Abstract
Visual information is processed in the cortex by ON and OFF pathways that respond to light and dark stimuli. Responses to darks are stronger, faster, and driven by a larger number of cortical neurons than responses to lights. Here, we demonstrate that these light-dark cortical asymmetries reflect a functional specialization of ON and OFF pathways for different stimulus properties. We show that large long-lasting stimuli drive stronger cortical responses when they are light, whereas small fast stimuli drive stronger cortical responses when they are dark. Moreover, we show that these light-dark asymmetries are preserved under a wide variety of luminance conditions that range from photopic to low mesopic light. Our results suggest that ON and OFF pathways extract different spatiotemporal information from visual scenes, making OFF local-fast signals better suited to maximize visual acuity and ON global-slow signals better suited to guide the eye movements needed for retinal image stabilization.
Highlights
The brain processes light and dark features in an image using two visual pathways that signal local luminance increments (ON) and decrements (OFF)
Differences that we discovered make large long-lasting stimuli to generate stronger ON than OFF cortical responses and small fast stimuli to generate stronger OFF than ON cortical responses. We show that this functional specialization of ON and OFF cortical pathways is robust, is maintained under a wide variety of luminance conditions, and has a correlate in the statistics of natural scenes
We investigated differences in spatiotemporal processing between ON and OFF cortical pathways by measuring visual cortical responses to dark (0.27 cd/m2) and light (239 cd/m2) stimuli
Summary
The brain processes light and dark features in an image using two visual pathways that signal local luminance increments (ON) and decrements (OFF). OFF cortical responses are known to be stronger than ON cortical responses in scenes dominated by mid-luminance backgrounds, low spatial frequencies, and optical blur (Kremkow et al, 2014; Pons et al, 2017). It remains unclear what stimulus conditions (if any) make ON cortical responses stronger than OFF cortical responses. In humans, darks remain more salient than lights under low mesopic light (Pons et al, 2017)
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