10.2 Long-Term Memory: Categories and Structure
- Describe and contrast explicit and implicit memory.
- Describe how aspects of long-term memory are measured.
- Describe how long-term memory may be structured.
Although it is useful to hold information in sensory and short-term memory, we also rely on our long-term memory (LTM). Long-term memories fall into two broad categories: those we are consciously aware of — explicit memories — and those that we are able to access and use without conscious awareness — implicit memories. This section will explain these two broad types of long term memory and show how they are measured.
When we assess memory by asking a person to consciously remember things, we are measuring explicit memory. Explicit memory — also referred to as declarative memory — refers to knowledge or experiences that can be consciously remembered. There are two types of explicit memory: episodic and semantic. Episodic memory refers to the firsthand experiences that we have had (e.g., recollections of our high school graduation day or of the fantastic dinner we had in New York last year). Semantic memory refers to our knowledge of facts and concepts about the world (e.g., that the capital city of Canada is Ottawa and that one definition of the word “affect” is “the experience of feeling or emotion”).
Explicit memory is assessed using measures in which the individual being tested must consciously attempt to remember the information. A recall memory test is a measure of explicit memory that involves bringing from memory information that has previously been remembered. We rely on our recall memory when we take an essay exam, because this test requires us to generate previously remembered information. A multiple-choice test is an example of a recognition memory test, a measure of explicit memory that involves determining whether information has been seen or learned before.
Your own experiences taking tests will probably lead you to agree with the scientific research finding that recall is more difficult than recognition. Recall, such as required on essay exams, involves two steps: first generating an answer, and then determining whether it seems to be the correct one. Recognition, as on multiple-choice tests, only involves determining which item from a list seems most correct (Haist, Shimamura, & Squire, 1992). Although they involve different processes, recall and recognition memory measures tend to be correlated. Students who do better on a multiple-choice exam will also, by and large, do better on an essay exam (Bridgeman & Morgan, 1996).
While explicit memory consists of the things that we can consciously report that we know, implicit memory refers to knowledge that we have but do not remember how we acquired it. Implicit memory — also referred to as nondeclarative memory — refers to things we can remember without awareness of having learned them. Implicit memory is important because it can affect our behaviour without us being aware of how.
A way of measuring implicit memory is to measure relearning (Nelson, 1985). Relearning involves coming back to something that you had forgotten to see how easily you can learn it again. For example, many English-speaking Canadian students take some French courses but then have few opportunities to use what they have learned and, consequently, forget it. If you studied another language when you were younger and were to study that language again, you’d learn the vocabulary much faster the second time around, even though you are not consciously remembering the first time you learned each word.
Procedural memory refers to our often knowledge of how to do things. Procedural memory can be implicit, because we are not required to consciously process the procedural steps for engaging in the activity (e.g., brushing your teeth or making toast). When we walk from one place to another, speak to another person in English, dial a cell phone, or play a video game, we are using procedural memory. Procedural memory allows us to perform complex tasks, even though we may not be consciously aware of the decision-making needed to perform them. A good example of this is driving a car on a very familiar route; you may perform the complex task of pulling out to pass a car and then return to the right-hand lane with no conscious awareness of the procedures involved.
A second type of implicit memory involves classical conditioning (see Chapter 6. Learning), in which we learn — without effort or awareness — to associate neutral stimuli, such as a sound or a light, with another stimulus, such as food, which creates a naturally occurring response, such as enjoyment or salivation. The memory for the association is demonstrated when the conditioned stimulus (e.g., the sound) begins to create the same response as the unconditioned stimulus (e.g., the food) did before the learning.
Implicit memory can also be shown by studies on priming, or changes in behaviour as a result of experiences that have happened frequently or recently. Priming refers both to the activation of knowledge (e.g., we can prime the concept of kindness by presenting people with words related to kindness) and to the influence of that activation on behaviour (e.g., people who are primed with the concept of kindness may act more kindly).
