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The ability of cochlear implant (CI) users to perceive music remains severely limited, primarily due to limited pitch resolution (Gfeller et al., 2002; Pijl, 1997). While studies have shown that CI users are able to adequately perceive temporal cues that convey rhythmic information, the perception of pitch and timbre remains quite poor with current CI hardware and processing strategies (Leal et al., 2003; McDermott, 2004). Previous studies have shown that CI users are severely impaired compared to normal hearing (NH) subjects in tests of pitch perception using acoustically presented stimuli, with CI users rarely exhibiting pitch discrimination thresholds of less than several semitones (Gfeller et al., 2002; Looi et al., 2004). Most published studies on pitch perception have focused on pitch discrimination, in which subjects are required to detect whether two sounds differ in pitch, and pitch ranking, in which subjects are asked to listen to two sounds presented in sequence and judge which one has the higher pitch. While these approaches are certainly valid, various elements (i.e., melody, harmony, rhythm, and timbre) usually occur simultaneously in music. In the context of the impaired pitch resolution described in CI users, it is germane that nearly all forms of music utilize at least some degree of polyphony (where multiple pitches occur simultaneously), an essential feature of harmony. Comparatively little research, however, has been done on the perception of polyphonic pitch (or harmony) in CI subjects. One recent study (Galvin et al., 2009) examined melodic contour segregation in CI subjects using acoustically presented stimuli and found that CI users have difficulty segregating competing melodic contours even in the presence of timbral cues.

The objectives of the present study were to evaluate the ability of post-lingually deafened adult CI users to perceive the number of pitches in acoustically presented stimuli and to compare their performance with that of NH adults. Subjects listened to acoustically presented stimuli consisting of one, two, or three simultaneous tones with different fundamental frequencies (f₀) within a single octave. Both pure tones and piano tones were used to assess the effect of harmonics on polyphonic pitch perception. We hypothesized that CI users, as a result of diminished pitch resolution, would show decreased ability to differentiate between single versus multiple tones in comparison to NH controls. We further hypothesized that the ability of CI users to detect polyphony would increase as a function of interval distance between pitches, due to the presumptive relationship between increased frequency separation and improved perception of polyphony.