The proportion of older adults in the populations of western countries continues to increase and is estimated to reach around 13 per cent by the end of the twentieth century. An understanding of the kinds of changes in cognitive processes and mental abilities that accompany normal ageing is important for many aspects of social policy, such as the appropriate age of retirement, the provision of housing suitable for older people and the need for support services.
The process of ageing is often confounded with other associated factors, such as deteriorating physical health, poor nutrition, bereavement, social isolation and depression, which also affect mental abilities so that it is difficult for researchers to isolate and identify the effects of ageing. In addition, poor performance may be the product of sensory deficits, anxiety or lack of motivation rather than of mental deterioration.
Many mental abilities do show age-related deficits but others are unimpaired. In the words of Rabbitt (1993) it is quite wrong to suppose that ‘it all goes together when it goes’. Different abilities show quite different rates and patterns of deterioration. Moreover, differences between individuals tend to increase in older populations. Most individuals begin to show some slight decline by the mid-sixties; with others problems begin earlier and are more severe; and about 10 per cent, the so-called ‘super-old’, preserve their faculties unimpaired into late old age. Traditional psychometric testing has yielded age norms for performance on batteries of standard intelligence tests. The results have led to a distinction between crystallized (or age invariant) intelligence and fluid (age sensitive) intelligence. Tests which measure intellectual attainments such as vocabulary, verbal ability and factual knowledge reflect crystallized intelligence and show relatively little effect of age. Tests measuring mental processes such as the speed and accuracy with which information can be manipulated as in backward digit span, digit-symbol substitution and reasoning, reflect fluid intelligence and generally reveal an age-related decline. Nevertheless, the pattern of decline within the category of fluid abilities is not uniform. The relationship between chronological age and performance on memory tasks is not necessarily the same as the relationship between age and speed of information processing. These complex patterns pose problems for theorists such as Salthouse (1992) who attribute age-related decline to the single global factor of ‘general slowing’.
Experimental techniques reveal not only which tasks are impaired by ageing but also which of the component stages or processes are affected. For example, experimental studies of memory indicate that the retrieval stage is relatively more affected than encoding or storage and that short-term or ‘working’ memory is relatively more impaired than long-term memory. Semantic memory, which stores general knowledge, is stable, whereas episodic memory, which records events and experiences, is more likely to be defective. Age differences are most evident in demanding and unfamiliar tasks which require conscious effortful attention and the observed age difference tends to increase linearly with task complexity.
Since the mid-1980s many researchers have turned their attention to the systematic study of the effects of cognitive ageing on performance in everyday life. Using questionnaires, observations and naturalistic experiments which mimic real-life situations, the practical problems which commonly confront older adults have been identified (Cohen 1993) and, in some cases, remedial therapies have been devised. For example, older people tend to have particular difficulty in calling proper names; in remembering to carry out intended actions; and in remembering whether an action such as taking medicine has been performed or only thought about. Memory for the location of objects and for novel routes is unreliable. Memory for the details of texts and conversations is less efficient, and memory for the source of information (who said what) also tends to be poorly retained. Skills which require rapid processing of information from several sources such as driving also deteriorate markedly. Nevertheless, older people often develop effective compensatory strategies for coping with such problems, making more use of mnemonic devices, making adjustments in lifestyle and devoting more effort and attention to selected activities.
Although the effects of cognitive ageing have been catalogued in considerable detail, much work remains to be done in developing a comprehensive theoretical framework and in mapping the cognitive changes on to the neurophysiological changs in the ageing brain.
Gillian Cohen
Open University
References
Cohen, G. (1993) ‘Memory and ageing’, in G.M.Davies and R.H.Logic (eds) Memory in Everyday Life: Advances in Psychology, vol. 100, Amsterdam.
Rabbit, P.M.A. (1993) ‘Does it all go together when it goes? The Nineteenth Bartlett Lecture’, Quarterly Journal of Experimental Psychology46A.
Salthouse, T.A. (1992) Theoretical Perspectives on Aging, Hillsdale, NJ.
Further reading
Craik, F.I.M. and Salthouse, T.A. (1992) Handbook of Aging and Cognition, Hillsdale, NJ.
