Various aspects of both physical and mental performance decline with age (see Figure 10.10, continuous lines) with maximal ability occurring between 18 and 25 years of age. However, some comprehensive research (Forsman, 1966) has shown that certain types of mental abilities remain fairly stable until a relatively advanced age. In certain cases, some of those types of mental abilities may even show an improvement.
The factors that usually decline with age are known as unstable factors, while those that do not change are called stable factors. Unstable factors include those
FIGURE 10.10 Changes in performance level with age.
concerned, for example, with short-term memory, such as the immediate repetition of a number of digits. A young person can usually remember six or seven digits without difficulty, and repeat them a short time later; for the same person 10 years later it can be considerably more difficult. The stable factors are those that depend on experience and for which there is no particular time limit for carrying them out.
The sense organs are also affected by increasing age; for example, visual acuity and dark-adaptation ability are reduced, the ability to differentiate tones decreases markedly, and the hearing threshold rises with increased age. Central processes such as reaction time increase and the ability to react to several signals at the same time is very much reduced with age. Physical strength drops and older people are also more sensitive to stress from their surroundings.
Older people have more difficulty translating from one code to another than do younger people. It is, for example, harder for an older person to start driving a left-hand drive car if he or she has always driven a right-hand drive car. It should, however, be emphasised that it is possible to teach new jobs and skills to older people if the teaching methods are suitably designed for their needs. In particular, one must remember that older people need a longer time for training. One must also be careful not to put up social barriers to training; for example, the types of books used in the education of schoolchildren should not be used with adults. Older people also have a greater need to test and prove themselves in their training.
Even though the sense organs and the motor functions change and deteriorate with the years, it is not these input and output mechanisms that are the most important factors for reduced performance in older people. These can very easily be compensated for with good ergonomic design of the environment and control panels and with individual aids such as spectacles and hearing aids. Increasing age does not particularly affect the greater part of attention and motor organisation. For certain types of job skills, it is possible that the abilities may be maintained relatively well because of increased experience.
The most important changes for the older person occur in the central processes. Decision making in different situations takes considerably longer for the more elderly. It is in this area that the greatest limitations occur for the older person in his or her working life, but it is also in this area that ergonomic measures can make it easier.
Age has relatively little effect on more complex decisions where there is little time limitation for carrying out the task, which is common in control room work. Instead, experience and motivation are the most important factors for efficiency. Older people can thus, in practice, often make difficult decisions as well as or better than younger people. There is also much to suggest that the character of the work can aid in the maintenance of a high-effectiveness capability with increased age. An interesting, stimulating, and variable job increases the likelihood of maintaining efficiency. Reduction in productivity also varies much from person to person and these variations are especially great at higher ages (over fifty-five to sixty years).