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White BJ, Kan JY, Levy R, Itti L, Munoz DP (2017) Superior colliculus encodes visual saliency before the primary visual cortex. Proceedings of the National Academy of Sciences USA, 114(35):9451-9456    
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Theories of visual attention postulate the existence of a saliency map that guides attention/gaze toward the most visually conspicuous stimuli in complex scenes. This study compared saliency coding in the two dominant visual gateways: the primary visual cortex (V1) and the evolutionarily older visual system that exists in the midbrain superior colliculus. Our results show that neurons in the superficial visual layers of the superior colliculus (SCs) encoded saliency earlier and more robustly than V1 neurons. This was surprising, because the dominant input to the SCs arises from V1. This result is in line with models that place a feature processing stage (V1) before the feature-agnostic saliency map in SCs
Abstract
Models of visual attention postulate the existence of a bottom-up saliency map that is formed early in the visual processing stream. Although studies have reported evidence of a saliency map in various cortical brain areas, determining the contribution of phylogenetically older pathways is crucial to understanding its origin. Here, we compared saliency coding from neurons in two early gateways into the visual system: the primary visual cortex (V1) and the evolutionarily older superior colliculus (SC). We found that, while the response latency to visual stimulus onset was earlier for V1 neurons than superior colliculus superficial visual-layer neurons (SCs), the saliency representation emerged earlier in SCs than in V1. Because the dominant input to the SCs arises from V1, these relative timings are consistent with the hypothesis that SCs neurons pool the inputs from multiple V1 neurons to form a feature-agnostic saliency map, which may then be relayed to other brain areas