The Effect of Phantom Stimulation and Pseudomonophasic Pulse Shapes on Pitch Perception by Cochlear Implant Listeners
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JARO (2020) DOI: 10.1007/s10162-020-00768-x D 2020 The Author(s)
Research Article
Journal of the Association for Research in Otolaryngology
The Effect of Phantom Stimulation and Pseudomonophasic Pulse Shapes on Pitch Perception by Cochlear Implant Listeners WIEBKE LAMPING,1,2,3
JOHN M. DEEKS,2 JEREMY MAROZEAU,1
AND
ROBERT P. CARLYON2
1
Hearing Systems Section, Department of Health Technology, Technical University of Denmark, DK-2800, Kgs. Lyngby, Denmark 2 Medical Research Council Cognition and Brain Sciences Unit, University of Cambridge, 15 Chaucer Road, Cambridge, CB2 7EF, UK 3
Department of Clinical Neurosciences, University of Cambridge, Cambridge, CB2 0SZ, UK
Received: 2 July 2019; Accepted: 31 July 2020
ABSTRACT It has been suggested that a specialized hightemporal-acuity brainstem pathway can be activated by stimulating more apically in the cochlea than is achieved by cochlear implants (CIs) when programmed with contemporary clinical settings. We performed multiple experiments to test the effect on pitch perception of phantom stimulation and asymmetric current pulses, both supposedly stimulating beyond the most apical electrode of a CI. The two stimulus types were generated using a bipolar electrode pair, composed of the most apical electrode of the array and a neighboring, more basal electrode. Experiment 1 used a pitch-ranking procedure where neural excitation was shifted apically or basally using so-called phantom stimulation. No benefit of apical phantom stimulation was found on the highest rate up to which pitch ranks increased (upper limit), nor on the slopes of the pitch-ranking function above 300 pulses per second (pps). Experiment 2 used the same procedure to study the effects of apical pseudomonophasic pulses, where the locus of excitation was manipulated by changing stimulus polarity. A benefit of apical stimulation was obtained for the slopes above 300 pps. Experiment 3 used an adaptive rate discrimination procedure and found a small but significant benefit of both types of apical stimulation. Correspondence to: Wiebke Lamping & Department of Clinical Neurosciences & University of Cambridge & Cambridge, CB2 0SZ, UK. email: [email protected]
Overall, the results show some benefit for apical stimulation on temporal pitch processing at high pulse rates but reveal that the effect is smaller and more variable across listeners than suggested by previous research. The results also provide some indication that the benefit of apical stimulation may decline over time since implantation. Keywords: cochlear implants, pitch perception, phantom stimulation, asymmetric pulses
INTRODUCTION Cochlear implants (CIs) can convey pitch along two orthogonal perceptual dimensions, related to the place of excitation in the cochlea and the temporal pattern of stimulation. However, the perception of pitch by CI users remains limited. The range of place pitches is restricted by shallow insertion depths, while the number of discriminable place pitches is restricted by the number of implantable electrodes and the
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