The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing, the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Observations by aviators and mountain climbers who attempt to ascend above 10,000 to 14,000 ft will often include references to impairments of cognitive abilities.Although known cognitive impairments occur at altitude, little has been done to research the perception of such decrements in performance. The purpose of this study was to evaluate potential differences in actual and perceived cognitive performance at moderate altitude (10,000 ft and 14,000 ft) under several environmental conditions. Ten subjects were exposed to each altitude condition on separate days and asked to perform a computer test, SYNWIN, while at rest at ground level (5,000 ft), at rest at altitude, after 10 minutes of exercise at altitude, and while breathing supplemental oxygen at altitude.Before and after each test at altitude, subjects were asked to provide pre-and post-test estimates regarding their performance on the cognitive test by rating their performance on a five-point scale, as compared to the most recently completed test. It was hypothesized that cognitive performance at 14,000 ft would be worse than that at 10,000 ft, with the difference exacerbated after exercise, but then eliminated by supplemental oxygen. It was also hypothesized that over-confidence would also manifest itself, to degrees corresponding to the hypothesized decrements in performance.Actual performance on the test was significantly greater at 10,000 ft compared to both ground level and 14,000 ft while at rest. Performance at 10,000 ft was also in significantly greater than that at 14,000 ft after exercise and oxygen supplementation.Post-exercise scores were significantly greater than pre-exercise scores, regardless of altitude. Performance while breathing supplemental oxygen was significantly greater than without oxygen, also regardless of altitude.Subjects were unable to accurately predict their performance on the test prior to taking the test regardless of test condition. Under-estimation was prevalent for the resting and post-exercise test, while over-estimation was common while breathing supplemental oxygen. After taking the test, the subjective performance estimates showed better correlations with actual performance changes, but no obvious trends (such as marked blocks of correlations while breathing supplemental oxygen) were apparent.Based on the improvements in performance following exercise and oxygen, both protocols could be recommended to pilots prior to or during crucial portions of the flight.Although over-confidence tendencies whi...