Physical Symbol Systems
- A Physical Symbol System (Newell, Simon, Pylyshyn, summarized by Harnad) is ...
- a set of arbitrary physical tokens (scratches on
paper, holes on a tape, events in a digital computer, etc.; things like
Bunny, distance, x, if, ()
that are...
- manipulated on the basis of explicit rules
if Veggie(x) and at(x, loc): execute(approach(loc))
that are...
- likewise physical tokens and strings of tokens.
The rule-governed symbol-token manipulation is based...
- purely on the shape of the symbol tokens (not
their "meaning"), i.e., it is purely syntactic, and consists of...
- rulefully combining and recombining symbol
tokens. There are...
- primitive atomic symbol tokens (including those
representing variables, conveying "sameness" independent
of particular content) and...
- composite symbol-token strings.
The entire cognitive system and all its parts — the atomic tokens,
the composite tokens, the syntactic manipulations
(both actual and possible) and the rules — are all...
- semantically interpretable: The syntax can be
systematically assigned a meaning
(e.g., as standing for objects, as describing states of
affairs).
How PSSs work
- Processes happen sequentially.
- There is a central controller which
coordinates the activities of the modules of the cognitive
system and selects among candidate processes at each point in time.
- The cognitive system interacts with the world through interfaces to
perception and action, which operate very differently from
the internal (cognitive) system.
- Time is often mapped onto space; that is, the cognitive system has
simultaneous access to all of a pattern of some length (word,
sentence, etc.).
Inputs may also be presented sequentially, but the problem of temporal
short-term memory is side-stepped because the inputs are
preprocessed.
- Knowledge is usually programmed into the
cognitive system by someone who has a theory of how
knowledge is organized.
Learning is also possible, but models that learn usually start
intelligent.
