Knowledge and the flow of information

Book reoiews

296

Fred 1. Dretske, Knowledge and the flow of information. MIT Press, 1981. $18.50 (hard cover).

Cambridge,

MA:

This book is a major endeavor to deal with some of the main problems in cognitive psychology, philosophy, and linguistics. These problems are related to definitions of concepts, semantics, belief and knowledge. forth D) analyzes these problems within a classic information

Dretske (hencetheoretic frame

of reference, i.e., in terms of reduction of uncertainty. D’s approach, for all its qualities, makes one wonder as to its outcome, given the slightly obsolete flavor of information theory in present day psychology, philosophy Within psychology (the reviewer’s field of research), certainly

and linguistics. few researchers

would think of information

to analyze

decades

ago, when it was applied to explanations

approach

mentioned

as a powerful

the

This

concepts

theory

explain

then had quite

above.

instrument

Information

a behavioristic

theory

had

of the structure flavor.

However,

its

and peak

of language. it should

be

stated right at the beginning that this book certainly does not belong in a behavioristic program; on the contrary, it strongly argues against behavioristic explanations

of concepts,

beliefs,

meaning,

and knowledge.

It should

also be

stated that, although the book certainly has a wide scope, it has a restricted ambition in the sense that it is confined to what is called de re knowledge. Roughly speaking, this means that this book is about ‘simple’ knowledge (or perceptual knowledge, in D’s terminology). It is concerned with such expressions as “this is red”, “this is a bird”, but not with statements like “I believe that my uncle is taller than your brother ever will be” (de ditto knowledge). The restriction to perceptual knowledge should not be regarded as something that is done on a principled basis, but is rather due to practical considerations. D’s

ultimate

cognitive

aim is to incorporate

and semantic

In the following, interesting One

and/or

essential

a theory

theory about complex

I will concentrate

of information

into

a genuine

types of knowledge.

on points

that I have found especially

problematic. point

in D’s

framework

is that

he distinguishes

between

informational relationships and causal relationships. Event A may contain information about event B, without event A being the cause of event B. And event A may cause event B, without B containing any information whatsoever about event A. A clarification can be given by one of D’s own examples. A series of well-known studies of frogs have shown that certain neurons react to small, moving bugs on a light background. This makes the frog catch the bug with its tongue: event A causes event B. According to D, this situation does not imply that the neurons receive the information that there is a bug. To be able to claim this, one must analyze what else might produce the same response in the frog’s neurons. The possible antecedents of the event must be known. If so, it is possible to determine the information value of the event. Since D wants to develop a genuine theory of information which is a theory

Book reviews

297

of knowledge and semantics, he adopts the view that communication theory can tell us something about the content of a signal, not only about the signal itself. This is achieved by arguing that information about quantities can tell us something about what may or may not be the content of the message. Furthermore, meaning is defined as something that is conventionally agreed upon leading to the view that language is the most important vehicle for conveying meaning. Meaning should be carefully distinguished from information. If a person is sweating and trembling, an observer might believe that he is nervous. But sweating and trembling does not mean a person is nervous, although his appearance carried the information that he is. In D’s terms, “signals may have a meaning but they curry information” (p. 44). Of course, natural languages are a means of communication where meaning and information often coincide. D also makes a distinction between analogue and digital forms of information. Sensory information is supposed to be in analogue form while cognitive states, processes, etc., are supposed to be in digital form. Cognitive activity is seen as an abstraction of the sensory information, a conversion from analogue to digital form. In this respect, it is a very conventional view upon the essential characteristics of cognitive activities and concepts (see, for instance, Lindsay and Norman 1977) but dressed in an unconventional terminology. For psychologists, it should now be clear that D’s theory is a philosophical counterpart to certain psychological theories about perception, especially that presented by Gibson (D explicitly refers to Gibson’s work). A central idea is that in sensory experience, there is all the information one needs for cognitive information (recognition, classification, identification, judgment, etc.). If information is to be classified as conceptual or cognitive, it must have been extracted from the sensory structure, which is analogical, and converted into a digital form. D then defines three levels, or orders, of intentionality. Only the highest order of intentionality contains a semantic content in the form of propositions. (However, all information processing systems have some order of intentionality.) The semantic content of a structure is the information which is carried in digital form and a belief is something that has a semantic-propositional content as its exclusive content. Furthermore, the beliefs are generated by the way the system encodes the information. The semantic structure of the system may consequently be viewed as the system’s interpretation of incoming information. Again, D’s principal view of a cognitive system is quite familiar to many psychologists in the sense that a typical feature of cognitive systems is that they do not reproduce a faithful picture of the input. Instead, such a system overlooks differences and thereby entails a loss of information. This process is, of course, ‘abstraction’ and a general feature of concepts and conceptual thinking. In relation to the above-mentioned distinction between causal and informa-

