Age Differences In Reaction Time
More generally, how does adult age affect RT? Information processing takes longer (Cerella; Salthouse) and its duration becomes more variable (Allen, Kaufman, Smith, and Propper) with increasing age. This has led many people to believe that aging is invariably associated with slowing and decline. However, increased adult age does not affect all processing stages equivalently.
For example, the lexical decision data in Figure 2 show that while older adults show a peripheral-process decrement, they show no drop in speed compared to younger adults in lexical access speed (a central process involving memory retrieval). Using a word-naming task, similar results were observed by Balota and Ferraro (1993). Reviews of the literature on lexical processing conclude that there are no appreciable age differences in central processes, but that older adults do show longer overall RTs due to slower peripheral processing (Allen, Madden, and Slane; Lima, Hale, and Myerson; Madden, Pierce, and Allen). Lexical tasks involve semantic memory or knowledge, including vocabulary (Tulving, E., 1985). Semantic memory tasks all tend to show a similar pattern of age differences: peripheral-, but no central-process decrements.
Other types of information processing, though, do show both central- and peripheral-process age differences. Episodic memory tasks ask individuals to remember personally experienced events and their temporal relations (e.g., what you had for breakfast this morning; see Tulving, E., 1985). Large age differences are found in episodic memory (Burke and Light, 1981; Light, 1991), and as can be observed in Figure 3 (from Allen et al., 1998, Experiment 1), these appear in both slope and intercept. The steeper slope shown by older adults across transposition distance—i.e., how far probe items are shifted relative to where they occurred as targets—provides specific evidence for slowing of central processes in this episodic task (smaller distances require more central processing). Central slowing is a hallmark of episodic memory tasks, as well as many other information-processing tasks (Cerella).
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