What is a representation?

Representations

Pictures, maps photos, symbols, logos, cartoons, animations, movies, written text, diagrams are all examples of external representations.

What is a representation?

• A representation is something that stands for something else.
• It must convey some aspects of the represented world.

Palmer's (1978) 5 features of a representational system:

1. what the represented world is
2. What the representing world is
3. What aspects of the represented world are being modeled
4. What aspects of the representing world are doing the modeling
5. What are the correspondences between the two worlds

Representational system

	Represented world	Representing world
		i	ii	iii
Objects		A		15
		B		4
Properties	height	Not directly represented	Line length	Numeric range
Relations	taller than	TALLER (A,B)	LONGER THAN	GREATER THAN

Mental Representations

What about representations in the mind?

• What features do they have?

Theories of mental representations are about representations of brain states and not of the world.

• represented world is brain states
• representing world is theoretical structures
• examples of theoretical structures include mental images, mental models, rules, analogies, concepts, schemas

Theories of mental representation - (i) mental images

What form do mental images take?

• Not pictures in the mind that are read by a little person inside the head (the homunculus fallacy).
• Not an infinite number of photos stored away in a library (the slide projector model).

So what are they?

• Images are generated, dynamic and transient.
• Images are used in a whole range of mental activities (solving problems, memorising information, daydreaming).

Theory of mental images

Kosslyn (1983) has developed a theory of mental imagery which uses the "brain is like a computer" metaphor.

Mental events (images, thoughts) are conceived as corresponding to the functional operations of a computer.

Images can be manipulated in a computer as symbols are, with operations such as rotation and deformation, and then displayed.

But who watches the display?

Theories of mental representations - (ii) Propositions

Most cognitive scientists have focused on theorising about propositional representational systems.

Knowledge about the world is assumed to be represented as a set of discrete symbols.

• These include relations (e.g. on, near, besides)

Knowledge is stored in terms of concepts, categories and properties of these.

• e.g. cat: animal, pet, furry, 4 legs, tail, purrs.

Concepts are represented by formal statements.

• e.g. is-a(cat, animal), under(cat, table), has(cat, 4 legs)
• On(c1, t1) [cat c1 is on table t1]

Other kinds of knowledge representation

Knowledge in long term memory is assumed to be represented in a variety of propositional formats.

• e.g. schemas, rules, semantic nets

Declarative vs. procedural knowledge

• Declarative is assumed to be represented as a formal proposition, e.g. rule.
• Procedural is assumed to entail an active process or procedure.

Example: semantic nets

Combine propositional statements with a graphical representation giving proximity to related bodies of knowledge.

References

• Aitkenhead, A.M. and Slack, J.M. (1985) Issues in Cognitive Modelling. Chapters 2, 3, 4.
• Kosslyn, S. (1983) Ghosts in the Mind's Machine.

Maintained by: David Young
With thanks to Yvonne Rogers