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The Modern Scientific Period 127

Working

Memory

Rehearsal

Long-Term

Memory

Sensory

Memory

Decay Response

Attention,

Pattern

Recognition

Sensory

Input Encoding

Retrieval

Figure 6.3 The standard model of information processing.

blocking others from access to consciousness. Organized in-
formation is stored briefly in working, or short-term, memory,
and some manages to get stored in long-term, or permanent,
memory. There is, of course, loss and distortion of informa-
tion along the way, so that what’s remembered is very seldom
a veridical record of what happened.
Only one aspect of contemporary cognitive psychology
was missing from Neisser and Atkinson and Shiffrin, the
computational metaphor of mind, then just making headway
in psychology.

The Program: Computation

In the information-processing perspective developed by
Broadbent, Neisser, and Atkinson and Shiffrin, the notion of
processingremained vague. Information itself is passive: It
has to be transformed and manipulated in order to effect
behavior. This problem was solved by the development of
another concept that today we take for granted, the computer
program. Again, the idea seems obvious, but did not come
into existence until the 1930s in the work of Alan Turing
(Hodge, 2000) and John von Neumann (MacRae, 1999).
Previously, all machines, including the calculators built by
Blaise Pascal, Gottfried Leibniz, and Charles Babbage, were
dedicated, single-purpose machines whose mechanical work-
ings defined the function they carried out. Computers, how-
ever, are general-purpose machines, capable of performing a
variety of tasks. Their operations are determined not by their
mechanical workings but by their programs, a series of in-
structions the computer carries out. Because they manipulate
information, programs are independent of their physical sub-
strate. A program written in BASIC (or any other computer
language) will run on any computer that understands BASIC,
whatever its physical makeup, whether it be an Apple, PC, or
a mainframe. As Turing (1950) pointed out, a human being
following a sequence of steps written on slips of paper is
functionally equivalent to a computer.
The computational approach to mind was complete and is
known in philosophy as functionalism. The mind is essen-
tially a computer program implemented in a meat-machine
(Clark, 2001) rather than a silicon-and-metal machine. The

program of the mind acts on and controls the flow of infor-

mation through the human information-processing system

the way a computer’s program controls the flow of informa-

tion through a computer. The program arrives at decisions

and controls the system’s—the body’s—behavior. The mind

is what the brain does (Pinker, 1998). Cognitive psychology

becomes a form of reverse engineering. In reverse engineer-

ing, computer scientists take a chip and without opening it

up, study its input-output functions and try to deduce what

program controls the chip’s processing. Often this is done to

imitate an existing chip without violating the patent holder’s

rights. In psychology, experiments reveal the human mind’s

input-output functions, and psychological theories attempt to

specify the computational functions that intervene between

input and output.

The Fruits of Computation: Cognitive Science

Mind Design and the Architectures of Cognition

Ironically, the first application of the computer conception of

mind arose not in psychology but in computer science, when

Alan Turing (1950) proposed that computer programs might

emulate human intelligence. Turing put forward no new

analysis of cognition but provided a now famous test by

which computer intelligence might be recognized. A person

interacts as in a chat room with two entities, one of which is

a human being and the other of which is a computer program.

Turing said that the program would have to be called intel-

ligent when the person could not tell if his or her conver-

sational partner was human or computer. As yet, no program

has passed the Turing test in the form Turing originally

suggested.

Obviously, constructing artificial intelligences has great

practical value. For cognitive psychology, the value of mind

design (Haugeland, 1981, 1985) is that it forces theorists to

think deeply and precisely about the requirements for intelli-

gent cognition. In an influential book, Marr (1982) specified

three hierarchically arranged levels at which computational

analysis takes place. In the case of artificial intelligence, the

levels define the job of making a mind, while in the case of

psychology—which studies an already evolved intelligence—

they define three levels of reverse-engineering psychological

theory. The levels are most readily described from the stand-

point of artificial intelligence.

• Thecognitive levelspecifies the task the AI system is to
  perform.


• Thealgorithm levelspecifies the computer programming
  that effects the task.