Abstract

It has been suggested that a specialized high-temporal-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. 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.

Highlights

  • 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

  • The limitations regarding the perception of temporal pitch are revealed by the finding that the discrimination of changes in the rate of pulses presented to a single electrode by cochlear implants (CIs) listeners is worse than the ability of normal-hearing listeners to detect changes in the fundamental frequencies of bandpass-filtered harmonic complexes

  • The left and right ordinates show log-transformed and linear rate discrimination ratio (RDR), respectively; all analyses were performed on the log RDRs, but the linear data are presented for ease of interpretation

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Summary

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. Temporal pitch deteriorates for most CI users above a subjectand electrode-dependent “upper limit” that ranges between 200 and 900 pulses per second (pps) and is on average around 300 pps (e.g., Zeng 2002). This upper limit is substantially lower than normal-hearing listeners’ upper limit for complex tones consisting of only unresolved harmonics, which ranges from 600 to 800 pps (Carlyon and Deeks 2002; Macherey and Carlyon 2014)

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