Neurophysiological investigation of phonological input: aging effects and development of normative data

A combined analysis of the effects of ageing on the neurophysiological correlates of word recognition and phoneme discrimination, based on different phoneme contrasts, has until now never been performed. This would provide important information in view of the potential use of event-related potentials (ERPs) in a clinical setting. Therefore, we investigated attended and unattended auditory phoneme discrimination using the P300 potential and Mismatch Negativity (MMN), respectively. Three phonemic contrasts present in the Dutch language were compared. Additionally, auditory word recognition was investigated with a lexical decision task. We wanted to obtain normative data for ERP latencies (ms) and amplitudes (µV) and examine aging influences. Seventy-one healthy subjects (21-83 years) were investigated and a linear regression analysis was performed. During phoneme discrimination aging was associated with increased latencies and decreased amplitudes. However, a discrepancy between phonemic contrasts, as well as between attended and unattended processing, was found. During lexical decision aging only had an impact on ERPs elicited by real words, indicating that mainly semantic processes were altered, leaving lexical processes unharmed. Early sensory-perceptual processes, reflected by N100 and P50, were not affected by age. In the future, the neurophysiological normative data can be applied in the evaluation of acquired language disorders