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The development of saturation diving has enabled man to work in the sea for long periods of time--and at great depths. This situation has created problems in speech communication due to the effects of breathing HeO2 gas mixtures at high ambient pressures. The paper describes program of empirical research (conducted at depths ranging from 250 to 825 feet) used to investigate the effects of HeO2/P on speech. Specifically, a series of experiments is described that relate the distorting effects of the HeO2/P environment to: intelligibility levels, phonemic confusions, non-linearity of vowel format shifts, speech adaptation over time, and speech modification techniques to improve intelligibility. The research demonstrates that the intelligibility of a diver's speech under HeO2/P conditions improves over time, i.e., even unsystematic speaker adaptation to the environment occurs as a function of the length of time the diver remains in HeO2/P. Finally, it was found that divers can systematically manipulate their speech characteristics in order to be more intelligible in the HeO2/P milieu. (Author Modified Abstract), Report on Underwater Speech Communication. See also AD-751 665.

A theory that divers hear primarily by bone conduction has been proposed. The present status of this theory is reviewed, as well as past theoretical concepts and data from reported experiments. Experiments have focused on auditory sensitivity in the hyperbaric situation and in water as a function of basic response, depth, contents of the external ear and contents of the middle ear. Findings provide further support for the hypothesis that underwater sound energy is transduced to the cochlea by bone conduction rather than by normal external and middle ear linkage. Implications of this theory relative to divers' auditory functioning underwater are discussed. (Author Modified Abstract), Report on Underwater Speech Communication.

Support for, and a refinement of, the hypothesis that divers hear primarily by bone conduction was provided by Hollien and Brandt. To further test this hypothesis, the thresholds of seven submerged listeners were obtained (at frequencies of 0.25, 0.50, 1.0, 4.0 and 8.0 kHz) under three different conditions: (1) while they wore a full 3/16 in. wet suit with no hood, (2) while wearing a full 3/16 in. wet suit with a 3/16 in. hood and (3) while wearing a full 3/16 in. wet suit and hood with 1/4 in. rubber tubes passing through the hood to the external auditory meatuses. There were no significant differences between the conditions involving the use of a hood but thresholds were significantly lower in the middle and high frequencies for the no-hood condition. These findings provide further support for the hypothesis that underwater sound energy is transduced by bone conduction rather than by the normal middle ear linkage. (Author), Report on Underwater Speech Communication.

Data are presented on relative speech intelligibility as processes via unscramblers under two conditions: on-line and off-line. The report provides a discussion of the strengths and weaknesses of current approaches to HeO2 speech processing and makes recommendations for the improvement of these devices., Report on Underwater Speech Communication.