One measure of the influence of priming on implicit memory is the word fragment test, in which a person is asked to fill in missing letters to make words. You can try this yourself. First, try to complete the following word fragments, but work on each one for only three or four seconds. Do any words pop into mind quickly?
- _ i b _ a _ y
- _ h _ s _ _ i _ n
- _ o _ k
- _ h _ i s _
Now, read the following sentence carefully:
- “He got his materials from the shelves, checked them out, and then left the building.”
Returning to the list above, try again to make words out of the word fragments.
You might find that it is easier to complete fragments 1 and 3 as “library” and “book,” respectively, after you read the sentence than it was before you read it. However, reading the sentence didn’t really help you to complete fragments 2 and 4 as “physician” and “chaise.” This difference in implicit memory probably occurred because as you read the sentence, the concept of “library” and perhaps “book” was primed, even though they were never mentioned explicitly. Once a concept is primed, it influences our behaviours. For example, if you are primed by the information you receive in the news, it may, unbeknownst to you, prompt your decision-making later on about buying a product, voting for a candidate, and so on.
Our everyday behaviours are influenced by priming in a wide variety of situations. Seeing the flag of our home country may arouse our patriotism, and seeing a student from a rival school may arouse our competitive spirit. These influences on our behaviours may occur without our being aware of them. The key point about implicit memory is that memories we are not consciously aware of can still affect our feelings and behaviour.
Priming outside awareness influences behaviour
One of the most important characteristics of implicit memories is that they are frequently formed and used automatically, without much effort or awareness on our part. In one demonstration of the automaticity and influence of priming effects, John Bargh, Mark Chen, and Lara Burrows (1996) conducted a study in which they showed undergraduate students lists of five scrambled words, each of which they were to make into a sentence. Furthermore, for half of the research participants, the words were related to stereotypes of the elderly. These participants saw words such as the following:
- In Victoria retired live people
- Bingo man the forgetful plays
The other half of the research participants also made sentences, but they made sentences from words that had nothing to do with elderly stereotypes. The purpose of this task was to prime stereotypes of elderly people in memory for some of the participants but not for others.
The experimenters then assessed whether the priming of elderly stereotypes would have any effect on the students’ behaviour — and indeed it did. When the research participant had gathered all of their belongings, thinking that the experiment was over, the experimenter thanked them for participating and gave directions to the closest elevator. Then, without the participants knowing it, the experimenters recorded the amount of time that the participant spent walking from the doorway of the experimental room toward the elevator. Participants who had made sentences using words related to elderly stereotypes took on the behaviours of the elderly by walking significantly more slowly as they left the experimental room (see Figure 10.6).
To determine if these priming effects occurred out of the awareness of the participants, Bargh, Chen, and Burrows (1996) asked still another group of students to complete the priming task and, this time, to indicate whether they thought the words they had used to make the sentences had any relationship to each other or could possibly have influenced their behaviour in any way. These students had no awareness of the possibility that the words might have been related to the elderly or could have influenced their behaviour.
The structure of long-term memory: Categories, prototypes, and schemas
Memories that are stored in LTM are not isolated but rather are linked together into categories — networks of associated memories that have features in common with each other. Forming categories, and using categories to guide behaviour, 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.” Additionally, when people have learned lists of words that come from different categories, they do not recall the information haphazardly. If they have just remembered the word “wrench,” spreading activation means they are more likely to remember the word “screwdriver” than they are to remember a word in a different category such as “daffodil” (Srull & Wyer, 1989). We can take advantage of spreading activation as students: we are able to link new words to previously learned concepts with a larger knowledge base because there is more capacity to activate concepts within a category.
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. However, most categories are not so well defined, and the members of the category may 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? In psychology, for example, what falls into the category “models of memory”?
