Individual Differences in Learning and Memory

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INDIVIDUAL DIFFERENCES IN LEARNING AND MEMORY

Individual differences in learning and memory abilities have fascinated people since they began thinking about how their minds work. In discussing his wax metaphor of memory, Plato (1953) noted that memories made of "pure and clear [wax] … easily learn and easily retain," whereas those made of "muddy and of impure wax [have] … a corresponding defect in the mind." Plato realized that people differ in what they learn and remember and in how well they do both. This is certainly true at the extremes, but how relevant is it over the normal range of memory abilities?

The psychological research supports four main conclusions about individual differences in learning and memory (Bors and MacLeod, 1996). First, people differ in what they know, their knowledge base. Second, people differ in their working memory capacity, the ability to hold information in consciously accessible memory. Third, people possess and invoke different strategies for learning. Fourth, people differ in the retrieval efficiency with which they can summon information from more permanent, long-term memory. To these can be added one "negative conclusion": There do not appear to be consistent sex differences in learning and memory ability, although women and men may choose to learn different information (which affects their knowledge base). This entry examines these four main conclusions in more detail.

Knowledge Differences

Standard intelligence tests (Wechsler, 1945, 1958) measure two aspects of memory, the first being general knowledge and vocabulary. People differ in their breadth and depth of knowledge. Consider the "paradox of the expert": A simple theory might claim that forgetting is caused by interference among related concepts in memory. This would imply that someone who knows more about a topic should be more subject to forgetting in that domain. But if this were true, how would one ever become an expert in a domain? One resolution is that people integrate their knowledge so that related ideas are joined, supporting rather than competing with each other (Smith, Adams, and Schorr, 1978).

Indeed, those with high knowledge learn and retain new facts in that domain more easily than do those with low knowledge (Voss, Vesonder, and Spilich, 1980). Furthermore, experts seem especially superior in remembering the important information. Popular memory metaphors of libraries or warehouses do not fit comfortably here. Instead, think of memory as a scaffolding: The more memories that are attached to the structure, the more places there are to attach new memories. The scaffolding may even guide people to where it would be best to attach each new memory.

People differ not only in what they know and how much they know, but also in how that knowledge is organized (Coltheart and Evans, 1981). Because retrieval relies heavily on the association between facts and ideas, organization influences how people retrieve their knowledge. An individual who has two facts directly connected in memory should be able to get from one to the other more quickly than someone who must go through multiple "way stations." Part of coming to understand a domain better is reorganizing one's knowledge more appropriately.

Each person is unique in part because of what he or she knows, both in terms of autobiographical knowledge and general world knowledge. Thus, content of memories is one major source of individual differences. The other three differences all relate more to how people acquire, store, transform, and use that knowledge—that is, the cognitive processes.

Capacity Differences

Probably the best known individual differences dimension in learning and memory is that of the capacity of conscious, working memory. This is the other aspect of memory that is directly measured in standard intelligence tests: memory span (Dempster, 1981). Individuals have a sharp limitation on how much they can consciously think about and retain at one time. Even in the normal range of intelligence, not everyone's span is the same. What causes these differences? There seem to be two main mechanisms underlying working memory span—the ability to identify the specific elements to be held and the ability to retain their order (Humphreys et al., 1983). Speed of scanning through the information held in working memory does not seem to differ reliably across individuals (Hunt, 1978), although speed is affected by age (Salthouse, 1996).

It is tempting to view span differences as irrelevant to the "real world." After all, how often do people listen to a string of items and then repeat them back? In fact, holding information in working memory is something people do constantly and rely upon heavily. Meredyth Daneman and Patricia Carpenter (1980; Hannon and Daneman, 2001; Miyake, 2001) showed that span differences have powerful implications for how successfully people read. Those with larger spans in reading (or in listening) show better comprehension of what they read: They can hold previous sentences in mind more easily, and thus assemble the overall meaning more effectively. This has led Marcel Just and Carpenter (1992) to a theory of comprehension based on working memory capacity.

