Colour perception deficiency affect almost 8% of the male population. It is believed to be inherited usually for the maternal grandfather. The typical red-greed colour perception deficiency can be greatly improved by Vision Training. Read on a learn more about colour perception and how it can be improved.

The scientific study of colour starts with Newton's great work, the Optick (1704). This is an extraordinary work detailing Newton's experiements in Trinity College, Cambridge. The Optick contains Newton's most speculative thoughts on physics and man's relation through perception of the Universe. Newton showed that white light is made up of all the spectral colours. The later wave theory made it clar that each colour corresponds to a specific frequency.

Newston's original sketch of an experiment with colour. He split sunlight into a spectrum through a large prism. The spectrun is again recombined into white light through a second prism.

Colour perception is our ability to see a range of spectral wavelengths from 380 nm Violet to 780 nm Red. As the wavelength change the colour perception changes. Red and Blue light combine into Violet. Red and Green light combine into Yellow and Blue and Green light become Turquise.

Thomas Young (1773 - 1829) proposed the trichomatic theory (1802) which suggest that there are three primary colours only. German scientist Herman von Helmholtz developed Young's ideas further and it became the Young-Helmholtz theory. There are three colour sensitive receptors (cone cells) which respectively responds to red, greed and blue. All colours are seen by a mixture of signals from the three colour receptors. Incidentally, this is the same principle behing your computer screen. In computer parlance it is known as the RBG colour system.

Hue discrimination

The hue defines the smallest wavelength of light with the smallest diffrence that is possible to diffrentiate by the human eye. We notice that there is a dramatic increase in the red-green sensitivity producing exceptional hue discrimination ability in the gree - yelloe - orange - red region. This is a very useful feature because various foods and fruits display their readiness to be eaten by their colour change. You can instantly see whether an apple is ready to eat or not by its colour.

Colour film is essentially a complex arrangement of the three primary colour filters. Kodachrome slides are able to reproduce all the complexity of colour seen in nature.

Colour vision is very complex and cannot be reduced to simple theories. Colour depends not only on the wavelengths and intensities, but also on differneces on intensities between regions, and whether the patterns are accepted as representing known objects. This involves high-level processing in the brian, which is extremely difficult to investigate.

The eye tends to accept as white not a particular mixture of colours, but rather the genreral illumination. Thus you see a car's headlights as white while on a country drive, but in town where there are bright white lights for comparison, they look quite yellow, and the same is true of candle light. This means that what is takes as reference for white can shift. Expectation and knowledge of the normal colour is an impportant factor in colour perception.

Colour perception deficiency

Surprisingly, the common confusion where red is confused with green, was not discovered before late eighteenth century when chemist John Dalton found that he could not distinguish certain substances by their colour although others could do so easily.

Colour vision tests depend on isolating colour as the one identifying characteristic, and then it is easy to show whether a person has normal ability to distinguish between colous, or whether he or she sees a single colour what to others appear different colours. It is most common to find a reduced sensitivity to some colours rather than a complete absense of colour.

The properties of red and green light required to match a monochromatic yellow is the most important measure of colour deficiency. Lord Rayleigh discovered in 1881 that people who confuse red with green, require a greater intensity of either red or green to match yellow. A special instrument has been developed for testing this colour deficiency, it is called an anomaloscope. This insturiment takes advantage of the fact that yellow is always seen as a mixture of red and green.

The reason for red-green colour perception deficiencies is not clear. However, experiements with the anomaloscope shows that colour anomaly cannot be due to colour adaptation. The general belief is that red-green colour perception deficiency is supposed to be a reduction in the sensitivity of one or more colour receptors of the retina, through partial loss of photo-pigment. There may be many causes, but it is certainly not due to shortage of photo-pigment or the anomaloscope would not work.

The common red-green colour perception deficiency is more likely to be an interpretation of sensory data provided to the visyal cortex processing colour vision.

German physiologist Edward Hering noted that red and green are never seen simultaneously also the colour red/green is never used. Colours are either red or green, but not both. The same is true for blue and yellow. This observation lead Hering to propose the opponent colour vision theory (1920 / 1964).

In the late 1950’s Leo Hurvich and Dorothes Jameson provided quantitative date in support of the notion that colour opponency plays an important role in processing colour information. They used a hue cancellation procedure (hue is added to the stimulus until it turns white) to determine spectral sensitivities of the red-green and blue-yellow opponent channels.

It is believed that the red-green and blue-yellow channels only code hue information. The brightness is presumably coded by an independent brightness channel. If the frequency of action potential is plotted as a function of wavelength. We see that low wavelength stimuli (below 550 nm) cause inhibition, or a decreased firing rate from this cell.
In contrast, long-wavelength stimuli (longer than 550 nm) produce excitation, or an increased rate of neural firing. When a photosensitive cell responds to one portion of the spectrum with excitation and another with portion with inhibition, it is referred to as colour opponent neuron.

The discovery of colour opponent neurons in the visual system tells us that the recetoral information (trichomacy)) is coded in an opponent fashion at post-receptoral levels. In other words the three classes of colour sensitive cone cells are “wired” together in such as way that they are spectrally antagonistic. The process occurs in the retina and the level of horizontal cells.

In summary, primary colour vision is thrichromatic, with this trichormatic signal encoded in an opponent fashion. This opponent processing occurs very early in the visual system, at the level of horizontal cells. It is scientifically established that hue information is encoded by red-green and blue-yellow neurons. It is not clear whether brightness information is encoded by these neurons or by a separate class of non-colour opponent cells