Do our eyes sometimes deceive us? Or is it our brains? The speaker at our September monthly meeting showed us some surprising examples of both, writes Bob Crooks
Our speaker Bill Stevenson (photo by Mike Docker)
Bill Stevenson, chair of Richmond U3A, kindly agreed at short notice to present his talk at our monthly meeting in September. His presentation was developed by the Society of Dyers and Colourists, and Bill began with a brief history of the society which was founded in 1884 when Britain was a world leader in the development of synthetic dyes and their use in the textile industry. It is now a professional society whose aim is “to communicate the science of colour in a changing world”.
Bill explained how colour vision had evolved to improve animals’ ability to find food and how different animals’ vision covered varying colour spectra depending on their environment.
The structure of the human eye was described, particularly how light is detected by the cells known as rods and cones which form the retina, with the six million cones of three different types being responsible for detecting red, green and blue light. It is defects in the cones which are the cause of colour vision deficiency (also known as colour blindness or daltonism).
There are various types of colour vision deficiency, with inability to distinguish red and green being the most common. In contrast some people have a condition known as tetrochromacy, in which they have four rather than the normal three types of cone cells giving them an enhanced ability to distinguish between colours.
One of the most interesting parts of the presentation showed how our perception of colour is a function of the brain as much as the eyes, and can be influenced by factors such as background or adjacent colour, or by varying light and shade. These effects are a form of optical illusion, and we were shown some intriguing examples.
This very enjoyable presentation showed once more that we cannot always believe the evidence of our own eyes.