Peripheral and central contributions to psychophysical spatial interactions

Increment thresholds for a steady light disc and amplitude-modulation thresholds for a time-modulated disc centered at 5 deg from the fovea have been measured in the presence of an annulus of variable diameter concentric to the disc and viewed either by the same eye as the disc or by the other eye. Facilitatory and inhibitory interactions between steady stimuli are found to occur only for homolateral presentation of the stimuli, whereas spatial interactions between time-modulated stimuli occur also with dichoptic stimulus presentation.