Training of cochlear implant users to improve pitch perception in the presence of competing place cues.

OBJECTIVES: Perception of musical pitch in cochlear implant (CI) systems is relatively poor compared with normal hearing and can be adversely affected by changes in spectral timbre coded by stimulation place. In this study, we evaluated whether the perception of musical pitch could be improved through specific training designed to teach listeners to attend to fundamental frequency (F0) exclusively for judgment of pitch and to spectral envelope exclusively for discrimination of spectral timbre.
DESIGN: A computer-based training program to improve musical pitch perception was developed that required listeners to match acoustic patterns of pitch and spectral timbre to visual patterns. Ten adult CI recipients participated: five used the training program and five acted as controls. Before training, F0 and center frequency discrimination for band-limited complex harmonic stimuli presented in the sound field were measured in all subjects using their standard clinical device(s). The F0 tests were conducted with and without spectral variations. The trainees subsequently used the training program at home for a period of 4 months, during which they were asked to train for approximately 30 min per day. The training schedule comprised two successive phases, each lasting 2 months. In the first phase, training employed a single cue (i.e., F0 for pitch or center frequency for spectral timbre) in the absence of other cue variations. In the second phase, training incorporated more complex sounds in which multiple cues were varied. Discrimination thresholds were remeasured in all subjects after each phase and again with trainees 3 months after training had ceased.
RESULTS: Trainees obtained significant improvements in F0 and center frequency discrimination as compared with control subjects for tests conducted at 2 months. The improvements in F0 discrimination were observed both in the absence and presence of small variations in place. However, the effect of training diminished for large variations in place or for higher F0s. Neither group showed further improvement in tests after additional training in the second phase. Tests conducted with trainees after training had ceased showed that F0 discrimination improvements were retained.
CONCLUSIONS: The results showed that performance on pitch and timbre discrimination can be improved by training with single cues (F0 and center frequency) in the absence of other cue variations. Although results indicated that training with single cues can improve F0 discrimination within more complex sounds in which multiple cues vary, little improvement was seen when large variations in place were present, which suggests a diminishing effect of the training with increased influence of place-pitch. These data imply that although such training techniques may help listeners to follow melody in music, changes in instrument are likely to affect perception of melody. Results of subsequent training with complex sounds in which multiple cues varied were less conclusive and showed no further improvement. Follow-up evaluations with trainees conducted well after training had ceased verified the robustness of the training effect on F0 but not center frequency discrimination. Further studies are needed, however, to determine whether and to what degree subject motivation may be an important factor in these outcomes.