Individual differences in working memory capacity do not influence only language. These effects are also apparent in spatial processing (Shah and Miyake, 1996) and in enumeration (Tuholski, Engle, and Baylis, 2001). Human ability to acquire and execute skills (Ackerman, 1987) is also a function of working memory capacity (Perlow, Jattuso, and Moore, 1997). Individual differences in working memory and attention, in fact, appear to be intimately linked (Kane, Bleckley, Conway, and Engle, 2001).

Learning Strategy Differences

There are many different ways to learn, from rote repetition to complex mnemonics. All learning involves recoding: Information must be transformed from its perceived form into a form suitable for remembering. It is well established that people differ in their speed and in their efficiency of recoding (Gagné, 1967). But people also differ in their learning styles, in which processes they use, and in when they use them (Sternberg and Zhang, 2001).

Studies of learning style suggest that, at a global level, learners emphasize either overall comprehension or specific detail, appearing to be either conclusion oriented or description oriented (Schmeck, 1983). Those who emphasize overall comprehension engage in deeper processing; those concerned with specific detail focus more on surface processing. Ordinarily such a strategic difference favors those who undertake deeper processing. Thus, note taking in a classroom induces deeper processing and better retention of important information.

Another illustration is individual differences in reported imagery ability (Richardson, 1999). People vary in whether they use more language-based or picture-based strategies to learn and remember. Indeed, research suggests that visual memory can be quite independent of verbal memory. People who recognize faces or pictures well will not necessarily remember what they read better than will people with poorer visual memory. Yet the widely held belief that some people learn best visually and others learn best auditorily has not been strongly supported experimentally. One can make sense of this by realizing that verbal skills need not be auditory.

There are many other techniques and strategies for learning. Thus it seems quite reasonable to suppose that different individuals learn most effectively using different strategies. However, evidence to support this intuition has been notoriously difficult to obtain. Usually a strategy that improves one person's learning also improves another person's learning. What may differ, then, are the choices that people make, a metacognitive issue as Christian Schunn and Lynne Reder (2001) argue, relating successful choice to working memory capacity. How people select optimal process (es) from their repertoire for a particular learning situation may be one of the most critical differences of all.

Retrieval Speed Differences

Retrieval time for information in working memory is not a reliable source of individual differences. Given the sharp capacity limitation, the small content of working memory is easily searched. But the same is not true of long-term memory, where all of a person's knowledge is stored. If the average person knows upward of 10 billion facts, as some scientists speculate, how can he or she find any one of them quickly? Even searching at the impossibly fast rate of 1 millisecond per fact, it would take months to find any single fact.

Extensive research (Hunt, 1978) has shown that different people retrieve information from long-term memory at different rates. Consider a very simple retrieval: It takes longer to determine whether two letters have the same name for Aa than for aa or AA. Presumably this is because long-term memory access is required only for Aa, where the two are not physically identical. On average, this retrieval time is about 80 milliseconds, but high-ability individuals are faster than low-ability individuals by about 30 milliseconds or more. A naive critic might say, "But this is a tiny difference." Consider reading, however. If one were to lose 30 milliseconds for every letter read in this entry, this time would quickly add up. And that is just for such highly learned facts as the letters of the alphabet; the problem must be vastly greater for more complex and unfamiliar types of knowledge. If the elementary processes are not executed as efficiently by one individual as by another, the cost for learning and memory as a whole can be large. Indeed, it is quite clear that working memory capacity also affects retrieval from long-term memory (Rosen and Engle, 1997).

Conclusion

The goal of this brief sketch has been to localize four of the more crucial individual differences in learning and memory and to provide some of the evidence for these differences. Of course, there are many other differences in how people learn and remember, but these are usually more isolated and less characteristic of the memory system as a whole. Scientists hope to find ways of recognizing these differences in educational systems around the world in order to realize the full potential of learning skills.

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Colin M.MacLeod

Learning and Memory