Comodulation masking release for speech stimuli.

Abstract

This study sought to determine whether speech recognition in a modulating noise background can be facilitated by a process attributable to comodulation masking release (CMR). Experiment 1 examined the masked identification of six filtered vowels as a function of the number of comodulated noisebands present. A benefit of increased number was observed, consistent with an interpretation in terms of CMR, although it could not be certain that the basis of the discrimination was word recognition in the semantic sense. Experiment 2 made use of a forced-choice rhyming test in which the response foils differed only in a single filtered consonant; again, the measure of interest was performance as a function of the number of comodulated noisebands present. No evidence for a suprathreshold CMR was observed. Experiment 3 made use of open-set sentence material and employed a different paradigm, which allowed a measure of CMR in terms of the difference between thresholds in correlated and uncorrelated noise to be determined. While a CMR for speech detection was observed, no CMR for speech recognition was found. It was concluded that CMR is most evident in masked detection tasks and that diminishing returns are encountered as the signal-to-masker ratio is raised.