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The Structure of LTM: Categories, Prototypes, and Schemas

23 September, 2015 - 17:15

Memories that are stored in LTM are not isolated but rather are linked together into categories— networks of associated memories that havefeatures in common with each other. Forming categories, and using categories to guide behavior, is a fundamental part of human nature. Associated concepts within a category are connected through spreading activation, which occurs when activating one element of a category activates other associated elements. For instance, because tools are associated in a category, reminding people of the word “screwdriver” will help them remember the word “wrench.” And, when people have learned lists of words that come from different categories (e.g., as in Retrieval"), they do not recall the information haphazardly. If they have just remembered the word “wrench,” they are more likely to remember the word “screwdriver” next than they are to remember the word “dahlia,” because the words are organized in memory by category and because “dahlia” is activated by spreading activation from “wrench” (Srull & Wyer, 1989). 1

Some categories have defining features that must be true of all members of the category. For instance, all members of the category “triangles” have three sides, and all members of the category “birds” lay eggs. But most categories are not so well-defined; the members of the category share some common features, but it is impossible to define which are or are not members of the category. For instance, there is no clear definition of the category “tool.” Some examples of the category, such as a hammer and a wrench, are clearly and easily identified as category members, whereas other members are not so obvious. Is an ironing board a tool? What about a car?

Members of categories (even those with defining features) can be compared to the category prototype, which is themember of the categorythat is most averageor typical of the category. Some category members are more prototypical of, or similar to, the category than others. For instance, some category members (robins and sparrows) are highly prototypical of the category “birds,” whereas other category members (penguins and ostriches) are less prototypical. We retrieve information that is prototypical of a category faster than we retrieve information that is less prototypical (Rosch, 1975). 2

Mental categories are sometimes referred to as schemas—patterns of knowledgein long-term memory that help us organize information. We have schemas about objects (that a triangle has three sides and may take on different angles), about people (that Sam is friendly, likes to golf, and always wears sandals), about events (the particular steps involved in ordering a meal at a restaurant), and about social groups (we call these group schemas stereotypes).

Schemas are important in part because they help us remember new information by providing an organizational structure for it. Read the following paragraph (Bransford & Johnson,1972) 3 and then try to write down everything you can remember.

The procedureis actually quite simple. First you arrange things into different groups. Of course, one pile may be sufficient depending on how mucthere is to do. If you haveto go somewhere else due to lacof facilities, that is the next step;otherwise you are pretty well set. It is important not to overdo things. That is, it is better to do too fethings at oncthan too many. In the short run this maynot seem important, but complications can easily arise. A mistake can be expensive as well. At first the whole procedure will seem complicated. Soon, however, it will become just another facet of life. It is difficult to foreseany end to theecessity for this task in theimmediate future, but then one never can tell. After the procedure is completed, one arranges the materials into different groups again. Then thecan be put into their appropriate places. Eventually thewill be used oncmorand the whole cyclwill then havto be repeated. However, that is part of life.

It turns out that people’s memory for this information is quite poor, unless they have been told ahead of time that the information describes “doing the laundry,” in which case their memory for the material is much better. This demonstration of the role of schemas in memory shows how our existing knowledge can help us organize new information, and how this organization can improve encoding, storage, and retrieval.