Pylyshyn: Against Imagery

From: Parker, Chris (
Date: Mon Nov 27 1995 - 08:41:25 GMT

Pylyshyn Chapter 3. The relevance of computation. The problem for me
was language, holding all the definitions of unfamiliar words while
trying to understand phrases that contained them.

Pylyshyn wants to maintain that computation is a literal model of
mental activity and not simply a simulation (p43 Chap2).

Both computation and cognition are rule governed processes (p57) yet
when we talk about similar functions we refer to similar input-output
pairs (p.50) in a formalist (not necessarily following the same set of
steps) and universal way that doesn't concern itself with internal
processes but can be applied to anything (p55)?? I'm confused. So what
do the rules apply to if it is not the internal process, or do the
rules only limit options rather than completely define mechanisms.

At this stage I lost the battle trying to understand "the Numerical

The computer or the organism are said to be responsible for any initial
goals (p79) but then environmental factors may occur which then share
the control of behaviour via feedback. I can see this OK for operand
conditioning, but if a fire alarm goes off while you are asleep, does
this mean that "your" goal was sleeping and that is modified by your
environment, and are there ever any pure initial goals?

The end of the chapter describes various control schemes including
Newell's novel, non-standard "production system" (p82-) which seemed to
me to be more understandable if fitted into a specific imaginary
example. I picked a runner on the starting block for an interpretation
of the scheme.

1) the runner is on the block waiting for the go and in her "production
system" there is a "workspace" which is a communication area and a set
of "productions" which are modular condition-action pairs. The
production system can only respond to a limited number of symbols (
originating from the environment or some earlier production) and then
evoke productions.

2) the starter pistol goes off and a symbol arrives in the workspace,
is recognised by satisfying some condition required by a specific
start-production, evoking the production which then results in the
action of starting (or "goal" to start). One symbol could represent a
whole group of other symbols to save limited workspace resources
(chunking). Other modular productions may be taking place at the same
or partially overlapping times.

Looking ahead to the next few chapters, there is some hint of what
comes next, ie functional architecture, which presumably is the
infrastructure for the production systems??

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