A neural model of binocular integration and rivalry based on the coordination of action-potential timing in primary visual cortex

In normal vision, the inputs from the two eyes are integrated into a singlepercept. When dissimilar images are presented to the two eyes, however,they compete for perceptual dominance, so that one eye's view suppressesthat of the other. Recent evidence suggests that this phenomenon, known asbinocular rivalry, arises through competition between alternative stimulusinterpretations in extrastriate cortex. Because eye-specific informationappears to be lost at this stage, it remains unclear how the stimulusconditions that yield binocular rivalry are distinguished from those thatproduce stable single vision. Using a neural network that models themammalian early visual system, I investigate here the hypothesis thatcongruent and conflicting stimuli are distinguished by their differenteffects on the relative timing of action potentials in primary visualcortex (V1), where monocular inputs are first combined. In the model,congruent stimulation of both eyes results in synchronization of dischargesamong binocular neurons in V1. By contrast, conflicting stimulation of thetwo eyes results in neuronal asynchrony in this area. This asynchrony thenproduces rivalrous response suppression at later stages in the visualpathway. Synchronization of firing in V1, however, prevents suchcompetition, thereby ensuring non-rivalrous responses. These novel effectsof spike timing on competition emerge naturally from the network dynamics.The results suggest that input-related differences in relative spike timingat an early stage of visual processing may play an important part in thephenomena both of binocular integration and rivalry; furthermore, theyindicate that the temporal patterning of cortical activity may be afundamental mechanism of selection among competing stimulusrepresentations.