Adults with unilateral congenital ear canal atresia - sound localization ability and recognition of speech in competing speech in unaided condition

Asymmetry in Cortical Thickness of the Heschl's Gyrus in Unilateral Ear Canal Atresia

HYPOTHESIS

Unilateral congenital conductive hearing impairment in ear canal atresia leads to atrophy of the gray matter of the contralateral primary auditory cortex or changes in asymmetry pattern if left untreated in childhood.

BACKGROUND

Unilateral ear canal atresia with associated severe conductive hearing loss results in deteriorated sound localization and difficulties in understanding of speech in a noisy environment. Cortical atrophy in the Heschl's gyrus has been reported in acquired sensorineural hearing loss but has not been studied in unilateral conductive hearing loss.

METHODS

We obtained T1w and T2w FLAIR MRI data from 17 subjects with unilateral congenital ear canal atresia and 17 matched controls. Gray matter volume and thickness were measured in the Heschl's gyrus using Freesurfer.

RESULTS

In unilateral congenital ear canal atresia, Heschl's gyrus exhibited cortical thickness asymmetry (right thicker than left, corrected p = 0.0012, mean difference 0.25 mm), while controls had symmetric findings. Gray matter volume and total thickness did not differ from controls with normal hearing.

CONCLUSION

We observed cortical thickness asymmetry in congenital unilateral ear canal atresia but no evidence of contralateral cortex atrophy. Further research is needed to understand the implications of this asymmetry on central auditory processing deficits.

Binaural advantages in sound temporal information processing by neurons in the rat inferior colliculus

Previous studies on the advantages of binaural hearing have long been focused on sound localization and spatial stream segregation. The binaural advantages have also been observed in speech perception in reverberation. Both human speech and animal vocalizations contain temporal features that are critical for speech perception and animal communication. However, whether there are binaural advantages for sound temporal information processing in the central auditory system has not been elucidated. Gap detection threshold (GDT), the ability to detect the shortest silent interval in a sound, has been widely used to measure the auditory temporal resolution. In the present study, we determined GDTs of rat inferior collicular neurons under both monaural and binaural hearing conditions. We found that the majority of the inferior collicular neurons in adult rats exhibited binaural advantages in gap detection, i.e., better neural gap detection ability in binaural hearing conditions compared to monaural hearing condition. However, this binaural advantage in sound temporal information processing was not significant in the inferior collicular neurons of P14-21 and P22-30 rats. Additionally, we also observed age-related changes in neural temporal acuity in the rat inferior colliculus. These results demonstrate a new advantage of binaural hearing (i.e., binaural advantage in temporal processing) in the central auditory system in addition to sound localization and spatial stream segregation.

A pilot study on spatial hearing in children with congenital unilateral aural atresia

Despite normal hearing in one ear, individuals with congenital unilateral aural atresia may perceive difficulties in everyday listening conditions typically containing multiple sound sources. While previous work shows that intervention with bone conduction devices may aid spatial hearing for some children, testing conditions are often arranged to maximize any benefit and are not very similar to daily life. The benefit from amplification on spatial tasks has been found to vary between individuals, for reasons not entirely clear. This study has sought to expand on the limited knowledge on how children with unilateral aural atresia recognize speech masked by competing speech, and how horizontal sound localization accuracy is affected by the degree of unilateral hearing loss and by amplification using unilateral bone conduction devices when fitted before 3 years of age. In a within-subject, repeated measures design, including 11 children (mean age = 7.9 years), bone conduction hearing device (BCD) amplification did not negatively affect horizontal sound localization accuracy. The effect on speech recognition scores showed greater inter-individual variability. No benefit from amplification on a group level was found. There was no association between age at fitting and the benefit of the BCD. For children with poor unaided sound localization accuracy, there was a greater BCD benefit. Unaided localization accuracy increased as a function of decreasing hearing thresholds in the atretic ear. While it is possible that low sound levels in the atretic ear provided access to interaural localization cues for the children with the lowest hearing thresholds, the association has to be further investigated in a larger sample of children.

Hearing Outcomes of a New Cartilage Conduction Device vs Bone Conduction Devices

OBJECTIVE

To compare audiometric outcomes of a new cartilage conduction hearing device (CCD) with traditional bone conduction hearing devices (BCDs).

STUDY DESIGN

Clinical trial and crossover study design.

SETTING

Tertiary academic center.

METHODS

Sixteen adults (19 ears) with congenital aural atresia or overclosed ear canals who previously underwent BCD implantation were fitted with a CCD. Audiometric data were collected with use of the BCD and the CCD.

RESULTS

The mean pretreatment 4-frequency pure tone average was 81 dB. The mean aided pure tone averages with the BCD and CCD were 27 and 32 dB (P = .002), and the mean functional gains were 54 and 49 dB (P = .002), respectively. The mean consonant-nucleus-consonant scores with the BCD were 90% (best aided) and 80% (aided ear isolated), and those with the CCD were 86% and 76%. Mean AzBio scores were 90% (quiet), 77% (+10 dB SNR [signal to noise ratio]), and 52% (+5 dB SNR) when isolating the BCD ear and 90%, 73%, and 41% when isolating the CCD ear. No difference in speech scores achieved statistical significance except the AzBio isolated to the aided ear in the +5-dB SNR condition, which favored the BCD (P = .01).

CONCLUSION

Pure tone audiometric outcomes with the BCD show a small advantage over the CCD, with the difference driven mainly by high-frequency responses. Speech outcomes were equivalent apart from the +5-db SNR condition, which favored the BCD.