SPEECH IN AN ARTIFICIAL ATMOSPHERE (30% HELIUM-70% OXYGEN).
Final rept. Oct 65-May 67,
DAYTON UNIV OHIO RESEARCH INST
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During a simulated space mission, speech was analyzed to investigate the effects on communication of a 56-day exposure to a cabin atmosphere composed of 30 helium and 70 oxygen at an altitude of 27,000 feet. Results of physical and subjective analyses indicated 1 Word intelligibility was satisfactory so long as the level of ambient noise in the speech frequency range did not exceed the speech level. 2 Fundamental frequency remained relatively unaffected by the 30 helium-70 oxygen gas mixture. 3 Mean second and third formant frequencies were 1.109 and 1.079 times higher in the helium exposure than in the initial ground level condition. 4 There was no adaptation in formant frequency shift as a function of time in the helium mixture, however, some persistency effects were seen during the post-exposure condition. 5 Calculated velocity of sound ratios were found to overestimate the measured amount of formant shift by a mean factor of 0.05 for the 30 helium mixture. 6 Speech quality was judged to deteriorate with increased duration of exposure to the 30 helium mixture. Comparisons were made between these findings and the results of a previous study which investigated speech produced in a 56 helium-44 oxygen atmospheric mixture. Author
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