One popular hypothesis is that older adults have reduced processing resources due to greater difficulty inhibiting the processing of irrelevant information (Hasher & Zacks, 1988; Persad, Abeles, Zacks, & Denburg, 2002). That is, older adults have more task-irrelevant thoughts during processing and have trouble keeping them out of their minds. This difference could explain why older people tend to have trouble with switching and dividing their attention.
The inhibition idea has considerable support (Kane, Hasher, Stoltzfus, Zacks, & Connelly, 1994; Persad et al., 2002). For example, McDowd, Filion, and Oseas-Kreger (1991) showed that when relevant and irrelevant information were both presented in the same modality (e. g., visually), older adults could not focus more attention on the relevant stimuli. That is, older adults distributed their attention more equally between the two types of information than younger adults. However, when relevant information was presented in one modality (say, visually) and irrelevant information in another (auditorally), older and younger adults both showed similar patterns of attention allocation. Thus, older adults apparently have more trouble selectively attending to relevant information when it and the irrelevant information are both presented in the same modality. One practical implication of this concerns driving, where lots of both relevant and irrelevant information occurs visually. Given these research findings, we would expect that older adults would have more difficulty in this situation, which could result in accidents. We will check our prediction a bit later in this chapter.
Additional research shows that the problem with inhibition is not universal across all aspects of stimuli (Connelly & Hasher, 1993; Gamboz, Russo, & Fox, 2002; Lustig, Hasher, & Toney, 2006). Adults were presented with letter pairs. They were required to name the target letter that always appeared in red and ignore the distracter letter that always appeared in green. The letter pairs were also presented in one of four locations. Young adults demonstrated appropriate inhibition, because their response time was slowed down when a previous target in red (e. g., the letter K) became a distracter in green on a subsequent trial. Older adults did not. Such age-related inhibitory deficits, however, may be limited to an item’s identity. When inhibition was assessed by examining location (i. e., the target stimulus appeared in the same location as the to — be-suppressed distracter on an earlier trial), there were no age differences. Moreover, attempts to get older adults to inhibit processing of key aspects of a distracter by increasing the time the target and distracter were displayed did not appear to work (Kane et al., 1994). Such data provide support for Hasher and Zacks’ (1988) inhibition hypothesis, but mean that inhibitory deficits are probably localized to specific aspects of stimuli.
Finally, it is interesting to note that there are strategies to compensate for older adults’ difficulties with inhibiting irrelevant information. You simply ask older adults to close their eyes or avert their gaze away from irrelevant information. Using this strategy, older adults were just as good as young adults in attending to auditory stimuli (Einsten, Earles, & Collins, 2002). More currently, researchers are asking whether there is a beneficial effect of the distraction incurred in one task on the performance of a subsequent task. In other words, is there a positive consequence of distraction that older adults are utilizing?
In a recent study by Kim, Hasher, and Zacks (2007) older and younger adults were instructed to ignore distraction when reading passages with interspersed distracting words. Some of the dis — tracters actually served as solutions to a subsequent set of verbal problems. Older adults showed significant activation and processing of the distraction
information (in other words, they could not “control” their attention so as not to process this information), whereas younger adults did not. Most interestingly, the age-related reductions in atten — tional control over information that was not initially relevant led to superior problem-solving performances for older adults in comparison to younger adults.
Once again, we embrace a life-span perspective: Adult developmental changes in cognitive functioning are characterized by both gains and losses. It is important to consider inhibitory loss in both ways. Under certain conditions it can be a hindrance, and in others it can be helpful. It all depends upon the situation (Healey, Campbell, & Hasher, 2008).