Speech perception in low-pass filtered noise for normal and hearing-impaired listeners

Two experiments were conducted concerning speech perception in noise. In Experiment 1, a comparison was made between adaptive and fixed-level procedures to estimate the S/N ratio at which 50% correct performance occurred for nonsense syllables for normal-hearing listeners. The two methods yield similar S/N ratio estimates, but the consonant confusions found with the fixed-level method could not be predicted accurately from the adaptive procedure. In Experiment 2, the adaptive procedure was used to estimate the S/N ratio for a 50% performance level in low-pass filtered noise with a range of cutoff frequencies. Data were obtained from 5 normal-hearing listeners at two speech levels (50 and 75 dB SPL) and 4 hearing-impaired listeners at one speech level (75 dB SPL). The hearing-impaired listeners required a better S/N ratio than the normal listeners at either presentation level for all except the widest bandwidth, where their S/N ratios began to converge with the normal values. In addition, the S/N ratios for the hearing-impaired listeners plateaued at relatively narrow bandwidths (0.75 to 2.5 kHz) compared to the normal-hearing group (3.0 to 5.0 kHz). That is, the addition of high-frequency components to the noise did not alter performance. These findings suggest that the hearing-impaired listeners may have relied upon either low-frequency cues or prosodic cues in the perception of these test items.