tional relationships, D introduces a very important qualification of the definition of semantic content. He states that a semantic content in no way carries information messenger. cause and empirical person’s

about its cause and origin or, expressed in another way, about the Consequently, belief states do not carry information about their origin. This statement opens up many interesting psychological questions.

beliefs?

Is it the case that there are no traces of the sources of a this means, among other things, that there is no

If so,

difference between beliefs whose origin information. Related topics have recently within psychology.

The most common

is visual as compared to verbal been the subject of much research

hypothesis

tion has been that there is only a stable memory a message, terminology,

not for the particular

concerning

verbal informa-

for the meaning

style or surface

structure.

or content

(Phrased

of

in D’s

this means that there is no trace of the source of the information).

Lately, however, a number of papers have been published that point to the contrary (e.g. Bates et al. 1980; Hjelmquist, in press). These findings have no direct relevance for the appropriateness of D’s theory, but they highlight the problem of what actually can constitute beliefs in D’s sense. The next step in D’s reasoning is that the cognitive content of a semantic structure heritage.

is solely determined by its informational origin or its informational In D’s terms, this is an “etiological” account of cognitive content in account. In an etiological account, the to a “consequentionalistic”

contrast emphasis is not on the consequences that the cognitive content or belief has on its environment; it is not effect-oriented. Instead, D defines a concept as a type of internal control

According structure

structure,

whose

semantic

content,

when

instantiated,

exercises

over the output of the system. to D, two concepts

without being different

in cognitive

structure

together

can be different

with respect

with respect to semantic

with a similarity

in semantic

content. content

to cognitive A difference means that

two concepts are compositionally different. For example, two persons might believe that something is a square (semantic content), but one of them may lack the notion that a square is a four-sided figure (cognitive structure). One important aspect of D’s theory is that it allows a person to have a concept without knowing its essential properties. (It is worthy of notice that D thus maintains a traditional view of concepts as defined by necessary features.) D claims that it is possible for a person to have the concept “robin” without knowing that it is a bird. This is so, despite the fact that receiving the information that S is a robin necessarily means that one receives the information that S is a bird. The distinction between these two types of information is that the information that “S is a robin” is digitalized, whereas the information that “S is a bird” is not. It should be noted that D does not actually give any hints to what the necessary properties really are for something to be a concept; for example, what is necessary for something to constitute the concept robin? (A similar lack of motivation for another basic idea in D’s theory was pointed

Book reoiews

out in connection

299

with his analysis of belief.)

