Amplification bandwidth and speech intelligibility for two listeners with sensorineural hearing loss.

The intelligibility of speech as a function of its bandwidth was measured for two listeners with similar, moderately severe sensorineural hearing losses. The shape of the speech spectrum was adjusted to approximate the individual listener's contour of most comfortable listening levels (MCLs) and the overall level was set so that the levels in each band were below (-7 dB), near to (+3 dB), or above (+13 or +18 dB) the MCLs. At each level, nine pairings of three low-frequency and three high-frequency cutoffs (266, 375 and 530 Hz; 3,000, 4,242 and 6,000 Hz) were used. These conditions were achieved by passing the speech through a Limiting Master Hearing Aid (LMHA) which allows independent control of gain and maximum output in each of nine, half-octave bands. It was found that the wider the bandwidth, the higher the score, and the greater the amount of speech energy above threshold, the higher the score. Listeners' ability to understand the test material, after adjustment for listener differences, was correlated (0.7 and 0.8) with the articulation index.