The neural basis of visual symmetry and its role in mid- and high-level visual processing : Neural basis of visual symmetry

Research into the perception of space, time and quantity has generated three separate literatures. That number can be represented spatially is, of course, well accepted and forms a basis for research into spatial aspects of numerical processing. Links between number and time or between space and time, on the other hand, are rarely discussed and the shared properties of all three systems have not been considered. I propose here that time, space and quantity are part of a generalized magnitude system. I outline A Theory Of Magnitude (ATOM) as a conceptually new framework within which to re-interpret the cortical processing of these elements of the environment.

The human capacity to recognize complex visual patterns emerges in a sequence of brain areas known as the ventral stream, beginning with primary visual cortex (V1). We develop a population model for mid-ventral processing, in which non-linear combinations of V1 responses are averaged within receptive fields that grow with eccentricity. To test the model, we generate novel forms of visual metamers — stimuli that differ physically, but look the same. We develop a behavioral protocol that uses metameric stimuli to estimate the receptive field sizes in which the model features are represented. Because receptive field sizes change along the ventral stream, the behavioral results can identify the visual area corresponding to the representation. Measurements in human observers implicate V2, providing a new functional account of this area. The model explains deficits of peripheral vision known as “crowding”, and provides a quantitative framework for assessing the capabilities of everyday vision.