Abstract
Using an S 1-S2-S3 Reaction-Time task paradigm, the contingent negative variations (CNVs) for S2 and S3 were examined. In the task, a subject was informed by S2 of the occurrence or non-occurrence of the immediate S3 which was an imperative stimulus given in a half of the total trials (go-no go task). It was found that the negative potential-shift preceding the S2 presentation was larger when S2 was informative than when S2 was redundant. After the resolution of this shift, a second negative shift developed toward S3 when S2 informed its presentation, but did not when S2 informed its non-presentation. Based on the Principal Component Analysis, it was concluded that the first shift was the late CNV for S2 while the second shift was the late CNV for S3. It might be suggested that the former was not associated with a motor preparation but with anticipatory attention to an informative stimulus, and the latter with a motor preparation.
