Attenuation of the pupillary response to luminance and color changes during interocular suppression

The present study investigated the effects of interocular suppression on the pupillary constriction to luminance and color changes. Stable interocular suppression was produced by presenting a flickering high-contrast grating to one eye and a spatially homogeneous field to the other eye. The results showed that the pupillary responses to luminance as well as color changes were clearly attenuated during interocular suppression; the pupillary constriction to stimulus changes was delayed and reduced in amplitude when those changes occurred in the suppressed eye. The attenuation of the pupillary response was observed over a wide range of test contrast extending to well above the threshold level. Moreover, the properties of the suppressive effect were very similar to those assessed psychophysically using both detection thresholds for weak stimuli and reaction times for suprathreshold stimuli. Overall, the present study provided converging evidence that the pupillary response can be a useful objective probe of interocular suppression in humans. The results are discussed in view of possible differential involvements of subcortical and cortical visual processing in driving the pupillary response as well as in interocular suppression.