Does Sentence-Level Coarticulation Affect Speech Recognition in Noise or a Speech Masker?

Purpose Three experiments were conducted to better understand the role of between-word coarticulation in masked speech recognition. Specifically, we explored whether naturally coarticulated sentences supported better masked speech recognition as compared to sentences derived from individually spoken concatenated words. We hypothesized that sentence recognition thresholds (SRTs) would be similar for coarticulated and concatenated sentences in a noise masker but would be better for coarticulated sentences in a speech masker. Method Sixty young adults participated (n = 20 per experiment). An adaptive tracking procedure was used to estimate SRTs in the presence of noise or two-talker speech maskers. Targets in Experiments 1 and 2 were matrix-style sentences, while targets in Experiment 3 were semantically meaningful sentences. All experiments included coarticulated and concatenated targets; Experiments 2 and 3 included a third target type, concatenated keyword-intensity-matched (KIM) sentences, in which the words were concatenated but individually scaled to replicate the intensity contours of the coarticulated sentences. Results Regression analyses evaluated the main effects of target type, masker type, and their interaction. Across all three experiments, effects of target type were small (< 2 dB). In Experiment 1, SRTs were slightly poorer for coarticulated than concatenated sentences. In Experiment 2, coarticulation facilitated speech recognition compared to the concatenated KIM condition. When listeners had access to semantic context (Experiment 3), a coarticulation benefit was observed in noise but not in the speech masker. Conclusions Overall, differences between SRTs for sentences with and without between-word coarticulation were small. Beneficial effects of coarticulation were only observed relative to the concatenated KIM targets; for unscaled concatenated targets, it appeared that consistent audibility across the sentence offsets any benefit of coarticulation. Contrary to our hypothesis, effects of coarticulation generally were not more pronounced in speech maskers than in noise maskers.

Does the semantic content or syntactic regularity of masker speech affect speech-on-speech recognition?

Speech-on-speech recognition differs substantially across stimuli, but it is unclear what role linguistic features of the masker play in this variability. The linguistic similarity hypothesis suggests similarity between sentence-level semantic content of the target and masker speech increases masking. Sentence recognition in a two-talker masker was evaluated with respect to semantic content and syntactic structure of the masker (experiment 1) and linguistic similarity of the target and masker (experiment 2). Target and masker sentences were semantically meaningful or anomalous. Masker syntax was varied or the same across sentences. When other linguistic features of the masker were controlled, variability in syntactic structure across masker tokens was only relevant when the masker was played continuously (as opposed to gated); when played continuously, sentence-recognition thresholds were poorer with variable than consistent masker syntax, but this effect was small (0.5 dB). When the syntactic structure of the masker was held constant, semantic meaningfulness of the masker did not increase masking, and at times performance was better for the meaningful than the anomalous masker. These data indicate that sentence-level semantic content of the masker speech does not influence speech-on-speech masking. Further, no evidence that similarities between target/masker sentence-level semantic content increases masking was found.