Speech Intelligibility and Spatial Release From Masking Improvements Using Spatial Noise Reduction Algorithms in Bimodal Cochlear Implant Users

State-of-the-Art on the Impact of Bimodal Acoustic Stimulation on Speech Perception in Noise in Adults: A Systematic Review

BACKGROUND/OBJECTIVES

Bimodal stimulation (BS), which combines the use of a cochlear implant (CI) in one ear and a hearing aid (HA) in the opposite ear, is an established strategy to treat hearing loss by exploiting the unique capabilities of each device. CIs stimulate the auditory nerve by bypassing damaged hair cells, while HAs amplify sounds by requiring a functional hearing residual. The aim of this systematic review is to investigate the advantages and disadvantages of BS such as speech perception in noise.

METHODS

We examined clinical studies published from October 2020 to July 2024, following the PRISMA guidelines, focusing on the advantages and disadvantages of BS on speech perception in noise in adulthood.

RESULTS

BS in adult patients significantly improves speech perception in quiet and noisy environments, especially for those with increased residual hearing. Unilateral CIs and BS perform similarly in quiet conditions, but BS significantly improves speech discrimination in noisy environments if loudness between the two devices is appropriately balanced.

CONCLUSIONS

Directional microphones and programming software are new technologies that succeed in reducing environmental noise and improving verbal perception outcomes, although their features in the literature are controversial. In addition, the individuals using BS may face temporal mismatches mainly due to differing device latencies, affecting sound localization. Compensating for these mismatches can enhance localization accuracy. However, modulated noise remains a significant obstacle to verbal perception in noise. Valuable assessment tools such as music tests provide further information on hearing performance and quality of life. More research is needed to define certain selection criteria.

[Effect of cochlear implantation on speech recognition under different listening modes in children]

Objective:To investigate speech recognition among children with a unilateral cochlear implant（CI）, bilateral CI, and bimodal hearing and identify the benefits of binaural hearing. Methods:A total of 67 children with severe sensorineural hearing loss who received bilateral CI, bimodal hearing, and unilateral CI from 2012 to 2021 were recruited, including 23 cases with unilateral CI, 25 cases of bimodal hearing, and 19 cases of bilateral CI. The aided hearing threshold at 250-4000 Hz and speech recognition performance of two-syllable words and short sentences in quiet and noisy environments were tested, respectively. Results:There was no significant difference in the hearing threshold results of the bilateral CI group, the bimodal hearing group, and the unilateral CI group by ANOVA（P>0.05）. According to the paired t-test within the group, the speech recognition of disyllabic words and short sentences in quiet and noisy environments were significantly different among the three groups（P<0.05）. There was no significant difference in the speech recognition rates of disyllabic words and short sentences among the three groups in a quiet environment（P>0.05）, but there was a statistically significant difference in a noisy environment（P<0.05）. Additional multiple linear regression analysis showed no significant difference in the recognition rates of disyllabic words and short sentences between the bimodal group and the bilateral CI group in quiet and noisy environments（β=-0.567, P>0.05; β=-0.643, P>0.05）. There was a statistically significant difference in speech recognition of disyllabic words and short sentences between the bimodal group and the unilateral CI group in the noise environment（β=-0.124, P<0.05）, but the difference was not statistically significant in a quiet environment（β=-0.671, P>0.05）; there was a statistically significant difference in the recognition rate of disyllabic words and short sentences between the bilateral CI group and the unilateral CI group in the noise environment（β=-0.226, P<0.05）, but the difference was not statistically significant in a quiet environment（β=-0.341, P>0.05）. Conclusion:Clinicians and guardians are encouraged to provide the most comprehensive audiological evaluation for children with hearing loss. Bilateral CI and bimodal hearing have demonstrated enormous advantages over unilateral CI regarding speech recognition in noise. Bimodal hearing deems a strong recommendation if the contralateral ear has sufficient speech recognition capability. Bilateral CI should be warranted if hearing aids deemed to be ineffective.

[Influence of directional microphones on listening effort in middle ear implant users]

BACKGROUND AND OBJECTIVE

Besides speech intelligibility, subjective listening effort is an important outcome for the success of hearing devices and their signal processing. The aim of the present study was to determine subjective listening effort for speech in a noisy background in patients with the active middle ear implant Vibrant Soundbridge (VSB) for omnidirectional and directional microphone settings, with and without occlusion of the contralateral ear.

MATERIAL AND METHODS

A total of 15 patients using a VSB were measured using the adaptive categorical listening effort scaling (ACALES) method in a ring of loudspeakers placed in an anechoic room. Different background noises from different directions and simultaneously presented sentences from the Oldenburg sentence test were combined in four different realistic acoustic scenes.

RESULTS

The directional microphone program reduced median subjective listening effort only numerically compared to the omnidirectional microphone program in acoustic scenarios with diffuse noise and with low signal-to-noise ratios; however, this difference failed to reach statistical significance. When occluding the ear contralateral to the VSB, all investigated listening effort categories were measured at significantly higher signal-to-noise ratios than with access to both ears.

CONCLUSION

Due to missing statistical significance in reduction of listening effort, this study delivered no recommendation for or against usage of the directional microphone program; however, reduced listening effort was shown for binaural listening in comparison to monaural listening. Therefore, patients should be encouraged to always listen with both ears for best results.