Peripheral vision
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Peripheral vision is a part of vision that occurs outside the very center of gaze. There is a broad set of non-central points in the field of view that is included in the notion of peripheral vision. "Far peripheral" vision exists at the edges of the field of view, "mid-perpheral" vision exists in the middle of the field of view, and "near-peripheral", sometimes referred to as "paracentral" vision, exists adjacent to the center of gaze[citation needed].
Peripheral vision is weaker in humans, compared with other animals, especially at distinguishing color and shape. This is because the density of receptor cells on the retina is greatest at the center and lowest at the edges (see visual system for an explanation of these concepts). In addition, there are two types of receptor cells, rod cells and cone cells; rod cells are unable to distinguish color and are predominant at the periphery, while cone cells are concentrated mostly in the center of the retina (the macula).
Peripheral vision is good at detecting motion (a feature of rod cells), however, and is relatively strong at night or in the dark, when the lack of color cues and lighting makes cone cells far less useful. This makes it useful for avoiding predators, who tend to hunt at night and may attack unexpectedly.
Peripheral vision loss may occur due to a number of ocular or neurological diseases or disorders. Glaucoma, stroke, branch retinal vein occlusion, branch retinal artery occlusion, ischemic optic neuropathy, and transient migraine are some of the more common causes, whereas retinitis pigmentosa, choroideremia, gyrate atrophy, pituitary tumors, optic disc drusen, brain tumors and aneurysms, and tilted optic discs are uncommon or rare. [1].
The distinctions between central and peripheral vision are reflected in subtle physiological and anatomical differences in the visual cortex. Different visual areas contribute to the processing of visual information coming from different parts of the visual field, and a complex of visual areas located along the banks of the interhemispheric fissure (a deep groove that separates the two brain hemispheres) has been linked to peripheral vision. It has been suggested that these areas are important for fast reactions to visual stimuli in the periphery, and monitoring body position relative to gravity [1]
[edit] References
- ^ Palmer SM, Rosa MG (2006). "A distinct anatomical network of cortical areas for analysis of motion in far peripheral vision.". Eur J Neurosci 24(8): 2389-405.
