Independent stereoscopic channels for different extents of spatial pooling.

We report two experiments with stimuli composed of dynamic noise stereograms in which binocular disparity was modulated sinusoidally with chan_res in vertical spatial position. The experiments demonstrated that the human visual system contains independent stereoscopic mechanisms selectively tuned for different spatial frequencies of disparity modulation. The first experiment showed that observers can just detect a compound disparity grating when at least one of two presented sinusoidal components is close to its own independent threshold amplitude. The second experiment demonstrated selective threshold elevation following prolonged viewing of a disparity grating (selective adaptation). The results suggest that the stereoscopic mechanisms have rather broad sensitivity to the spatial frequency of disparity modulation: 2-3 octaves full-bandwidth at half-amplitude. We conclude. first. that there exist multiple stereoscopic mechanisms each characterized by a different extent of spatial pooling. Secondly. the bandpass characteristic we have observed implies that these mechanisms must receive lateral inhibition from disparity detectors tuned to adjacent positions in space.