Place-Pitch Interval Perception With a Cochlear Implant

Abstract

Objectives: Pitch is poorly perceived by cochlear implant (CI) users. However, as it is not well understood how pitch is encoded with electric stimulation, improving pitch representation with a CI is challenging. Changes in place of stimulation along the cochlea have been described as changes in pitch and can be accurately ranked by CI users. However, it remains unknown if place-pitch can be used to encode musical intervals, which are a necessary attribute of pitch. The objective of these experiments is to determine if place-pitch coding can be used to represent musical intervals with a CI. Design: In the first experiment, 10 CI users and 10 normal hearing (NH) controls were tested on their sensitivity to changes in the semitone spacing between each of the notes in the melody “Happy Birthday.” The changes were implemented by uniformly expanding or compressing the frequency differences between each note in the melody. The participant’s task was to scale how “out-of-tune” the melody was for various semitone spacing distortions. The notes were represented by pure-tones ≥440 Hz to minimize potential useful temporal information from the stimuli. A second experiment replicated the first experiment using single-sided deafened CI users allowing for a within-subject control. A third experiment verified that the CI users who participated in Experiment 1 were each able to determine pitch direction reliably. Results: Unlike NH listeners, CI listeners often ranked all distortions of interval spacing similarly in both the first and second experiment, and no effect of interval spacing was detected across CI users. Some participants found distorted interval spacings to be less out-of-tune than the nominally correct interval spacings. However, these patterns were inconsistent across listeners. Although performance was better for the NH listeners, the third experiment demonstrated that the CI listeners were able to reliably identify changes in pitch direction from place-pitch coding. Conclusions: The data suggest that place-pitch intervals are not properly represented through a CI sound processor. Some limited support is found for place-pitch being useful for interval encoding as some participants demonstrated improved ratings for certain interval distortions. Presumably the interval representation for these participants could be improved by a change to the frequencies represented by each electrode. However, as these patterns vary across listeners, there is not a universal correction to frequency representation that will solve this issue. As results are similar for single-sided deafened CI users, the limitations in ratings are likely not limited by an eroded representation of the melody caused by an extended duration of deafness.

Musical Interval Perception With a Cochlear Implant Alone and With a Contralateral Normal Hearing Ear

“…Six of the 10 subjects used the advanced combination encoder (ACE) sound coding strategy which provides no useful temporal cues in response to pure tones ( Stupak et al, 2021 ; Swanson et al, 2009 ) and one used HiRes Optima-P which provides reliable temporal cues only for pure tones above 306 Hz (Appendix of Stupak et al, 2021 ). However, the two subjects using FS4 or FS4p strategies were provided reliable temporal and place cues in response to the pure tones (Appendix of Stupak et al, 2021 ). Sung vowels are more complicated stimuli which provide both place and temporal modulation cues through a processor.…”

“…Place coding can also distort perceived intervals. Using x-ray data from Landsberger et al (2015) , Stupak et al (2021) documented that the average number of semitones per degree represented by the default frequency allocation was smaller than the number of semitones per degree represented by the corresponding characteristic frequency (CF) of the spiral ganglion ( Stakhovskaya et al, 2007 ). Although the number of semitones per degree varied considerably across insertions and devices, the compression of intervals across the cochlea was consistently found for all manufacturers.…”

“…They found that intervals presented to a CI were indeed perceived as smaller than the same intervals presented to a contralateral acoustic-hearing ear, although the size of this distortion highly varied across listeners. Stupak et al (2021) conducted a variant of the Todd et al (2017) experiment using pure tones presented to a sound processor to emphasize place-pitch coding ( Swanson et al, 2009 and the supplemental appendix of Stupak et al, 2021 ). They found that when presented to an implanted ear, presentations of Happy Birthday were rated as similarly out-of-tune when the semitone spacing was correct, compressed or expanded.…”

Computer-based musical interval training program for Cochlear implant users and listeners with no known hearing loss

“…Existing studies have shown that cochlear implant users have poor interval identification compared to their normal-hearing peers, especially above middle C. Pitch and relative intervals can be conveyed by stimulation timing (i.e., the modulation or stimulation rate) but with much variability in pitch salience and in the upper frequency that can be conveyed by stimulation rate ( Pijl and Schwarz, 1995a , b ; Pijl, 1997 ; Todd et al, 2017 ). Place cues for pitch (i.e., active electrodes and stimulation configuration) provide a strong sense of pitch but one that is compressed compared to normal ( Stupak et al, 2021 ). Stupak et al (2021) found consistent warping of intervals amongst cochlear implant users, suggesting the ability to perceive intervals is likely not linked to duration of deafness.…”

“…Place cues for pitch (i.e., active electrodes and stimulation configuration) provide a strong sense of pitch but one that is compressed compared to normal ( Stupak et al, 2021 ). Stupak et al (2021) found consistent warping of intervals amongst cochlear implant users, suggesting the ability to perceive intervals is likely not linked to duration of deafness. Spitzer et al (2021) investigated musical interval distortion in cochlear implant users who had normal hearing in their non-implanted ear (i.e., single-sided deafness).…”