For our vivid perception of a 3-D world, the stereoscopic function begins in our brain by detecting slight shifts of image features between the two eyes, called binocular disparity. The primary visual cortex is the first stage of this processing, and neurons there are tuned to a limited range of spatial frequencies (SFs). However, our visual world is generally highly complex, composed of numerous features at a variety of scales, thereby having broadband SF spectra. This means that binocular information signaled by individual neurons is highly incomplete, and combining information across multiple SF bands must be essential for the visual system to function in a robust and reliable manner. In this study, we investigated whether the integration of information from multiple SF channels begins in the cat primary visual cortex. We measured disparity-selective responses in the joint left-right SF domain using sequences of dichoptically flashed grating stimuli consisting of various combinations of SFs and phases. The obtained interaction map in the joint SF domain reflects the degree of integration across different SF channels. Our data are consistent with the idea that disparity information is combined from multiple SF channels in a substantial fraction of complex cells. Furthermore, for the majority of these neurons, the optimal disparity is matched across the SF bands. These results suggest that a highly specific SF integration process for disparity detection starts in the primary visual cortex.
SIGNIFICANCE STATEMENT Our visual world is broadband, containing features with a wide range of object scales. On the other hand, single neurons in the primary visual cortex are narrow-band, being tuned narrowly for a specific scale. For robust visual perception, narrow-band information of single neurons must be integrated eventually at some stage. We have examined whether such an integration process begins in the primary visual cortex with respect to binocular processing. The results suggest that a subset of cells appear to combine binocular information across multiple scales. Furthermore, for the majority of these neurons, an optimal parameter of binocular tuning is matched across multiple scales, suggesting the presence of a highly specific neural integration mechanism.