Hearing Aid Efficiency in a Competing Speech Situation

Abstract

Discrimination for monosyllabic words heard against competing sentences was measured at the same sensation level during unaided and aided listening using four types of subject: normal hearers, conductive loss cases, nonpresbycusic sensorineurals, and presbycusics. There were 12 subjects per group. Listening against competing sentences was binaural, monaural direct, and monaural indirect at nominal primary-to-secondary ratios of +18 and +6 dB. Unaided measures, including SRT and monosyllabic discrimination, were obtained by sound field testing conditions; aided measures were obtained with the subject in a separate room wearing the hearing aid receiver and earmold while the hearing aids were mounted on an artificial head placed in the sound field test chamber. The aided measures were obtained at two sound field levels (70 dB and 60 dB SPL) and at two gain settings (50 dB and 40 dB). The main findings were (1) that the hearing-impaired required more of an increase in SPL, re performance in the sound field, to achieve spondee threshold via the hearing aid than can be accounted for by the difference in methodology alone, (2) that intelligibility of monosyllabic words in quiet was somewhat poorer during aided listening than during unaided listening even though sensation level was held constant, (3) that subjects with presbycusis and other sensorineural losses were less resistant to masking by competing sentences during unaided listening than were subjects with normal hearing or with conductive loss, and (4) that all groups exhibited reduced intelligibility for a constant sensation level. This last effect was particularly severe for patients with presbycusic and other sensorineural hearing loss. The practical implications of these findings are discussed.