Both theoretical and experimental studies suggest that response properties in the visual system are shaped by signals in the natural environment. Recent studies showed that, in the primary visual cortex (V1), neurons preferring light decrements (OFF stimuli) outnumber those preferring light increments (ON stimuli). However, it is not clear whether the OFF-dominance in V1 neurons is related to the contrast statistics in natural images. By analysing the distribution of negative and positive contrasts in natural images at several spatial scales, we showed that optimal coding of the natural contrast signals would lead to a contrast-dependent OFF-dominant response, with a stronger degree of OFF-dominance at a higher contrast. Using bright and dark stimuli at various contrast levels to measure the receptive fields of neurons in cat V1, we found an increasing degree of OFF-dominance of the neuronal population as the contrast was increased. By modeling receptive fields exhibiting OFF- and ON-dominance, we found that contrast-dependent OFF-dominance facilitated the discrimination of stimuli with natural contrast distribution. Thus, by matching contrast-dependent OFF-dominance to the statistics of contrast distribution in natural images, V1 neurons may better discriminate contrast information in natural scenes.
We showed that optimal coding of the natural contrast signals would lead to a stronger degree of OFF-dominance in neuronal response at a higher contrast. Such contrast-dependent OFF-dominance was indeed observed in the responses of cat V1 neuronal population. Further analysis with receptive field models showed that the contrast-dependent OFF-dominance may allow better discrimination of stimuli with natural contrast statistics.