A theoretical analysis of normal- and impaired-hearing intensity discrimination

Interpretation of psychophysical data from impaired-hearing individuals on intensity discrimination tasks has been confounded by the fact that some impaired individuals´ performance is near-normal in quiet, whereas for others, the difference limen is elevated. It has been observed that a subject´s discrimination abilities may be related to the underlying audiogram configuration, which is often dependent on the type of physiological damage that has occurred. This suggests that data be grouped and analyzed according to the type of hearing loss. An experimental study by Schroder et al. (1994) tested the hypothesis that the near-normal performance of some impaired subjects was the result of a normal spread of excitation, rather than greater intensity resolution due to loudness recruitment. In this paper, we replicate the trends observed in Schroder et al.´s experimental data using a combination of signal detection theory and a computational auditory model. By linking simulated psychophysical predictions with the corresponding simulated physiological responses, this theoretical analysis provides further qualitative support for the hypothesis that the observed performance is due to the spread of excitation.