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CHAPTER 5
Cognitive ageing in older workers and its impact on lifelong learning 93

5.3. Fluid and crystallised intelligence

There is great variation on which cognitive functions decline earlier during the
life span. Most researchers agree that crystallised and fluid intelligence are
affected differently in normal ageing. Horn and Cattell (1966) explained that
crystallised intelligence involves general acquired knowledge and vocabulary
and is related to linguistic ability and expression. Fluid intelligence refers to
ability to think logically and to solve novel problems, to reason and to draw
conclusions. It is particularly relevant in scientific, mathematical, technical
abstract thinking. Age-related differences in fluid intelligence have been
identified using brain-scanning techniques (Bugg et al., 2006) that document
a strong relation with a decline in speed of processing. On the other hand,
crystallised intelligence remains relatively unaffected across the life span with
a peak in middle adulthood (40-55 years) (Horn and Cattell, 1967). However,
recent studies challenge the notion of early cognitive ageing suggesting that
changes in cognition do not become evident before the age of 65 years
(Nilsson et al., 2009).
Following the distinction between fluid and crystallised intelligence, it has
been found that verbal ability, general knowledge and certain numerical skills
are least affected by ageing. Other functions such as memory and speed of
processing start deteriorating as early as middle adulthood and may cause
downstream effects to other cognitive abilities. For example, slow speed of
processing is associated with weak language abilities and poor memory in
older adults. These cognitive functions seem to be more involved in everyday
activities and significantly affect job-related performance. Therefore, it is
important to explore the link between cognitive ageing in middle-aged and
older adults and job-related performance in a multidisciplinary way.

5.4. Memory and ageing

One of the most significant functions of the cognitive system is the ability to
encode, maintain/store and retrieve information. Memory is expressed in
different modalities depending on the involved sensory system through which
it is acquired. Visual and auditory inputs are among the most important in
survival and evolution and have been studied extensively in relation to
cognitive ageing. Memory involves external stimuli, oneself, space and time,
rituals and routines, goals and aims as well future plans. There are different
memory systems depending on the amount and type of information they can