Effects of hyperbaric $HeO2$ breathing mixtures on divers' speech

It has been shown that heliox breathing mixtures, plus high ambient pressures, have a deleterious effect upon speech communication. This report attempts to provide more comprehensive information relative to the effects of the $HeO2/P$ environment on speech—especially speech intelligibility, speaking fundamental frequency, and vowel formant shifts; data also are reported on the performance of a speech processor (i.e., the Marconi “unscrambler”). The data base was developed from the recorded speech of divers who read word lists during the decompression phase of a 1600‐ft dive; the speech at the surface and at 560, 1000, 1400, and 1600 fsw was analyzed. Speech intelligibility was found to be severely degraded as a function of depth and helium concentration—but not as seriously as had been reported earlier. These effects probably were due to the experience of the divers and improved equipment. As expected, speaking fundamental frequency rose as a function of increasing depth; the shifts were consistent with those previously reported. The vowel formant data provide, for the first time, a comprehensive evaluation of the $HeO2$ effects on these speech features. As expected, the data revealed an upward shift in the formants as a function of increasing depth but the patterns were not as systematic as expected. The data were utilized to compute “K factors” for the formant shifts [G. Fant and J. Lindquist, STL‐QPR 1, 7–17 (1968)]. Finally, the effectiveness of the Marconi system, and its implications, will be discussed. [Work supported by the Norwegian Underwater Institute, Bergen.]