Biological Functions and Perceptual Content

T 1 HE computational approach to perception has become increasingly prominent over the last decade or so.The recent publication of David Marr's Vision' makes computational theories accessible to philosophers, who may now judge for themselves how unified, wide-ranging, powerful, and intellectually satisfying the program has proved to be.A striking feature of computational theories of perception, from the philosophical point of view, is that they employ the intentional characterizations of perceptual states insisted upon by Edmund Husserl and other phenomenologists.Most other scientific treatments of perception concentrate on the external causes of perception and how they result in the stimulation of the sensory organs, the neurological organization of perceptual systems, and the discriminatory resources afforded to organisms by the perceptual systems.Though not ignoring these important topics, the computationalists characteristically regard perceptual states as representing the external world and seek to explain them under this rubric.Marr claims, for example, that vision represents three-dimensional surfaces as composed of "generalized cones," and tries to show how such representations may be derived from representations of two-dimensional outlines of the sort found in line drawings and how the latter may, in turn, be extracted from a pattern of optical stimulation present on the retina.Most philosophers today, and most computational theorists, are materialistically inclined: they are not inclined to allow that there * A version of this paper was read to the philosophers at Dalhousie Universitv.I am grateful to them all for lively discussion