[Experimental conditions which modify the visual evoked potential]

The effect of the visual stimulus intensity on the latency and morphology of the visual evoked potential (VEP) components is studied in cats with chronic implanted electrodes. A lessening in the luminous stimulus intensity is observed to produce a progressive diminution in the amplitude of the initial waves of the VEP till its disappearance, as well as a progressive increase in the latency, following an exponential function. Since the integration in a cortex zone is achieved by pathways of various lengths, the impulses arrive with different delays. It is suggested that stimuli of little intensity generate trains of impulses whose integration, in a small cortex area, is likely characterized by a delay in the appearance of high relative frequencies; whereas high intensity stimuli are more likely to produce high frequencies, in the same cortex area, and with earlier appearance. This may be considered as the explanation for the delay of analogous waves generated by stimuli of lesser intensity.