Dichotic presentation of speech signal using a critical filter bank for bilateral sensorineural hearing impairment

Sensorineural hearing-impaired listeners face a particular problem in view of a decrease in the frequency resolving capacity of an ear due to the spread of masking of frequency components by adjacent frequency components. Filtering a speech signal by a bank of critical band filters and adding signals from alternate bands for presenting to the two ears is likely to reduce the effect of the spread of masking along the cochlear partition, and thus may help in improving the speech intelligibility. This processing scheme has been implemented with 18 critical bands for experimental evaluation through listening tests. The scheme was found to be helpful in improving recognition scores and transmission of speech features in listening tests with normal hearing subjects with simulated sensorineural hearing loss. Listening tests were carried out using 12 vowel–consonants–vowel and consonant–vowel nonsense syllables presented in quiet (no masking noise), on ten subjects with mild to very severe sensorineural hearing loss. The stimulus response confusion matrices were analyzed using relative improvement in recognition scores and information transmission analysis. The relative improvement in recognition scores is up to 25%. Information transmission analysis indicated that the overall improvement is contributed to by improvements in transmission of the speech feature of voicing, place, and manner. The mean response time has also been found to decrease significantly.