Introduction

It is well known that sensory information on a number of modalities is arranged in a spatial “map” in biological brains, such that information from similar sensors arrives close together in the cortex. For example, much visual sensory information is represented in a map in the primary visual cortex, which is arranged roughly as the image coming in through the eyes. The human somesthetic cortex receives touch information arranged so that sensors which are close to each other on the body tend to be represented in close areas in the cortex. Similarly the bat auditory cortex receives information arranged by frequency, so that close frequencies produce a similar response.

A common feature of these feature maps is that the representation scale is non-uniform: some areas are magnified when compared with others. For example, the area of the visual cortex which corresponds to the fovea is magnified much more than that for peripheral vision (in terms of angle on the retina). The cortical area given over to touch sensors in the lips and fingers is proportionally much greater than that given over to the back. The bat has a much magnified representation for frequencies around its echo-location frequency than elsewhere (Anderson and Hinton, 1981).

These magnified areas of feature maps all seem to correspond to receptors which are proportionally more important than others. Information from the fovea is required for discernment of detail in an object; information from the fingertips or lips is needed for fine manipulation of tools or food; while the detailed frequency differences around the bat's echo-location frequency are important if it is to find and catch its prey.