What are the functions of primary visual cortex (V1)?

Although Hubel and Wiesel established decades ago how individual V1 neurons transform retinal inputs, functions of V1 as a whole are being discovered only recently. First, V1 acts as a motor cortex for exogenously guiding saccades by constructing a bottom-up saliency map of the visual field. Second, V1 initiates a processing bottleneck: a massive reduction of visual information begins at its output to downstream areas. Third, downstream recognition is limited by impoverished information; thus V1 provides additional information queried by top-down feedback from downstream areas; this feedback is directed predominantly to central visual field representations. These V1 functions underpin a framework in which vision is mainly looking and seeing through the bottleneck. Looking selects a fraction of visual information into the bottleneck, largely by saccades that center selected contents at gaze. Seeing recognizes the selected contents. Looking and seeing rely mainly on processing in the peripheral and central visual fields. • Primate V1 serves vision’s main function of looking and seeing through a bottleneck. • It creates a bottom-up saliency map to exogenously guide looking via gaze shifts. • It initiates an information bottleneck at V1’s output to downstream brain areas. • It supports feedback queries mainly directed to the central visual field. • The queried information aids ongoing visual recognition in light of the bottleneck.