Limits of binocular fusion in the short wave sensitive ("blue") cones

Stereoscopic depth perception is possible when the short wave sensitive (SWS or "Blue") cones are isolated using a yellow adapting field. We have measured the maximum disparity that can be fused (the diplopia threshold) as a function of the separation between pairs of dots or lines. Under all conditions, these diplopia thresholds are the same for the isolated SWS cones as for the entire visual system. In addition, SWS diplopia thresholds vary as a linear function of dot or line separation, so that they exhibit disparity scaling. Further experiments show that disparity scaling is dependent upon the presence of low spatial frequencies in the stimulus and not upon the retinal eccentricity of stimulation. These data indicate that the SWS cones provide information to the disparity processing system through more than one low spatial frequency channel but not through high frequency ones.