David P. Herrmann

Fitting cochlear implant (CI) users can be challenging. Anatomy-based fitting (ABF) maps may have the potential to lead to better objective and subjective outcomes than conventional clinically based fitting (CBF) methods. ABF maps were created via information derived from exact electrode contact positions, which were determined via post-operative high-resolution flat panel volume computer tomography and clinical fitting software. The outcome measures were speech understanding in quiet and noise and self-perceived sound quality with the CBF map and with the ABF map. Participants were 10 experienced bilateral CI users. The ABF map provided better speech understanding in quiet and noisy environments compared to the CBF map. Additionally, two approaches of reducing the frequency-to-place mismatch revealed that participants are more likely to accept the ABF map if their electrode array is inserted deep enough to stimulate the apical region of their cochlea. This suggests an Angular Insertion Depth of the most apical contact of around 720°–620°. Participants had better speech understanding in quiet and noise with the ABF map. The maps’ self-perceived sound quality was similar. ABF mapping may be an effective tool for compensating the frequency-to-place mismatch in experienced bilateral CI users.

Modern cochlear implants employ charge-balanced biphasic and triphasic pulses. However, the effectiveness of electrical pulse shape and polarity is still a matter of debate. For this purpose, in a previous study (Bahmer & Baumann, 2013) electrophysiological and psychophysical measurement after triphasic pulse stimulation with cathodic second phase was determined. Depending on the pulse shape configuration, the stimulation effectiveness differed similarly for electrophysiological and psychophysical measurements. However, the experiments were limited to stimulation pulses with cathodic second phase. In this study, cathodic and anodic second phase stimulation was applied. Evoked compound action potentials (ECAPs) and psychophysical responses were recorded in eleven cochlear implant recipients (SYNCHRONY/SONATAti100/PULSARci100 devices, MED-EL Innsbruck). We compared the strength of the ECAP responses with individual psychophysical threshold levels depending on the pulse shape. Results for pulses with cathodic second phase showed the weakest ECAP response and highest psychophysical thresholds for symmetric triphasic pulse shapes, and the strongest ECAP response and lowest psychophysical thresholds for biphasic pulses. The ECAP responses for anodic second phase differed from the results of triphasic stimulation with cathodic second phase. The U-shape of the ECAP response with increasing phase amplitude ratio (PAR) for cathodic second phase could not be observed for the anodic second phase. Instead, a flat curve was observed. In contrast, psychophysical threshold curves with increasing PAR were similar between cathodic and anodic second phase stimulation.