Relationship between amplitude modulation in psychophysical tasks and speech in listeners with normal and impaired hearing

Abstract

Previous work suggests that listeners with hearing loss may be unable to discriminate high‐rate amplitude modulations, even when the modulation depth is above the modulation detection threshold [Grant et al., J. Acoust. Soc. Am. (1998)] 104, 1051-60. For listeners with normal hearing, high‐rate amplitude modulations contribute to speech understanding when spectral information is degraded [Xu et al., 117, 3255-3267 (2005)]. In listeners with hearing loss, the ability to use amplitude modulation in speech may be limited to frequencies at which modulation frequency discrimination is possible. To test this, amplitude modulation detection and discrimination thresholds were measured in listeners with normal hearing and mild‐to‐moderate sensorineural loss. The signal was a broadband noise carrier sinusoidally amplitude modulated at rates of 10-640 Hz. Sentence and nonsense syllable recognition was measured for the same listeners. To restrict spectral information, speech was vocoded with a sinusoidal carrier modulated with three or six channels of envelope information. Envelope filter cutoff frequency was varied from 10-640 Hz. Compared to listeners with normal hearing, the listeners with hearing loss had more variable modulation frequency discrimination and that discrimination was related to their ability to use high‐rate modulation information in speech recognition. [Work supported by NIH.]