The terminal CNV and stimulus discriminability in motor and sensory tasks.

Slow EEG potentials were recorded during the foreperiod of a signal detection task which involved different levels of discrimination difficulty. The subject was required to react to S2 as quickly as possible or to delay his response by 1 s. It was found that the contingent negative variation (CNV) was attenuated when no speeded response was required and that larger amplitudes preceded the easy rather than the difficult discrimination. In addition, no differences were found between correct and incorrect detections. On these grounds it is concluded that the CNV is not positively correlated with perceptual sensitivity.