Auditory lexical-semantic processing impairments in aphasic patients reflected in event-related potentials (N400)

Event-related potentials (ERPs) and response latencies were recorded from aphasic subjects with auditory language processing impairments and age-matched normal controls, while performing a lexical-semantic evaluation task, aiming at clarifying whether ERPs could be a reliable measure for indicating language impairments in aphasic patients.

The stimuli were 50 pairs of spoken words (prime word-target word): 25 pairs, which were semantically and/or associatively related to each other, and 25 pairs which were not. The subjects pressed a switch in response to the presentation of target words semantically related to the prime words. The ERP component analyzed in this study was N400.

With the performances, the response latencies were longer in the aphasic subjects than in the normal controls. With the ERPs, onset latencies of N400 were shifted behind in the aphasic patients compared to the normal controls. For the aphasic patients, there were correlations between the size of N400 and performances in auditory comprehension evaluated in the aphasia test.

The conclusions drawn from the results are that not only response latencies in the lexical-semantic judgement task, but also N400 effects, may be a reliable clinical measure of the severity of even mild lexical-semantic impairments in aphasic patients.