Abstract
BackgroundHarmony is an important part of tonal music that conveys context, form and emotion. Two notes sounded simultaneously form a harmonic interval. In normal-hearing (NH) listeners, some harmonic intervals (e.g., minor 2nd, tritone, major 7th) typically sound more dissonant than others (e.g., octave, major 3rd, 4th). Because of the limited spectro-temporal resolution afforded by cochlear implants (CIs), music perception is generally poor. However, CI users may still be sensitive to relative dissonance across intervals. In this study, dissonance ratings for harmonic intervals were measured in 11 unilaterally deaf CI patients, in whom ratings from the CI could be compared to those from the normal ear.MethodsStimuli consisted of pairs of equal amplitude MIDI piano tones. Intervals spanned a range of two octaves relative to two root notes (F3 or C4). Dissonance was assessed in terms of subjective pleasantness ratings for intervals presented to the NH ear alone, the CI ear alone, and both ears together (NH + CI). Ratings were collected for both root notes for within- and across-octave intervals (1–12 and 13–24 semitones). Participants rated the pleasantness of each interval by clicking on a line anchored with “least pleasant” and “most pleasant.” A follow-up experiment repeated the task with a smaller stimulus set.ResultsWith NH-only listening, within-octave intervals minor 2nd, major 2nd, and major 7th were rated least pleasant; major 3rd, 5th, and octave were rated most pleasant. Across-octave counterparts were similarly rated. With CI-only listening, ratings were consistently lower and showed a reduced range. Mean ratings were highly correlated between NH-only and CI-only listening (r = 0.845, p < 0.001). Ratings were similar between NH-only and NH + CI listening, with no significant binaural enhancement/interference. The follow-up tests showed that ratings were reliable for the least and most pleasant intervals.DiscussionAlthough pleasantness ratings were less differentiated for the CI ear than the NH ear, there were similarities between the two listening modes. Given the lack of spectro-temporal detail needed for harmonicity-based distinctions, temporal envelope interactions (within and across channels) associated with a perception of roughness may contribute to dissonance perception for harmonic intervals with CI-only listening.
Highlights
Along with language, music is a near-universal part of the human experience
All participants were paid for their participation and provided written informed consent in accordance with the Institutional Review Board Procedures of New York University (IRB #S14-00809 and #S14-00435) and in accordance with the Declaration of Helsinki
Pleasantness ratings were scaled from 0 to 10 according to where participants clicked on the rating bar
Summary
Music is a near-universal part of the human experience. cochlear implants (CIs) can enable those with severe hearing loss to understand speech with high levels of intelligibility, these devices are extremely poor at conveying most tonal aspects of music (e.g., melody and harmony) that are crucial for music perception and appreciation. The coarse spectro-temporal resolution provided by a CI is adequate for speech recognition, due to the availability of low-frequency temporal envelope cues. This coarse resolution is not sufficient for music perception, especially perception of pitch, timbre, harmonicity, etc. Distorted perception of melodic (i.e., sequential) intervals contributes to CI users’ poor melody perception, especially when rhythm cues are unavailable (e.g., Gfeller et al, 2002, 2007; Kong et al, 2004; Vongpaisal et al, 2006). While perception of melodic intervals has been extensively studied, relatively little is known about CI users’ perception of harmonic (i.e., simultaneous) intervals. Dissonance ratings for harmonic intervals were measured in 11 unilaterally deaf CI patients, in whom ratings from the CI could be compared to those from the normal ear
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