Overview

Vision in the animal world is unbelievably diverse. The compound eyes of insects have a resolution of a few cycles per degree (cpd), whereas eagle resolution is almost a hundred times greater at almost 200 cpd. Insects frequently have colour vision and some have ultra-violet sensitivity, whereas many mammals have weak colour vision and few are trichromats like man. Most mammals are dichromats (Ahnelt & Kolb, 2000). Stereopsis is present in mammals, but not all animals. On the other hand the flicker fusion frequency (§7.5), the frequency at which images blend together as in the cinema, is about three times greater in flies than in man.

In the face of such diversity, what are the useful information processing principles in common? They are as discussed in Chapters 1 and 2: the nature of the physical stimulus and its fundamental limitations; transduction, the conversion of light to an electrical signal; noise and information; and information streaming. These principles are what the designer of robots or virtual reality systems needs to take away. They find use in human computer interaction and the compression of sensory data for optimal trade-offs between bandwidth and perceptual quality. This chapter deals with the overall architecture, later chapters look at colour and object properties, movement and binocular vision. So the plan is to start right at the optics of the eye and track upwards as visual data is streamed into the brain.