Effects of target area and letter complexity on event-related potentials and reaction time.

The idea that an area of the visual field stimulated by a recognizable image activates a corresponding area of neural tissue that generates the recognition potential (RP) was examined. Sixteen subjects detected targets in a stream of non letter character arrays. The targets were one or five rows of a repeated letter (O or G). RT was less for the larger targets and less for O than for G. RP latency differences agreed with the RT differences. RP amplitude was substantially greater for large than for small targets and moderately larger for G than for O. P3 amplitude showed a different relationship. The observed amplitude-latency relationships indicated that differences in stimulus strength were not responsible for the greater RP evoked by the larger targets. The results strengthened the neural area explanation for RP amplitude modulation by the area of the visual fields impinged on by recognizable images.