Effect of Masker Head Orientation, Listener Age, and Extended High-Frequency Sensitivity on Speech Recognition in Spatially Separated Speech

Abstract

Objectives: Masked speech recognition is typically assessed as though the target and background talkers are all directly facing the listener. However, background speech in natural environments is often produced by talkers facing other directions, and talker head orientation affects the spectral content of speech, particularly at the extended high frequencies (EHFs; >8 kHz). This study investigated the effect of masker head orientation and listeners' EHF sensitivity on speech-in-speech recognition and spatial release from masking in children and adults.Design: Participants were 5-to 7-year-olds (n = 15) and adults (n = 34), all with normal hearing up to 8 kHz and a range of EHF hearing thresholds. Speech reception thresholds (SRTs) were measured for target sentences recorded from a microphone directly in front of the talker's mouth and presented from a loudspeaker directly in front of the listener, simulating a target directly in front of and facing the listener. The maskers were two streams of concatenated words recorded from a microphone located at either 0° or 60° azimuth, simulating masker talkers facing the listener or facing away from the listener, respectively. Maskers were presented in one of three spatial conditions: co-located with the target, symmetrically separated on either side of the target (+54° and −54° on the horizontal plane), or asymmetrically separated to the right of the target (both +54° on the horizontal plane).Results: Performance was poorer for the facing than for the nonfacing masker head orientation. This benefit of the nonfacing masker head orientation, or head orientation release from masking (HORM), was largest under the co-located condition, but it was also observed for the symmetric and asymmetric masker spatial separation conditions. SRTs were positively correlated with the mean 16-kHz threshold across ears in adults for the nonfacing conditions but not for the facing masker conditions. In adults with normal EHF thresholds, the HORM was comparable in magnitude to the benefit of a symmetric spatial separation of the target and maskers. Although children benefited from the nonfacing masker head orientation, their HORM was reduced compared to adults with normal EHF thresholds. Spatial release from masking was comparable across age groups for symmetric masker placement, but it was larger in adults than children for the asymmetric masker.Conclusions: Masker head orientation affects speech-in-speech recognition in children and adults, particularly those with normal EHF thresholds. This is important because masker talkers do not all face the listener under most natural listening conditions, and assuming a midline orientation would tend to overestimate the effect of spatial separation. The benefits associated with EHF audibility for speech-in-speech recognition may warrant clinical evaluation of thresholds above 8 kHz.

Individual variability and similarity in horizontal directivity patterns for speech

“…One question is whether such individual differences in directivity are perceptually relevant. For example, it has been demonstrated that differences in head orientation between a target talker and background talkers can lead to improvements in speech recognition due to the low-pass filtering effect of turning the head [6][7][8]. Furthermore, we have demonstrated talker effects on listeners' ability to detect changes in head orientation [7], raising the possibility that individual differences in speech directivity may be perceptually relevant.…”

The ecological utility of extended high frequencies for speech recognition

“…This is likely because the rotating of the masker talkers' heads leads to reduced EHF levels, unmasking EHFs in the target speech. Interestingly, pure-tone thresholds at 16 kHz were correlated with full-band speech-in-speech recognition when masker talkers faced away from the listener, but not when masker talkers faced the listener, and this was true whether target and masker were co-located or were spatially separated [15].…”

Extending the High-Frequency Bandwidth and Predicting Speech-in-Noise Recognition: Building on the Work of Pat Stelmachowicz

“…Trine and Monson 35 reported correlations between EHF thresholds (measured from 9 to 16 kHz) and female-speech-in-noise recognition using the mismatched head orientation task from Monson et al 33 with young, normal-hearing listeners. Braza et al 40 also used this paradigm with normal-hearing listeners, demonstrating that correlations between EHF thresholds and female-speech-in-noise performance reached significance when the target talker faced the listener while background talkers faced away from the listener, but not when target and background talkers were all facing the listener (the traditional testing paradigm). Mishra et al 41 found a relationship between EHF thresholds for normal-hearing listeners (measured at 10, 12.5, 14, and 16 kHz) and male-speech-in-noise recognition using a multi-talker babble masker (11-kHz bandwidth).…”