Ocular dominance column development: analysis and simulation

Article Abstract:

In many mammals, the visual system is composed of a chain of nerve cells or neurons which connect from the retina to cells in neurons found deep in the brain and ultimately to the cerebral cortex. At the point where they terminate in the cerebral cortex, nerve processes alternate in patches called "ocular dominance columns" which serve either the left or the right eye. This nonoverlapping pattern is established during the developmental period of the animal from an initial organizational pattern in which the nerves overlap completely. If vision from one eye is blocked, or if impulses arriving from the two eyes are not synchronized, the fibers fail to separate and ocular dominance columns do not develop. This means that if one eye is closed (for any reason, e.g., bandaging) for an extended period of time, an abnormal visual cortex will develop. Activity patterns are required for proper development. The current paper develops a mathematical model which allows the development of such a system to be experimentally developed and allows for the prediction of outcome if the system rules are changed. The system allows simulations of phenomena such as those discussed above.

Models, Visions

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Ocular responses to linear motion are inversely proportional to viewing distance

Article Abstract:

The visual reflexes that improve vision during movement were evaluate in four rhesus monkeys. An experiment was conducted to examine the phenomenon whereby, when viewed from a moving vehicle, nearby objects appear to speed by while distant objects scarcely move at all. The monkeys were shown flashing lights while being pulled on sleds. Their compensatory eye movements were measured and analyzed. Two types of reflexes were studied, visual reflexes of the eyes and vestibular reflexes of the otolith organs in the base of the skull. Both visual and vestibular reflexes produced compensatory eye movements that stabilized the image reaching the retina in back of the eye, onto which images are projected. The amount of visual and vestibular response to the monkey's movement depended on the inverse of the distance between the monkey and the flashing light being observed. The inverse is a simple mathematical transformation, so the important conclusion was that both reflexes were distance-dependent. It is suggested that both reflexes respond to the same information about the environment by way of a shared pathway, and also cooperate to compensate for the observer's motion.

Visual perception, Visual pathways, Visual pathway

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Indeterminate organization of the visual system

Article Abstract:

A computer algorithm was developed in response to a recent study that suggested a hierarchy of areas in the monkey visual cortex. The model showed that there were a great many possible hierarchies within the given anatomical constraints. A reply suggests further constraints.

Brain, Localization (Brain function)

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