When environmental conditions are such that a person's adaptive and
coping resources are strained or taxed, the environment is not only less
than optimal, it is also stressful. Examples of environmental stressors in-
clude noise, heat, cold, pollution, and crowding or density (crowding and
density are reviewed in a separate section of this chapter under "Human
Spatial Behavior"). Stressors that are intense, prolonged, unpredictable, and
uncontrollable are particularly distressing and debilitating. First of all, un-
predictable and uncontrollable stressors make heavy demands on atten-
tional capacity because of the effort required to "tune out" the distracting
aspects of the stimulus or to monitor the threatening aspects of the stim-
ulus. Prolonged exposure to such stressors results in cognitive fatigue and
a depletion of attentional resources that persists even after the stressful
experience has ended ( Cohen, 1978). Second, exposure to unpredictable
and uncontrollable stressors can lead to learned helplessness ( Seligman,
1975)--people come to believe that their inability to cope with a specific
stressful situation is indicative of a general inability to cope with life-tasks
and events, resulting in motivational, emotional, and cognitive deficits.

The cognitive-fatigue hypothesis suggests that unpredictable, uncontrol-
lable noise should lead to a reduction in people's sensitivity to social cues.
In one study, Mathews and Canon ( 1975) arranged for an assistant of the
experimenters to drop a box of books on a city street. In one condition,
the assistant's arm was in a plaster cast; in the other condition, there was
no plaster cast. The incident was staged either under noisy conditions (a
nearby power mower) or quiet conditions. When the street was quiet, pass-
ers-by were much more likely to help the assistant with an arm cast than
without a cast. Under noisy conditions, not only was there less helping
overall, but passers-by were also no more likely to help the assistant with
the arm cast than the assistant without the cast, because passers-by were
less likely to notice the arm cast.

The role of perceived control in moderating the after-effects of noise
stress was highlighted by Sherrod and Downs ( 1974). Subjects worked on
a task under one of three noise conditions. In one condition (low stress),
subjects were exposed to soothing sounds; in a second condition (high
stress/low control), subjects were exposed to distressing sounds which could
not be terminated; in a third condition (high stress/high control), subjects
were also exposed to distressing sounds but could turn off the noise if they
wished. After completion of the task and on their way out of the labora-
tory, subjects were asked by a second experimenter for help in a research
project. Subjects who had been exposed to the soothing sounds volunteered

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