Critical Band based Frequency Compression and Speech Perception in Noise in Individuals with Cochlear Hearing Loss

Abstract

Human cochlea is thought of a series of band pass auditory filters with tails of the adjacent filters slightly overlapping. These auditory filters are responsible for the frequency selectivity of the auditory system which acts as a crucial factor for the speech intelligibility of the auditory signal. The frequency selectivity is poor in individuals with hearing loss owing to widened auditory filters and thus results in poor consonant and vowel perception in quiet as well as in presence of noise. One of the approaches to compensate for reduced frequency selectivity is by applying appropriate compression to the incoming signal. This has been shown to be effective in enhancing speech perception in quiet but was not investigated adequately in presence of noise. Therefore the present study aimed to evaluate the effect of critical band based frequency compression on speech perception in individuals with sensorineural hearing impairment along with their normal counterpart. Twenty eight individuals with moderate to moderately severe sensorineural hearing loss and 23 individuals with normal hearing sensitivity were participants of this study. They were presented with 6 lists of seven sentences each varying in signal to noise ratio (SNR) from +20 dB to -10 dB per lists with 5 dB decrement in SNR per sentences. The sentences were filtered by passing through 32 band 4th order gamma tone filters. The output was further processed to generate 3 different conditions, with no compression, 20% and 50% compression of the incoming signal. The participant‟s task was to repeat the sentences and the key words were scored. The results showed no effect of critical band based frequency compression on speech identification scores in individuals with normal hearing but showed enhanced identification scores for individuals with cochlear hearing loss. The effect was evident especially at 0 and 5 dB SNR for both 20% and 50% compression. The outcome of the present study advocates the use of critical band based frequency compression for individuals with hearing impairment of cochlear origin.