Introduction

This chapter takes an overview of sensory systems and some of the general principles needed to understand them. It also takes a very brief look at the brain itself. Although the focus of the book is really at the input and encoding end of the brain, a knowledge of its basic structure is helpful in understanding how the various information processing pathways fit together.

Before looking at each of the principle sensory modalities possesed by humans it is intriguing to ask what senses might exist. Have animals learned to exploit every possible known physical force or interaction? On the other hand are there senses yet to be discovered, where there are no established physical mechanisms? The first of these questions is tractable, at least in principle, and §2.2 offers a framework. The second lies outside the scope of the book.

By starting with the physics the limits to information processing (§2.3) become apparent (and in fact animals are pretty good). Two overarching methodologies arise out of the physics viewpoint: the representation of signals, the subject of Chapter 3, a key idea in Horace Barlow's early work, and information theory, the subject of Chapter 4. They form the theoretical core of the book. But perception is not a simple one way transmission of information from eye or hand to brain. It is highly conditioned by what we know and what we expect. Thus what happens at the periphery depends to some extent on what happens deep inside the brain.