Low bandwidth aids to speechreading based on conveying speech band amplitude envelopes

Abstract

The amplitude envelopes of filtered bands of speech can improve speechreading by normal hearing listeners substantially [Grant et al., J. Acoust. Soc. Am. 89, 2952–2960 (1991)]. Acoustic signals that convey these envelopes to listeners with severe hearing impairments are currently being evaluated in field and laboratory studies. An initial field study used SiVo aids to derive the amplitude envelope of the octave band of speech centered at 500 Hz and modulate a 200-Hz tone. Of two listeners who used the aids for two months, one benefitted substantially from the amplitude modulated signal and continues to use the aid in preference to conventional hearing aids. In the laboratory study, four normal-hearing listeners compared speechreading supplements derived from one and two filtered bands of speech. Presenting the envelopes of octave bands at 500 and 3300 Hz by modulating the amplitudes of 200- and 240-Hz tones led to keyword scores in IEEE sentences of 74% correct, compared to 76% corrrect when 200- and 500-Hz tones were modulated, and 63% when only a single 200-Hz tone was modulated. Modulating pairs of tones with closely spaced frequencies may thus assist speechreading by listeners with limited hearing. [Work supported by NIH.]