As a physician, A. A. Tomatis began his research when he was examining ammunition factory workers to determine the extent of their hearing losses. He observed a particular pattern of consistent deficiencies in the high frequencies among the group. At the same time, he worked with opera singers who could no longer produce certain quality of sounds with their voices. When medical treatments failed to provide an effective solution for the singers’ deficient voices, A. A. Tomatis gave them hearing tests and observed deficiencies in their hearing similar to those of the factory workers. He further observed that the sounds missing from the singers' hearing were the same sounds missing from their voices.
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