Individual Optimization of the Insertion of a Preformed Cochlear Implant Electrode Array

Purpose. The aim of this study was to show that individual adjustment of the curling behaviour of a preformed cochlear implant (CI) electrode array to the patient-specific shape of the cochlea can improve the insertion process in terms of reduced risk of insertion trauma. Methods. Geometry and curling behaviour of preformed, commercially available electrode arrays were modelled. Additionally, the anatomy of each small, medium-sized, and large human cochlea was modelled to consider anatomical variations. Finally, using a custom-made simulation tool, three different insertion strategies (conventional Advanced Off-Stylet (AOS) insertion technique, an automated implementation of the AOS technique, and a manually optimized insertion process) were simulated and compared with respect to the risk of insertion-related trauma. The risk of trauma was evaluated using a newly developed “trauma risk” rating scale. Results. Using this simulation-based approach, it was shown that an individually optimized insertion procedure is advantageous compared with the AOS insertion technique. Conclusion. This finding leads to the conclusion that, in general, consideration of the specific curling behaviour of a CI electrode array is beneficial in terms of less traumatic insertion. Therefore, these results highlight an entirely novel aspect of clinical application of preformed perimodiolar electrode arrays in general

Implant technology and TFS processing in relation to speech discrimination and music perception and appreciation

Direct stimulation of the auditory nerve via a Cochlear Implant (CI) enables profoundly deaf subjects to perceive sounds. Many CI users find language comprehension satisfactory in quiet and accessible in the presence of noise. However, music contains different dimensions which need to be approached in different ways. Whilst both language and music take advantage of the modulation of acoustic parameters to convey information, music is an acoustically more complex stimulus than language, demanding more complex resolution mechanisms. One of the most important aspects that contributes to speech perception skills, especially when listening in a fluctuating background, is Temporal Fine Structure processing. TFS cues are pre-dominant in conveying Low Frequency (LF) signals. Harmonic (HI) and Disharmonic (DI) In-tonation are tests of pitch perception in the LF domain which are thought to depend on avail-ability of TFS cues and which are included in the protocol on this group of adult CI recipients. One of the primary aims of this thesis was the production of a new assessment tool, the Italian STARR test which was based on the measurement of speech perception using a roving-level adaptive method where the presentation level of both speech and noise signals varied between each sentence presentation. The STARR test attempts to reflect a better representation of real world listening conditions where background noise is usually present and speech intensity var-ies according to vocal capacity as well as the distance of the speaker. The outcomes for the Italian STARR in NH adults were studied to produce normative data, as well as to evaluate inter-list variability and learning effects. (Chapter 4). The second aim was to investigate LF pitch perception outcomes linked to availability of TFS cues in a group of adult CI recipients including bimodal users in relation to speech perception, in particular Italian STARR outcomes. Here it was seen that age had a significant effect on performance especially in older adults. Similarly, CI recipients (even better performers) showed abnormal findings in comparison to NH subjects. On the other hand, the significant effect of CI thresholds re-emphasized the sensitivity of the test to low intensity speech which a CI user can often encounter under everyday listening conditions. Statistically significant correlations between HI/DI and STARR performance were found. Moreover, bimodal benefit was seen both for HI/DI and STARR tests. Overall findings confirmed the usefulness of evaluating both LF pitch and speech perception in noise in order to track changes in TFS sen-sitivity for CI recipients over time and across different listening conditions which might be provided by future technological progress. (Chapter 5) Finally, the last and main aspect taken into account in this thesis was the study of the difficul-ties experienced by CI users when listening to music. An attempt was made to correlate find-ings resulting from the previous phases of this study both to Speech in Noise and to the com-plex subjective aspects of Music Perception and Appreciation: correlation analysis between HI/DI tests and the main dimensions of Speech in Noise (STARR and OLSA) and Music Ap-preciation was performed. (Chapter 6). Interestingly, positive findings were found for the two most complex types of Music (Classical, Jazz), whereas Soul did not seem to require particular competence in Pitch perception for the appreciation of the subjective variables taken into con-sideration by this study