A Survey of Architecture and Function of the Primary Visual Cortex (V1)
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Research Article A Survey of Architecture and Function of the Primary Visual Cortex (V1) Jeffrey Ng,1 Anil A. Bharath,1 and Li Zhaoping2 1 Department 2 Natural
of Bioengineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK Intelligence Laboratory, Department of Psychology, University College London, Gower Street, London WC1E 6BT, UK
Received 1 December 2005; Revised 6 September 2006; Accepted 18 September 2006 Recommended by Gloria Menegaz The largest visual area, known as the primary visual cortex or V1, has greatly contributed to the current understanding of mammalian and human visual pathways and their role in visual perception. The initial discovery of orientation-sensitive neurons in V1, arranged according to a retinotopic mapping, suggested an analogy to its function as a low-level feature analyser. Subsequent discoveries of phase, spatial frequency, color, ocular origin, and direction-of-motion-sensitive neurons, arranged into overlapping maps, further lent support to the view that it performs a rich decomposition, similar to signal processing transforms, of the retinal output. Like the other cortical areas, V1 has a laminar organization with specialization for input from the relayed retinal afferents, output to the higher visual areas, and the segregation of the magno (motion) and parvo (form) pathways. Spatially lateral connections that exist between neurons of similar and varying properties have also been proposed to give rise to a computation of a bottom-up saliency map in V1. We provide a review of the selectivity of neurons in V1, laminar specialization and analogies to signal processing techniques, a model of V1 saliency computation, and higher-area feedback that may mediate perception. Copyright © 2007 Jeffrey Ng et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1.
INTRODUCTION
The primary visual cortex (V1) contains orientation-tuned neurons, arranged in a retinotopic map, which have become the hallmark of early cortical computation in the primate visual system. Prior to the discovery of such neurons, the important role of V1 in the human visual system was known in the early twentieth century through patients who suffered total or partial loss of vision depending on the extent of damage to that area. The systematic correspondence between affected V1 area and regions of the field of view led Holmes [1] to deduce the retinotopic organization before the advent of in vivo extra cellular recording. Since then, anatomical examinations have shown that the visual signals from the retina enter the visual cortex mainly through V1, which in turn feeds the higher visual areas [2, 3]. The primary visual cortex thus plays an important role in visual perception in humans. Attention was first drawn to the primary visual cortex by the discovery of edge and line “detector” neurons by Hubel and Wiesel in the late 1950s (see
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