Symbolic behavior: your ideas (and mine)

Q450/B490

• Representation: symbol and thing represented
• Conventionality, arbitrariness
• Words as symbols
• Constraints on the form of the symbol?
• Other animals: difference a matter of degree or kind?
• Reference
• Separation from the hear-and-now
• Can be exchanged (portability, compactness)
• Symbolism in art and literature
• Non-linguistic symbols: faces, religious symbols
• Symbols and thought/reasoning

History

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

Physical Symbol Systems (Newell and Simon)

(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 of symbol systems

• 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

• Representational primitives
  • object constants ('book23')
  • relation constants ('have', 'give')
  • function constants ('lex' (return the lexicalization of the argument))
  • variables ('?buyer')
• If you're producing an English sentence about an action that an 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',
   {['agent', '?ag'], ['patient', '?pt'], ['action', '?ac'],
    ['time', '?tm'], ['focus', '?ag']}),
   ('sentence',
    ('lex', '?pt'),
    ('morph', 'be', ('tense', '?tm')),
    ('morph', ('lex', '?ac'), 'pp'),
    'by', ('lex', '?ag')))
  

• When a buyer buys some merchandise from a seller for a price, in the situation before the buying, the buyer has the price and the seller has the merchandise, and in the situation that results from the buying, the buyer has the merchandise and the seller has the price.

  buying = \
  ((['have', '?buyer', '?price', '?situ'],
    ['have', '?seller', '?merch', '?situ']),
   (['have', '?buyer', '?merch',
     ['buy', '?buyer', '?seller', '?merch', '?price', '?situ']],
    ['have', '?seller', '?price',
     ['buy', '?buyer', '?seller', '?merch', '?price', '?situ']]))