ERPS, SEMANTIC PROCESSING AND AGE

ERPs (N400, LPC and CNV) were elicited in two sets of subjects grouped according to age (young vs. elderly) using a word-pair category match ing paradigm. Each prime consisted of a Japanese noun (constructed fro m two to four characters of the Hiragana) followed by one Chinese char acter (Kanji) as the target, this latter representing one of five sema ntic categories. There were two equally probable target conditions: ma tch or mismatch. Each target was preceded by a prime, either belonging to, or not belonging to, the same semantic category. The subjects wer e required to respond with a specified button press to the given targe t according to the condition. We found RTs to be longer in the elderly subjects and under the mismatch condition. N400 amplitude was reduced in the elderly Subjects under the mismatch condition and there was no difference between match and mismatch response, which were similar in amplitude to that under match condition for the young subjects. In ad dition, the CNV amplitudes were larger in the elderly subjects. These results suggested that functional changes in semantic processing throu gh aging (larger semantic networks and diffuse semantic activation) we re the cause of this N400 reduction, attributing a subsidiary role to attentional disturbance. We also discuss the importance of taking age- related changes into consideration in clinical studies. (C) 1998 Elsev ier Science B.V.