Unilateral congenital deafness affects binaural cues differently

Content The congenitally deaf cats (CDC) have been used to study binaural sensitivity in monaural and binaural early deafness. Unilateral congenital deafness (UCD) resulted in functional preference for the hearing ear (Kral et al., 2013, Brain). While binaural integration and sensitivity for interaural time differences (ITDs) have already been studied in UCD (Tillein et al., 2016, Cereb Cortex), sensitivity for interaural level differences (ILDs) has not been explored yet.

Here, 4 hearing, 4 bilaterally CDCs and 4 unilaterally CDCs were used. All animals were bilaterally stimulated using cochlear implants (CI). For ABRs, single biphasic electric pulses (200 μs/phase) were delivered to CI in broad bipolar configuration. The cortical responses were evoked by a train of 3 biphasic electric pulses (200 μs/phase, 500 Hz) at intensities up to 12 dB above ABR threshold. Multiunit activity were recorded using linear multichannel arrays covering all layers of the primary auditory cortex. The firing rates with relation to binaural cues were compared. Cortical responses showed a shift in favor of the hearing ear irrespective of the recorded cortical hemisphere in UDC. Binaural responses were weakly modulated by ITDs. ILDs responses were dominated by the intensity function of the hearing ear. Thus, while ITD showed no preference for a particular spatial location, ILDs were strongly biased to the hemifield ipsilateral to the hearing ear. Also the eABRs showed a corresponding phenomenon, indicating that the effect is inherited from the brainstem (the olivary complex). The study suggests an inconsistency of binaural cues with respect to spatial location of the sound source that may contribute to difficulties in spatial localization after cochlear implantation in early single-sided deafness.

Poster-PDF A-1399.pdf

DFG (Exc 2177) & MedEl Company, Innsbruck, Austria

Publication History

Article published online:
13 May 2021