Symbolic behavior

Some of your ideas

• Symbols: creating and understanding them; finding meaning in things
• Meaning, representation, reference, ...
• Separating name and thing
• But what about other animals? A matter of degree?
• Multiple interpretations, layers of meaning
• Rules
• Conventionality
• Arbitrariness: anything can mean, the shape doesn't matter
• Separation from here-and-now
• Can be exchanged (portability, compactness)
• Modeling
• Reflection, awareness
• Modularity
• Relation of abstractions to one another
• Pictures, religion, superstition, poetry
• Language
  • Symbols the medium for L
  • Symbols a prerequisite for L
  • L a prerequisite for symbols

History

• Predicate logic
• Saussure's sign
• Language of thought (Fodor)
• Physical Symbol System Hypothesis (Newell and Simon)

Physical Symbol Systems

(as summarized by Harnad)

• A set of arbitrary physical tokens (scratches on paper, holes on a tape, events in a digital computer, etc.) that are
• manipulated on the basis of explicit rules 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 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).

Other properties

• 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.
• Knowledge is usually programmed into the cognitive system by someone who has a theory of how knowledge is organized. Learning is also possible, but it is not central to most models.
• 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.

Examples of representation

• Object constants, relation constants ('have'), function constants ('lex'), variables ('Buyer')
• If you're producing an English sentence about an action that agent performs on a patient, and you want to "focus" on the patient, you can produce a passive sentence by making the patient the subject, making BE the tensed verb, putting the verb for the action in the past participle, and optionally including the agent in a BY-phrase.

  passivization = \
  (('assert',
    set((('agent', 'Ag'), ('patient', 'Pt'), ('action', 'Ac'),
         ('time', 'Tm'), ('focus', 'Ag')))),
   ('sentence',
    ('lex', 'Pt'),
    ('morph', 'be', ('tense', 'Tm')), ('morph', ('lex', 'Ac'), 'pp'),
    'by', ('lex', 'Ag')))
  

• If a buyer buys some merchandise from a seller for a price, the merchandise now belongs to the buyer and the price to the seller.

  buying = \
  ((('have', 'Buyer', 'Price', 'Sit'),
    ('have', 'Seller', 'Merch', 'Sit')),
   (('have', 'Buyer', 'Merch',
     ('buy', 'Buyer', 'Seller', 'Merch', 'Price', 'Sit')),
    ('have', 'Seller', 'Price',
     ('buy', 'Buyer', 'Seller', 'Merch', 'Price', 'Sit'))))
  

© 2006. Indiana University and Michael Gasser. www.indiana.edu/~gasser/Q450/symbols.html 2006-09-05