Lombard speech detection in case of spatial separation between noise source and talkers of different genders

The spatial selectivity of hearing to speech signals was studied when the target signal and interference were separated by distance between their sources and the listener. In the work, the hypothesis about the improvement of hearing selectivity due to more intensive activation of the high-frequency binaural mechanism due to the shift of the speaker’s voice spectrum occurs in noisy environment towards high frequencies, was tested. The thresholds for detecting the target signal – a two-syllable word uttered by male or female, were evaluated in the two-alternative two-interval forced choice paradigm in 4 series. Series differed by the type of target signal (ordinary or Lombard speech) and the location of target source and noise (multi-talker noise) one. The both sources were located at a distance of 1 and 4 m opposite the subject at the level of his head. The detection threshold was defined as the ratio of signal and noise levels at the listener’s place (S/N). The threshold for detecting the target signal (male and female speaker voices together) was -11 dB S/N for ordinary as well as Lombard speech. It did not depend on which of the sources - the target signal or noise, was closer to the listener. In normal speech, the detection thresholds on average differed for male and female voices, but the difference was not significant. In Lombard speech, these thresholds were significantly different: for a male voice, the threshold at a detection level of 0.67 was -10 dB S/N, and for a female voice – -12.5 dB S/N.