Topography in the auditory and other sensory systems

Abstract

The goal of the presentation will be to describe and discuss basic and common features of sensory representations in the auditory, somatic, and visual systems of mammals. Each system consists of a number of interconnected representations of a sensory surface. Most representations are simple or first‐order transformations, although higher‐order representations occur. Advanced mammals may have more representations than primitive mammals, so that only some are homologous across species, while others evolve in certain lines. The borders of adjoining representations typically are matched for the same locations along a sensory surface. Such congruent borders suggest an activity dependent developmental mechanism. Within some representations for some species, there is now considerable evidence for modular organization. Thus, primary visual cortex of monkeys has bands of orientation, specific neurons, and occular dominance neurons. Area 3b of somatosensory cortex of monkeys has bands of slowly adapting and rapidly adapting neurons, and primary auditory cortex in cats has bands for alternating types of binaural neurons. These types of modular organization may not exist, however, in the same fields in a number of other mammalian species. Representations can be characterized in terms of fidelity and receptive field scatter, receptive field size, and proportions devoted to equal divisions of the receptor surface (magnification factors). When such features are considered, general rules emerge.