Spectral Ripples in Normal and Electric Hearing Models

Devising a psychophysical test to assess spectral resolution has not been easy. Two tests that have been used previously are the spectral ripple test and the spectral-temporally modulated ripple test (SMRT). Over time, questions have been raised about the validity of these tests. We introduce a new computational electric hearing (with a cochlear implant, CI) model that can simulate how sound is transferred through a speech processor and is received by the cochlear nerve fibers. With this electric hearing model and a normal hearing model, we investigated whether the known limitations of these tests can be detected. For the spectral ripple test, we could show the limitations in the output of the CI, the information conveyed to the cochlear nerve, to estimate the threshold, and show the benefit of current steering. In addition, we reproduced the aliasing effect with normal hearing in the SMRT, as well as the reduced ripple resolution in CI users. Our computational modeling framework can serve as a first-step assessment of the validity of new psychophysical tests. Moreover, it could be used to test new speech coding strategies.