Contrast and hemispheric asymmetry: an electrophysiological investigation

Visual evoked potentials by 8 Hz phase-reversed sinusoidal gratings of different spatial frequency were recorded from occipital and temporal leads of left and right hemispheres. Seven adult subjects were investigated. At low contrast, the VEP amplitudes in the two hemispheres were symmetrical. At medium and high contrast, the amplitudes were larger in one hemisphere. On the contrary, the "phase advance" as a function of contrast was comparable in the two hemispheres. The results were discussed according to the literature on different neural population involved in contrast perception.