Members of categories, even those with defining features, can be compared with the category prototype, which is the member of the category that is most average or typical of the category. Some category members are more prototypical of, or similar to, the category than others (see Figure 10.7). For instance, some category members (e.g., robins and sparrows) are highly prototypical of the category “birds,” whereas other category members (e.g., 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).
Mental categories are sometimes referred to as schemas — patterns of knowledge in long-term memory that help us organize information. We have schemas about objects (e.g., a triangle has three sides and may take on different angles), about people (e.g., Sam is friendly, likes to golf, and always wears sandals), about events (e.g., the particular steps involved in ordering a meal at a restaurant), and about social groups (i.e., stereotypes). Schemas can be used as mental shortcuts; if seeing someone or something activates a schema, we may think we know more about the thing or person specifically than we actually do.
Schemas are important in part because they help us remember new information by providing an organizational structure for it. Read the following paragraph, and then try to write down everything you can remember:
The procedure is actually quite simple. First you arrange things into different groups. Of course, one pile may be sufficient depending on how much there is to do. If you have to go somewhere else due to lack of 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 few things at once than too many. In the short run, this may not 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 foresee any end to the necessity for this task in the immediate future, but then one never can tell. After the procedure is completed, one arranges the materials into different groups again. Then, they can be put into their appropriate places. Eventually, they will be used once more, and the whole cycle will then have to be repeated. However, that is part of life. (Bransford & Johnson, 1972, p. 722)
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.
- Explicit memory refers to experiences that can be intentionally and consciously remembered, and it is measured using recall, recognition, and relearning. Explicit memory includes episodic and semantic memories.
- Implicit memory refers to the influence of experience on behaviour, even if the individual is not aware of those influences. Implicit memory is evident in procedural memory, classical conditioning, and priming.
- Information is better remembered when it is meaningfully elaborated.
- Long-term memory is structured by categories, prototypes, and schemas.
Exercises and Critical Thinking
- Plan a course of action to help you study for your next exam, incorporating as many of the techniques mentioned in this section as possible. Try to implement the plan.
- Next time you go shopping, try to create a mental list using the knowledge you have gained in this section rather than relying on a written list.
- Make a list of some of the schemas that you have stored in your memory. What are the contents of each schema, and how might you use the schema to help you remember new information?
Figure 10.6. Used under a CC BY-NC-SA 4.0 license.
Figure 10.7. Mac OS X Lion’s New Wallpapers by Halil Gokdal is used under a CC BY-NC-SA 2.0 license; Orange Cat on the Wall by Tambako The Jaguar is used under a CC BY-ND 2.0 license; Siamese (Cat) by Radosiewka is in the public domain; Gatos Pelados by Rogelio A. Galaviz C. is used under a CC BY-NC 2.0 license.
Bargh, J. A., Chen, M., & Burrows, L. (1996). Automaticity of social behavior: Direct effects of trait construct and stereotype activation on action. Journal of Personality & Social Psychology, 71, 230–244.
Bransford, J. D., & Johnson, M. K. (1972). Contextual prerequisites for understanding: Some investigations of comprehension and recall. Journal of Verbal Learning & Verbal Behavior, 11(6), 717–726.
Bridgeman, B., & Morgan, R. (1996). Success in college for students with discrepancies between performance on multiple-choice and essay tests. Journal of Educational Psychology, 88(2), 333–340.
Haist, F., Shimamura, A. P., & Squire, L. R. (1992). On the relationship between recall and recognition memory. Journal of Experimental Psychology: Learning, Memory, and Cognition, 18(4), 691–702.
Nelson, T. O. (1985). Ebbinghaus’s contribution to the measurement of retention: Savings during relearning. Journal of Experimental Psychology: Learning, Memory, and Cognition, 11(3), 472–478.
Rosch, E. (1975). Cognitive representations of semantic categories. Journal of Experimental Psychology: General, 104(3), 192–233.
Srull, T., & Wyer, R. (1989). Person memory and judgment. Psychological Review, 96(1), 58–83.