Eight male unacclimatized subjects were selected for the present investigation.
The subjects were all in excellent health and ranged in age between 25 and
35 years. Subjects performed one-dimensional horizontal compensatory tracking, the
Critical Instability Tracking Task (CITT), in each of eight environmental conditions for
an hour. Two levels of ambient temperature were used: 22°C (72°F) and 35°C
(95°F). Two levels of relative humidity were used: 45% RH and 80% RH. The resulting
Wet-bulb Globe Temperatures were 18°C (64°F) WBGT, 21°C (70°F) WBGT,
29°C (85°F) WBGT, and 34°C (93°F) WBGT. Two levels of tracking difficulty were
used: easy ()λlow = 1.0 and λhigh = 2.0) and moderate (λlow = 1.0 and λhigh = 5.0). Prior
research has demonstrated that both ambient temperature and tracking difficulty affected
significantly tracking performance (root-mean-square error) and perceived
workload (SWAT rating). However, in this study, hu midity did not affect either measure
significantly. This might be attributable to the upper bound of humidity (80% RH)
used in this research. Therefore, research needs to be done above 80% RH to examine
the effects of humidity in further detail. Results also indicated that the Subjective
Workload Assessment Technique (SWAT) can be used as a good indicator of
the actual changes in mental workload on tracking in heat. Finally, results showed
that tracking performance decrement occurred at a lower temperature (29°C (85°F) WBGT) than did the perception of significant mental workload on tracking (which occurred
at 34°C (93°F) W8GT).
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