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Abstract
Objective
To assess the auditory performance of Digisonic® cochlear implant users with electric stimulation (ES) and electro-acoustic stimulation (EAS) with special attention to the processing of low-frequency temporal fine structure.
Method
Six patients implanted with a Digisonic® SP implant and showing low-frequency residual hearing were fitted with the Zebra® speech processor providing both electric and acoustic stimulation. Assessment consisted of monosyllabic speech identification tests in quiet and in noise at different presentation levels, and a pitch discrimination task using harmonic and disharmonic intonating complex sounds ( Citation). These tests investigate place and time coding through pitch discrimination. All tasks were performed with ES only and with EAS.
Results
Speech results in noise showed significant improvement with EAS when compared to ES. Whereas EAS did not yield better results in the harmonic intonation test, the improvements in the disharmonic intonation test were remarkable, suggesting better coding of pitch cues requiring phase locking.
Discussion
These results suggest that patients with residual hearing in the low-frequency range still have good phase-locking capacities, allowing them to process fine temporal information. ES relies mainly on place coding but provides poor low-frequency temporal coding, whereas EAS also provides temporal coding in the low-frequency range. Patients with residual phase-locking capacities can make use of these cues.
Acknowledgements
This work was supported by a grant from the European Commission (FP7-SME-222291 DUALPRO). B.V. received a PhD grant for this work from the IWT (Agency for Innovation by Science and Technology, Baekeland grant IWT090287).