Age Differences in Attention Relevant to Interval Timing

Attention plays an important role in interval timing performance, but as described above, timing can also be affected by influences on memory, the pacemaker, or other components of the information-processing model. Furthermore, the term attention is a broad one and has been operationalized in many procedures that have no apparent relation to one another. Not every cognitive function that falls under the rubric of "attention" will have an influence on interval timing (see discussion by Meck and Benson, 2002), and not all of these functions will change with age. Furthermore, many aspects of attention, such as the efficacy of different types of attentional cues, have been studied separately in the contexts of aging (e.g., on visual attention tasks, see Curran et al., 2001; Greenwood et al., 1993) and interval timing (e.g., Chen and O'Neill, 2001; Meck, 1984), but the effects of age differences in those aspects of attention on older adults' interval timing performance have yet to be explored.

The majority of experiments on older adults' interval timing performance, and thus the bulk of this chapter, focus on age differences in the allocation and maintenance of attention to a particular task or stimulus, and the consequences of these differences for older adults' timing accuracy. As described below, there is some controversy in the cognitive aging literature regarding the characterization of and reasons for age differences in attentional function (see reviews by Hartley, 1992; McDowd and Birren, 1990; Rogers and Fisk, 2001).

Despite these controversies, most investigators agree that automatic aspects of attention are for the most part spared in normal aging, whereas controlled aspects of attention are subject to age-related declines (e.g., Hasher and Zacks, 1979; Jennings and Jacoby, 1993). Automatic aspects of attention are those that occur without intention, do not necessarily give rise to awareness, and do not interfere with other processing (Posner and Snyder, 1975). Examples include the way in which a bright flash of light in a particular location will draw attention to that location, or how we understand the words we are reading without deliberately and effortfully retrieving their meaning. Controlled aspects of attention usually require awareness and intention, and tax the system so that only a limited number can be carried out at one time. One example is directing attention to a peripheral location in response to a centrally located arrow pointing to that location. Controlled attention also plays an important role on the Stroop test, which requires participants to say the ink color of conflicting color names (e.g., the word red printed in green ink). In this situation, attention must be effortfully directed away from the word information and toward the color information.

Most cognitive processes exist somewhere on the continuum between controlled and automatic, and their position can change over time. In particular, an initially effortful process (e.g., driving) can become more automatized through repeated practice. In contrast, under adverse conditions, a largely automatized process can require more control. For example, under normal circumstances, most of us do not find it difficult to walk and chew gum at the same time, reflecting that these are both highly automatized processes that do not interfere with each other. In a state of inebriation, however, walking can require a great deal more effort and attempted control. More benignly, when pondering a difficult problem, we may literally stop and think about it — redirecting attention from walking to our thoughts.

There is general agreement that the controlled aspects of attentional performance are the ones that most change with age, but the reasons for those changes are a matter of some debate. One group of theories focuses on the idea that older adults have reduced controlled attention resources. Evidence for these ideas comes from experiments showing that asking young adults to divide their attention between multiple tasks can reduce their performance to the level of older adults who are tested under full attention conditions. This is especially the case when the performance measure is subsequent memory for information studied during the divided attention task (e.g., Craik, 1977; Craik et al., 1996; Anderson et al., 1998). The explanation given for these findings is that the requirements of the additional task reduce the amount of controlled attention that young adults have available to devote to the studied information, and that this experimentally induced reduction in young adults simulates preexisting resource deficits in older adults.

Reduced-resource views are a popular way of explaining age deficits in performance and receive support from a variety of findings. For example, compared to young adults studying under full attention conditions, older adults and participants studying under divided attention conditions may show similar activity reductions in left frontal brain areas associated with later successful memory (Anderson et al.,

2000). On behavioral tests, the memory costs of divided attention are often similar for young and older adults, but older adults show larger impairments on the secondary task (Anderson, 1999; Anderson et al., 1998). Data analyzed using the process dissociation procedure (Jacoby, 1991) have also been used to argue that controlled, but not automatic aspects of memory change with divided attention and age (Schmit-ter-Edgecombe, 1999), consistent with the distinction described above.

Another group of theories focuses on potential age differences in the allocation of attentional resources, rather than amount. For example, the inhibitory deficit hypothesis posits that many of older adults' problems in experimental tasks and in daily life stem from a reduced ability to keep attention and working memory free of irrelevant information (Hasher and Zacks, 1988; Hasher et al., 1999; McDowd et al., 1995). This reduced ability to keep irrelevant information out of the focus of attention may result in older adults' functionally being in a divided attention situation much of the time (Hasher et al., 2001).

A third perspective emphasizes the possibility that older adults have different priorities for the allocation of attention, and that declines in perceptual and motor abilities may result in the same task requiring more attention from older adults than from young adults (Baltes, 1997; Baltes and Baltes, 1990; Freund et al., 1999). When driving down unfamiliar roads on a dark, snowy night, most of us will turn off the radio and cut down on conversation because we require more concentration — that is, attention — to perceive what lies ahead of us and control the car. Likewise, impairments in sensory and motor functioning due to age (rather than bad weather) may require older adults to devote more attention to the simple perception and execution of a task than is the case for young adults.

This idea was tested directly in a series of experiments that asked participants to memorize a list of words while walking on a course filled with obstacles (Li, Lindenberger, Freund, and Baltes, 2001). Performance in the dual-task condition was compared to performance on each task performed individually. Over different combinations of task difficulty, older adults showed larger dual-task costs on the memory task than did young adults, whereas the two groups showed equivalent costs on walking performance. Furthermore, older adults used the aid provided for the walking task (a handrail) more often than the aid provided for the memorizing task (more time), but young adults showed the opposite pattern. These results suggest that older adults devoted their attention and efforts to the walking task, whereas young adults focused on memorizing.

In summary, there are different views on how to characterize older adults' difficulties on controlled attention tasks, but all converge on a functional level to suggest that older adults often devote less controlled attention to a particular task than do young adults. As described in the following section, age differences in the allocation and prioritization of controlled attention have important consequences for older adults' perception of time.

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