The ecological significance of extended high-frequency hearing in humans

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The World Health Organization reports that nearly a half billion people suffer from a disabling hearing loss worldwide. Hearing loss is typically measured in the standard audiometric frequency range, 250 to 8,000 Hz. However, the young, healthy human frequency range of hearing extends to about 20,000 Hz. Extended high- frequency hearing loss (>8,000 Hz) is rarely assessed in the clinic but is a widespread, natural, age-related condition that begins as early as young adulthood. It is unknown to what extent extended high-frequency hearing loss affects daily functioning. This proposal assesses the ecological value of extended high-frequency hearing for speech perception and spatial awareness in realistic settings, which will include spatially separated talkers having different head orientations in reverberant conditions. There are three specific aims. Aim 1 will generate a high-fidelity multi-directional anechoic speech database with a representative cohort of adult native speakers of American English. This database is designed to be used for speech perception experiments and will be made publicly available. Speech spectral energy across the full range of human hearing will be examined, as well as the nature of speech radiation toward different directions around the talkers. Aim 2 will test the effect of simulated loss of extended high frequencies on speech perception and spatial awareness for listeners with normal hearing out to 16 kHz. These experiments are based on our recent observation that extended high frequencies in speech provide a benefit for speech-in-speech recognition. We will determine the magnitude of this benefit in realistic settings and the factors responsible for it. Aim 3 will test the effect of natural loss of extended high frequencies on speech perception and spatial awareness. Forms of natural loss that will be studied include hearing loss at extended high frequencies and the wearing of face coverings (masks) by talkers. The proposed studies will establish the ecological utility of extended high frequencies for speech communication. Valuable insight will be gained as to how extended high-frequency hearing loss impacts daily living for otherwise normal-hearing listeners. It is expected that results of the proposed studies will aid in ongoing efforts to (1) improve clinical measures of hearing loss and (2) improve hearing-aid processing techniques.