It should be stressed here that the informational heritage of concepts only holds for primitive concepts. Complex concepts, for example, including those of non-existing in fact,

things such as unicorns,

they carry

no information

do not have an informational at all. This

is a somewhat

heritage; frustrating

contention, since it is not obvious how D’s theory can coherently take care of primitive as well as complex concepts. Further development of this point will maybe come in D’s future work. However, for primitive concepts there is no way of escaping the informational heritage and D is careful to point this out by examples and argumentation. His chief example is that of a person who does not know the concept “red”,

but is taught to use the word red in response

to a white object’s

surface,

viewed under a red light. D argues that the concept this person learns to apply to the white surface under the red light and to other, properly red objects, is not the concept

“red”

but rather that of “looking

that applies both to objects is a consequence

red”, or maybe

something

that actually are, and those that only look red. This

of D’s view that a concept

is determined

by its informational

heritage. Among the strange consequences of this view is that of people having different concepts, but still communicating efficiently with each other and functioning in social interaction without obvious problems and obstacles. That they should do this on the basis of totally different concepts is, at least from a psychological point of view, counter-intuitive. The main problem with D’s theory is thus to explain how people develop concepts that are, if not identical, at least sufficiently alike, to make social relations and communication possible. D leaves this problem open, assuming something like the ‘normal’ situation, which results in “normally trained subjects” (p. 228). Dretske thus leaves it to people’s physical and cultural that are, in essential aspects, problem.

From a cross-cultal

surroundings to develop conceptual structures similar for all. This is by no means a trivial point of view, it might be questioned

whether,

in

D’s view, one could claim that people from different cultures actually have the same concepts. According to D, this can only be evaluated by looking at what information dilemma

is available in different

as, according

informational

heritage

cultures.

to D, semantic

But this puts us in something

concepts

of a

and beliefs are only defined by

and not by their consequences

on human

behavior,

or

by their effects on the environment. However, at least some of the concepts that people hold are clearly developed to efficiency (a point of view which is also acknowledged by D). With respect to environmental consequences, the concepts that are necessary for survival and efficient adjustment of he species, are the same for all human beings (unless one wants to claim that there are essential differences between people living in different parts of the world). It would have been interesting to have D’s opinions on what such concepts actually are, and also what concepts are culture-specific and of no relevance

Book reorews

300

for efficient adaptation and adjustment. Taking D’s example of concept attainment seriously could lead us to adopting an ‘inverted’ version of the Whorfian because

hypothesis.

In D’s theory,

they speak different

people

languages,

have different

but because

cepts, even though they speak the same language, D’s form of relativism much more palatable concepts by definition strange,

however,

starts

world

views, not

they have different

con-

use the same vocabulary,

out from conceptual

differences.

etc.

As such, it is

than the kind of relativism proposed by Whorf, since can be said to represent different world views. What is

is that differences

between

two concepts

do not seem

to

matter for communication purposes, as pointed out above. This may have something to do with the fact that D does not give us a principled account of the necessary

similarities

or differences

for instances

to belong

to one and the

same concept, at the same time as he accepts a necessary-properties account of concepts. Nevertheless, D has written an interesting and provocative book that impresses with its persistence in pursuing the limits of a theoretical On a very general level, his conclusions often fit in well with current cognitive

paradigm. theories of

psychology. Erland Hjelmquist Dept. of Psychology University

of Goteborg

Goteborg,

Sweden

References Bates,

E., W. Kintsch,

ellipsis in texts: Learning Gibson,

and Memory

Fletcher memory

and V. Guiliani, experiments.

E., in press. Memory

P.H.

and D.A.

1980.

Journal

The role of pronominalization

of Experimental

Psychology.

and

Human

6: 616-691.

J.J., 1966. The senses considered

Hjelmquist, Lindsay,

CR.

Some

Norman.

as perceptual

for conversations. 1972.

Human

systems.

Discourse information

Boston:

Houghton.

Processes. processing.

New York:

Academic

Press.

Fernando Miho-Garcb, Early reading acquisition: Six psycholinguistic studies. Washington, DC: Georgetown University Press, 1981. $5.95.

case

In this book, Miito-Garces (hereafter, MG) presents his observations on six preschoolers who ‘acquired’ reading at home by the Lado method and at a Montessori kindergarten by a phonics method. The Lado method consists of a series of 11 books for teaching preschoolers to read either in English or in Spanish, progressing from single words (Book One) to sentences (Book Two), and finally to stories (Book Six). Lado’s is a whole-word method: a word is