Introduction

"Time flies when you're having fun," but "a watched pot never boils."

These popular sayings reflect our intuition that the amount of attention we pay to time directly influences our perception of its passing. Many aspects of attention change with advancing age, raising the question: How does time fly for older adults?

This chapter attempts to organize the existing literature on older adults' interval timing performance, that is, judgments about durations in the seconds-to-minutes range. Age differences in the perception of time have both practical and scientific significance. Successful performance of many tasks — from hitting a baseball to cooking the perfect hamburger to changing lanes on a busy freeway — depends critically on the ability to "get the timing right." Age-related disruptions in time perception can make these tasks more difficult for older adults. From a research perspective, there is a great deal of overlap in the areas of interest for investigators in interval timing and cognitive aging. Questions about attention, memory, and frontal-striatal brain circuits are of central importance in both domains.

These shared interests and growth in the fields of both interval timing and cognitive aging have led to a recent upswing in experiments on older adults' perception of time (e.g., Craik and Hay, 1999; Fernandez and Pouthas, 2001; Lustig and Meck, 2001a; Malapani et al., 1998; McCormack et al., 1999; Perbal et al., 2002; Wearden et al., 1997). Some of these studies ask questions about time judgments in tasks that are unique to humans, whereas others use procedures that have already been well studied in the established literature on animal timing. In some cases, neuropsychological or neuroimaging techniques have also been used to explore the brain correlates of age-related behavioral differences in interval timing (e.g., Fernandez and Pouthas, 2001; Malapani et al., 1998). Many of these experiments start from the assumption of age differences in attention and memory functioning and ask how these changes influence older adults' perception of time. Age differences in timing may also influence age differences on other cognitive tasks, particularly those that require speeded performance or the accurate timing and sequencing of multiple operations.

The increase in experiments on older adults' interval timing performance has led to many intriguing results, but in general, there is a lack of an organizing framework within which to understand those results, their relation to each other, and how they might fit into more general theories of interval timing or cognitive aging. This chapter attempts to provide such a framework by considering how the dominant information-processing model of interval timing, scalar expectancy theory (SET) (Gibbon et al., 1984), might be affected by age differences in attention and memory. This model includes components such as attention, memory, and processing speed that are of central importance to cognitive aging researchers, and those components have been heavily investigated using both behavioral and biological techniques. These features make SET an ideal starting point for understanding how interval timing may change with age.

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