Academic journal article Memory & Cognition

An Analysis of Age Differences in Perceptual Speed

Academic journal article Memory & Cognition

An Analysis of Age Differences in Perceptual Speed

Article excerpt

Tests of the generalized slowing hypothesis have demonstrated the strong predictive power of tests of perceptual comparison speed in accounting for age differences across a range of cognitive domains. The goals of this study were to determine whether short-term memory (STM) and perceptual demands contribute to age differences on two commonly used tests of perceptual comparison speed, the letter and pattern comparison tests, and to test whether these task components account for unique variance in predicting age differences in working memory and reasoning. Results showed that, after controlling for visual contrast sensitivity and a general slowing factor, age differences increased with increases in both STM load and perceptual degradation. Only STM load, however, accounted for a significant portion of the relationship of age with higher level cognition. We concluded that perceptual comparison tests are dependent on multiple age-sensitive abilities, not all of which are related to age differences in higher level cognition.

A large body of work has demonstrated the lack of independence in age-related declines across a wide range of cognitive domains (Salthouse, 1991, 1996). Furthermore, relatively simple cognitive skills, as measured by perceptual comparison speed tasks, such as the letter and pattern comparison tests (LC-PC tests; Salthouse & Babcock, 1991) and variants of the Digit-Symbol Substitution Test (Wechsler, 1997), are among the strongest predictors of age-related variance in higher level cognition, including long-term memory, working memory (WM), and reasoning (Babcock, 1994; Finkel, Reynolds, McArdle, & Pedersen, 2007; Fisk & Warr, 1996; Fristoe, Salthouse, & Woodard, 1997; McCabe & Hartman, 2003; Salthouse, 1991, 1996). Perceptual comparison tests consistently account for more age-related variance in higher level cognition than do tests that are either cognitively simpler or more complex (Salthouse, 1991, 1994, 1996).

The most prominent interpretation of the role of perceptual comparison tests attributes the shared effects of age to the slowing of a relatively small number of low-level cognitive processes (Salthouse, 1996; Salthouse & Ferrer- Caja, 2003). The challenge remains, however, to specify these processes, and existing theory provides little guidance. Furthermore, isolating the critical processes is difficult because of the imprecise mapping of cognitive processes to tasks and because of the intrinsic impossibility of creating process-pure tests. The Digit-Symbol Substitution Test, for example, has separable components related to feature encoding, memory, and visual search (Gilmore, Royer, Gruhn, & Esson, 2004) and relies on visuomotor coordination and response speed as well (Lezak, 2004; Piccinin & Rabbitt, 1999). The LC-PC tests are likely to be similarly complex. On each item of these paperand- pencil tests, participants compare two letter strings or two geometric patterns and decide as quickly as possible whether they are the same or different. Performance is likely to involve visual sensory ability, visual perception, short-term memory (STM), comparison processes, response selection, and motor speed. Age differences in many of these abilities have been well documented in the research literature. For instance, older adults have reduced sensory and perceptual function (Schneider & Pichora- Fuller, 2000) and STM function (Verhaeghen, Marcoen, & Goossens, 1993), as well as slowed decision and response selection processes (Kausler, 1991; Salthouse, 1996) and motor speed (Deary & Der, 2005). Reduced speed for older adults on the LC-PC tests may involve any one or more of these abilities.

To date, most researchers of perceptual comparison tests have used them in statistical models (e.g., hierarchical, structural equation) to predict age-related declines in cognition. Additional research strategies are needed, however, in order to decompose the sources of age differences on these tests at the level of cognitive operations and to assess their contributions to generalized cognitive decline. …

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