Twelve healthy male subjects were required to make speeded judgements
concerning the orientation of visual stimuli while breathing air at re
duced partial pressure in a hypobaric chamber at altitudes of 7000 and
12 000 ft. A control condition was also conducted at sea level, and s
ubjects received practice on the task at sea level prior to the commen
cement of the experiment. Significantly slower response times were obt
ained at 7000 and 12 000 ft relative to sea level. A signal-detection
analysis showed that accuracy of judgement was significantly poorer at
12 000 ft, but oxygen deprivation has no systematic effect on respons
e criterion.