Spatial Frequency Integration for Binocular Correspondence in Macaque Area V4

Laboratory for Cognitive Neuroscience, Graduate School of Frontier Bioscience, and Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan Submitted 29 January 2007; accepted in final form 15 October 2007 Neurons in the primary visual cortex (V1) detect binocular disparity by computing the local disparity energy of stereo images. The representation of binocular disparity in V1 contradicts the global correspondence when the image is binocularly anticorrelated. To solve the stereo correspondence problem, this rudimentary representation of stereoscopic depth needs to be further processed in the extrastriate cortex. Integrating signals over multiple spatial frequency channels is one possible mechanism supported by theoretical and psychophysical studies. We examined selectivities of single V4 neurons for both binocular disparity and spatial frequency in two awake, fixating monkeys. Disparity tuning was examined with a binocularly correlated random-dot stereogram (RDS) as well as its anticorrelated counterpart, whereas spatial frequency tuning was examined with a sine wave grating or a narrowband noise. Neurons with broader spatial frequency tuning exhibited more attenuated disparity tuning for the anticorrelated RDS. Additional rectification at the output of the energy model does not likely account for this attenuation because the degree of attenuation does not differ among the various types of disparity-tuned neurons. The results suggest that disparity energy signals are integrated across spatial frequency channels for generating a representation of stereoscopic depth in V4. Address for reprint requests and other correspondence: I. Fujita, Laboratory for Cognitive Neuroscience, Graduate School of Frontier Biosciences, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka, 560-8531, Japan (E-mail: fujita{at}fbs.osaka-u.ac.jp )