Differential binocular input and local stereopsis

Using fractal noise images, we measured the dependence of Dmin and Dmax for stereo on the interocular differences of spatial frequency and contrast. Dmin exhibits a strong dependence on the highest spatial frequency contained in the image, while Dmax exhibits a weaker dependence on the lowest spatial frequency contained within the image. Neither relationship was found to be different when the filtering was restricted to only one eye's image, although the effect of differential lowpass filtering for Dmin was greater than that of binocular lowpass filtering. Contrast is thought to affect stereo performance particularly when it is reduced in only one eye's image. We show that, at least for broadband fractal images representative of everyday natural images, interocular contrast differences are no more disruptive than binocular ones. These results bear upon the nature of the matching process in stereopsis. The fact that these interocular spatial frequency and contrast manipulations do not selectively degrade stereopsis beyond that expected from a consideration of purely monocular effects is consistent with matching occurring within multiple spatial channels prior to their combination.