Mapping procedures can produce non-centered auditory images in bilateral cochlear implantees

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In normal-hearing (NH) listeners, elevation perception is produced by the spectral cues imposed by the pinna, head, and torso. Elevation perception in cochlear-implant (CI) listeners appears to be non-existent; this may be a result of poorly encoded spectral cues. In this study, an analog of elevation perception was investigated by having 15 CI and 8 NH listeners report the intracranial location of spectrally simple signals (single-electrode or bandlimited acoustic stimuli, respectively) in both horizontal and vertical dimensions. Thirteen CI listeners and all of the NH listeners showed an association between place of stimulation (i.e., stimulus frequency) and perceived elevation, generally responding with higher elevations for more basal stimulation. This association persisted in the presence of a randomized temporal pitch, suggesting that listeners were not associating pitch with elevation. These data provide evidence that CI listeners might perceive changes in elevation if they were presented stimuli with sufficiently salient elevation cues.

Section: Discussionsupporting

confidence: 81%

Internalized elevation perception of simple stimuli in cochlear-implant and normal-hearing listeners

Thakkar

Goupell

2014

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“…One explanation is that in order to obtain an equal loudness percept, differing amounts of neurons may be recruited in each ear. This may inadvertently create an interaural level difference across the ears when integrating across all stimulated frequency, leading to the perception of an off-centered auditory image (Goupell et al, 2013a). However, this probably cannot explain the systematic nature of the lateral shift with increasing interaural mismatch.…”

Section: Discussionmentioning

confidence: 93%

Effect of mismatched place-of-stimulation on binaural fusion and lateralization in bilateral cochlear-implant users

Kan¹,

Stoelb²,

Litovsky³

et al. 2013

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145

245

Bilateral cochlear implants (CIs) have provided some success in improving spatial hearing abilities to patients, but with large variability in performance. One reason for the variability is that there may be a mismatch in the place-of-stimulation arising from electrode arrays being inserted at different depths in each cochlea. Goupell et al. [(2013b). J. Acoust. Soc. Am. 133(4), [2272][2273][2274][2275][2276][2277][2278][2279][2280][2281][2282][2283][2284][2285][2286][2287] showed that increasing interaural mismatch led to non-fused auditory images and poor lateralization of interaural time differences in normal hearing subjects listening to a vocoder. However, a greater bandwidth of activation helped mitigate these effects. In the present study, the same experiments were conducted in post-lingually deafened bilateral CI users with deliberate and controlled interaural mismatch of single electrode pairs. Results show that lateralization was still possible with up to 3 mm of interaural mismatch, even when off-center, or multiple, auditory images were perceived. However, mismatched inputs are not ideal since it leads to a distorted auditory spatial map. Comparison of CI and normal hearing listeners showed that the CI data were best modeled by a vocoder using Gaussian-pulsed tones with 1.5 mm bandwidth. These results suggest that interaural matching of electrodes is important for binaural cues to be maximally effective.

“…This experiment was performed to investigate if centering can improve JNDs for the CI and NH listeners. CI listeners often have non-centered auditory images for approximately loudness-balanced stimulation across the ears (Goupell et al, 2013a) and interaural mismatch systematically causes sound images to lateralize to the ear with more basal stimulation (Goupell et al, 2013b;Kan et al, 2013). Therefore, it is highly likely that many of the conditions in experiment 1 had non-centered stimuli and this may have impaired performance.…”

Section: Experiments Ii: the Effect Of Centering On Envelope Corrementioning

confidence: 96%

Interaural envelope correlation change discrimination in bilateral cochlear implantees: Effects of mismatch, centering, and onset of deafness

Goupell

2015

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Bilateral cochlear implant (CI) listeners can perform binaural tasks, but they are typically worse than normal-hearing (NH) listeners. To understand why this difference occurs and the mechanisms involved in processing dynamic binaural differences, interaural envelope correlation change discrimination sensitivity was measured in real and simulated CI users. In experiment 1, 11 CI (eight late deafened, three early deafened) and eight NH listeners were tested in an envelope correlation change discrimination task. Just noticeable differences (JNDs) were best for a matched place-of-stimulation and increased for an increasing mismatch. In experiment 2, attempts at intracranially centering stimuli did not produce lower JNDs. In experiment 3, the percentage of correct identifications of antiphasic carrier pulse trains modulated by correlated envelopes was measured as a function of mismatch and pulse rate. Sensitivity decreased for increasing mismatch and increasing pulse rate. The experiments led to two conclusions. First, envelope correlation change discrimination necessitates place-of-stimulation matched inputs. However, it is unclear if previous experience with acoustic hearing is necessary for envelope correlation change discrimination. Second, NH listeners presented with CI simulations demonstrated better performance than real CI listeners. If the simulations are realistic representations of electrical stimuli, real CI listeners appear to have difficulty processing interaural information in modulated signals.