The interaction of vocal characteristics and audibility in the recognition of concurrent syllables.

In concurrent-speech recognition, performance is enhanced when either the glottal pulse rate (GPR) or the vocal tract length (VTL) of the target speaker differs from that of the distracter, but relatively little is known about the trading relationship between the two variables, or how they interact with other cues such as signal-to-noise ratio (SNR). This paper presents a study in which listeners were asked to identify a target syllable in the presence of a distracter syllable, with carefully matched temporal envelopes. The syllables varied in GPR and VTL over a large range, and they were presented at different SNRs. The results showed that performance is particularly sensitive to the combination of GPR and VTL when the SNR is 0 dB. Equal-performance contours showed that when there are no other cues, a two-semitone difference in GPR produced the same advantage in performance as a 20% difference in VTL. This corresponds to a trading relationship between GPR and VTL of 1.6. The results illustrate that the auditory system can use any combination of differences in GPR, VTL, and SNR to segregate competing speech signals.