were not observed for the N400 component. A non-significant trend towards the hypothesized age by presentation level interaction for latencies was observed for both components. indicating that older adults benefited more from an increase in the auditory signal. Observed results provide support for the SCIT and the Effortfulness Hypothesis. and challenge other theories of cognitive aging that historically have not taken into account the contribution of sensory factors.