Stimulus repetition and an amplitude increase of the occipital late positive component in the human visual evoked...

VEPs to number and checkerboard stimuli were measured from F3, F4, P3, P4, Cz, O1 and O2 electrode loci. A trial was composed of 8 successive stimuli: a warning stimulus (WS) and 7 task stimuli. The task stimuli were a hexad composed of 6 identical stimuli (intratrial stimulus positions 1-6) and a single stimulus (position 7). A subject's task was either naming the numbers or pattern matching the checkerboards in the hexad and in position 7. Centrofrontal N140s and parietal N180s to the number and checkerboard stimuli did not change in amplitude across stimulus positions 1-7. Parietal and centrofrontal P350s were large in amplitude at positions 1 and 7 and decreased at positions 2-6. Parietal P270s and centrofrontal P200s to the number and checkerboard stimuli behaved in the same way as the P350s with respect to the stimulus positions. Occipital N180s to the number and checkerboard stimuli were maximum in amplitude at position 1, decreased with stimulus repetition (positions 2-6) and increased at position 7. Occipital P270s to the number and checkerboard stimuli were almost the same in amplitude at position 1. The P270 to the number stimulus increased in amplitude with stimulus repetition (positions 2-6) and decreased at position 7. The P270 to the checkerboard stimulus was the same in amplitude at positions 1-3 increased at positions 4-6 and slightly decreased at position 7. These P270 amplitude changes were interpreted as due to the amplitude changes of the overlapping occipital N250 which reflected task-specific perceptual activities.