Abstract
Background: The ability to process interaural time differences (ITDs) is essential to listening in complex acoustic environments. Accordingly, several reports show that bilateral CI-users benefit from binaural input: speech perception in noise usually improves due to ‘better ear’ listening, whilst interaural level differences (ILDs) provide information about the source location. Nevertheless, spatial listening remains poor in most bilateral CI-users, because sensitivity to ITDs is poor. This is largely due to the fact that current CI-fitting procedures take no account of the requirement to match inputs from the two devices. There is considerable interest in enhancing binaural benefit from bilateral CI by matching the input from the CI electrodes between the two ears. This study assesses whether the interaural phase modulation following response (IPM-FR) –i.e. an EEG response to periodic transitions of interaural phase differences (IPDs) –can be used to identify CI-electrode pairs with maximum binaural sensitivity, using CI-simulations in normal hearing listeners.
Methods: Eleven normal hearing listeners have been included. IPDs were conveyed in the envelope of band-filtered click trains. IPMs switched between 0° to 180° IPD, at a rate of 7.1 Hz. To assess whether frequency mismatches affect neural processing of envelope ITDs, the centre frequency of the filter varied in the left ear (3.5, 4.5, or 5.5 kHz band-pass filter), while kept constant in the right ear (4.5 kHz). These conditions are referred to as -1, 0, and +1 kHz frequency offset, respectively.
Results: IPM-FRs were obtained in seven out of eleven participants. In these seven subjects, response amplitude ranged from 0.2 to 0.6 μV. Pairwise comparison reveals significantly smaller responses for -1 than 0 kHz frequency offsets (t(8.2)=-2.71, p=0.03). The +1 and 0 kHz frequency offsets were not statistically different (t(7.8)=2.04, p=0.08).
Conclusions: IPM-FRs can be elicited by ITDs in the envelope of high-frequency sounds, albeit highly variable across subjects. The data suggest that the IPM-FR deteriorates when an interaural frequency mismatch is introduced. This finding may have repercussions for bilateral cochlear implant users, as it suggests that interaural electrode mismatches may be detrimental for spatial hearing.
Methods: Eleven normal hearing listeners have been included. IPDs were conveyed in the envelope of band-filtered click trains. IPMs switched between 0° to 180° IPD, at a rate of 7.1 Hz. To assess whether frequency mismatches affect neural processing of envelope ITDs, the centre frequency of the filter varied in the left ear (3.5, 4.5, or 5.5 kHz band-pass filter), while kept constant in the right ear (4.5 kHz). These conditions are referred to as -1, 0, and +1 kHz frequency offset, respectively.
Results: IPM-FRs were obtained in seven out of eleven participants. In these seven subjects, response amplitude ranged from 0.2 to 0.6 μV. Pairwise comparison reveals significantly smaller responses for -1 than 0 kHz frequency offsets (t(8.2)=-2.71, p=0.03). The +1 and 0 kHz frequency offsets were not statistically different (t(7.8)=2.04, p=0.08).
Conclusions: IPM-FRs can be elicited by ITDs in the envelope of high-frequency sounds, albeit highly variable across subjects. The data suggest that the IPM-FR deteriorates when an interaural frequency mismatch is introduced. This finding may have repercussions for bilateral cochlear implant users, as it suggests that interaural electrode mismatches may be detrimental for spatial hearing.
Original language | English |
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Title of host publication | 2019 Conference on Implantable Auditory Prostheses |
Place of Publication | California |
Pages | 326 |
Number of pages | 1 |
Publication status | Published - 2019 |
Event | 2019 Conference on Implantable Auditory Prostheses - Lake Tahoe, United States Duration: 14 Jul 2019 → 19 Jul 2019 |
Conference
Conference | 2019 Conference on Implantable Auditory Prostheses |
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Country/Territory | United States |
City | Lake Tahoe |
Period | 14/07/19 → 19/07/19 |