Download The Symbol Grounding Problem

The Symbol Grounding
Problem
A Symbol System is:
1.
2.
3.
4.
5.
6.
7.
8.
A set of arbitrary "physical tokens"
Manipulated on the basis of "explicit rules" that are
Likewise physical tokens and strings of tokens
Manipulation is based purely on the shape of the symbol
tokens
Consists of "rulefully combining" and recombining symbol
tokens
Primitive atomic symbol tokens
Composite symbol-token strings
The entire system is "semantically interpretable"
(Harnad, 1990)
A thermostat is not
a symbol system


Behaving in accordance with the rule
(implicit) is not necessarily following a rule
(explicit)
Semantic interpretability must be coupled
with explicit representation (2), syntactic
manipulability (4), and systematicity (8) in
order to be symbolic
Computers are symbol systems
A binary command
11000110
Says “copy memory in the register denoted by
the fifth and sixth positions to the register
denoted by the seventh and eighth positions”
Strong AI


Symbol strings capture mental
phenomenon
The symbolic level is independent of its
physical realization
Computationalism



A function is effectively computable if and
only if it is Turing computable
Persons are Turing machines
The Turing Test (or Total Turing Test) is
valid
The Turing Test
The Total Turing Test
The Total Turing Test
Computationalism




A function is effectively computable if and
only if it is Turing computable
Persons are Turing machines
The Turing Test (or Total Turing Test) is
valid
We will succeed in producing artificial
persons
Functionalism



The mind is what the brain does
If we find the key functions for intelligence
then we can create algorithms to perform
those functions
The functions capture mental phenomenon
Implications for Computers



ANY computable function can be
implemented as a lookup table
All human inputs could be mapped to
appropriate outputs
AI is about computing the functions that
underlie intelligence within the constraints of
reality
Grounding
Meaning is coupled to
environmental states
Meaning of ‘meaning’ #1
Appropriate action results from input
Meaning of ‘meaning’ #2
The agent knows why it produces a
particular action as a result of an input and
a given situation

–
–
–
–
Goals
Planning
Explicit knowledge of what states result from its
actions
Consciousness??
Meaning of ‘meaning’ #3

Symbols derive there meaning solely based
on what other symbols they are associated
with
Meaning of ‘meaning’ #4

The system contains concepts
(representations) that are discernable as
appropriately matching the environment
Coupled to the Environment

Several interpretations:
–
–
–
Shape of symbols capture some form of the
sensory input
The symbol system must physically exist within
the environment without “software”
The agent and environment mutually perturb each
other
Is a thermostat grounded?

Meaning #1
–

Meaning #2, 3, and 4
–

Yes
No
Coupled
–
Yes
Humans

Humans are grounded

Are humans symbol systems?
The Problem
Given a symbol system, can the symbols
be truly grounded?
"The question of whether a computer can
think is no more interesting than the
question of whether a submarine can
swim."
- E. W. Dijkstra
Criteria for Symbol Grounding
Lee McCauley
Definitions

Grounding – a representation is grounded
when the agent can reason about all of the
perceivable features of the entity represented
and can construct an instantiation of the
category
–
–
“can reason” does not mean “will reason”
“an instantiation of a category” does not mean
recreating a particular episode
Definitions (cont.)

Meaning – a grounded representation’s
associations with other grounded
representations
–
“associations” include all possible relationships




Logical (isa, hasa, etc.)
Temporal
Spatial
Implicit
What properties are necessary for
symbol grounding?




Primitives
Iconic Representations/Perceptual Symbols
Structural Coupling
Systemic Learning
Primitives

The agent must have some primitive
semantic elements
–
–
–

Perceptual primitives
Primitive motivators
Primitive actions
Why primitive motivators?
–
Value judgment is impossible without them.
Iconic/Perceptual Symbols

Every representation in the system needs to
be an icon of the features that feed into it
–
–
–
This is very much (although not exactly) like
Barsalou’s perceptual symbols
No matter what depth the representation might be
at, it “resembles” the salient features that
comprise it
There are no truly arbitrary symbols
Structural Coupling/Synchronization



The agent is embodied within its environment
The agent can change the environment
through its actions in such a way that the
environment’s impact on the agent is
modified (mutual perturbation)
Without this, the links through iconic
representations break down
Systemic Learning

Systemic learning means that the structure of the
representations change, not just the contents
–
Examples:



Neural networks
Some symbolic systems (would be possible in Lisp)
For any complex enough agent in a complex enough
environment to be interesting, the iconic
representations and embodiment require a systemic
learning mechanism to change how they think (not
just what they think)
Motivational adaptation (a form of
Systemic Learning)


Any sufficiently complex environment/agent
interaction has intermediate goals that are
not expressed by the primitive motivators
A grounded agent should be able to modify
its motivational structure in a way that
increases its ability to satisfy its primitive
motivators
Properties: What’s missing or
shouldn’t be present?





Primitives
Iconic Representations/Perceptual Symbols
Structural Coupling
Systemic Learning
??
Quotes

"It is possible to store the mind with a million
facts and still be entirely uneducated."
-- Alec Bourne

"Knowledge must be gained by ourselves.
Mankind may supply us with the facts; but the
results, even if they agree with previous ones,
must be the work of our mind."
-- Benjamin "Dizzy" Disraeli (1804-81), [First Earl of
Beaconsfield] British politician
Quotes (cont.)

“Computers are useless. They can only
give you answers.”
-- Pablo Picasso (1881 - 1973)

"The best computer is a man, and it's the
only one that can be mass-produced by
unskilled labor."
-- Wernher Magnus Maximilian von Braun
(1912-77), German-born American rocket
engineer
Quotes (cont.)
“What is real? How do you define real? If you're
talking about what you can feel, what you
can smell, what you can taste and see...then
real is simply ... electrical signals interpreted
by your brain.”
- Morpheus, The Matrix
Quotes (cont.)

"The factory of the future will have two
employees: a man and a dog. The man's
job will be to feed the dog. The dog's job
will be to prevent the man from touching
any of the automated equipment."
-- Warren G. Bennis (b. 1925), American
writer, educator, University of Southern
California sociologist