Academic journal article Memory & Cognition

Age-Related Differences in Executive Control of Working Memory

Academic journal article Memory & Cognition

Age-Related Differences in Executive Control of Working Memory

Article excerpt

In two experiments, we used dual-task methodology to assess the effect of aging on executive control of working memory. We hypothesized that (1) age-related dual-task costs would be observed even when individual tasks represent different perceptual modalities; (2) age would modulate the effect of increased temporal overlap on dual-task performance; and (3) the vulnerability of specific memory mechanisms to interference would be age related. We found that aging was associated with disproportionate dual-task costs that increased when extending the overlap between individual tasks. The effect of interference with encoding, and arguably output, was disproportionately larger in old than in young individuals. Ensuring that individual tasks represent different perceptual modalities is important but insufficient when using dual-task methodology to assess the effect of aging on executive function. The degree of temporal overlap between individual tasks and the sensitivity of specific memory operations to interference should be considered, as well.

Dual-task methodology has been used to evaluate one aspect of executive control-the allocation and monitoring of attentional resources to competing task demands (Baddeley, 1996, 2001; Baddeley & Hitch, 1974). While the effect of aging on dual-task performance has been studied extensively (for a review, see Hartley, 1992; McDowd & Shaw, 2000) and evaluated using meta-analytic procedures (Verhaeghen & Cerella, 2002; Verhaeghen, Marcoen, & Goossens, 1993; Verhaeghen, Steitz, Sliwinski, & Cerella, 2003), the findings have been inconsistent. A number of studies have found that aging is associated with increased costs in dual-task performance (e.g., Crossley & Hiscock, 1992; Li, Lindenberger, Freund, & Baltes, 2001; Salthouse, Rogan, & Prill, 1984; Whiting & Smith, 1997), but others failed to demonstrate this relation (e.g., Nyberg, Nilsson, Olofsson, & Backman, 1997; Somberg & Salthouse, 1982; Tun & Wingfield, 1994; Wickens, Braune, & Stokes, 1987). Moreover, the theoretical basis for those changes remains controversial (Meyer, Glass, Mueller, Seymour, & Kieras, 2001).

The present experiments were intended to shed light on our understanding of the effect of aging on executive control of working memory. To accomplish this goal, we designed a dual-task paradigm with specific methodological and theoretical considerations in mind. The two individual tests were selected to represent visual and verbal aspects of working memory. This was done to examine whether using single tasks that represent different perceptual modalities insulates against age-related dual-task costs. In addition, two dual-task conditions were created that differ in the temporal arrangement of the tasks. In the first dual-task condition, overlap was limited to the retention phase of the visual task. In the second dual-task condition, the overlap extended over the encoding, retention, and output phases of the visual task. Executive control of working memory was conceived as the ability to monitor and allocate attentional resources to two competing individual working memory tasks and was measured in terms of the dual-task costs incurred relative to performance on the single tasks. Moreover, comparing performance costs in the two dual-task conditions afforded insight into whether executive control of working memory was differentially taxed in young and old persons when extending the temporal overlap to the encoding and output phases of the visual task. Performance on the verbal task afforded a more direct examination of the sensitivity of specific memory operations to interference.

A series of studies have used dual-task methodology to examine executive control of working memory in normal aging and in people with Alzheimer's disease (Baddeley, Baddeley, Buck, & Wilcock, 2001; Baddeley, Bressi, Delia Sala, Logie, & Spinnler, 1991; Baddeley, Logic, Bressi, Della Sala, & Spinnler, 1986). …

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