Abstract
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.
Highlights
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
Wandell [12] estimates the number of neurons in primate V1 to be at least 150 million which puts the ratio of V1 neurons to retinal ganglion output cells at 100 : 1. Even after allowing for the compression performed by the ganglion cells prior to transmission over the bandwidth-limited optic nerve, V1 produces more outputs than visual inputs leading to an overcomplete representation of the visual field [13]
The underlying mechanism of V1 selectivity has been shown to be more than a feedforward weighted-sum filtering of stimuli from the receptive fields [78]
Summary
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. We provide a short review of key information about the function and architecture of V1 that may be used to build a blueprint of this crucial stage of the human visual system We hope that this may assist efforts to reverse engineer the early human visual system or to transfer successful cortical strategies to computer vision and signal processing algorithms. The ventral pathway consists of V1 → V2 → V3 → V4 → temporal lobe, which is called the “what” pathway involved in object recognition tasks [10] The segregation of these two parallel processing streams is far from being distinct as there are numerous two-way interconnections between the cortical areas, including V1 [11]. Those of linear neurons can be expressed as a linear combination of its inputs, which is analogous to the finite impulse response (FIR) of linear filters
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