Disparity sensitivity in man and owl: Psychophysical evidence for equivalent perception of shape-from-stereo.

The perception of shape-from-stereo is best characterized by the spatial disparity-contrast sensitivity function (DSF). This is the stereo analogue of the well-known luminance-contrast sensitivity function (CSF). In principle, the DSF and CSF portray a visual system's ability to detect spatial modulation as specified by changes in binocular disparity and luminance, respectively. In humans, less fine detail is visible in the stereo domain than is possible in the luminance domain. Here, we characterize for the first time the DSF in a non-human species, viz. the barn owl. At the same time, we re-examined the human DSF with identical apparatus and methods to directly compare between two vertebrate species that evolved stereovision independently. We discovered a close relationship between the owl and human ability to detect shape-from-stereo. In particular, the shift in absolute position between the human and owl DSF, as measured here, closely corresponds to the shift in absolute position between their respective CSFs, as known from the literature. In conclusion, our study establishes unprecedented experimental proof of a striking similarity in the prowess of humans and owls to achieve shape-from-stereo.