Unilateral Conductive Hearing Loss Disrupts the Developmental Refinement of Binaural Processing in the Rat Primary Auditory Cortex

[Prediction of speech understanding with the transcutaneous partially implantable bone conduction hearing system Osia®. German Version]

BACKGROUND

The active transcutaneous, partially implantable osseointegrated bone conduction system Cochlear™ Osia® (Cochlear, Sydney, Australia) has been approved for use in German-speaking countries since April 2021. The Osia is indicated for patients with conductive (CHL) or mixed hearing loss (MHL) with an average bone conduction (BC) hearing loss of 55 dB or less, or with single-sided deafness (SSD).

OBJECTIVES

The aim of this retrospective study was to investigate the prediction of postoperative speech recognition with Osia and to evaluate the speech recognition of patients with MHL and an aided dynamic range of less than 30 dB with Osia.

MATERIALS AND METHODS

Between 2017 and 2022, 29 adult patients were fitted with the Osia, 10 patients (11 ears) with CHL and 19 patients (21 ears) with MHL. MHL was subdivided into two groups: MHL‑I with four-frequency pure-tone average in BC (BC-4PTA) ≥ 20 dB HL and < 40 dB HL (n = 15 patients; 20 ears) vs. MHL-II with BC-4PTA ≥ 40 dB HL (n = 4 patients; 5 ears). All patients tested a bone conduction hearing device on a softband preoperatively. Speech intelligibility in quiet was assessed preoperatively using the Freiburg monosyllabic test unaided and with the test system and postoperatively with Osia. The maximum monosyllabic score (mEV) unaided and the monosyllabic score with the test system at 65 dB SPL were correlated with the postoperative monosyllabic score with Osia at 65 dB SPL.

RESULTS

Preoperative prediction of postoperative outcome with Osia was better using the mEV than the EV at 65 dB SPL with the test device on the softband. Postoperative EV was most predictive for patients with CHL and least predictive for patients with mixed hearing loss with 4PTA BC ≥ 40 dB HL. For the test device at softband, results tended to show the minimum achievable outcome and the mEV tended to predict the realistically achievable outcome.

CONCLUSION

Osia can be used for the treatment of CHL and MHL within the indication limits. The average preoperative bone conduction hearing threshold also provides an approximate estimate of the postoperative EV with Osia, for which the most accurate prediction is obtained using the preoperative mEV. Prediction accuracy decreases from a BC-4PTA of ≥ 40 dB.

Prediction of postoperative speech comprehension with the transcutaneous partially implantable bone conduction hearing system Osia®

BACKGROUND

The active transcutaneous, partially implantable osseointegrated bone conduction system Cochlear™ Osia® (Cochlear, Sydney, Australia) has been approved for use in German-speaking countries since April 2021. The Osia is indicated for patients either having conductive (CHL) or mixed hearing loss (MHL) with an average bone conduction (BC) hearing loss of 55 dB HL or less, or having single-sided deafness (SSD).

OBJECTIVES

The aim of this retrospective study was to investigate the prediction of postoperative speech recognition with Osia® and to evaluate the speech recognition of patients with MHL and in particular an aided dynamic range of less than 30 dB with Osia®.

MATERIALS AND METHODS

Between 2017 and 2022, 29 adult patients were fitted with the Osia®, 10 patients (11 ears) with CHL and 19 patients (25 ears) with MHL. MHL was subdivided into two groups: MHL‑I with four-frequency pure-tone average in BC (BC-4PTA) ≥ 20 dB HL and < 40 dB HL (n = 15 patients; 20 ears) vs. MHL-II with BC-4PTA ≥ 40 dB HL (n = 4 patients; 5 ears). All patients tested a bone conduction hearing device on a softband preoperatively. Speech intelligibility in quiet was assessed preoperatively using the Freiburg monosyllabic test in unaided condition, with the trial BCHD preoperatively and with Osia® postoperatively with Osia®. The maximum word recognition score (mWRS) unaided and the word recognition score (WRS) with the test system at 65 dB SPL were correlated with the postoperative WRS with Osia® at 65 dB SPL.

RESULTS

Preoperative prediction of postoperative outcome with Osia® was better using the mWRS than by the WRS at 65 dB SPL with the test device on the softband. Postoperative WRS was most predictive for patients with CHL and less predictable for patients with mixed hearing loss with BC-4PTA ≥ 40 dB HL. For the test device on a softband, the achievable outcome tended to a minimum, with the mWRS tending to predict the realistically achievable outcome.

CONCLUSION

Osia® can be used for the treatment of CHL and MHL within the indication limits. The average preoperative bone conduction hearing threshold also provides an approximate estimate of the postoperative WRS with Osia®, for which the most accurate prediction is obtained using the preoperative mWRS. Prediction accuracy decreases from a BC-4PTA of ≥ 40 dB HL.

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.