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Zirn, Stefan (2011): Entwurf eines Hörtests zur Bestimmung des Comodulation Masking Release bei Cochlea Implantat-Trägern. Dissertation, LMU München: Medizinische Fakultät



Normal hearing (NH) listeners commonly perform better when listening to speech in modulated than in steady state maskers. This improvement is often labeled as a “release of masking”. Cochlear-implant (CI) listeners generally don’t receive a masking release in speech perception tests and the reasons are indistinct. This study for the first time investigates the comodulation masking release, an underlying psychoacoustic effect, in a flanking band setup acoustically in CI users. The focus of the experiments was, if CI users can use across-frequency cues to improve signal detection in (co-)modulated interfering noise. The test bases upon a forced choice paradigm to determine detection thresholds of a sinusoidal signal in fluctuating maskers. The maskers consisted of one or five amplitude modulated narrow noise-bands. The masking noise-bands were either incoherently or coherently modulated (comodulated). The difference of the detection threshold of the sinusoidal signal in these two conditions is defined as comodulation masking release (CMR). Two parameters of the masking noise complex were varied: the bandwidth/modulation frequency and the spectral alignment. 18 NH and 28 CI users participated in this study. The measured detection thresholds in CI users were highly reproducible. In contrast, the inter-individual standard deviation was higher for CI users compared to NH. Nevertheless, CMR in CI users was significant (p<0.01). The results clearly show that CI users can benefit from across-frequency cues and achieve a significant CMR under the described test conditions. So, the basis for a release of masking in speech perception tests in CI users seems to exist.