Improving the Accuracy of Baha® Fittings through Measures of Direct Bone Conduction

ObjectivesVariability in Baha® sound processor fittings may arise from the nature of the implant-to-bone transmission as well as transcranial attenuation for patients with single-sided sensorineural deafness (SSD). One method of improving the predictability of Baha fittings is to measure the individual patient's actual bone conduction thresholds, thereby removing the influences of skin thickness and/or the implant location site.MethodsTwenty adult wearers of the Baha bone conduction implant system participated in the study. Direct bone conduction thresholds were obtained through the BC Direct function of the Baha Fitting Software combined with the Cochlear Baha BP100 sound processor. For comparison, the masked and unmasked bone conduction responses of the patients were collected through standard audiometric testing techniques. Test-retest reliability measurement was performed for all participants. Data for each frequency and frequency range were analyzed separately.ResultsThe results confirm the improved transmission of sound through the implant rather than transcutaneously through the skin. On average, the BC Direct thresholds were closer to the patient's unmasked thresholds than the masked values. In subjects with SSD, BC Direct results were poorer than contra-lateral bone conduction thresholds, most likely due to transcranial attenuation. The test-retest reliability for the BC Direct measurements was within +/-5 dB. The comparison of preferred amplification, based on direct bone conduction or bone conduction audiometry, found higher agreement for fittings based on direct bone conduction measurements.ConclusionWhile the transfer function between the implant and the skin can be predicted on average, there are a number of patients for whom measurement is essential to determine the required amplification. These were patients with: 1) SSD, 2) asymmetrical hearing loss, 3) unusual implant location or skull formation, and 4) users of Testband or Softband. The result for the clinician is that a fitting can take place with less fine-tuning and a greater understanding of the variability of bone conducted sound transmission

A PEM-Based Frequency-Domain Kalman Filter for Adaptive Feedback Cancellation

Adaptive feedback cancellation (AFC) algorithms are used to solve the problem of acoustic feedback, but, frequently, they do not address the fundamental problem of loudspeaker and source signal correlation, leading to an estimation bias if standard adaptive filtering methods are used. Loudspeaker and source signal prefiltering via the prediction-error method (PEM) can address this problem. In addition to this, the use of a frequency-domain Kalman filter (FDKF) is an appealing tool for the estimation of the adaptive feedback canceler, given the advantages it offers over other common techniques, such as Wiener filtering. In this paper, we derive an algorithm employing a PEM-based prewhitening and a frequency-domain Kalman filter (PEM-FDKF) for AFC. We demonstrate its improved performance when compared with standard frequencydomain adaptive filter (FDAF) algorithms, in terms of reduced estimation error, achievable amplification and sound quality.status: publishe

Measurement and Analysis of Feedback and Nonlinearities for the Codacs Direct Acoustic Cochlear Implant

© 2013 IEEE. Acoustic feedback is a very common problem in hearing instruments. Not only does it occur in common behind-the-ear or in-the-ear hearing aids, it also affects bone conduction implants, middle ear implants, and more recent devices, such as the direct acoustic cochlear implant (DACI). In this paper, we present the data and analysis relating to the feedback path characterization of the Cochlear™ Codacs™ DACI, performed on fresh frozen cadaver heads in four different measurement sessions. The general objectives were the following: 1) To measure and analyze the feedback path of the system and check for possible specimen-dependent variabilities; 2) To assess whether this feedback path is affected by an incorrect implantation; 3) To check for nonlinear behavior; and 4) To determine differences between tissular and airborne feedback. The data analysis reveals that the feedback seems to be dependent on the specific head morphology of the implanted specimen, and that an incorrect implantation might strongly affect the feedback path; additionally, the analysis reveals that some nonlinear behavior at high stimulus levels can be expected and, finally, that the feedback path is characterized by a tissular feedback component with a rather different frequency content compared to the airborne feedback component.status: publishe

Complementary results on the feedback path characterization for the cochlear (TM) Codacs (TM) direct acoustic cochlear implant

status: publishe