Eye, Brain and Mind

By: Anna Franklin

Left: No colour vision deficiency.
Right: Severe colour vision deficiency.

There have been decades of highly focused scientific studies that have aimed to identify how the eye, brain and human mind enable humans to experience colour. These reveal a complex set of neural processes within the retina (back of the eye) and multiple regions of the cortex (surface of the brain).

In a nutshell, wavelengths of light are detected by receptors in the retina called ‘cones’. In most individuals, there are three types of cone, which are maximally sensitive to short wavelengths (bluish light); medium wavelengths (greenish light) and long wavelengths (reddish light) respectively.

The signals from these cones are then contrasted and combined to form two separate neural pathways to the brain. One of these pathways captures how red-green the colour is, and the other captures how blue-yellow the colour is. A third pathway captures how much light there is in the colour.

The combination of signals from these pathways enables humans to detect millions of different colours. Initially, an area at the back of the brain, called the visual cortex, processes these neural signals and computes different characteristics of the colour taking account of the context (e.g. the lighting or the background). Other regions of the brain can then draw on this information to make judgments, such as determining the colour of objects, forming an aesthetic view of a colour, or to name and communicate about colours.

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Professor Anna Franklin is a leading expert in colour psychology. She is a Director of the Sussex Colour Group in the School of Psychology at the University of Sussex in England.