ATCS (lec02) Mental Representation

What is a representation?

• map of sussex campus?
• sussex crest?
• photo of sussex library?

Representations

Criteria

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

Palmer's features

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

• For example, we might represent a big lion as a vertical thing of a certain length (and a small tortoise as a much smaller vertical thing).
• But what about abstract things such as relationships (e.g., taller-than)?

Mental Representations

• What features do they have?

• 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

• 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?
• No-one, since mental images are not pictures but symbols in a matrix.

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

• e.g. schemas, rules, semantic nets

• 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

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.