Academic journal article Memory & Cognition

Age-Related Differences in Immediate Serial Recall: Dissociating Chunk Formation and Capacity

Academic journal article Memory & Cognition

Age-Related Differences in Immediate Serial Recall: Dissociating Chunk Formation and Capacity

Article excerpt

We assessed the contribution of two hypothesized mechanisms to impaired memory performance of older adults in an immediate serial recall task: decreased temporary information storage in a capacity-limited mechanism, such as the focus of attention, and a deficit in binding together different components into cohesive chunks. Using a method in which paired associations between words were taught at varying levels to allow an identification of multiword chunks (Cowan, Chen, & Rouder, 2004), we found that older adults recalled considerably fewer chunks and, on average, smaller chunks than did young adults. Their performance was fairly well simulated by dividing attention in younger adults, unlike what has been found for long-term associative learning. Paired-associate knowledge may be used in an implicit manner in serial recall, given that younger adults under divided attention and older adults use it well despite the relatively small chunk capacities displayed by these groups.

The decline in memory with old age (e.g., Craik & Jennings, 1992) seems to affect only some memory functions. Episodic recall is especially affected, a finding for which competing explanations have been suggested (see Light, 1991). In the present study, we will examine the effects of aging on working memory, defined broadly as the limited amount of information kept accessible concurrently for use in cognitive tasks (Cowan, 1999; cf. Baddeley & Logie, 1 999). Older adults usually show a deficit in the shortterm or immediate memory tasks used to examine working memory, although the size of the deficit depends on the specific task (Kausler & Puckett, 1979; Salthouse & Babcock, 1991; Wingfield, Stine, Lahar, & Aberdeen, 1988).

We will focus on the effect of aging on immediate serial recall. In such tasks, recall is to follow the order in which items were presented. Although Miller (1956) pointed out that young adults can recall lists of about seven items, subsequent work has qualified that statement in various ways. Baddeley, Thomson, and Buchanan (1975) noted that the accuracy of recall depended on the number of items that an Individual could recite hi about 2 sec, and subsequent work indicated that the recitation rate slowed with aging (Kynette, Kemper, Norman, & Cheung, 1990), in keeping with a cognitive-slowing theory of aging (Salthouse, 1 996). Other factors that are critical in serial recall, for which the effects of aging remain uncertain, include (1) a basic capacity limit and (2) a process of chunking. It is age-related changes in these two factors that will be investigated here.

A Basic Capacity Limit

Broadbent (1975) argued that there is a basic working memory capacity of three separate items. Miller's (1956) estimate of about seven items was said to depend on the contribution of mnemonic processes that complement the basic capacity. Illustrations of this basic capacity in young adults included the number of items that could be repeated with 0% error and the number of items recalled without hesitation in a single burst from a large category in longterm memory. For example, individuals asked to recall all of the states within the United States do so in bursts of about three items (cf. Graesser & Mandler, 1978). Cowan (2001) obtained a similar estimate of average young adult capacity of between three and five separate items, in a literature review of diverse procedures related to working memory. The effect of aging on this basic capacity in serial recall is unknown, although there is evidence of a decline in capacity with aging, as estimated in a visual array comparison task (Cowan, Naveh-Benjamin, KiIb, & Saults, 2006), and evidence that visual array comparisons and verbal serial recall may depend, in part, on a common, core amodal capacity (Morey & Cowan, 2005).

Chunking

A key factor that influences immediate recall is chunking. Miller (1956) showed that performance in such tasks depends on how stimuli are associated with one another to produce larger chunks. …

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