Spatial sensitization in the short wavelength sensitive pathways under dichoptic viewing conditions

Spatial sensitization (Westheimer) functions were measured under conditions that isolated the short wavelength sensitive pathways. The variable diameter pedestal and the test probe were either presented to the same eye (monoptic presentation) or to different eyes (dichoptic presentation). The most significant new finding was that a dichoptically presented, small, blue pedestal caused threshold elevations of about 1-2 long units for an S cone detected probe. However, a large pedestal caused little or no change in threshold. This result contrasts with previous results using white light stimuli, which showed that steadily presented dichoptic pedestals caused little or no threshold change. Furthermore, we show there is little masking when the probe is detected by the isolated M or L cone pathways. These data thus demonstrate a binocular, size dependent interaction revealed only when S cones detect the probe.