Functions of the colour-opponent and broad-band channels of the visual system

Article Abstract:

In primates, including man, the color-opponent and broad-band channels involved in vision begin in the retina of the eye, and continue to the brain through several different neural stations. Research from single cells has shown that the ganglia (nerve cells in the retina that comprise the color component) have small receptive fields, respond for prolonged periods of time, and receive inputs from different spatially segregated cells, known as cones. The broad-band cells have large receptive fields, respond for short periods of time, and receive impulses from cones that are not separated. The visual capacities of rhesus monkeys were examined before and after disrupting areas of the brain (where the various channels are located) with small lesions. It was shown that the color-opponent channels are necessary for the processing of color and texture, the discrimination of fine patterns, and seeing objects in three dimensions. The broad-band channels are essential for perception of motion. Neither of the channels is involved in the discrimination of brightness, the processing of coarse shapes, and contrast sensitivity. These studies have increased the understanding of vision, and can lead to applications in the treatment of various medical problems relating to vision. (Consumer Summary produced by Reliance Medical Information, Inc.)

Eye

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Vision in blind mole rats

Article Abstract:

Experiments involving behaviorally blind mole rats proved that the visual system is divided into subsystems that serve varying purposes. Howard M. Cooper and colleagues chose this unusual rodent as their subject because its vestigial, almost nonexistent eyes would aid in differentiating the functions of the visual system. The injection of tracers into the mole rats' eyes showed that the retina's targets are likewise much diminished in size. The mole rats' ability to detect light despite their reduced ocular organs showed that they have lost some but not all of the visual system's functions.

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Effect of lesions in visual cortical area V4 on the recognition of transformed objects

Article Abstract:

The visual cortical area, V4, is necessary for three visual analyses, visual learning, selection of non-salient objects in the visual scene and the recognition of visual objects when there is image transformation. The visual system of primates has the ability to recognize objects in spite of the variety of images they form on the retinal surface with respect to change in size, contrast, color and obstruction by other stimuli. This ability is affected by lesions in the visual cortical area though multiple occurrences of the same sized and colored object is still recognizable.

Visual perception, Rhesus monkey

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