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. 2014 Dec;53(12):871-9.
doi: 10.3109/14992027.2014.932024. Epub 2014 Oct 30.

Evaluation of a cochlear-implant processing strategy incorporating phantom stimulation and asymmetric pulses

Robert P Carlyon  1 , Jolijn Monstrey, John M Deeks, Olivier Macherey
Affiliations
Free PMC article

Evaluation of a cochlear-implant processing strategy incorporating phantom stimulation and asymmetric pulses

Robert P Carlyon et al. Int J Audiol. 2014 Dec.
Free PMC article

Abstract

Objective: To evaluate a speech-processing strategy in which the lowest frequency channel is conveyed using an asymmetric pulse shape and "phantom stimulation", where current is injected into one intra-cochlear electrode and where the return current is shared between an intra-cochlear and an extra-cochlear electrode. This strategy is expected to provide more selective excitation of the cochlear apex, compared to a standard strategy where the lowest-frequency channel is conveyed by symmetric pulses in monopolar mode. In both strategies all other channels were conveyed by monopolar stimulation.

Design: Within-subjects comparison between the two strategies. Four experiments: (1) discrimination between the strategies, controlling for loudness differences, (2) consonant identification, (3) recognition of lowpass-filtered sentences in quiet, (4) sentence recognition in the presence of a competing speaker.

Study sample: Eight users of the Advanced Bionics CII/Hi-Res 90k cochlear implant.

Results: Listeners could easily discriminate between the two strategies but no consistent differences in performance were observed.

Conclusions: The proposed method does not improve speech perception, at least in the short term.

Keywords: Cochlear implants; asymmetric pulses; phantom stimulation; speech perception.

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Figures

Figure 1.
Figure 1.
The large panels show extracellular potential as a function of cochlear place for three methods of stimulation: (a) symmetric phantom (σ = 0.75), (b) symmetric bipolar (σ = 1.0), (c) asymmetric pulses in bipolar mode (σ = 1.0). The smaller panels, to the left of each large panel, show the current at each of two intra-cochlear electrodes. As in Macherey & Carlyon (2012, Figure 1) and for illustration purposes, neural elements are assumed to be arranged along an axis parallel to the electrode array and located 3 mm away from it. The medium is assumed to be homogeneous. The dashed lines show the locations of the stimulating electrodes.
Figure 2.
Figure 2.
Results of experiment 1. Each panel shows one listener’s percent correct as a function of the level of the PS stimulus relative to the loudness-balanced level.
Figure 3.
Figure 3.
Results of the consonant identification task of experiment 2. (a) Percent correct for each listener for the SYM and PS strategies. (b) Transmission of each phonetic feature averaged across listeners. Nas = manner (nasality), Pls = manner (plosive), Frc = manner (fricative), Voc = voicing, Lab = place (labial), Cor = place (coronal), Dor = place (dorsal).
Figure 4.
Figure 4.
Percent correct for each listener and strategy in the sentence test of experiment 3. Error bars show 95% confidence intervals.
Figure 5.
Figure 5.
Speech reception thresholds for the identification of sentences in the presence of a competing talker (experiment 4). Each panel shows the results for one listener, separately for the male and female target talkers. Error bars show 95% confidence intervals.
See this image and copyright information in PMC

References

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