Hemisphere asymmetry of the visually evoked potentials elicited by gratings of varying spatial frequency

Visually evoked potentials (VEP) were recorded upon hemifield stimulation with sinusoidal gratings of varying spatial frequency (SF). Recording was bipolar from 0.1-0.2. The gratings were presented randomly in the left, in the right or in both visual hemifields. No systematic VEP asymmetry was observed at low SF. At SFs above 1.5-2 cpd, however, the early wave peaking at about 100 msec after grating onset was usually of greater amplitude when the grating was presented in the left visual field. In previous experiments of our, contrast sensitivity was almost the same in both hemifields. Thus, the VEP data suggest right-hemisphere specialization in processing high SFs and their comparison with the contrast sensitivity data suggests that this specialization occurs at a level higher than stimulus detection or is evident at suprathreshold contrast levels only.