Simulating the effects of spread of electric excitation on musical tuning and melody identification with a cochlear implant

Purpose: To determine why, in a pilot study, only 1 of 11 cochlear implant listeners was able to reliably identify a frequency-to-electrode map where the intervals of a familiar melody were played on the correct musical scale. The authors sought to validate their method and to assess the effect of pitch strength on musical scale recognition in normal-hearing listeners. Method: Musical notes were generated as either sine waves or spectrally shaped noise bands, with a center frequency equal to that of a desired note and symmetrical (log-scale) reduction in amplitude away from the center frequency. The rate of amplitude reduction was manipulated to vary pitch strength of the notes and to simulate different degrees of current spread. The effect of the simulated degree of current spread was assessed on tasks of musical tuning/scaling, melody recognition, and frequency discrimination. Results: Normal-hearing listeners could accurately and reliably identify the appropriate musical scale when stimuli were sine waves or steeply sloping noise bands. Simulating greater current spread degraded performance on all tasks. Conclusions: Cochlear implant listeners with an auditory memory of a familiar melody could likely identify an appropriate frequency-to-electrode map but only in cases where the pitch strength of the electrically produced notes is very high.