Toward A Single-Cell Account For Binocular Disparity Tuning: An Energy Model May Be Hiding In Your Dendrites

Hubel and Wiesel (1962) proposed that complex cells in visual cortex are driven by a pool of simple cells with the same preferred orientation but different spatial phases. However, a wide variety of experimental results over the past two decades have challenged the pure hierarchical model, primarily by demonstrating that many complex cells receive monosynaptic input from unoriented LGN cells, or do not depend on simple cell input. We recently showed using a detailed biophysical model that nonlinear interactions among synaptic inputs to an excitable dendritic tree could provide the nonlinear subunit computations that underlie complex cell responses (Mel, Ruderman, & Archie, 1997). This work extends the result to the case of complex cell binocular disparity tuning, by demonstrating in an isolated model pyramidal cell (1) disparity tuning at a resolution much finer than the the overall dimensions of the cell's receptive field, and (2) systematically shifted optimal disparity values for rivalrous pairs of light and dark bars-both in good agreement with published reports (Ohzawa, DeAngelis, & Freeman, 1997). Our results reemphasize the potential importance of intradendritic computation for binocular visual processing in particular, and for cortical neurophysiology in general.