Judging the Number and Gender of Talkers Present in an Auditory Scene Aided by Acoustic Beamforming.

The perceived numerosity of simultaneous, spatially separated speech sources was used to evaluate the effectiveness of triple beamformer processing, compared to that of both a single-channel beamformer and natural listening. Participants made judgments of the total number of talkers present in a simulated sound field and the gender composition of the talker group. The perceived numerosity was always underestimated for groups of more than three talkers. Performance with the triple beamformer was roughly equivalent to that of natural listening, including a beneficial effect of spatial separation of the sources in azimuth. The gender mix of the talker group also affected the numerosity judgments although the perceived gender ratio was generally accurate even when the total group count was underestimated. Time-reversing the speech resulted in lower numerosity judgements (increased error) under both natural and triple beamformer listening, suggesting an influence of linguistic processing on source numerosity judgments. Overall, factors that enhanced source segregation and speech stream coherence decreased errors in numerosity judgments. A stimulus-derived metric-the composite of glimpsed energy retained for all talkers in the sound field-was found to be a reasonably accurate predictor of the subjective numerosity judgments.