Memory:Superset Schemas, Part hierarchy, Slots Have More Schemas

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Cognitive Psychology PSY 504

Lesson 37

Memory

Representation of knowledge

Schema Theory

Superset Schemas

A special slot in each schema is its superset schema. In House, it is Building

Building has walls, roof, it is built on the ground etc.

Generalization hierarchies

Supersets schemas are basically hierarchies' that we saw with semantic networks. In this case of

schemas, they are sometimes called generalization hierarchies. These hierarchies provide a lot of

information about an object.

Part hierarchy

Schemas have another type of hierarchy, called part hierarchy. Thus, Parts of houses, such as

walls and rooms, have their own schema definitions. Stored with schemas for walls and rooms we

would find that these have windows and ceilings. Thus, using the part relationships, we would be

able to infer that houses have windows and ceilings.

Schemas are designed to facilitate making inferences about the concepts. If we know something

a house, we can use the schema definition to infer that it is probably made of wood or brick, and it

has walls, windows, and the like. However the inferential processes for schemas must be able to

deal with exceptions. It is also necessary to understand the constrains between slots of a

schemas.

Slots Have More Schemas

Part: Rooms

Rooms Schema would ensure that we know about rooms having windows and doors. So the

House would have windows by default.

Psychological Reality of Schemas

Brewer & Treyens (1981) provided an interesting demonstration of the effects of schemas in

memory inferences.

In that experiment, 30 subjects were brought individually to a room.

They were told it was an office of the experimenter and were asked to wait there. After 35

seconds the experimenter returned and took the subject to a nearby seminar room and subjects

were asked to write down everything they could remember about the room. The picture of

experimenter office or room is given below;

Experimental Room

Schema in Action

Prediction:

Subjects' recall would be greatly

influenced by their schema of what an

office contains. Subjects would do well at

recalling parts of schema.

Subjects would not do so well at recalling

items that are not part of office schema.

They should falsify recall things that are

part of the typical office but not of this one.

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Cognitive Psychology PSY 504

This is just the pattern of results that they found.

Results

The results of that experiment were

29 out of 30 recalled Chair, desk, and walls

Only 8 subjects recalled it had a skull

9 subjects recalled it had books which it did not

Memory for location is influenced by the person's schema for that location.

Schemas as a formalized for representing knowledge were developed in the field of artificial

intelligence, where they have proven very useful for organizing and reasoning about large and

complex knowledge bases. Although Brewer and Treyens indicated that humans have

knowledge representations like schemas, it is not clear that human schemas have all only the

properties associated with schemas as they are used in artificial intelligence.

Schemas Represent Natural Categories

One of the important features of schemas is that they allow variation in the objects that might fit a

particular schema. There are constraints on what typically occupies various slots of a schema,

but there are few absolute prohibitions. This suggests that if schemas encode our knowledge

about various object categories, we ought to see shading from less typical to more typical

members of the category as the features of the members better satisfy the schema constraints.

There is now considerable evidence that natural categories like birds have the kind of structure

that would be expected of a schema. Schemas can represent natural categories such as birds.

This would help explain the data collected by Rosch or prototypes and exemplars. She had

subjects rate the typicality of various members of a category on a 1 to 7 scale, 1 meant very

typical and 7 meant very atypical. Subjects rated some members as more typical than other

members. In the bird category, robin got an average of 1.1 and chicken rated on 3.8. Murder was

rated a very typical crime 1.0 whereas vagrancy was not 5.3. It would also help incorporate

propositional information. Schemas don't have boundaries.

Scripts: Event Schemas

It is not just objects and concepts that can be encoded by schemas. It is alos possible to

represent events as schemas. That is we can encode our knowledge about stereotypic events,

such as going to a movie, according to their parts- for instance, going to the theatre, buying the

ticket, buying refreshments, seeing the movie, and returning from the theater. Each of these can

be divided into its parts. So, as with object schemas, we have part hierarchies. We also have

generalization hierarchies going to a driver in theatre is a special case of going to a movie.

Events are represented by special schemas called `Scripts'.

Schank and Abelson (1977) at Yale University have worked extensively on event schemas or

scripts. They pointed out that many circumstances involve stereotypic sequences of actions. For

instance, people go to the restaurant and the stereotypic aspects of dinning at a restaurant might

be (given below), and represent the components of a script for such an occasion.

Going to a restaurant: Entering, Sitting down, Ordering, Eating, Paying the Bill, Exiting

Another example of event schema can be understood by the example of marriage. We know

there are different events or things that make difference between marriage and birthday party.

Like, at marriage there are colorful clothes, bride, groom, dholak, food (lunch or dinner) etc.

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