Fleet DJ, Wagner H, and Heeger DJ, Modelling Binocular Neurons in the Primary Visual Cortex, in Computational and Biological Mechanisms of Visual Coding, M. Jenkin and L. Harris, eds, Cambridge University Press, p. 103-130, 1997.
Abstract: This chapter presents a formal description and analysis of a binocular energy model of disparity selectivity. According to this model, disparity selectivity results from a combination of position-shifts and/or phase-shifts. Our theoretical analysis suggests how one might perform an experiment to estimate the relative contributions of phase and position shifts to the disparity selectivity of binocular neurons, based on their responses to drifting sinusoidal grating stimuli of different spatial frequencies and disparities.
We also show that for drifting gratings stimuli, the binocular energy response (with phase and/or position shifts) is a sinusoidal function of disparity, consistent with the physiology of neurons in primary visual cortex (area 17) of the cat. However, Freeman and Ohzawa (1990) also found that the depth of modulation in the sinusoidal disparity tuning curves was remarkably invariant to interocular contrast differences. This is inconsistent with the binocular energy model.
As a consequence we propose a modified binocular energy model that incorporates two stages of divisive normalization. The first normalization stage is monocular, preceding the combination of signals from the two eyes. The second normalization stage is binocular. Our simulation results demonstrate that the normalized binocular energy model provides the required stability of the depth of response modulation. Simulations also demonstrate that the model's monocular and binocular contrast response curves are consistent with those of neurons in primary visual cortex.