Effects of stimulus and response contingencies on a surface negative slow potential shift in man.

Abstract A slow wave potential (CNV) was recorded extracranially from eleven subjects during the interval between a warning stimulus (flash of light) and a burst of clicks which they terminated by pressing a lever. When subjects were not required to respond to the clicks, no CNV appeared. When they were told to turn off the clicks the CNV increased in amplitude at a rate that depended on individual prior experience with the paired flash-clicks contingency. Omission of clicks with no warning to the subjects resulted in gradual diminution of the CNV; subsequent reinstatement of clicks caused the CNV to increase in amplitude again. A significant negative correlation between size of CNV and reaction time was found over a large group of trials. The relation of the CNV to subjective expectancy and intention to respond was discussed.