Abstract
The nervous system has evolved in an environment with structure and predictability. One of the ubiquitous principles of sensory systems is the creation of circuits that capitalize on this predictability. Previous work has identified predictable non-uniformities in the distributions of basic visual features in natural images that are relevant to the encoding tasks of the visual system. Here, we report that the well-established statistical distributions of visual features -- such as visual contrast, spatial scale, and depth -- differ between bright and dark image components. Following this analysis, we go on to trace how these differences in natural images translate into different patterns of cortical input that arise from the separate bright (ON) and dark (OFF) pathways originating in the retina. We use models of these early visual pathways to transform natural images into statistical patterns of cortical input. The models include the receptive fields and non-linear response properties of the magnocellular (M) and parvocellular (P) pathways, with their ON and OFF pathway divisions. The results indicate that there are regularities in visual cortical input beyond those that have previously been appreciated from the direct analysis of natural images. In particular, several dark/bright asymmetries provide a potential account for recently discovered asymmetries in how the brain processes visual features, such as violations of classic energy-type models. On the basis of our analysis, we expect that the dark/bright dichotomy in natural images plays a key role in the generation of both cortical and perceptual asymmetries.
Highlights
One of the major insights of modern neuroscience is the recognition that regularities in the environment are embedded and exploited in neural circuitry [1, 2]
We show that these patterns, when combined with neural transforms in the early visual pathways, produce statistical regularities in the signals arriving to primary visual cortex
We model the stages of early visual processing—which themselves contain several dark/bright asymmetries—and measure the statistical distribution of the cortical inputs from natural scenes after they have been processed through the ON and OFF pathways
Summary
One of the major insights of modern neuroscience is the recognition that regularities in the environment are embedded and exploited in neural circuitry [1, 2]. We show that these patterns, when combined with neural transforms in the early visual pathways, produce statistical regularities in the signals arriving to primary visual cortex. These regularities in the input to cortex provide a simple explanation for a range of recent neurophysiological findings: cells in visual cortex respond asymmetrically to brights and darks [9,10,11,12,13,14,15,16,17], with greater cortical responses to dark features at high visual contrasts, low spatial frequencies, and far depths [12, 13, 15]
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