Effects of high intensity on recognition of low- and high-frequency speech in noise

Abstract

For listeners with normal hearing (NH), speech recognition scores often decrease when intensities exceed moderate levels (rollover is observed). It is currently unclear whether the factors leading to rollover in NH listeners also limit performance for hearing-impaired (HI) listeners at high sound levels. This study aimed at clarifying the stimulus conditions most clearly associated with rollover and whether rollover effects are similar for NH listeners and listeners with mild hearing impairment. In Stage 1, NH and HI listeners heard digitally-filtered sentences and adaptive procedures were used to determine high- and low-frequency bandwidths yielding 70%-correct word recognition in quiet at moderate levels. In Stage 2, broadband and band-limited stimuli (based on the high-, and low-frequency passbands measured in quiet in Stage 1) were tested at moderate levels in background noise. Noise levels were varied adaptively to determine signal-to-noise levels supporting 30%-correct recognition. Stimulus conditions leading to criterion performance at moderate presentation levels in Stage 2 were then retested at higher levels in Stage 3. NH listeners showed larger and more consistent rollover effects for high-frequency than for low-frequency or broadband stimuli. The results for HI listeners showed greater variability but also indicated clear rollover effects for high-frequency stimuli at high levels.