Age differences in inhibition: Possible causes and consequences

The relations among age, inhibition, perceptual speed, susceptibility to interference, and working memory were examined in a sample of 301 adults age 20 to 90. Younger adults were found to have more efficient inhibitory mechanisms than were older adults. Significant inhibition, however, was found in all age groups, including the older age group. Older adults were also found to be more susceptible to interference from irrelevant information. There was a small negative relation between interference and inhibition, suggesting that participants with the most efficient inhibitory functioning may be the least susceptible to interference. Perceptual speed, an index of processing efficiency, was found to mediate nearly all of the age-related variance in inhibition and interference. Interference, but not inhibition, was found to mediate some of the age-related variance in working memory. Age-related changes in the efficiency of inhibitory functions in the attentional system have been hypothesized to contribute to age differences in working memory (Hasher & Zacks, 1988). Hasher and Zacks (1988) proposed that changes in working memory function with increased age may be due to two processes: (a) a decreased ability to inhibit or prevent irrelevant information from entering into working memory, and (b) an increase in the susceptibility to interference or distraction from irrelevant information. A malfunction of inhibitory functions, therefore, is hypothesized to allow irrelevant information into working memory leading to poorer memory performance. Not only is more irrelevant information allowed into working memory but, in addition, once this irrelevant information is in working memory, it may remain in working memory longer for older than for younger adults (May, Kane, & Hasher, 1995). Because a malfunction in the inhibitory system allows irrelevant information to be present in working memory, it may lead to an increase in interference from this irrelevant information. Thus a decrease in inhibitory function may contribute to age differences in susceptibility to interference. One consequence of these changes may be poorer working memory function. One paradigm used to measure inhibitory function in selective attention is the negative priming paradigm. Negative priming refers to an