PSSH & Lot

The Physical Symbol System Hypothesis

Other people argue that geology/(other science) is the most influence for physical things, cognitive sciences argue that a physical symbol system has the necessary and sufficient means for general intelligent action

Alan Newell/Herbert Simon

• Necessity claim = Anything capable of intelligent action is a physical symbol system

• Sufficiency claim = Any (sufficiently sophisticated) physical symbol system is capable of intelligent action

Physical symbol system has the necessary and sufficient means for general intelligent action.

Which combinations of symbols are recursive and follow logic

1. Symbols are physical patterns.

2. These symbols can be combined to form complex symbol structures.

3. They physical symbol system contains processes for manipulating symbols and complex symbol structures.

4. The processes for generating and transforming complex symbol structures can themselves by represented by symbols and symbol structures within the system.

Thinking & The Physical Symbol System Hypothesis

The essence of intelligent thinking is the ability to solve problems by evaluating options (e.g. chess)

• Intelligence is the ability to work out, when confronted with a range of options, which of those options best matches certain requirements and constraints

• Problem-solving is relative to a problem-space (search-space in your book)

Basic components of a representation

• Description of given situation

• Initial state: starting point

• Operators for changing the situation

• Goal state: desired end situation (e.g. capturing the king)

• Tests to determine whether the goal has been reached

Problem space: branching tree of achievable situations

defined by potential application of operators to initial situation

Traveling salesperson problem

• Initial State: A salesperson needs to visit multiple cities starting and ending in a specific city (e.g., Berkeley).

• Goal State: Visit all cities as quickly and efficiently as possible.

General Problem Solver (GPS) (example of a heuristic)

1. Evaluate the difference between the current state and the solution state.

2. Identify a transformation that reduces the difference between the current state and the solution state.

3. Check that the transformation in step 2 can be applied to the current state.

   1. If it can, then apply it and go back to step 1.

   2. If it can't, then return to step 2.

Heuristic search: evaluate the most promising moves without checking every possible move.

• Means-end analysis: reducing the difference between the current and solution states.

Heuristic search and algorithms

The Physical Symbol System Hypothesis is a reductive characterization of intelligence

• It is only illuminating if physical symbol systems are not themselves intelligent

• This means that the physical symbol systems must function algorithmically

• Breaks down symbols into rules; system must not be intelligent/must be mechanical

  • This is important because it would just be intelligent

  • PSSH functions by step-by-step 

  • How they manipulate symbols according to rules

Physical Symbol Systems → Language of Thought

Jerry Foder: The content of a thought depends on external relations: on the way that the thought is related to the world. not on the way that it is related to other thoughts

Language of Thought Hypothesis (Fodor)

The basic symbol structures in the mind that carry information are sentences in an internal language of thought (sometimes called Mentalese and generally abbreviated as LoT). Information processing works by transforming those sentences in LoT.

3 Basic Claims

1. Psychological states are realized by physical states

   1. applies to both personal-level states (e.g. beliefs) and sub-personal states (e.g. states of the early visual system)

2. Psychological states represent the world

3. Psychological states enter into causal relations

   1. with other psychological states and ultimately with behavior

Propositional Attitudes

1. Attitudes toward proposition

   1. Proposition: “That person will drown”

   2. Proposition: “It is snowing in St. Louis”

2. Attitudes: Belief, desire, other psychological states

Intentional realism treats beliefs and desires as the sorts of things that can cause behavior through a special type of causation:

Causation by content

• Depends on representations

  • Physical objects (e.g., patterns of sound waves)

  • Semantic properties (e.g., beliefs and desires)

Formal Properties vs. Semantic Properties

How can the brain be an information-processing machine

• if it is blind to the semantic properties of the representation?

• If all it can process are the formal properties of representations?

Language of Thought Hypothesis: Relation between Syntax and Semantics

Claims:

1. Causation through content takes place through causal interactions between physical states.

2. These physical states have the structure of sentences, and their sentence-like structure determines how they are made up and how they interact with each other.

3. Causal transitions between sentences in the LoT respect the semantic relations between the meanings of those sentences.

Syntax pertains to the rules governing symbols and their combinations, analogous to

grammar in natural languages. Semantics concerns the meanings of symbols and what determines the truth or falsehood of sentences.

The Russian Room Argument & Turing Test

The Russian/Chinese Room Argument (Searle):

Searle objects to the above model

Argument: No machine built according to the physical symbol system hypothesis could possibly be capable of intelligent behavior

Searle argues the Russian room does not genuinely understand Russian, demonstrating only an illusion of intelligence.

• The Russian room manipulates symbols based on their syntactic properties, aligning with the physical symbol system hypothesis.

• The semantic properties of input symbols (questions) and output symbols (answers) are preserved through correct syntactic manipulation.

Turing Test cannot adequately prove real intelligence

• it only measures indistinguishable responses from a human and a machine.