IV Memory augmentations: How can memory capacities be improved?

Individual differences in working memory and aging

INDIVIDUAL DIFFERENCES IN WORKING MEMORY AND AGING*

Timothy A. Salthouse

This chapter reviews research conducted in my laboratory over the past 25 years in which aspects of working memory (WM) have been examined in adults of different ages. My thinking has been strongly influenced by Welford’s discussions of the role ofWM in age differences in cognitive functioning in his 1958 book Ageing and Human Skill. Although I don’t believe he used the term working memory, his description in the following passage of a fundamental age-related limitation clearly resembles contemporary ideas about the relation between aging and working memory:

It is conceived that data are somehow held in a form of short-term storage while other data are being gathered. Obviously, unless data can be so held, the amount of information that can be simultaneously applied to any problem is very small indeed. It would appear that in old people the amount that can be stored tends to diminish, and that what is stored is more liable than it is in younger people to interference and disruption from other activity going on at the same time. Such a decline in short-term retention would be capable of accounting for a very wide range of observed age changes in learning and problem solving ...

(p. 285)

As implied by the quotation above,WM has been ofinterest primarily because ofits relation to other aspects of cognition; in fact, WM can be defined as memory in the service of cognition. Because a wide range of cognitive tasks have been reported to have negative age relations, WM has been postulated to be a critical limiting factor, or a processing resource, that could be contributing to adult age differences in many different cognitive tasks. This view was articulated by Salthouse and Skovronek (1992) in their statement that:

|I]ncreased age seems to be associated with progressively greater difficulties when information must be simultaneously stored and either transformed or abstracted. This decreased ability to keep the intermediate products of earlier processing available, while also transforming or abstracting information, necessarily impairs the identification of abstract relations among sets of elements... Because the solution of many cognitive tasks requires abstraction of higher order relations, people with smaller working-memory capacities, such as older adults, are likely to be less successful than those with larger capacities, such as young adults.

(pp. 119-120)

Indirect evidence for a role ofWM in age differences in cognition is available in numerous studies in which larger age differences favoring young adults have been found when conditions in the tasks could be assumed to make greater demands on working memory. Examples of this phenomenon in my research are findings that the age differences in performance were larger with: more complex (i.e. alternating or second-order relations compared to simple sequential relations) series completion problems (Salthouse & Prill, 1987), larger angular discrepancy between cubes in a cube comparison task (Salthouse & Skovronek, 1992), more operations in spatial integration tasks (Salthouse, 1987, 1988; Salthouse & Mitchell, 1989), geometric analogy tasks (Salthouse, 1988), paper folding tasks (Salthouse, 1988,1992a; Salthouse et al. 1989b), integrative reasoning tasks (Salthouse, 1992a; Salthouse et al. 1989b) and cube assembly tasks (Salthouse, 1992a).

A more detailed investigation of the phenomenon of larger age differences at greater levels of task complexity with integrative reasoning and paper folding tasks was conducted by Salthouse et al. (1989b).The specific goal in that project was to investigate whether this “complexity effect” at least in part reflected a failure to preserve earlier information during the performance of the task. The procedure consisted of comparing decision accuracy when all relevant information was available in a single display with accuracy when the relevant information was distributed across multiple displays, and therefore information integration was presumably required. The critical finding was that the slopes of the functions relating decision accuracy to number of premises or number of folds were very similar when only a single premise or fold was relevant to the decision as when the relevant information was distributed across multiple displays, and that this was equally true at all ages. Because no integration is required when the relevant information is presented in a single display, poorer performance with additional premises or folds can be presumed to reflect inability to preserve earlier information during the presentation and processing of later information.These results are therefore consistent with the interpretation that most of the age differences in these tasks are attributable to a failure to retain information from early premises or folds during the presentation of subsequent premises or folds, and that they are unlikely to be due to a limitation associated with integrating information.

A related finding was reported by Salthouse, Mitchell, and Palmon (1989a) with a spatial integration task. In this case, no age differences were evident in the accuracy of merely recognizing information, but young adults were more accurate than older adults when the trials involved several displays but all of the relevant information was contained in a single display. As in the other study, these results imply that the age-related difficulty was in maintaining information during the performance of the task. In both situations the inability to preserve relevant information during the processing of other information is consistent with a failure of working memory.

 
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