Properties of pupillary responses to dynamic random-dot stereograms.

Pupillary response can be elicited by a number of visual stimuli. In the present experiments, the pupillary responses to stereo gratings with various spatial frequencies and disparity amplitudes were measured. The spatial frequency was from 0.1 to 1.2 cycles per degree (cpd), and the disparity amplitude was from 4 to 24 min arc. The results showed that pupillary responses can be elicited by all these stereo gratings except when either the spatial frequency or disparity amplitude was reduced to zero. When the disparity amplitude was fixed to 8 min arc, the pupillary response amplitude increased with increasing spatial frequency, eventually reaching a plateau. While the spatial frequency was fixed to 0.3 cpd, the pupillary response amplitude continued to increase within the range of disparity amplitude. This provides a different approach to demonstrate that these pupillary responses were induced by stereo information. In addition, the stereo pupillary responses may be further developed as an objective method to study stereopsis. Finally, plausible underlying mechanisms of the stereo pupillary response are discussed.