Active Control mitigating the Ear Canal Occlusion Effect caused by Hearing Aids

The World Health Organization (WHO) estimates the prevalence of a disabling hearing loss to be above 5% world-wide 1. A treatment with a hearing aid - be it behind-the-ear (BTE), in-the-ear (ITE) or receiver-in-canal (RIC) - involves some degree of occlusion of the external ear canal. In many cases, this so-called occlusion effect (OE) leads to an unfamiliar perception of the hearing aid user’s own voice. This fact represents a limiting factor regarding the acceptance of hearing aids by potential users. This thesis focuses on modeling the physical occlusion effect caused by hearing aids and the investigation of active control approaches mitigating this adverse effect. A simple model based on audiological transfer functions is presented, discussed and validated in the first part of the thesis. This model is subsequently used as a basis for the analysis and the synthesis of an active control approach based on sound pressure feedback. The objective and subjective validation of this approach implemented as a prototype setup in a user-study is presented. Finally, the use of the insights from the first part for fitting a hearing aid incorporating such active occlusion control is suggested.

Lateralization of the primary auditory cortex, in patients with unilateral tinnitus

Naghmeh Ghazaleh, Melissa Saenz, Wietske Van der Zwaag

Tinnitus, the chronic perception of ringing or other phantom sounds, is typically associated with hearing loss. The reduction of auditory input that conveys to auditory cortex leads to the changes in the balance of excitatory and inhibitory activation of the corresponding neurons in this area and is possibly the cause of tinnitus. From the other hand a recent study (Gordon et al. Beain 2013) has shown that bilateral input protects the cortex from unilaterally driven reorganization. Based on this finding we could expect that in patient with unilateral hearing loss and tinnitus the input from unimpaired ear has not been transfered sufficiently to the bilateral hemisphere and this loss of input has resulted in reorganization in neuronal activity of the auditory cortex. To test this hypothesis we compare the amplitude of the neuronal activity bold response of the auditory cortex in the ipsilateral and contralateral hemisphere to the hearing ear in response to different frequency tones. Ten tinnitus patients with chronic unilateral hearing loss and tinnitus and age-matched normal controls (ages 26-49) were tested. (Patients had chronic subjective non-pulsatile tinnitus associated with moderate to severe unilateral sensorineural hearing loss in one ear only with at least PTA>40dB on three consecutive frequencies between 1 and 4 KHz; tinnitus duration < 6 months). The recruitment of patients with unilateral hearing loss allowed unimpaired sound delivery via the unimpaired ear, bypassing any abnormal responsiveness at the peripheral level. Our high-resolution functional MRI at 7 Tesla (1.5 mm isotropic voxels) (Da Costa et al. J Neurosci 2011) provides us fine scale tonotopic maps in controls and tinnitus patients and using that we are able to compare the amplitude of the neural activity in the auditory cortex of the unilateral and ipsilateral hemisphere to the hearing ear for each group of different frequency responding neurons. Our first finding shows that the activity difference in tinnitus patient is higher than the activity difference in controls. In more detail the activity amplitude in the contralateral hemisphere to the hearing ear in tinnitus patient is much higher than the activity amplitude in ipsilateral hemisphere, in comparison to controls. This result suggests that the auditory pathway in tinnitus patients is less capable to convey the sound bilaterally and it could be a probable cause of their tinnitus.

2014

Lateralization of the primary auditory cortex, in patients with unilateral tinnitus

Naghmeh Ghazaleh, Melissa Saenz, Wietske Van der Zwaag

2014