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.