Ergonomics and Aging - Fundamentals and Assessment Tools for Occupational Ergonomics - page 404

on older workers. Age-related anatomic and physiologic changes have been well-documented.
For example, pupil size decreases with age, which is associated with a condition called senile miosis
(Loewenfeld, 1979). Senile miosis is most severe and disruptive in low-illumination conditions
(Loewenfeld, 1979). Age-associated yellowing and opacification of the lens can also lead to vision diffi-
culties in low-illumination conditions (Weale, 1992).
In addition to anatomic and physiologic changes, aging is associated with changes in visual func-
tioning, the most notable of which are declines in visual acuity, which occur progressively after 50
years of age (Schieber and Baldwin, 1996). Presbyopia, a condition associated with loss of flexibility
in the lens resulting in a decreased ability to accommodate (ciliary muscles are not strong enough to
focus thickened lens on either near or far targets in the environment), is the major factor that affects
visual acuity (Fozard and Gordon-Salant, 2001). Visual acuity declines are amplified in low-illumina-
tion and with low-contrast objects (Sturr et al., 1990). The acuity of peripheral vision is also reduced
with age (Kline and Scialfa, 1996). Similarly, the useful field of view, which is the functional visual
field, declines with age (Cerella, 1985). Age-related declines in visual acuity may affect the reading
speed of older adults. However, Akutsu (1991) found that older adults read as fast as younger
adults, unless the characters are very small (less than 0.3 ). The same range of

character sizes that maximized reading speed for older adults was optimal for younger adults
as well. Hence, older adults may benefit from adjusting the size of icons and text presented on
computers.

8 ) or very large (1.0 8

In addition, printed materials should be designed such that the character size is

between 0.3 and 1.0 .

The ability of the eye to adapt to darkness is reduced with age, which may contribute to night vision
problems, which are frequently experienced by older adults (Jackson et al., 1999). Contrast sensitivity
refers to the amount of contrast that is necessary between a target and its background for the target
to be perceived. Contrast sensitivity loss is associated with aging, especially at higher spatial frequencies
(Owsley et al., 1983). Glare is also much more disruptive for older adults than for young adults and older
adults' eyes take longer to recover from glare (Pulling, 1980). Increased sensitivity to glare may make
reading from a computer screen particularly difficult for older adults (Park, 1992). Aging is also associ-
ated with loss of color discrimination (Fiorentini et al., 1996), which may make color discrimination
more difficult for older adults, particularly blue

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green comparisons (Charness and Bosman, 1992).
Visual declines associated with aging may impact the work performance of older adults, particularly if
tasks rely heavily on processing visual information or if task parameters are not changed to
accommodate age-related declines in vision. Glare-reducing monitors and individually adjusted contrast
levels on monitors could aid in reducing the effects of age-related contrast sensitivity loss and glare
sensitivity.
Age-related hearing loss is one of the most prevalent chronic disorders reported by older adults
(Willott, 1991). Physiological changes in the inner ear that cooccur with chronological age often
result in presbycusis, a condition associated with decreased sensitivity to higher frequency sounds
(i.e., over 6000 Hz). Accompanying presbycusis, a lifetime of previous work experience in noisy work
environments may result in noise-induced hearing loss such that sensitivity to mid-range frequencies
(i.e., 4000 Hz) is also reduced. Because presbycusis and noise-induced hearing are additive, older
workers may demonstrate decreased sensitivity to much of the auditory spectrum. As a consequence,
older adults often experience difficulty in processing auditory information such as speech and demon-
strate a reduced ability to filter out background noise (Kline and Scialfa, 1997). Deficits in speech per-
ception are quite small when older adults are presented with auditory stimuli in a quiet environment,
however, these deficits become substantial as background noise increases (Helfer, 1992). Furthermore,
older adults tend to miss information from multiple speakers in a noisy environment because they
have to selectively attend to pertinent information received by one ear while ignoring competing infor-
mation from the other (Barr and Giambra, 1990). Many of these factors associated with age-related
auditory decline may interact in the work environment to reduce older adults' abilities to meet
job-related demands.

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