Direction selectivity for perceived motion in strabismic and anisometropoic amblyopia.

Interactions between direction-selective mechanisms for motion were examined in strabismic and anisometropic amblyopia. Amblyopes were found to have a marked reduction in sensitivity to flicker or movement when the amblyopic eye was presented with a combination of two gratings drifting in opposite directions at the same velocity (i.e., a counterphase grating). Sensitivity to flicker of the counterphase grating was improved by preadapting the amblyopic eyes to a single grating which was drifting nasalward, but there was no improvement if the drift of the adapting grating was temporalward. Sensitivity to flicker was also improved by reducing field size from 10 degrees to 3 degrees. However, occluding the central 4 degrees of the 10 degrees field did not significantly alter the sensitivity to flicker. These data suggest that inhibition between motion detectors in the parafovea of amblyopic eyes reduces slow-motion perception in both the parafovea and the fovea. The results also demonstrated a reduction in amblyopic eyes of direction slectivity for motion detection.