2014 European Phoniatrics Hearing EUHA Award

Transcription

1 2014 European Phoniatrics Hearing EUHA Award Processing of music by prelingually and postlingually deafened patients with cochlear implant: Electrophysiological evidence Author: Lisa Bruns, Dresden

2 Published by Europäische Union der Hörgeräteakustiker e.v. Neubrunnenstraße 3, Mainz, Germany Phone +49 (0) Fax +49 (0) Website: All the documents, texts, and illustrations made available here are protected by copyright. Any use other than private is subject to prior authorisation. EUHA 2014 Impressum i

3 Abstract Processing of music by prelingually and postlingually deafened patients with cochlear implant: Electrophysiological evidence This thesis addresses the processing of music in patients using a cochlear implant (CI) due to deafness or severe hearing impairment. Listening to music is an especially difficult task for CI patients because of the acoustic complexity of music as an auditory stimulus. Not only is the discrimination of acoustic stimuli affected, but also the sound quality conveyed by the CI and individual perception when listening to music. These soft characteristics of music perception have not sufficiently been validated until now. The main aim of this study therefore is to evaluate objective measuring parameters for, and possible influencing factors of, the perception of musical qualities by CI patients. This study has a clinical experimental design comparing two groups of adult CI patients (prelingually and postlingually deafened) with each other as well as with a normal hearing control group. Patients with prelingual hearing impairment suffered from severe hearing loss from the time before or during language acquisition; patients with postlingual hearing impairment suffered from severe hearing loss after language acquisition. The thesis evaluates characteristics of music perception using three complementary methods. Influencing factors such as musical experience and anamnesis of hearing impairment are collected using questionnaires. Furthermore, the ability to acoustically differentiate certain aspects of music, such as rhythm or pitch, is measured by a musical discrimination test, similar to a hearing test, but using musical stimuli. The new approach of this study is to objectively examine the processing of musical qualities and contents by CI patients using event-related potentials (ERPs) in the electroencephalogram. The N400 effect is measured as an electrophysiological parameter in the processing of musical semantics. Complex musical pieces are used for this purpose. With this method, it is possible to measure musical perception as a whole on a higher level of processing than the discrimination of single musical aspects. Ultimately, the correlations of the data gathered are presented. The basic hypothesis of this work is the assumption that, compared to normal hearing listeners, CI patients would show impaired musical discrimination abilities. Because they had poorer hearing experience, prelingual CI patients were expected to show higher deficits. The main question is whether CI patients can perceive musical contents in spite of their impaired discrimination abilities, and the extent to which these cognitive processes are reflected in the ERP. Abstract Page 1

4 The analysis of the questionnaires confirmed that postlingual CI patients enjoyed music less often than before implantation, and also less often compared to normal hearing listeners. Prelingual CI patients, on the other hand, showed almost no difference when comparing their enjoyment of music before and after implantation. Furthermore, their counts in the evaluation did not differ much from the control group. The discrimination abilities of the CI patients were impaired in almost all subtests of the musical discrimination test compared to the control group. The comparison between prelingual and postlingual CI patients, however, did not show much divergence. In the ERP analysis, postlingual CI patients demonstrated an N400 effect comparable to normal hearing listeners, while prelingual CI patients did not show such an effect. Parameters such as speech comprehension or CI characteristics had no influence on the N400 effect. The results indicate that the point in time of the onset of hearing loss is crucial for the processing of semantic content in music. In contrast to postlingual CI patients, prelingual CI patients with impaired language acquisition showed no N400 effect as an electrophysiological correlate of semantic processing. However, the two CI groups did not differ much in either their discrimination abilities or their subjective rating of the musical semantics. Therefore, acoustic influences before implantation seem to be crucial for the processing of musical semantics, rather than current discrimination or speech comprehension abilities with the implant. The method of ERPs presented here is significant for the exploration of music perception in CI patients as it serves as an objective measuring parameter in the evaluation of the outcome after cochlear implantation. However, music and speech perception in CI patients do not correlate strongly enough to draw conclusions from one to the other. So far, the analysis of the perception of musical qualities by CI patients had been based on subjective statements collected using questionnaires. Electrophysiological investigations referred to discriminative or syntactic characteristics in music. In this study, the N400 effect objectively reflects whether semantic associations were activated in CI patients when listening to music. The ERP analysis conducted broadens the range of methods available in musical research on CI patients. Thus, objective statements about the processing of semantic musical content on a higher level of processing in CI patients can be made. This method is only valid when group averages across participants are calculated. Therefore, control measurements, such as validation of therapy success after cochlear implantation, should focus on longitudinal group measurements. In this study, the perception of musical pieces was examined as a complex entirety. Further research should characterise the musical elements that carry semantic content (e.g. tonality or rhythm) to receive more precise information about the difficulties of perceiving musical semantics with CI. On this basis, it could be possible to recommend specific music to CI patients and to expand musical auditory training by semantic content based on evidence. Abstract Page 2

5 This study compared objective discriminative and qualitative aspects of music perception between postlingually and prelingually deafened CI patients for the first time. It has become evident that especially acoustic influences before implantation affected the perception of musical qualities with CI. Based on these findings, an important next step would be the investigation of the musical N400 effect in prelingual CI patients who were implanted in early childhood. These patients can only refer to the hearing impression conveyed by the CI with the background of a relatively normal language acquisition process. Because of the historical development of cochlear implantation in Germany, this generation of CI patients is currently in adolescence, which makes it possible to investigate the issue described above in the near future. Thus, it would be possible to further evaluate the extent to which hearing with a cochlear implant or impaired hearing development influence the perception of musical qualities. Contact: lisa.bruns@briefhansa.de Abstract Page 3