Psychological Reality of Schema?

Consider the many things we know about houses, such as
● Houses are a type of building.
● Houses have rooms.
● Houses can be built of wood, brick, or stone.
● Houses serve as human dwellings.
● Houses tend to have rectilinear and triangular shapes.
● Houses are usually larger than 100 square feet and smaller than 10,000 square feet.
The importance of a category is that it stores predictable information about specific instances of that category. So when someone mentions a house, for example, we have a rough idea of the size of the object being referred to.
Semantic networks, which just store properties with concepts, cannot cap- ture the nature of our general knowledge about a house, such as its typical size or shape. Researchers in cognitive science (e.g., Rumelhart & Ortony, 1976) proposed a particular way of representing such knowledge that seemed more useful than the semantic network representation. Their representational struc- ture is called a schema. The concept of a schema was first articulated in AI and computer science. Readers who have experience with modern programming languages should recognize its similarity to various types of data structures. The question for the psychologist is: What aspects of the schema notion are ap- propriate for understanding how people reason about concepts? I will describe some of the properties associated with schemas and then discuss the psycho- logical research bearing on these properties.
Schemas represent categorical knowledge according to a slot structure, in which slots are attributes that members of a category possess, and each slot is filled with one or more values, or specific instances, of that attribute. So we have the following partial schema representation of a house:
House
● Isa: building
● Parts: rooms
● Materials: wood, brick, stone
●Function: human dwelling 
● Shape: rectilinear, triangular
● Size: 100–10,000 square feet
In this representation, such terms as materials and shape are the attributes or slots, and such terms as wood, brick, and rectilinear are the values. Each pair of a slot and a value specifies a typical feature. Values like those listed above are called default values, because they do not exclude other possibilities. For instance, the fact that houses are usually built of materials such as wood, brick, and stone does not mean that something built of cardboard could not be a house. Similarly, the fact that our schema for birds specifies that birds can fly does not prevent us from seeing ostriches as birds. We simply overwrite this default value in our representation of an ostrich.
A special slot in each schema is its isa slot, which points to the superset. Basically, unless contradicted, a concept inherits the features of its superset. Thus, with the schema for building, the superset of house, we would store such features as that it has a roof and walls and that it is found on the ground. This information is not represented in the schema for house because it can be in- ferred from building. isa links can create a structure called a generalization hierarchy.
Schemas have another type of structure, called a part hierarchy. Parts of houses, such as walls and rooms, have their own schema definitions. Stored with schemas for walls and rooms would be the information that they have win- dows and ceilings as parts. Thus, using the part hierarchy, we would be able to infer that houses have windows and ceilings.
Schemas are abstractions from specific instances that can be used to make inferences about instances of the concepts they represent. If we know something is a house, we can use the schema to infer that it is probably made of wood, brick, or stone and that it has walls, windows, and ceilings. The inferential processes for schemas must also be able to deal with exceptions: We can understand that a house without a roof is still a house. Finally, it is necessary to understand the constraints between the slots of a schema. If we hear of a house that is underground, for example, we can infer that it will not have windows.
■ Schemas represent concepts in terms of supersets, parts, and other attribute-value pairs.
Psychological Reality of Schemas The fact that schemas have default values for certain slots or attributes provides schemas with a useful inferential mechanism. If you recognize an object as being a member of a certain category, you can infer—unless explicitly contradicted—that it has the default values associated with that concept’s schema. Brewer and Treyens (1981) provided an interesting demonstration of the effects of schemas on memo- ry inferences. Thirty participants were brought individually to the room. Each was told that this room was the office of the experimenter and was asked to wait there while the experimenter went to the laboratory to see whether the previous participant had finished. After 35 s, the experimenter returned and took the waiting participant to a nearby seminar room. Here, the participant was asked to write down everything he or she could remember about the experimental room. What would you be able to recall?
Brewer and Treyens predicted that their participants’ recall would be strongly influenced by their schema of what an office contains. Participants would recall very well items that are default values of that schema, they would recall much less well items that are not default values of the schema, and they would falsely recall items that are default values of the schema but were not in this office. Brewer and Treyens found just this pattern of results. For instance, 29 of the 30 participants recalled that the office had a chair, a desk, and walls. Only 8 participants, however, recalled that it had a bulletin board or a skull. On the other hand, 9 participants recalled that it had books, which it did not. Thus, we see that a person’s memory for the properties of a location is strongly influ- enced by that person’s default assumptions about what is typically found in the location. A schema is a way of encoding those default assumptions.
■ People will infer that an object has the default values for its cate- gory, unless they explicitly notice otherwise.