Colour perception

There is a highly complex series of connections between the detector and fibres making up the optic nerve taking the resulting signals to the visual cortex. This link can be depicted using a simplified hypothetical framework (Hunt 1998). There appear to be not four but three types of nerve fibre. One carries achromatic or brightness information, the other two carry colour information -the opponent colour mechanisms. This model is shown in Fig. 2.2. 

Measuring colour, 3rd edition, 1998. ISBN 0863433871. Published by Fountain Press, an imprint of Newpro UK Ltd, Old Sawmills Road, Faringdon, Oxon. 

Colour information from the retina is obtained from a series of signal differences. 

These are transmitted as two signals, Ci and (C2 — C3). The achromatic signal under daylight conditions comprises all three p, 7, and (3 responses, weighted to compensate for the differing number of each type of cone (40 20 1) in the retina. That is, 

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Visual judgement of whiteness is highly subjective. Many factors, such as the observer s age, sex and colour perception, and even the hue of white materials normally encountered in the observer s country, help to decide on individual preference for either a red-violet or a... 

On the other hand there are also assumptions built into our perception, which are, for example, the basis of our visual illusions. Thus we perceive the moon moving against the clouds, since we hypothesize that objects move in a static environment, which fits to our immediate earthly environment. Here it is important to spot a moving object, be it a predator or prey, in minimum time. That we fall prey to an illusion, when we look up at the sky, does not really matter. In addition we know that we categorize and thus impose an order onto and into what we perceive. Colour perception is a good example. 

Buchshaum G 1980 A spatial processor model for object colour perception. Journal of the Franklin Institute 310(1), 337-350. 

Retrobulbar neuritis can be part of a disulfiram-induced polyneuritis, with dramatic reduction in visual acuity and impaired colour perception (SEDA-10, 349) (12). This complication is rare but serious. It occurs at dosages of 500 mg/day, and there is a latent period of 2-36 months. Tobacco abuse is thought to be a predisposing factor. Disulfiram can cause optic neuropathy (13,14). 

A commonly-used device for testing colour perception is the Isihara test. This consists of a number of plates composed of numerous spots of different colours and sizes. Incorporated into this random arrangement are a number of dots, tracing out numerals, which are of a colour distinguishable from the remainder. The colour sensitivity of the observer s eye is assessed by his ability to read these numbers. It is also possible to detect different kinds of colour blindness with the plates. Four of them, for example, each contain two numbers one in scarlet and the other in purple. Those who suffer from panatropy cannot see the scarlet spots and only read the purple ones, but the deuteranopes read only the scarlet numerals those with normal vision see both numbers. (For further information see JORDINSON AND MlNSHALL, J. 5.D.C., 1959, 75, 585.)... 

The Giles-Archer colour perception unit consists of a lamp with three apertures one of 5 mm, another of 0 5 mm, and finally a 0-5-mm aperture covered with a neutral filter. Filters transmitting six different colours can be placed over the apertures by rotating a disc on which they are mounted. The observer, standing at least 6 ft from the lamp, must name the colours, using the three apertures in turn. Severe cases of red and green blindness cannot differentiate between the large exposures of these hues, and are often unable to see any of the colours when the small apertures are used. 

Derived from the seeds of Artemesia species. Blyth and Blyth (1920) reported 18 cases of poisoning when the drug had been used as a worming agent. Disturbance of colour perception, taste andsmell. Convulsions, dilated pupils, heart slow and weak, collapse, death. 

Scientific studies into the mechanism of vision and human colour perception began in the seventeenth century with the recognition that the eye s lens must somehow project an image of the object viewed onto the back of the eye. Newton s classic experiments on the refraction of light led him to conclude that... 

Principles of colour appearance and measurement Volume 1 Object appearance, colour perception and instrumental measurement... 

Taste and colour perception are also influenced by chirality, hardly surprisingly. For example, S-limonene has a lemon flavour while i -limonene tastes of oranges. Similarly, 5-carvone tastes of caraway and iJ-carvone of spearmint. 

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