Band-envelope speechreading supplements derived from noisy speech

Abstract

Listeners with severe-to-profound hearing losses often rely on speechreading for communication. Previous studies [Grant etal., Q. J. Exp. Psychol. 43A, 621–645 (1991); J. Acoust. Soc. Am. 95, 1065–1073 (1994)] have shown that amplitude envelope signals derived from bands of speech can substantially enhance speechreading. This study evaluated the effects of additive noise on this benefit. The supplement consisted of three tones (500, 1600, and 3300 Hz) amplitude modulated by the envelopes of the outputs of two-thirds-octave filters centered at 500, 1600, and 3300 Hz, respectively. This three-envelope signal improved word scores on CUNY sentence materials [Boothroyd etal., CUNY Rpt. RCI-10 (1985)] for 32% with speechreading alone to 94% when the supplement was derived from speech at +12 dB S/N. Roughly half of the benefit is retained at S/N=0 dB (60% correct). This result suggests that the band envelope signals can be successfully adapted for presentation to listeners with severely restricted dynamic ranges, since at an S/N of 0 dB, excursions of the component envelope signals are limited to roughly 12–15 dB by the relatively constant background noise. [Work supported by NIH.]