A Surprisingly Simple Neural-Based Relationship Predicts Binocular Facilitation

Two eyes are better than one - but not by much. Most binocular facilitation models incorporate incomplete binocular summation (e.g., the Minkowski equation). One complication is that the Minkowski exponent for binocular facilitation varies with spatial frequency. We find that a simple alternative models both psychophysical and neural data without taking spatial frequency into account. There are cortical neurons that only fire for one eye, but amplify their firing rates if both eyes are stimulated (Dougherty, 2019). We find that binocular amplification for these monocular neurons follows a power law, with a compressive exponent of 0.84 (r=0.96), remarkably close to power law multisensory interactions (Billock & Havig, 2018). Next, we modeled the relationship between the dominant eye's firing rate and the binocular firing rate in binocular V1 facilitatory neurons. Unexpectedly, the same rule also applies to cortical facilitatory binocular neurons (exponent=0.87, r=0.97); binocular neurons can be approximated as gated amplifiers of dominant monocular responses, if both eyes are stimulated. Finally, the same power law models binocular facilitation of contrast sensitivity in Winterbottom (2016) and our unpublished psychophysical data (pooled data's exponent is 0.89; r=0.98); binocular response is a gated amplification of the more sensitive eye. This unexpected result fits with growing evidence that non-driving modulatory neural interactions affect sensory processing.