In order to measure improvement in cochlear implant performance due to new technologies, good outcome measures are required. Typically, speech recognition tasks have been used as a clinical outcome measure in cochlear implant research, but they are not ideal tool for comparing performance among different sound processing strategies because speech perception ability changes over time with experience. In addition, a speech measure does not always reflect the underlying advantage or disadvantage of the signal processing. To solve those problems, we propose to use psychophysical measures as an engineering development tool for cochlear implant sound processing strategies. We hypothesize that psychophysical measures through the sound processors are more sensitive than speech or music outcome measures to signal processing manipulations. In order to test our hypothesis, we propose to use four different signal processing strategies including Fidelity120, HiResolution, ACE (Advanced combination encoder), and MP3000. Three psychophysical measures including a spectral-ripple discrimination test, modulation detection test, and Schroeder-phase discrimination test will be run to determine the temporal and spectral sensitivity of each sound processing strategy. Three different clinical outcome measures including speech recognition in quiet and noise, and music perception will be conducted. In addition, we propose a single-channel Schroeder-phase test as a test of within-channel temporal fine structure sensitivity. If the single-channel Schroeder-phase test is sensitive to changes with the different sound processing strategies and if any of strategies improves within-channel temporal fine structure encoding, we hypothesize that the single-channel Schroeder-phase test will show it. To test this hypothesis, we will use two different sound processing strategies including CIS (continuous interleaved sampling) and SAS (simultaneous analog stimulation). The knowledge gained from the present study might simplify the analysis of how and why clinical sound processor do or do not improve hearing. Through the proposed study, the problem can be broken down into evaluating the effect of sound processing on several clinically relevant acoustic elements, saving from the complexities of hearing speech, speech in noise or music, and providing a more detailed understanding of how well a sound processor can deliver acoustic information. The main point of the proposed study is to address the effect of sound processors on the ability of cochlear implant users to hear acoustic changes that are relevant to their clinical success.
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