Factors underlying masking release by voice-gender differences and spatial separation cues in multi-talker listening environments in listeners with and without hearing loss

Spatial release from masking in the median plane with non-native speakers using individual and mannequin head related transfer functions

Spatial release from masking (SRM) in speech-on-speech tasks has been widely studied in the horizontal plane, where interaural cues play a fundamental role. Several studies have also observed SRM for sources located in the median plane, where (monaural) spectral cues are more important. However, a relatively unexplored research question concerns the impact of head-related transfer function (HRTF) personalisation on SRM, for example, whether using individually-measured HRTFs results in better performance if compared with the use of mannequin HRTFs. This study compares SRM in the median plane in a speech-on-speech virtual task rendered using both individual and mannequin HRTFs. SRM is obtained using English sentences with non-native English speakers. Our participants show lower SRM performances compared to those found by others using native English participants. Furthermore, SRM is significantly larger when the source is spatialised using the individual HRTF, and this effect is more marked for those with lower English proficiency. Further analyses using a spectral distortion metric and the estimation of the better-ear effect, show that the observed SRM can only partially be explained by HRTF-specific factors and that the effect of the familiarity with individual spatial cues is likely to be the most significant element driving these results.

Fusion of dichotic consonants in normal-hearing and hearing-impaired listenersa)

Hearing-impaired (HI) listeners have been shown to exhibit increased fusion of dichotic vowels, even with different fundamental frequency (F0), leading to binaural spectral averaging and interference. To determine if similar fusion and averaging occurs for consonants, four natural and synthesized stop consonants (/pa/, /ba/, /ka/, /ga/) at three F0s of 74, 106, and 185 Hz were presented dichotically-with ΔF0 varied-to normal-hearing (NH) and HI listeners. Listeners identified the one or two consonants perceived, and response options included /ta/ and /da/ as fused percepts. As ΔF0 increased, both groups showed decreases in fusion and increases in percent correct identification of both consonants, with HI listeners displaying similar fusion but poorer identification. Both groups exhibited spectral averaging (psychoacoustic fusion) of place of articulation but phonetic feature fusion for differences in voicing. With synthetic consonants, NH subjects showed increased fusion and decreased identification. Most HI listeners were unable to discriminate the synthetic consonants. The findings suggest smaller differences between groups in consonant fusion than vowel fusion, possibly due to the presence of more cues for segregation in natural speech or reduced reliance on spectral cues for consonant perception. The inability of HI listeners to discriminate synthetic consonants suggests a reliance on cues other than formant transitions for consonant discrimination.

Effects of presentation level on speech-on-speech masking by voice-gender difference and spatial separation between talkers

Many previous studies have reported that speech segregation performance in multi-talker environments can be enhanced by two major acoustic cues: (1) voice-characteristic differences between talkers; (2) spatial separation between talkers. Here, the improvement they can provide for speech segregation is referred to as "release from masking." The goal of this study was to investigate how masking release performance with two cues is affected by various target presentation levels. Sixteen normal-hearing listeners participated in the speech recognition in noise experiment. Speech-on-speech masking performance was measured as the threshold target-to-masker ratio needed to understand a target talker in the presence of either same- or different-gender masker talkers to manipulate the voice-gender difference cue. These target-masker gender combinations were tested with five spatial configurations (maskers co-located or 15°, 30°, 45°, and 60° symmetrically spatially separated from the target) to manipulate the spatial separation cue. In addition, those conditions were repeated at three target presentation levels (30, 40, and 50 dB sensation levels). Results revealed that the amount of masking release by either voice-gender difference or spatial separation cues was significantly affected by the target level, especially at the small target-masker spatial separation (±15°). Further, the results showed that the intersection points between two masking release types (equal perceptual weighting) could be varied by the target levels. These findings suggest that the perceptual weighting of masking release from two cues is non-linearly related to the target levels. The target presentation level could be one major factor associated with masking release performance in normal-hearing listeners.