eyal@wisdom.BITNET (Eyal mozes) (07/01/86)
"The Evidence of the Senses" by David Kelley Louisiana State University Press, 1986, 262 pp., $27.50 ------------------------------------------------------- "The Evidence of the Senses: a Realist Theory of Perception" is a comprehensive philosophical treatment of perception, integrating classical and recent work in philosophy and psychology. To those who agree with its conclusions, it offers a sound, detailed framework for psychological, biological and AI work in perception; to those who don't, it offers an illuminating, profound and thought-provoking alternative theory. Dr. Kelley is formerly an assistant professor of philosophy and member of the Cognitive Science program at Vassar College, and currently a senior research fellow of the Ayn Rand Institute. His work is based on the philosophy of Objectivism. Almost all contemporary work in the theory of perception, including the writings of philosophers, is devoted to detailed consideration of specific issues, while taking for granted a wider context of basic philosophical assumptions. In sharp contrast to this procedure, Dr. Kelley makes his own basic assumptions fully explicit, defends them on general philosophical grounds, and only then applies them to specific issues. This makes it possible for him, when arguing against opposing views, to argue in terms of essentials by recognizing the basic - often hidden - assumptions on which these views and the arguments for them rely. A central theme of the book is the rejection of the "diaphanous model of awareness" - the view that awareness of objects can't be mediated by any process whose nature affects the way the objects appear; Dr. Kelley demonstrates that this model has been accepted, explicitly or implicitly, by almost all philosophers of perception since Kant, and it is the root of all three common views of perception: naive realism, which claims that our sensory apparatus is indeed diaphanous, and has no effect on the appearance of external objects; representationalism, which claims that we don't perceive external objects, but internal representations which give information about these objects; and idealism, which denies the existence of external objects. Chapter 1 sets up the general epistemological framework for the book; Dr. Kelley contrasts the diaphanous model with his own basic assumption, "the primacy of existence" - the principle that consciousness is the faculty of perceiving existence - which dispenses with the need for making any prior assumptions about how consciousness "should" work. Chapters 2 through 5 apply this principle to perception. Chapter 2 deals with the relation between perception and sensation; Dr. Kelley challenges the "sensationalist" approach - including its modern "computational" version - which claims that perception is a process of inference on sensations; he provides philosophical support for James Gibson's theory of "direct perception" - which holds that external objects are perceived directly, and that perception is a distinct form of awareness, not composed out of sensation - and answers the major criticisms against Gibson. Chapter 3 treats the relation of an object to its sensory qualities. The treatment is based on Ayn Rand's concept of "form of awareness", which designates all perceived qualities which are relative to the perceiver, distinguishing them from the perceived object and its intrinsic properties; Dr. Kelley uses this concept to demonstrate the consistency of perceptual relativity with direct realism, and illustrates the principle in a discussion of visual illusions and in a detailed treatment of colors; he then treats in this framework the traditional distinction of primary vs secondary qualities. Chapter 4 uses the principles established in previous chapters to answer the major arguments for representationalism; this includes a discussion of hallucinations and their relation to perception. Chapter 5 concludes the discussion of perception by giving a full definition - "perception is direct awareness of discriminated entities by means of patterns of energy absorption by sense receptors" - and discussing in detail each element in the definition and its implications for each of the five senses. Chapters 6 and 7 deal with perceptual knowledge, and the role of perception as the base of conceptual knowledge. Chapter 6 discusses the two common theories about the nature of justification: the "foundational" theory, which holds that propositions about experiential states are self-justifying and provide the foundation on which all other knowledge is built as a hierarchy; and the "coherence" theory, which holds that no single proposition can be justified outside the context of the rest of a man's knowledge, and that the only way to justify knowledge is by its self-consistency. Dr. Kelley identifies and challenges the common premise implicit in both these positions - "the propositional theory of justification", which holds that the only way to justify a proposition is by inference from other propositions. Chapter 7 deals with "perceptual judgments" - conceptual identifications of perceived entities and their attributes. Dr. Kelley's treatment of this subject is not complete, and he does not offer a full theory; but he does indicate the direction such a theory should take, and its implications for concept-formation. He discusses the relation between the perceptual discrimination of an entity and the reference to it in a perceptual judgment; the difference between "construction" and "discovery" models of concept-formation, and their relation to the possibility of justifying a perceptual judgment without need for an inference from other propositions; the implications of perceptual relativity for forming concepts of sensory qualities; and the autonomy of perception, answering the various philosophical and scientific arguments for the claim that perception and perceptual judgments are affected by previous knowledge or desires. The book is thoroughly organized, with careful attention to integration of the various issues and to illustration of the abstract points; the result is that, despite its highly technical content, it is very readable. All technical terms are carefully explained, and therefore, while reading the book will be easier for those with a previous background in the theory of perception, such a background is not necessary. The book contains extensive surveys of previous work and of different views and arguments, with heavy use of references, and this makes it an ideal starting-point for a study of the subject. In conclusion, I strongly recommend this book to anyone seriously interested in the theory of perception, and I think it is a must read for any psychologist, biologist or AI researcher whose work involves this subject. Eyal Mozes BITNET: eyal@wisdom CSNET and ARPA: eyal%wisdom.bitnet@wiscvm.ARPA UUCP: ..!ucbvax!eyal%wisdom.bitnet