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Experiment 1 replicated the finding that normal-hearing listeners identify speech better in modulated than in unmodulated noise. This modulated-unmodulated difference ("MUD") has been previously shown to be reduced or absent for cochlear-implant listeners and for normal-hearing listeners presented with noise-vocoded speech. Experiments 2-3 presented normal-hearing listeners with noise-vocoded speech in unmodulated or 16-Hz-square-wave modulated noise, and investigated whether the introduction of simple binaural differences between target and masker could restore the masking release. Stimuli were presented over headphones. When the target and masker were presented to one ear, adding a copy of the masker to the other ear ("diotic configuration") aided performance but did so to a similar degree for modulated and unmodulated maskers, thereby failing to improve the modulation masking release. Presenting an uncorrelated noise to the opposite ear ("dichotic configuration") had no effect, either for modulated or unmodulated maskers, consistent with the improved performance in the diotic configuration being due to interaural decorrelation processing. For noise-vocoded speech, the provision of simple spatial differences did not allow listeners to take greater advantage of the dips present in a modulated masker.

A common finding in the cochlear implant literature is that the upper limit of rate discrimination on a single channel is about 300 pps. The present study investigated rate discrimination using a procedure in which, in each block of two-interval trials, the standard could have one of the five baseline rates (100, 200, 300, 400, and 500 pps) and the signal rate was a given percentage higher than the standard. Eight Med-El C40+ subjects took part. The pattern of results was different than those reported previously: six Med-El subjects performed better at medium rates (200-300 pps) compared to both lower (100 pps) and higher (400-500 pps) rates. A similar pattern of results was obtained both with the method of constant stimuli and for 5000-pps pulse trains amplitude modulated at rates between 100 and 500 Hz. Compared to an unmatched group of eight Nucleus CI24 listeners tested using a similar paradigm and stimuli, Med-El subjects performed significantly better at 300 pps and higher but slightly worse at 100 pps. These results are discussed in relation to evidence on the limits of temporal pitch at low and high rates in normal-hearing listeners.