Overview

Two aspects of the what, or ventral pathway, are colour and texture. In the biological world colour and texture are properties of surfaces which help in identifying objects, often rapidly. This realisation that colour did little in defining the boundaries in an image (§8.5.2) and the shape of things is relatively recent, the last few decades, whereas interest in colour itself goes back to the time of Newton and before.

Colour is essentially concerned with what things are, the nature of surfaces and the objects they represent. In mammals it plays a minimal role in form analysis, separating objects from one another or in analysing their shape. It travels exclusively along the P/K-cell pathways from the retina (§6.6.2) to the area V4 where colour, as opposed to wavelength of incoming light, is extracted (§8.4.2).

Colour does not carry anywhere near as much information as the monochromatic channels and subserves nowhere near as many functions. Yet it fascinates us, with writings from the ancient Greeks onwards, which Wade discusses in his book on the history of vision (Wade, 1998). It seems to generate emotional connotations. We talk of red with anger or green with envy. Kandinsky based his abstract art on elaborate theories of colour, while some of the great abstract expressionists, such as Mark Rothko, relied almost entirely on subtle shades of colour to generate a deep impact out of pictures with little figural content.