1034 PSYCHOLOGICAL ASPECTS OF MAN’S ENVIRONMENT
Inadequate Lighting Lighting may be inadequate either
because it is too low, or because it causes glare. Excessive
light intensities, such as those generated by lasers, can cause
physical damage to the eye. While the eyes can adapt to a
wide range of light conditions, the thresholds of the phot-
opic receptors in the fovea of the eye are higher than in the
periphery (scotopic vision). The density of receptors in the
fovea is also higher, and the functioning of these receptors is
important for tasks requiring good visual acuity. Therefore,
if the light levels fall below the photopic threshold, such
tasks will suffer. Visual acuity may be tested by means of
Landolt rings (circles) with small breaks whose orientation
the subject must detect) or by means of grids of varying fine-
ness and orientation. Effects of light composition have also
been shown on some tasks, even well above the photopic
threshold. For most visual tasks, light levels well above the
photopic threshold should be maintained.
Glare causes discomfort, and may interfere with vari-
ous tasks. Two kinds of glare are distinguished; direct glare
from a light source in the visual field; and specular glare due
to light reflected from surfaces within the visual field. Both
types of glare can be controlled by suitable adjustment of
the environment. Direct lighting offers maximum light at the
working surface when the source is directed downward, but
it is likely to produce shadows, glare and undesirable bright-
ness contrasts. Indirect lighting avoids these problems, and
while it may lessen visual efficiency in reading over very
prolonged periods, it has been shown superior to direct light-
ing in tests of 3 hr in length.
It should also be realized that color vision depends on
the receptors in the fovea. Therefore, tasks requiring the use
of colors must be performed with adequate lighting. The
color of surfaces depends on the spectrum of the light which
falls on them, so illuminants must be chosen to provide the
proper colors for tasks involving color coding.Special EnvironmentsChanges in Sensory Input Early reports on the effect of iso-
lated environments from polar expeditions and the like are in
agreement with later experimental findings on the undesir-
able effects of restricted sensory inputs. Studies on extreme
sensory restriction as carried out at McGill University,
where subjects wore translucent goggles and stayed in low
variability environments, have shown that such effects as
loss of ability to concentrate and hallucinations may result.
Polar expeditions have reported compensatory behavior in
the form of the development of unusually structured groups,
and special interests and hobbies on the part of individual
members. Similar patterns sometimes develop in such isola-
tion situations as solitary confinement.
Studies on early sensory restriction in animals have sug-
gested that deficits of varying degrees of permanence may
develop in subsequent behavior as a result. Extreme depriva-
tion of sensory input and social contact is known to result in a
variety of deficits in human infants, even though the physical
needs of the infants have been met. The monotonous effects
of long periods at tasks such as monitoring sonar screensfor infrequent signals, and other vigilance tasks have shown
deleterious effects in terms of missed targets.
The effects of excessive sensory input are less clear. Any
situation which overloads the information processing capac-
ities of an individual will be likely to result in decremental
performance. However, apart from such short-term effects,
it is not clear that there are long-term effects from an overly
complex environment.
The reticular activating system in the brain stem, which
has been shown to have an alerting effect, has been sug-
gested as a possible locus for some of the effects of sensory
isolation.
Other Special Environments Some other special environ-
ments that have received a good deal of study are submarines
and simulated space capsules. The outstanding feature of the
submarine environment is its limited space. Most studies
have focused on physical problems associated with this envi-
ronment, but a few have been concerned with the psycho-
logical effects. In general, adaptation to crowded conditions
is seems to be good, though there are some losses of person-
nel attributed the confined conditions. One study reported
a loss of 7% of 187 men over 6 months due to this factor.
Complaints about lack of privacy have been reported also.
The problem of diurnal cycles arises in connection with
such environments. The usual night–day shifts are lacking,
of course, in extended undersea cruises, and time confusion
has been reported: for example, inability to remember if it is
8.090 a.m. or p.m. It has been found desirable to introduce
features, such as news reports and evening entertainments,
into the daily routine which will avoid the sensation of being
cut off from the rest of the world and which serve to mark
diurnal cycles. It also appears that, although such cycles
can be influenced by the environment to some extent, there
are limits to the process. Alluisi reports evidence of diurnal
cycling in performance under a variety of work–rest sched-
ules, including some as extreme as 4 hr of work followed by
four of rest.
Simulated space capsule environments have many of
the features associated with sensory deprivation conditions,
plus the added factor of fatigue. Prolonged exposure to
such environments has been shown to produce decrements
in a number of tasks, from vigilance tasks to complex deci-
sion making functions. Diurnal rhythms in efficiency have
also been reported. However, it has also been found that
trained pilots, who were familiar with the concept of diurnal
rhythms, did not show such effects. Both motivational and
adaptation processes may be at work here. It has been shown
repeatedly that measures of “can” and “will” are often very
different for special environments.
Diurnal cycles may be important in less exotic environ-
ments. Efficiency in a number of tasks has been shown to vary
with the diurnal cycle. These variations appears to be related
to the body temperature, which reaches its lowest point after
several hours of sleep, and does not reach its maximum until
the evening of the next day. These variations create prob-
lems for jobs with several shifts, since operator efficiency is
constantly varying. While individual cycles show adaptation
to changes in times spent awake and asleep, this adaptationC016_012_r03.indd 1034C016_012_r03.indd 1034 11/18/2005 11:03:54 AM11/18/2005 11:03:54 AM