Phase discrimination and stimulus level in normal‐hearing and hearing‐impaired listeners.

Abstract

In a linear filterbank there is a simple trade‐off between filter bandwidth and duration of the impulse response. This suggests that hearing‐impaired listeners with broad auditory filters will have abnormally acute temporal sensitivity, and would be more sensitive than normal to phase manipulations in harmonic stimuli. However, repeated attempts to substantiate this prediction have largely failed. Linear models fail to account for the loss of gain associated with outer haircell damage in the impaired cochlea. In preparation for modeling phase discrimination with an active cochlea model, phase discrimination thresholds were measured at a number of stimulus levels for normal‐hearing and hearing‐impaired listeners in a standard/2AFC experiment. Stimuli were 21‐component harmonic complexes with a fundamental frequency of 125 Hz. The standard had all components in cosine phase. Test stimuli had odd‐numbered harmonics in cosine phase and even‐numbered harmonics shifted a fixed number of degrees as determined by an adaptive track. For both groups of listeners, phase discrimination deteriorated as stimulus level decreased below 30–40 dB SL. The importance of sensation level to these results and their lack of dependence on frequency resolution will be discussed in terms of linear and level‐dependent models of cochlear function. [Work supported by NIH.]