Rate pitch discrimination in cochlear implant users with the use of double pulses and different interpulse intervals

Abstract

The rate pitch discrimination ability of cochlear implant (CI) users is poor compared to normal-hearing (NH) listeners. At low pulse rates, the just noticeable difference (JND) is on average 20% of the base rate, while NH listeners can discriminate small frequency differences of 0.2% at 1 kHz. Recent investigations suggest that double pulses with short interpulse intervals (IPIs) may have a beneficial effect on rate pitch discrimination in CI users. In a first experiment psychophysical tests were carried out to establish whether rate pitch in CI users could be improved by applying double pulses with equal amplitude and short IPIs. Pulse trains with base rates of 200 and 400 pps, composed of either single pulses or double pulses with IPIs of 15, 50, and 150 μs were presented. In a second experiment pairwise comparisons were carried out between pitch of a pulse train composed of alternating double and single pulses with pitch of pulse trains composed of single pulses. The alternating pulse train had a base rate of 400 pps, the pulse trains with solely single pulses had base rates of 200, 300, and 400 pps. The loudness and pitch perception of the different stimulus types were evaluated and compared. A significant loudness difference was found between single and double pulses for both pulse rates. The JND for pitch discrimination between double-pulse IPIs had a high inter-subject variability, and no significant group effect was found. No subject reported a pitch change between double pulse and single pulse stimulation. In contrast, most of the subjects recognized a change in pitch between single-pulse trains and pulse trains with alternating double and single pulses. The latter was lower in pitch than the single-pulse train stimulation. To conclude, using (equal amplitude) double pulses instead of single pulses in a pulse train does not effect pitch perception. Instead, loudness differs between double pulses and single pulses with the same amplitude.

Keywords:

• Pitch perception
• Facilitation
• Temporal information
• Just noticeable difference
• Fine structure processing
• FSP

Acknowledgments

We thank our cochlear implant subjects for their participation in our study. We also thank Michael Todd (MED-EL) for editing the English of a version of this manuscript and Reinhold Schatzer, Stephanie Traub and Stefan Brill (MED-EL), who proof-read and edited a version of this manuscript.

Disclaimer statements

Conflict of interest No potential conflict of interest was reported by the authors.

Funding The study was funded by the manufacturer MED-EL (Innsbruck, Austria).

Ethics approval The measurements were performed under the authorization of the Ethics Committee of the University of Würzburg (31/15).

Notes on contributors

Sabrina H. Pieper is a PhD student at the ENT-Department of the University Hospital in Würzburg. She completed her BEng and MSc in Hearing Technology and Audiology at the Jade University and the Carl von Ossietzky University in Oldenburg. She is trained in programming and assessing psychoacoustic measurements with normal hearing and cochlear implant patients. She has also recorded electrophysiological responses after electrical stimulation of the auditory system.

Andreas Bahmer is a Professor since 2015 for Clinical-experimental Hearing research and Theoretical/Applied Neurophysiology at the ENT-Department of the University Hospital in Würzburg. He is head of the research unit of the Comprehensive Hearing Center. He studied physics and medicine in Kiel, Bonn, Frankfurt, and Darmstadt. He completed his diploma in theoretical optics, his PhD in theoretical neurophysiology (simulation of neuronal networks in the cochlear nucleus, Neuroacoustic lab of Gerald Langner) and theoretical medicine. He finished his habilitation (development and outcome measurement of bio-inspired coding strategies in auditory prostheses) in Frankfurt in the Audiological Acoustics Lab of Uwe Baumann. Currently, his research focuses on psychoacoustics, electrophysiology in auditory prostheses, slice and tracing experiment with modern holographic stimulation, imaging and virus techniques.

ORCID

Sabrina H. Pieper http://orcid.org/0000-0002-5488-4695

Andreas Bahmer http://orcid.org/0000-0003-0908-0011