Memory

Another view of memory is more closely based on the observation that age differences in memory tasks seem to be determined by the degree of deliberate processing required to perform the task. Deliberate processing requires processing resources, and if processing resources are diminished in older adults, then the ability to Figure 2 Venn diagram showing relationship of age, memory, and cognitive resources. SOURCE: Author engage in deliberate processing will be reduced. According to this view, age differences in memory are assumed to be caused by an age-related reduction in cognitive resources available to perform memory tasks as well as other cognitive tasks. Support for this theoretical position comes from studies which show that individual differences in measures of cognitive resources can account for age-related differences in memory performance. This research approach is represented in Figure 2. The circles in the figure represent individual differences in age, memory, and cognitive resources. Overlap in the circles represents shared variance among the variables. The age-related variance in memory is reflected by the overlap in the age and memory circles (a + b). The degree to which processing resources mediate the relationship between age and memory is shown by b.

Four mechanisms have been suggested as estimates of cognitive resources: perceptual speed, working memory, inhibitory function, and sensory function (Park).

Perceptual speed. Older adults are slower at performing simple perceptual/motor operations. In one test, for example, individuals are asked to look at two strings of letters (e.g., xpltvg — xpltvg) and indicate in the space between them whether the strings are the same or different. The number of letter comparisons that can be completed in ninety seconds declines significantly across the life span. Perceptual speed is assumed to be an estimate of the efficiency of neural functioning, and thus to be a possible mechanism to account for age differences on memory and other cognitive tasks (Salthouse). Timothy Salthouse has produced an impressive amount of evidence that individual differences on simple measures of perceptual speed can account for most of the age-related variance in complex cognitive tasks, even those that do not require completion in a given time (i.e., speeded).

Working memory. Many researchers believe that working memory is a good measure of processing resources. Like perceptual speed, individual differences in working memory can account for much of the age-related differences on long-term memory tasks. Denise Park and her colleagues conducted a study with over 300 adults of different ages that measured perceptual speed, working memory, and different measures of long-term episodic memory. The long-term memory measures included free recall of a word list (looking at a word list and then recalling as many words as possible), cued recall (presenting word pairs at encoding and then presenting one word from each pair as a cue for the other word at retrieval), and spatial recall (remembering what quadrant of the computer screen words had been presented in earlier) (Park, Smith, et al. 1996). This study showed that when perceptual speed as a construct was included in a model of memory performance, it accounted for essentially all of the age-related variance in memory performance. Measures of working memory, however, were also important in the model with the more effortful measures of episodic memory, free and cued recall. Speed alone accounted for the age differences in the less effortful spatial recall task, but both speed and working memory were necessary to account for the age differences in free and cued recall, tasks that are assumed to require more processing resources. These results suggest that no single mechanism may be adequate and that multiple measures may be necessary to account for age differences in memory.

Inhibitory function. Another construct that has been suggested as the mechanism for cognitive resources is inhibition (Hasher and Zacks). Inhibitory function allows the individual to focus on information relevant to the task and suppress information that may be activated but is irrelevant to the task. Lynn Hasher and Rose Zacks suggest that older adults are less able to inhibit irrelevant information, and thus cannot focus as well on the information needed to perform the task. According to this view, it is not working memory capacity that is limited in older adults, but the inability to inhibit irrelevant information from cluttering up the content of working memory. The result of this "mental clutter" is that older adults experience more interference at both encoding and retrieval. There is a great deal of evidence that older adults are in fact deficient in inhibiting irrelevant information when performing memory tasks (Zacks et al.).

Sensory function. Paul Baltes and Ulman Lindenberger, in their large-scale Berlin Aging Study, found that auditory and visual acuity can account for much of the age-related variance on a variety of cognitive tasks, including associative memory. In one study, they found that sensory function accounted for over 90 percent of the age-related variance in cognition. Other research, however, has shown that this relationship is not simply due to the fact that poorer vision and hearing cause a decline in cognition. Instead, Baltes and Lindenberger suggest that the sensory measures are one of a large number of physical and cognitive variables that reflect the efficient functioning of the nervous system. According to their view, there is a "common cause" related to biological aging that affects a variety of abilities, both cognitive and somatic, are affected by aging.