Variability and uncertainty in masking by competing speech

Abstract

This study investigated the role of uncertainty in masking of speech by interfering speech. Target stimuli were nonsense sentences recorded by a female talker. Masking sentences were recorded from ten female talkers and combined into pairs. Listeners' recognition performance was measured with both target and masker presented from a front loudspeaker (nonspatial condition) or with a masker presented from two loudspeakers, with the right leading the front by 4 ms (spatial condition). In Experiment 1, the sentences were presented in blocks in which the masking talkers, spatial configuration, and signal-to-noise (S-N) ratio were fixed. Listeners' recognition performance varied widely among the masking talkers in the nonspatial condition, much less so in the spatial condition. This result was attributed to variation in effectiveness of informational masking in the nonspatial condition. The second experiment increased uncertainty by randomizing masking talkers and S-N ratios across trials in some conditions, and reduced uncertainty by presenting the same token of masker across trials in other conditions. These variations in masker uncertainty had relatively small effects on speech recognition.

Contextual variability during speech-in-speech recognition

“…It is, however, clear from the present research that speech-in-speech recognition accuracy can display sensitivity to contextual variation as it extends beyond the time-frame of the target signal itself. In contrast to previous work that showed little or no effect of cross-trial variation in acoustic or spatial characteristics known to influence speech-in-speech recognition (e.g., Brungart and Simpson, 2004;Freyman et al, 2007;Jones and Litovsky, 2008), this study has shown sensitivity to contextual variation in terms of the matching or mismatching of the language being spoken in the target and in the background. This sensitivity extended to languages as similar in sound structure as English and Dutch.…”

“…Whereas previous work focused on contextual variation (i.e., masker uncertainty) in terms of talkers, semantic content or location of the background speech signal (Brungart and Simpson, 2004;Freyman et al, 2007;Jones and Litovsky, 2008), we focus here on background language variation, a dimension of variation that is increasingly common in an era of globalization and that, as mentioned above, previous work has suggested (but not yet indisputably verified) may introduce a source of informational, in addition to energetic masking. Moreover, in an effort to more closely match real-world communicative settings, we use meaningful sentence stimuli with an open set response format, rather than formulaic sentences with a closed-set response format or nonsense sentences.…”

“…Previous work has only shown small or no effects of cross-trial masker variation for speech-in-speech recognition in which talkers, semantic content, or location of the background speech signal was held constant or varied across trials (Brungart and Simpson, 2004;Freyman et al, 2007;Jones and Litovsky, 2008), suggesting that speech-in-speech recognition accuracy may be dominated by within-trial target and masker characteristics (i.e., energetic factors) with a severely limited role for cross-trial, contextual (i.e., informational) factors. These studies all used multi-talker background babble that matched the language spoken in the target (e.g., English-in-English).…”

Effect of fundamental-frequency and sentence-onset differences on speech-identification performance of young and older adults in a competing-talker background

“…This was motivated given the contradictory findings on the contribution of uncertainty to speech recognition between young and old listener groups (Brungart and Simpson, 2004;Freyman et al, 2007;Humes and Coughlin, 2009;Humes et al, 2006;Mackersie et al, 2011;Sommers, 1997). For the competing speech environment, it is well known that target-masker similarity and stimulus uncertainty are associated with informational masking (Durlach et al, 2003;Freyman et al, 2007). Freyman et al (2007) varied the amount of masker uncertainty for a speech-recognition task and expected to observe more informational masking with increasing uncertainty of the masker.…”

“…For the competing speech environment, it is well known that target-masker similarity and stimulus uncertainty are associated with informational masking (Durlach et al, 2003;Freyman et al, 2007). Freyman et al (2007) varied the amount of masker uncertainty for a speech-recognition task and expected to observe more informational masking with increasing uncertainty of the masker. Unexpectedly, they found a relatively small effect of masker uncertainty on nonsense sentence identification for YNH listeners.…”