Comparison of P100 and P300 cortical potentials in spatial frequency discrimination.

The P300 cortical evoked potential was compared to the P100 wave of the visual evoked potential by means of appearance/disappearance gratings. The spatial frequency of the novel stimulus was varied to compare the effect of task sensory difficulty on both P100 and P300 potentials. The P100 showed a steady increase in latency with the spatial frequency of the uncommon stimulus, and a degree of amplitude tuning consistent with the contrast sensitivity function. The P300 showed marked changes in both amplitude and latency dependent almost wholly on the proximity of the uncommon stimulus spatial frequency to that of the common stimulus. Motor reaction time showed elements of both the P100 and P300 response patterns. The results are consistent with a model in which, after visual information arrives at the visual cortex, processing is parallel and interdependent. In this model, the amplitude and latency of the P100 cortical evoked potential are governed solely by properties intrinsic to the stimulus, whereas the amplitude and latency of the P300 are functions of the degree of stimulus mismatch.