Apparent Motion Suppresses Responses in Early Visual Cortex: A Population Code Model

摘要

Two stimuli alternately presented at different locations can evoke a percept of a stimuluscontinuously moving between the two locations. The neural mechanism underlying thisapparent motion (AM) is thought to be increased activation of primary visual cortex (V1)neurons tuned to locations along the AM path, although evidence remains inconclusive.AM masking, which refers to the reduced detectability of stimuli along the AM path, hasbeen taken as evidence for AM-related V1 activation. AM-induced neural responses arethought to interfere with responses to physical stimuli along the path and as such impair theperception of these stimuli. However, AM masking can also be explained by predictive coding models, predicting that responses to stimuli presented on the AM path are suppressedwhen they match the spatio-temporal prediction of a stimulus moving along the path. In thepresent study, we find that AM has a distinct effect on the detection of target gratings, limiting the maximum performance at high contrast levels. This masking is strongest when thetarget orientation is identical to the orientation of the inducers. We developed a V1-like population code model of early visual processing, based on a standard contrast normalizationmodel. We find that AM-related activation in early visual cortex is too small to either causemasking or to be perceived as motion. Our model instead predicts strong suppression ofearly sensory responses during AM, consistent with the theoretical framework of predictivecoding.