LAMBDA RESPONSES IN RELATION TO VISUAL EVOKED RESPONSES IN MAN

1. 1. In five normal subjects, midline parieto-occipital averaged EEG responses to shifts of the image of a spot of light from an oscilloscope screen on the retina were examined. The shifts of the position of the image on the retina were accomplished in two different ways: (a) by alternation of the direction of visual gaze, the position of the spot of the oscilloscope screen remaining unchanged (lambda responses), and (b) by alternation of the position of the spot on the oscilloscope screen, the direction of gaze remaining fixed (ordinary visual evoked responses). In order to insure comparability of the time course of retinal stimulation, the motion of the spot on the oscilloscope screen was controlled by a previously recorded electro-oculogram from the same subject. Additional recordings under several different experimental conditions were also included, for fuller definition of the phenomena under study. 2. 2. In no case were the EEG responses for the two conditions identical, although for some subjects there was a marked similarity for responses resulting from a shift of the image of the spot from the periphery onto the fovea of the retina; for the reverse, wave forms and similarities were much less well defined. 3. 3. In all instances of voluntary eye movements (i.e., alternation of gaze between bright and dim, or between dim and dim spots, in total darkness, or when the spot on the oscilloscope screen moved congruently with the eyes so that its image remained constantly on the fovea), an EEG potential change was evident, the onset of which preceded the initiation of eye movements by 150-200 msec; this anticipatory potential change was absent for the involuntary or compensatory eye movements occurring upon passive turning of the head. 4. 4. These findings are discussed in relation to the phenomena of expectancy waves, decreases in the amplitude of evoked responses and increases in visual threshold associated with eye movements, and in relation to mechanisms of supposed perceptual blanking associated with eye movements. © 1969.