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Cognitive Science 6: Physical Symbol Systems and the Language of Thought


This is the first chapter attempting to address how information is processed within and across cognitive systems.

The physical symbol system hypothesis

Defined as “A physical symbol system has the necessary and sufficient means for general intelligent action” (146).

A physical symbol system is made of four basic ideas:

  1. Symbols are physical patterns
  2. These symbols can be combined to form complex symbol structures
  3. The physical symbol system contains processes for manipulating complex symbol structures
  4. The processes for generating and transforming complex symbol structures can themselves be represented by symbols and symbol structures within the system (147).

The physical patterns could be what makes up the 0’s and 1’s in a computer. There is no 0 or 1 physically existing, but these are symbols for physical differences within the computer.

Intelligence only comes into play when there’s a search space- a list of possible answers from which a sufficient answer must be chosen, like a list of chess moves, one of which fulfills the sufficient answer of a check mate.

From physical symbol systems to the language of thought

Fodor’s language thought hypothesis is an example of an application of the physical symbol system to explaining how human minds work. Language, for Fodor, is the basic structure of thought.

Fodor’s view depends on intentional realism, which states that beliefs and desires are real and cause behavior. E.g. my desire to eat and my belief that there is a hoagie in the fridge causes my action to get it. A difficulty is in bridging from formal properties (physical properties) from semantic properties (properties of sentences/language). This is solved by looking at how computers translate binary into non-binary outputs. The mind is also a computer, and translates certain types of information in an analogous way.

The Chinese room argument

John Searle’s Chinese room argument is an attempt to falsify any attempt to explain intelligent behavior using a physical symbol system. It tries to show an example of a successful (the exactly correct outputs) physical symbol system that has no intelligence or understanding. The Chinese room argument also works against the Turing test for intelligence.

One response is to say that the person in the room doesn’t understand Chinese, but the system as a whole does.

A second response is to say the Chinese room doesn’t provide the outputs one would need to reasonably understand Chinese. That involves coordination with others, carrying out Chinese instructions, and conversations. Embedding a good enough Chinese room in a robot that could do the above would perhaps be sufficient to call understanding Chinese. Searle just says that this still doesn’t count. Stopping when one sees the symbol for stop doesn’t count as understanding, just as a conditioned automatic response.

The related symbol grounding problem looks at how words and thoughts gain meaning to the speakers.

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