Primate monocular vision is intrinsically unstable: a side-effect of binocular homeostasis

Abstract

Short-term deprivation of one eye of 1-2 hours in human adults results in reciprocal changes in the interocular balance that last 30-90 minutes, assumed to be the consequence of a change in the contrast gain within the binocular circuitry. What is not known is how these changes emerge and with what dynamic. One possibility is that they are initiated once the patch is removed. The alternative is that they result from a dynamic build-up from the moment the patch is applied. In this study, we measure the monocular dynamics of the non-deprived eye activation during the deprivation of the other eye in humans, using psychophysics, and in awake non-human primates, using functional ultrasound imaging (fUS) of the primary visual cortex (V1). In humans, we show that the contrast threshold increases overtime during the deprivation of the other eye. This observation indicates that the patching effect slowly builds up over the deprivation period at a binocular site. In the awake macaque, we show that during monocular deprivation the cerebral blood volume (CBV) increases in the non-deprived eye ocular-dominance bands, but not the deprived eye bands with similar dynamics as observed in human psychophysics. We show that human behavioral results can be predicted by a simple interocular normalization model that uses non-human primate CBV dynamics as a descriptor of the normalization pool activity. In conclusion, our results highlight a hitherto unknown feature of primate vision: monocular vision per se is intrinsically unstable.