Abstract
Patients with retinal damage rarely perceive holes in the visual field and are often unaware of their scotomas. One explanation for this is that the brain interpolates missing information from the surrounding visual field leading to perceptual “filling-in”. Research in animal models and patients suggests that (population) receptive fields ((p)RF) around the scotoma remap. This has been interpreted as evidence that perceptual filling-in is caused by cortical plasticity leading to changes in connectivity. Several studies suggest that this remapping is adaptive, with (p)RFs changing their position away from the scotoma towards spared portions of the visual field. However, there is also evidence of non-adaptive position changes outside the scotoma. Moreover, similar patterns of remapping have also been observed in healthy participants in response to simulated scotomas. These counterintuitive findings suggest that cortical remapping following scotomas is not necessarily a sign of functional plasticity and may be independent of perceptual filling-in. Here, we demonstrate that a divisive normalization model of visual pRFs could account for the remapping observed with scotomas. Simulations based on this model show that varying the scotoma centre will affect the responsiveness of the model to stimuli in the same location. This change in responsiveness can result in apparent changes in position preference around the scotoma. These positional changes are caused by the scotoma affecting suppressive and excitatory inputs differently, leading to changes in the balance of excitation and inhibition and consequently the centre-of-mass of the (p)RF. Moreover, depending on the location of the scotoma relative to the (p)RF, the change of centre-of-mass may be towards or away from the scotoma. Importantly our account does not assume any changes in cortical circuitry or plasticity. Hence, divisive normalization provides a biologically plausible and parsimonious account of remapping in the visual cortex which can be validated in future experiments.