Stereoscopic Depth Discrimination in the Visual Cortex: Neurons Ideally Suited as Disparity Detectors

Abstract

The possibility has been explored that a subset of physiologically identifiable cells in the visual cortex is especially suited for the processing of stereoscopic depth information. First, characteristics of a disparity detector that would be useful for such processing were outlined. Then, a method was devised by which detailed binocular response data were obtained from cortical cells. In addition, a model of the disparity detector was developed that includes a plausible hierarchical arrangement of cortical cells. Data from the cells compare well with the requirements for the archetypal disparity detector and are in excellent agreement with the predictions of the model. These results demonstrate that a specific type of cortical neuron exhibits the desired characteristics of a disparity detector.

The complementary brain: unifying brain dynamics and modularity

“…Such emergent boundary and surface representations, rather than just the energy impinging on our retinas, define the form percepts of which we are consciously aware. Precise orientationally tuned comparisons of left eye and right eye inputs are used to compute sharp estimates of the relative depth of an object from its observer 25,26 , and thereby to form three-dimensional boundary and surface representations of objects separated from their backgrounds 7 .…”

Binocular Disparity and the Perception of Depth

“…They classified cells into a few discrete categories, although it now appears that Center for Neurobiology and Behavior Columbia University these categories represent idealized cases from a continuous distribution (LeVay and Voigt, 1988). More reNew York, New York 10032 cently, Ohzawa et al (1990Ohzawa et al ( , 1996 provided detailed quantitative mapping of binocular receptive fields of the We perceive the world in three-dimensions even though cat visual cortical cells and suggested models for simuthe input to our visual system, the images projected lating their responses. While these and many other exonto our two retinas, has only two spatial dimensions.…”

“…These curves alone are not very useful from a computational point of view because a response can be read from a disparity tuning curve only when the stimulus disparity is already known. We need a quantitative procedure for computing an unknown disparity in a pair of retinal images from the responses of complex cells to the images.Fortunately, a method for determining the responses of binocular complex cells has recently been proposed by Ohzawa et al (1990) based on their quantitative physiological studies (see also Ferster, 1981). These investigators found that a binocular complex cell in the cat primary visual cortex can be simulated by summing up the squared responses of a quadrature pair of simple cells, and the simple cell responses, in turn, can be simulated by adding the visual inputs on their left and right receptive fields (see Figure 5).…”

“…(Two binocular simple cells are said to form a quadrature pair if there is The complex cell (labeled C) sums squared outputs of a quadrature pair of simple cells (labeled S 1 and S 2 ). Each simple cell in turn sums Ohzawa et al, 1990.) The remaining questions are the contributions from its two receptive fields on the left and right whether the model complex cells constructed this way retinas.…”

“…The squaring operation could presumably be performed by are indeed independent of stimulus Fourier phases and a multiplication-like operation on the dendritic tree of the complex if so, how their preferred disparities are related to their cell (Mel, 1993). Ohzawa et al (1990) pointed out that to consider receptive field parameters.the fact that cells cannot fire negatively, each simple cell should be These issues have recently been investigated through split into two with inverted receptive field profiles, so that they can mathematical analyses and computer simulations (Qian, carry the positive and negative parts of the firing, respectively. The resulting complex cell model will contain four half-wave rectified 1994; Zhu and Qian, 1996; Qian and Zhu, 1997).…”