Hume Studies

"Magic Buffalo" and Berkeley's Theory ofVision: Learning in Society David M. Levy Introduction Berkeley's Theory of Vision contains the remarkable claim that the perception ofdistance is learned by experience. This thesis is rooted in Berkeley's doctrine that the physical basic of optical perception is angular. An impression of angle ? impacts upon the optic nerve. The interpretative problem confronting an individual is that of reconstructing two pieces ofinformation, distance d and magnitude m, from one datum T. Let the ratio ofm/d form arctan T. How do we come to distinguish between the pair m1,d1 and the pair m2,d2 when m^d 1 = m2/d2 ? How do we distinguish big objects at a distance from small objects up close? The evidence Berkeley provides for this thesis is of a funny sort. He gives examples that we do, in fact, distinguish large distant objects from small near objects. Since the arctan of the pair m1, d 1 is by hypothesisthe sameas thatofthepairm2, d2thenrecognizingdistance must be alearned abihty. We cannotextractd and m from ? alone. The proper interpretation ofBerkeley's philosophy ofscience is a matter of considerable debate.1 Nonetheless, as a working theorist of visual perception he is afairly simple-minded falsificationist. Here is what he says: find a person born blind who comes by surgery to see. If that person can distinguish at a glance big distant objects from small near objects, 111 amend my theory.2 The literature on Berkeley's Theory ofVision can be fairly said to bifurcate between those who "see" the argument and those who don't. Berkeley's most important eighteenth century disciple, Adam Smith, extended Berkeley's teaching to encompass the remarkable claim that we learn to perceive our economic interest (Levy 1992a, 1992b). The negative reaction to Berkeley's theory starts in 1842 with Samuel Bailey who pronounced himself mystified by the very claim that we learn to perceive distance. The debate between Bailey and John Stuart Mill, a debate which has twentieth century counterparts, has all the characteristics ofpeople talking past each other. Volume XLX Number 1 223 DAVID M. LEVY The missing social dimension The problem, as I see it, with Berkeley's proposed critical test—stipulating his own doctrine—is that a blind person would grow up in a sighted community. Perhaps, if he grew up in a blind community, and most of the community became sighted at the same time he did, all the community might be able to perceive distance. The problem with Berkeley's test is that ifhe himself is correct about the importance ofheuristics in making the visual distinctions, the fate of one individual is somewhat beside the point. One individual surely cannot create the necessary heuristics. This learning requires some evolutionary social process. Thus, while Berkeley's thesis requires some claim about some verybasicsocial epistemology(Fuller 1988), his proposed test, asking about a blind person growing up in a community silently presumed to be sighted, does not take into account the social dimension oflearning. Having said this, it is easy to think ofa better test for Berkeley's theoryofvision. Let us find an entire community where life takes place without the visual perception of great distance. Take any individual from this community and ask Berkeleian questions. Now, we know the answer becausejust such a dialogue was reported thirtyyears ago. One society which fulfils the test criterion is that ofthe BaMbuti people who lived their life in a very dense African forest. The American anthropologist Colin Turnbull took his friend from the BaMbuti, Kenge, to the top of a hill. Here is TurnbuH's famous report: Then he saw the buffalo, still grazing lazily several miles away, far downbelow. He turned to me and said, "Whatinsects are those?" At first I hardly understood; then I realized that in the forest the range of vision is so limited that there is no great need to make an automatic allowance for distance when judging size. Out here in the plains, however, Kenge was looking for the first time Over apparently unending miles of unfamiliar grasslands, with not a tree worth the name to give him any basis for comparison. The same thing happened later on...