The effects of eye fixation and stimulus and response location on the Contingent Negative Variation (CNV)

Abstract

Vertex and parietal cortical slow waves and horizontal and vertical eye movement were recorded from 16 male subjects. Each subject was run in four constant-foreperiod reaction time conditions, in which the location of the auditory stimulus (speaker position above or below; to the subject's left or right) and the presence or absence of an eye focusing light was varied. Eye movements were unrelated to stimulus location, but were correlated with the position of the response key. Eye fixation resulted in reduced eye movement; however, it markedly reduced the cortical potential (CNV), unless the fixation light also served as the imperative stimulus. The relationship of eyeblinks and eye movement to the CNV was shown to be complex, and no method provided perfect correction for this artifact. The study also demonstrated the biphasic character of the cortical potential during the RT foreperiod. An early negative phase is apparently related to signal stimulus orientation, and habituates over trials; a separate, later negativity, appearing just before the imperative stimulus, appears to be the true CNV.