Music Perception of Cochlear Implant Users
Objectives: This study investigated the music perception skills of cochlear implant (CI) users, compared to hearing aid (HA) users who met the audiological criteria for a CI. Further, to eliminate some of the inter-subject variability that arises when making such betweengroup comparisons, a group of patients on the waiting list for a CI were tested prior to implantation whilst utilising their HA, and then again post-surgery, with the CI. It was hypothesised:
1) That experienced CI users (CI subject group) would score lower than HA users (HA subject group) on the pitch, instrument identification, and melody tests, but not the rhythm test;
2) That subjects on the waiting list for a CI (WL subject group) would score higher on the pitch, instrument identification, and melody tests when tested with their HA pre-implantation than post-surgery with their CI; and 3) That subjects utilising a HA (i.e., both the HA subject group and the WL subject group when tested with their HA pre-implantation) would rate music to sound more pleasant than the subjects utilising a CI (i.e., the CI subject group and the WL subject group when tested post-implantation). Method: Fifteen postlingually deafened adults utilising a Nucleus CI (i.e. the CI group) were compared to 15 postlingually deafened adults using a HA (i.e. the HA group); both of these subject groups had at least one year’s experience with their respective devices. Of the CI subject group, 8 subjects used the CI24 device with the ACE speech-processing strategy, and 7 subjects used the CI22 device with the SPEAK speech-processing strategy. All of the HA subjects met the audiological criteria for a CI in terms of hearing thresholds and speech perception scores. Further, 9 subjects on the waiting list (WL) for a cochlear implant were also tested pre-surgery with their HAs, and subsequently 3 ii months post switch-on of their CI24 device, implemented with the ACE speechprocessing strategy. A series of music tests were developed for this research incorporating four major tasks: (i) discrimination of 38 pairs of rhythms; (ii) pitch ranking of sung vowels, one-octave, half-octave, and a quarter-octave apart; (iii) instrument recognition and appraisal involving three subtests, each comprising 12 different instruments or ensembles; and (iv) recognition of 10 familiar melodies where the pitch and rhythm cues were preserved. The tests were initially verified with a group of normally hearing subjects. Stimuli were presented at comfortable presentation levels either via direct audio input or through a neck loop system activated by the telecoil on a subject’s HA. The test battery was administered to each subject on two separate occasions. Results: The results of the assessments partially supported the first two hypotheses, but not the third. For the first hypothesis, as expected there was no significant difference between the CI and HA subjects on the rhythm test. The CI group scored significantly lower on the pitch and melody tests (p < 0.001 for both comparisons), but equivalent to the HA subjects on the instrument recognition tests. The second hypothesis only held true for the one-octave and quarter-octave subtests of the pitch task (p = 0.007, and p < 0.001, respectively), with lower pitch-ranking scores obtained post-surgery with the CI than pre-surgery. There were no significant differences between the pre- and post-surgery test scores for the rhythm, instrument identification, or melody tests. The third hypothesis was not supported by the findings of this research with the subjects utilising a CI rating the music stimuli to sound more pleasant than the subjects utilising a HA (WL subjects: p = 0.005 for subtest 2, and p = 0.009 for subtest 3). Conclusions: Regardless of their experience with the device, CI users at best only scored equivalently to, and for the pitch tasks, significantly worse than, HA users. However, the HA users did not score as well as what may be expected with normally hearing listeners. These findings suggest that despite the two devices using contrasting modes of auditory iii stimulation, and providing different perceptual cues for the listener, neither the CI nor the HA enabled the subjects in this study to achieve satisfactory or effective music perception.