Influence of implantable hearing aids and neuroprosthesison music perception.

The identification and discrimination of timbre are essential features of music perception. One dominating parameter within the multidimensional timbre space is the spectral shape of complex sounds. As hearing loss interferes with the perception and enjoyment of music, we approach the individual timbre discrimination skills in individuals with severe to profound hearing loss using a cochlear implant (CI) and normal hearing individuals using a bone-anchored hearing aid (Baha). With a recent developed behavioral test relying on synthetically sounds forming a spectral continuum, the timbre difference was changed adaptively to measure the individual just noticeable difference (JND) in a forced-choice paradigm. To explore the differences in timbre perception abilities caused by the hearing mode, the sound stimuli were varied in their fundamental frequency, thus generating different spectra which are not completely covered by a CI or Baha system. The resulting JNDs demonstrate differences in timbre perception between normal hearing individuals, Baha users, and CI users. Beside the physiological reasons, also technical limitations appear as the main contributing factors.

Timbre discrimination in cochlear implant users and normal hearing subjects using cross-faded synthetic tones.

The identification and discrimination of timbre are essential features of music perception in cochlear implant users. As timbre differences appear as multidimensional cues, the spectral shape, the spectral fluctuation, and the rise time are the most dominating parameters of timbre in normal hearing listeners. Recently, a psychoacoustical test was developed to determine the timbre discrimination abilities using only the spectral shape difference as a cue. Therefore, a synthetically generated tone continuum was used in an adaptive alternative forced choice paradigm. The spectral shape was modified by cross-fading the tones adaptively, depending on the listeners' response which allows very precise determinations of the just noticeable difference (JND). With this behavioral test, the spectral shape JND for complex tones with different fundamental frequencies was measured in cochlear implant users and compared to normal hearing listeners. The results confirm the applicability of the test to measure timbre discrimination in cochlear implant users. The resulting individual spectral shape JND profiles reveal a maximum with a fundamental frequency of 525 Hz, whereas the JND profiles were rather flat in the normal hearing individuals.