MODULE: Colour perception

Step 05 of 09: Subjectivity in contrast

The human visual perceptive system has evolved to make certain adjustments to the colours we see as light changes so that familiar objects or the overall context of what is presented to us influences the colours we perceive to be in the world. This is because light changes in hue and brightness under different circumstances and colour is interpreted in a subjective way, not at the photoreceptors, but by the visual cortex of the brain, thereby making it subjective and often susceptible to being misled. This is reflected in its early identification in Edwin LAND's (McCANN, 1971) retinex theory, attributing the effect to a combination of the RETInal photoreceptors and the visual cortEX. Take the Checker Shadow illusion created by ADELSON to show how the brain is influencing our perception of colour based on context;

Swatches A and B when viewed as a whole seem to be opposite colours on a checkered grid. In truth they are exactly the same colour in the real world, reflecting light at the same wavelength when received by the retina, but re-interpreted by the visual cortex. Given the brain's familiarity with the way shadows dull colours and our experiences with checkerboards as well as the local contrast surrounding swatch B, we are prone to believe it is actually a slightly lighter shade of grey than swatch A. But when we cover the rest of the image and overlay a shape touching both swatches in the same colour, it becomes evident that several factors at play influenced us to believe they were vastly different. The reason for this is mainly local contrast (REID & SHAPLEY, 1988), whereby the neighbouring brightness of elements impacts our perception of the item in question.