1032 PSYCHOLOGICAL ASPECTS OF MAN’S ENVIRONMENT
THE PHYSICAL ENVIRONMENT AND BEHAVIORSensory ProcessesJudged purely in terms of their adequacy as detectors, sen-
sory systems are very efficient for many types of stimuli. The
auditory system, for example, is capable of detecting sound
near the level of Brownian motion under suitable test con-
ditions. The number of photons required to obtain a visual
response has been estimated as low as 5–14 photons under
optimal conditions. The olfactory system is also exceedingly
sensitive. As has been noted, the intensity of a sensation goes
up approximately as a logarithmic function of increases in
intensity of the physical stimulus (the Weber–Fechner law).
It applies to such sensory domains as vision, audition, etc.
In specific applications, of course, this information is inad-
equate for most purposes and more precise information is
needed. The apparent loudness of a noise will depend on its
frequency as well as its intensity, for example.
When qualitative factors are under consideration, it is
more difficult to make any statements. The annoying prop-
erties of a noise are a complex function of specific com-
binations of frequency and intensity and it is still not well
understood. See the article on noise in this volume for a
more complete discussion of this problem.
There are, however, a few general statements about sen-
sory systems which may be of use to environmentalists. First,
of course, the primary channels of information to human
beings are the visual and auditory systems. Senses such as
touch, taste, smell, and so on are of far less importance than in
the case of many animals. Of the major channels, vision has
the larger channel capacity, in the information theoretic use of
that term. However, this is not equivalent to an expression
of their social importance. The auditory channel is the primary
means of face-to-face communication between human beings,
and studies indicate that loss of hearing may produce more
profound personality changes than loss of vision. Early loss of
hearing can produce a disastrous effect on language learning.
For many purposes in adults, they may be equivalent for infor-
mation transmission. When one is dealing with tasks which
are purely informational, the visual channel may be more effi-
cient, since in tasks like reading, humans can process more
words than they can listen to in a given period of time.
Knowledge of visual and auditory parameters is important
in the proper design of a number of environments. Consider
the hazards associated with sources of glaring light along high-
ways at night, for example. The visual system adapts relatively
rapidly (usually within a minute) to large increases in light.
The process of dark adaptation is much slower, however; it
may take as long as half an hour to fully dark adapt the visual
system. Rapid changes in the external light levels at night can
therefore constitute a hazard, since they may keep the eyes of
drivers in a state of adaptation to relatively high illumination
levels even though the average level is relatively low.Effects of Various Pollutants on BehaviorIonizing radiation Perhaps the pollutant whose behavioral
effects have been studied most extensively is ionizingradiation. Studies on both lethal and sublethal doses of
both particulate and non-particulate radiation have been
done. The conclusion has been that there is relatively little
effect of either on the learning behaviors for most organ-
isms. Insofar as tests are available, this seems to be true of
man also. However, the activity levels of young rats have
been reported to be affected when the mothers had been
irradiated with one dose of 200 r. during pregnancy.
This does not mean, however, that organisms are not
sensitive to radiation. Radiation has been used to condition
avoidance to a saccharine solution (normally preferred by
rats). It was found to produce an 80% decrease in response
rate under some conditions. The amount of the decrement has
been shown to be dose dependent. Russian research, using
classical conditioning techniques, has reported a variety of
behavioral effects, occasionally for doses as low as 5 r.
Air Pollutants The effects of carbon monoxide (CO) on
behavior have received a good deal of study. Among other
effects, 90 min of exposure to 50 ppm CO has been shown
to impair ability to discriminate among relative lengths of
short time intervals. The effect of CO on the electroen-
cephalogram (EEG) patter in rats has been investigated. The
results suggest a possible depressive effect of CO on central
nervous system function. Significant reductions in tests of
manual dexterity have been observed with blood carboxy-
haemoglobin (COHb) levels in excess of 25%; such levels
may be reached in garages and other enclosed areas con-
taining motor vehicles. CO is known to elevate the visual
threshold.
Since CO and some other pollutants have as one of
their effects the reduction of the oxygen level in the blood
supply, studies on the effects of hypoxia (oxygen deficiency)
are relevant to the behavioral effects of gaseous pollutants.
The visual threshold is very sensitive to hypoxia; significant
impairment can occur at altitudes as low as 5000 ft, and at
15,000 ft twice as much light is required for minimum vis-
ibility as is required at sea level. Auditory and speech per-
ception thresholds may also be affected slightly, especially
for long exposures. Tasks requiring complex coordination,
such as handwriting, deteriorate above 10,000 ft, and higher
altitudes can affect simpler tasks and reaction times. Various
cognitive tasks, such as card sorting, are affected, usually
more than simple psychomotor tasks.
The physiological effects of a number of other pollutants
such as NO 2 and SO 2 have been studied and information about
their olfactory effects is also available. The olfactory system
is very sensitive, and may give adequate warning for some
pollutants. Sulfur dioxide, though extremely toxic is difficult
to inhale at lethal concentrations without warning because
of its intensely irritating properties. Habituating effects do
occur with repeated exposure, however, and severe poison-
ings have occasionally been reported among workers who
have adapted to high levels of this pollutants. It is important
to note that the olfactory sense adapts very rapidly to most
odors. This consideration is important when using odor tests,
for chlorine in water, for example.
A number of other substances are not readily detect-
able by smell, however. Carbon monoxide is odorless, andC016_012_r03.indd 1032C016_012_r03.indd 1032 11/18/2005 11:03:54 AM11/18/2005 11:03:54 AM