The neural mechanism of binocular depth discrimination

Abstract

S'UMMARY 1. Binocularly driven units were investigated in the cat's primary visual cortex.2. It was found that a stimulus located correctly in the visual fields of both eyes was more effective in driving the units than a monocular stimulus, and much more effective than a binocular stimulus which was correctly positioned in only one eye: the response to the correctly located image in one eye is vetoed if the image is incorrectly located in the other eye.3. The vertical and horizontal disparities of the paired retinal images that yielded the maximum response were measured in 87 units from seven cats: the range of horizontal disparities was 6.60, of vertical disparities 2.20.4. With fixed convergence, different units will be optimally excited by objects lying at different distances. This may be the basic mechanism underlying depth discrimination in the cat. INTROD'UCTIONThe image formed by a single eye is a two-dimensional projection of the three-dimensional world which entirely lacks representation of those distances in the three-dimensional world that are possibly of greatest survival value to an animal, namely the distances of the external objects from the eye. It is true that the third dimension of apparent depth can be added to the visual image of a single eye by using a number of indirect cues, such as the angular subtense of an object of known size, motion parallax, accommodative effort, and the obscuration of distant objects by nearer ones. However, these cues can only be utilized in special circumstances, and most of them require rather complex image-processing. In animals where the visual fields of the two eyes overlap the situation becomes much more favourable, for between them the different projections * Harkness Fellow, 1965-67. t Present address:

Sensitivity to relative disparity in early visual cortex of pigmented and albino ferrets

“…In the present experiments, we were able to demonstrate the presence of a possible neuronal substrate for 3D vision, i.e. neurons that preferred diVerent horizontal disparities similar to neurons previously described in cat (Barlow et al 1967;Pettigrew et al 1968;DeAngelis et al 1995;Ohzawa et al 1996Ohzawa et al , 1997 and in monkey (Poggio and Fischer 1977;Poggio et al 1988;Bridge et al 2001; Mean § standard error of relative neuronal activities of tuning curves collapsed from all relative disparity-sensitive neurons recorded in this study, normalized to the range from 0 to 1 (ordinate) and Wtted with a Gaussian. The Gaussian has a half width at half height (HWHH) of 3.95° of visual angle.…”

“…Neurophysiological studies by Barlow et al (1967) and Pettigrew et al (1968) described disparity-selective neurons in the primary visual cortex (V1) of anesthetized cats and provided Wrst evidence for binocular disparity in V1 as a possible basis for stereopsis. Subsequent studies in alert, Wxating monkeys conWrmed the concept of stereopsis in the early visual areas (Poggio and Fischer 1977;Poggio et al 1988;Cumming and Parker 1999).…”

“…Thus, this classiWcation is still commonly used, but it should be emphasized that the early visual areas code for the whole range of disparities. This led to the assumption that stereopsis is equivalent to depth perception (Barlow et al 1967). Although this hypothesis is no longer valid (Cumming and Parker 1999), it remains that neurons in V1 perform essential preprocessing underlying stereoscopic depth perception in higher areas.…”

Processing of color, form and disparity information in visual areas VP and V2 of ventral extrastriate cortex in the macaque monkey

“…Binocular parallax creates horizontal disparities between the retinal images that can be used as neuronal signals of distance from the fixation plane (Barlow et al, 1967). Disparity-selective cells have been found in V 1, dorsal V2, and MT in the macaque (Hubel and Wiesel, 1970;Maunsell and Van Essen, 1983b;Poggio and Fischer, 1977).…”

Contextual Masking of Oriented Lines: Interactions Between Surface Segmentation Cues

“…All had CRFs located within the central 5°of the lower-right visual field [mean eccentricity: 2.9°Ϯ 0.86°(SD)]. CRF locations and boundaries were determined using the minimum response field method (Barlow et al 1967), which involved moving a bright or dark bar over a gray background while amplified neuronal signals were played on an audio monitor. For a subset of cells, basic properties of the CRF were subsequently assessed using an automated sequence of dark and bright flashes: Small dark and bright squares (0.10 -0.22°square) were flashed for 100 ms at random locations in a square grid (1-2.0°centered on the hand-mapped coordinates) followed by a 100-ms pause.…”