Why do some cognitive processes decline with age?

Most cognitive processes decline with age

It does appear that most component processes of cognition decline with advanced age if the difficulty level is sufficiently high. For example, the following processes have all shown age effects:

• processes involving attention
• working memory capabilities (the amount of information you can work with without losing track of any)
• understanding text
• making inferences
• encoding(putting information into memory) and retrieval (finding information in memory)

Other processes however, show little or no decline with age, for example:

• picture recognition
• implicit memory (information that can't be brought to mind but can be seen to affect behavior)
• prospective memory (remembering things you need to do)

Additionally, older adults’ performance on highly practiced expert skills can match that of young adults (e.g., typing, bridge playing, chess).

Cognitive decline in normal aging mainly due to a reduced working memory capacity?

It would seem from this that cognitive decline in old age may be primarily due to the reduction in processing capacity - understanding text, making inferences, paying attention are all processes that depend heavily on your working memory capability. Accordingly, it has been theorized that cognitive aids that minimize the use of processing resources might be effective in helping older adults.

Since picture recognition is one of those cognitive processes that don't appear to be affected by age, pictures may well provide effective memory support for older adults. For text, instructions that explicitly present material rather than requiring subtle inferences (which requires more processing), would be better.

This theory that age-related cognitive decline is due to decreased processing resources also suggests that automatizing components of complex behaviors would be an effective strategy for older adults.

Any skill that is practiced sufficiently becomes "automatized" (think of driving a car or playing the piano). A skill or habit that has been practiced to sufficient level to become automatic will never be completely lost. Unfortunately, research does suggest that older adults require a lot more practice than younger adults to achieve automatization - but the benefit to them may well be greater.

Other theories for age-related cognitive decline

It has also been theorized that age-related cognitive decline may result primarily from the slowing down that occurs with age. There is certainly little doubt about the fact of age-related slowing. But it seems likely that there is more involved than simply this, as age differences are still found on many tasks even when there is unlimited time to do them. It may well be that there is an interaction between slower processing and decreased capacity, causing timing to be more critical in complex situations (e.g., approaching a complex traffic interchange on a freeway at relatively high speed). Practice does improve speed in older adults (though not to the level that it does in younger adults).

Another theory is that older adults develop problems with the inhibitory mechanisms in working memory (the part of our brain that enables us not to pay attention to irrelevancies), and it is this that gives the impression that there has been a decrease in processing resources. A faulty inhibitory mechanism would cause older adults to pay more attention to irrelevant detail and encourage incorrect interpretations of context. There is some evidence that older adults find irrelevant information more distracting than do young adults.