Abstract
Previous studies in patients with single-sided deafness (SSD) have reported results of pitch comparisons between electric stimulation of their cochlear implant (CI) and acoustic stimulation presented to their near-normal hearing contralateral ear. These comparisons typically used sinusoids, although the percept elicited by electric stimulation may be closer to a wideband stimulus. Furthermore, it has been shown that pitch comparisons between sounds with different timbres is a difficult task and subjected to various types of range biases. The present study aims to introduce a method to minimize non-sensory biases, and to investigate the effect of different acoustic stimulus types on the frequency and variability of the electric-acoustic pitch matches. Pitch matches were collected from 13 CI users with SSD using the binary search procedure. Electric stimulation was presented at either an apical or a middle electrode position, at a rate of 800 pps. Acoustic stimulus types were sinusoids (SINE), 1/3-octave wide narrow bands of Gaussian noises (NBN), or 1/3-octave wide pulse spreading harmonic complexes (PSHC). On the one hand, NBN and PSHC are presumed to better mimic the spread of excitation produced by a single-electrode stimulation than SINE. On the other hand, SINE and PSHC contain less inherent fluctuations than NBN and may therefore provide a temporal pattern closer to that produced by a constant-amplitude electric pulse train. Analysis of mean pitch match variance showed no differences between stimulus types. However, mean pitch matches showed effects of electrode position and stimulus type, with the middle electrode always matched to a higher frequency than the apical one (p < 0.001), and significantly higher across-subject pitch matches for PSHC compared with SINE (p = 0.017). Mean pitch matches for all stimulus types were better predicted by place-dependent characteristic frequencies (CFs) based on an organ of Corti map compared with a spiral ganglion map. CF predictions were closest to pitch matches with SINE for the apical electrode position, and conversely with NBN or PSHC for the middle electrode position. These results provide evidence that the choice of acoustic stimulus type can have a significant effect on electric-acoustic pitch matching.
Highlights
Over the last two decades, the population of hearing-impaired people undergoing cochlear implantation has greatly evolved
Pitch match distributions were comparable between conditions, which was confirmed using a two-way repeated-measures analyses of variance (ANOVA) with the factors standard frequency (250 Hz or 1 kHz) and stimulus type (SINE, narrow bands of Gaussian noises (NBN), or pulse spreading harmonic complexes (PSHC)), which showed neither within-subject effects nor interaction effects
This finding showed that pitch matching accuracy for NBN and PSHC substantially decreased at high frequencies and was not included in the testing of single-sided deafness (SSD) subjects
Summary
Over the last two decades, the population of hearing-impaired people undergoing cochlear implantation has greatly evolved While this treatment originally targeted patients with bilateral profound deafness, there are increasingly more cochlear implant (CI) users with significant residual acoustic hearing in their ipsilateral or, more frequently, contralateral ear. Previous pitch matching studies have shown that such measurements are difficult to conduct and usually produce very variable data (Carlyon et al, 2010; Goupell et al, 2019). This variability may have several causes, including methodological limitations as well as the choice of the acoustic stimulus type
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