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
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"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
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