| dc.description.abstract | The purpose of this study is to investigate the effects of different parameters in cochlear implant (CI). We used advanced combination encoding (ACE) as a speech processing strategy to simulate cochlear implant. There were nine normal-hearing (NH) adults participating in this experiment. We used monosyllabic words as speech materials to compare the difference between white noise carrier and sine wave carrier. Additionally, we compared four stimulation rates (250 Hz, 900 Hz, 1200 Hz, and 1800 Hz) with conditions of two carriers. As a result, the word recognition was significantly poorer in 250 Hz than those of the others under the condition of white noise carrier. There were no significant differences with the stimulation rates beyond 900 Hz. Besides, the variation of four tones corresponded to the clinical results in the condition of white noise carrier. For this reason, we used white noise as the carrier for CI simulation in the following experiments. Eight subjects from previous experiment attended the next test. In the section of experiment for the disyllabic words, we evaluated four kinds of stimulation channels (4 ch, 8 ch, 12 ch, and 16 ch) and four stimulation rates (the same with the previous test). We found that the recognition rate of 4 ch was significantly lower than those of the others, but there were no significant differences in four stimulation rates. The standard deviation of 250 Hz was much higher than those of the others, so 900 Hz was a more stable stimulation rate. Furthermore, we tested five signal-to-noise ratio (SNR), including -5 dB, 0 dB, 5 dB, 10 dB, and Quiet, for disyllable and sentences. The speech recognition rates decreased with the SNR descending for both speech materials. When we added the signal (cutoff frequency 500 Hz) of hearing aid (HA) in the opposite ear, the test scores all rose up, especially for low SNRs (Quiet condition was not included in this test). For comparison purpose, four CI subjects were tested on different SNR conditions with disyllabic words for both CI only and CI combined with HA conditions. The results show that there were significant differences between 0 dB and Quiet for CI only condition, and significant differences among 0 dB vs. 5 dB, 10 dB, Quiet, and 10 dB vs. Quiet for CI combined HA condition. The speech recognition rates roughly increased with the increasing SNR. Our clinical results show there were no significant benefits when CI was combined with HA for all SNR conditions.
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