1/5/2024 0 Comments Syte visual conception ltd![]() The strategy used by the mammalian visual system is to reduce the representation of the visual scene to a limited number of specialized, parallel output channels. Specialized circuits extract basic sensory cues, such as spatial contrast and temporal frequency from the initial intensity distribution, and encode these properties across approximately 1.5 million ganglion cells which form the optic nerve that connects the eye to the brain.ĭue to the anatomical bottleneck of the optic nerve, retinal output must be efficiently condensed. Remarkably, many of these computations are carried out within the retina, before visual signals even leave the eye. Nevertheless, computations carried out within our visual system are supplied with enough information to support highly precise hue discriminations and other perceptual abilities that inform our everyday behaviour. Much information is lost from the outset, such as the exact spectral composition of the image. The photoreceptor mosaic encodes the intensity of light as a function of position (two dimensions), wavelength and time ( Box 1). ![]() The first steps in seeing begin in the retina, where a dense array of photoreceptors convert the incoming pattern of light into an electrochemical signal 11. The visual cortex has the job of extracting the relevant information from this reduced signal and to further elaborate and integrate the information into a unified and coherent perceptual experience. These circuits comprise at least a dozen parallel pathways that project to the brain for further processing 10. Probably owing to these constraints, incoming visual signals are processed by at least 80 anatomically and physiologically distinct neural cell populations and 20 separate circuits within the retina. This representation, however, must also be sufficiently condensed so that the axons carrying this information can pass through the optic nerve, which forms an anatomical bottleneck along the route from the eye to the brain. Within just a few hundred microns of retinal thickness, this initial signal encoded by our photoreceptors must be transformed into an adequate representation of the entire visual scene. Remarkably, this complexity in our visual surroundings is first encoded as a pattern of light on a two dimensional array of photoreceptors, with little direct resemblance to the original input or the ultimate percept. Colour, depth, shape and motion are just a few of the many dimensions by which we interpret our visual environment and generate appropriate behaviour 9. The need for parallel processing in the visual system is immediately appreciated when one considers the multitude of qualities that are present in the visual environment and the physical limitations of the way this information is initially encoded and signaled to the brain ( Box 1). These early discoveries laid the foundation for our current understanding of the nervous system’s parallel processing strategies 3 – 8. This work was shortly followed up by Bishop 2 who proposed that the three different classes of axons he found in the optic nerve process different sensory qualities related to vision. Gasser and Erlanger 1 first demonstrated that the sensations of pain and temperature are transmitted through axons of different caliber than those transmitting touch. ![]() Parallel processing of sensory information is a commonly used strategy in the mammalian brain, not only between sensory modalities but across features of a single sense as well. Yet, rather than perceiving the world as a disjointed collection of attributes, we most often experience a single unified percept. Each of these sensations is transmitted to our brains through distinct biological machinery such as that found in the nose or under the skin. ![]() Our richest life experiences and longest-lasting memories are formed through our interactions with the sensory world around us and have a profound impact on our personality and sense of self.
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