Experiment on the relationship between the dynamic range of hearing and psychophysical tuning curves

Abstract

In this study, we hypothesized that improving the dynamic range of hearing for adults with hearing loss would improve spectral resolution by providing better audibility across frequency and—due to the higher sensation level—improved phase locking. However, limited outer hair cell (OHC) function and spread of excitation likely curtail the benefit of improved audibility on spectral resolution. In this experiment, the relationship of the dynamic range of hearing to measures of psychophysical tuning curves was quantified for 13 adults with hearing loss. Twenty-one adults with normal hearing served as controls. A dynamic range of hearing was manipulated by systematically adjusting hearing-aid gain and compression ratios. To better understand the mechanisms that support the encoding of spectral resolution with amplification, the behavioral data were modeled using a cochlear excitation model. For most listeners, the psychophysical tuning curves were similar regardless of changes in the dynamic range of hearing. For a subset of participants, tuning on the low frequency side improved as the dynamic range of hearing was increased—which could be accounted for in the model by residual OHC function. The model better accounted for unaided than aided measures of tuning.