Mind, Body, World- Foundations of Cognitive Science, 2013a

new physical state, the direction it moves, the symbol that it writes—is controlled by
a machine table that depends only upon the current symbol being read and the current
state of the device. One uses a Turing machine by writing a question on its tape,
and setting the machine head into action. When the machine head halts, the Turing
machine’s answer to the question has been written on the tape.
What is meant by the claim that different information processing devices are
available? It means that systems that are different from Turing machines must
also exist. One such alternative to a Turing machine is called a finite state automaton
(Minsky, 1972; Parkes, 2002), which is illustrated in Figure 3-9. Like a Turing
machine, a finite state automaton can be described as a machine head that interacts
with a ticker tape. There are two key differences between a finite state machine and
a Turing machine.
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Instructions
State
State
Symbol
Machine Head
Figure 3-9. How a finite state automaton processes the tape. Note the differences
between Figures 3-9 and 3-8.
First, a finite state machine can only move in one direction along the tape, again one
cell at a time. Second, a finite state machine can only read the symbols on the tape;
it does not write new ones. The symbols that it encounters, in combination with the
current physical state of the device, determine the new physical state of the device.
Again, a question is written on the tape, and the finite state automaton is started.
When it reaches the end of the question, the final physical state of the finite state
automaton represents its answer to the original question on the tape.
It is obvious that a finite state automaton is a simpler device than a Turing
machine, because it cannot change the ticker tape, and because it can only move in
one direction along the tape. However, finite state machines are important information
processors. Many of the behaviours in behaviour-based robotics are produced
using finite state machines (Brooks, 1989, 1999, 2002). It has also been argued
that such devices are all that is required to formalize behaviourist or associationist
accounts of behaviour (Bever, Fodor, & Garrett., 1968).
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