Efficacy of Frequency Transposition Hearing Aid In Dead Region Subjects

Abstract

A hearing aid is an electroacoustic device which enables a hearing impaired individual to make maximum use of his residual hearing. Decreased audibility, reduced dynamic range, decreased frequency resolution and temporal resolution are common problems in individuals with sensorineural hearing loss. Sensorinueral hearing loss is also commonly called cochlear loss, inner ear loss and nerve loss. The sensory mechanism comprises of the Outer hair cells (OHC‟s) and the inner hair cells (IHC‟s). Damage to OHCs will lead to a reduction in the compressive mechanism of the cochlea. Damage to IHCs will lead to a reduction in sound transduction process. For this reason such regions are referred to as “Dead regions”. Steeply sloping hearing loss is often associated with cochlear dead regions and also high frequency part of speech contributes no information in such individuals. Thus, it is essential to transpose high frequency information to the useful hearing at low frequencies in order to make high frequency information accessible. Hence, the present study aimed at evaluating 10 subjects (15 ears) with Dead regions. Subjects who were diagnosed as having dead regions using Modified Threshold Equalising Noise (TEN) test participated in the study. Frequency transposition hearing aid was fitted for individual who have dead region. Speech identification performance was evaluated with High frequency sentence and word list in Transposition and No Transposition conditions. The results revealed that with frequency transposition there is statistically significant amount of benefit than non transposed condition for individuals with steeply sloping hearing loss with dead regions.