Perception of Sentences in Noise Using Different Number of Channels in Simulated Cochlear Implant Listeners

Previous literature in cochlear implant has revealed that ability to recognize speech increases with the corresponding increase number of channels [1-3]. Various studies have also reported that speech perception gets improved with increase in number of channels in quite listening condition to the extent 4 to 7 channels [4,5]. Fishman et al. [6], investigated perception of speech in subjects with the help of Nucleus-22 SPEAK speech processing strategy with increase in number of electrodes. Result showed deprived performance in all the subjects using single electrode processor whereas the average performance improved over all the test materials as the number of electrode increased from 1 to 4. They also observed that on an average performance there was no difference found on any test in 7-, 10-, and 20-electrode conditions. Similarly, Friesen et al. [7] in 2001 measured speech recognition using consonant, vowel, word, and sentence in 24 listeners. Among those 24 listeners, 5 normal hearing, 10 subjects with Nucleus 22 and 9 with Advanced Bionics Clarion. In their study, speech perceptions were measured with increase in number of electrodes and signal to noise ratio. They reported that as the electrode number added up to 7 or 8, the performance increased. They also found that for all noise levels, with SPEAK speech processor, vowel and consonant recognition did not enhance after seven electrodes. Whereas the performance continued to improve till 20 channels for normal hearing listeners. In Nucleus 22 cochlear implant listeners, with the increase in electrode numbers from 7 to 10, the recognition of speech was found to be significantly improved even over speech materials with greater difficulty which comprises of words and sentences. Verschuur [8] in 2009 also had conducted similar kind of research in which he observed that consonants perception had improved with increase in number of channels in users with Nucleus 24. In a similar line, Friesen et al. [3] in 2009 investigated test on speech recognition with CVC stimuli at various spectral channels such as 2, 4, 8, 12, and 16 on 10 subjects with normal hearing. Results revealed that as the number of spectral channels increased the perception of CVC was enhanced. Perreau et al. [9] in 2010 measured speech recognition performance in spatially separated noise with different number of channels. They observed that the performance of the individuals was affected when the number of electrodes was reduced. Zeitler et al. [10] in 2009 through his study studied speech perception outcomes by decreasing quantity of functional electrodes post implantation. The finding of the study revealed that even after deactivation of electrodes didn’t have any straight effect on speech perception, but loss of 5 or more electrodes indicated imminent failure of the device. From the above stated literature it can be inferred that many of these studies were conducted in quiet and feasible hearing conditions, whereas in our day to day life situations we cannot avoid the presence of background noise. So, there is an importance to take up a study that could reveal the effect of various SNRs in Volume 8 Issue 4 2017