The Effect of Bimodal Stimulation on Pitch Ranking and Speech Recognition in Children with Cochlear Implants (2010)
Type of ContentTheses / Dissertations
Degree NameMaster of Audiology
PublisherUniversity of Canterbury. Communication Disorders
Data from normal-hearing (NH) listeners indicates that access to the low-frequency, lownumbered harmonics in complex sounds is important for the perceptual segregation of competing sounds (see Oxenham, 2008 for a review). Poor frequency selectivity is experienced by many listeners with sensorineural hearing loss, resulting in reduced perceptual access to individual harmonics (Arehart, 1994; Bernstein & Oxenham, 2006b; Moore, 1996). In addition, the commercially available speech processing strategies used in current cochlear implants (CIs) provide little or no representation of individual harmonics (see B. C. J. Moore, 2003 and; Wilson & Dorman, 2008 for a review). Improvements in CI technology and concurrent improvements in speech perception outcomes have led to an expansion of the implantation criteria to include individuals with residual acoustic hearing in one or both ears. A growing body of evidence supports the use of bimodal stimulation (BMS) in such individuals (e.g. Beijen, Mylanus, Leeuw, & Snik, 2008; Ching, Incerti, & Hill, 2004; Ching, Incerti, Hill, & van Wanrooy, 2006; Dunn, Tyler, & Witt, 2005; Luntz, Shpak, & Weiss, 2005; Mok, Grayden, Dowell, & Lawrence, 2006). Bimodal stimulation involves the electrical stimulation of one ear via a CI, and acoustic stimulation of the contralateral ear via a hearing aid (HA). Evidence suggests that BMS may improve the speech recognition in noise performance of CI users, and allow for improved music perception through the provision of additional pitch cues (Ching, Psarros, Hill, Dillon, & Incerti, 2001; Kong & Carlyon, 2007; Kong, Stickney, & Zeng, 2004; McDermott, Sucher, & Simpson, 2009; Mok, Galvin, Dowell, & McKay, 2007; Sucher, 2007; Sucher & McDermott, 2007). The present study compared the speech recognition and pitch ranking abilities of 16 NH children, 8 children using a unilateral CI (CI-only group); 6 children with a severe-profound hearing loss using bilateral HAs (HA-only group), and 9 children who were experienced users of BMS (eBM group). In addition, a single CI-only user (Case A) with residual hearing in their non-implanted ear was fitted with a contralateral HA, and their performance was assessed using their CI-alone and after 3 months experience using BMS. It was hypothesised that: (i) The eBM group would score higher than the CI-only group for tasks of word recognition in quiet; (ii) there would be no difference between the sentence recognition in quiet scores of the CI-only, HA-only and eBM groups; (iii) the eBM and HAonly groups will score higher than the CI-only group on tasks of sentence recognition in noise; (iv) the eBM group will rank pitch more accurately than the CI-only group, but not the HA-only group, and; (v) that the addition of an optimally fitted HA in the non-implanted ear of children using a CI will result in improved speech recognition in quiet and noise, and improved pitch ranking accuracy. Participants were assessed using their normal listening devices using; the Consonant- Nucleus-Consonant (CNC) word lists in quiet; the Hearing In Noise sentence test (HINT) in quiet (S0) and in spatially coincident (S0N0) and spatially separated (S0NCI, S0NHA) 4- talker babble, using a 10 dB signal-to-babble ratio; and a pitch ranking task (PRT) using 1, ½ and ¼ octave interval sizes. All testing was conducted in a soundfield. There were no significant differences between the mean scores of the CI-only, HA-only and eBM groups for either the CNC word lists in quiet, or the HINT sentences in quiet or noise, participants scoring at ceiling levels for all four HINT listening conditions. There was also no improvement in Case A’s CNC word scores, however their HINT sentence scores improved by 23.7% points in quiet and by an average of 11.9% points in noise following the addition of a contralateral HA. These improvements were greater in size than the largest learning effect seen in the CI-only and HA-only groups for 3 of the 4 HINT listening conditions. For the PRT, there were no significant differences between the scores of the CIonly and eBM groups. As expected, the NH group scored significantly higher than the CIonly and eBM groups on all three subtests (p < 0.05). The HA-only group scored significantly higher than the CI-only and eBM groups on the 1 and ½ octave subtests. There were no significant differences between the scores of the NH group and HA-only groups on all three subtests. Case A’s PRT scores were higher in the BMS (M = 83.3% correct) than the CI-only condition (M = 74.0%). This improvement was considerably greater than the largest learning effect seen in the CI-only and HA-only groups for the 1 and ½ octave subtests for stimuli with fundamental frequencies ≤ 262 Hz. Overall, we found limited evidence in support of the hypothesis that the additional lowfrequency pitch information provided via acoustic hearing in BMS allows for improved speech perception in quiet and noise, and improved pitch perception in prelingually deafened CI users. However, child CI users (CI-only and eBM groups) did rank pitch more accurately than adult CI-only users in previous studies. The higher plasticity of the central auditory nervous system of child CI users may have enabled more effective adaptation to electrical stimulation, allowing them to more effectively utilise available pitch cues than their adult counterparts. We recommend that future research isolate the contribution of the non-implanted ear to auditory perception in children using BMS, and investigate whether musical training is capable of enhancing pitch perception in users of a unilateral CI or BMS. To listen to simulations illustrating the benefits of bimodal stimulation for music perception, created during this study, please visit ‘thelisteningtree.wordpress.com’
RightsCopyright Christopher John Radford
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