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The present study investigates the relationship between sentence intelligibility, band importance, and patterns of spectro-temporal covariation between frequency bands. Sixteen listeners transcribed sentences acoustically degraded to 5, 8, or 15 frequency bands. Half of the sentences retained the frequency bands that captured more signal covariance. The other half retained the bands accounting for less signal covariance. Sentence intelligibility was significantly higher in the high-covariance condition. Critically, this finding was predicted by differences in band importance across reconstructed sentences. These findings provide a mechanistic relationship between the contributions of signal covariance and band importance to sentence intelligibility.

A robust clear speech intelligibility benefit for a variety of talkers, listeners, and communication challenges is well-documented. In this talk, I will review research that focuses on how conversational to clear speech modifications facilitate linguistic processes and cognitive functioning beyond word recognition in noise. In one line of work, using a visual-world paradigm, we showed that clear speech enhanced speech segmentation and reduced lexical competition. In another, we showed that clear speech benefit extended to the improved sentence recognition memory and recall of words and sentences. Finally, in a series of experiments using a dual-task paradigm, we showed that hearing clear speech increased reaction times on a concurrent visual task suggesting that the clear speech processing benefits may arise through the increased engagement of the attentional resources toward the more salient hyperarticulated speech. The results contribute evidence that clear speech facilitates signal-dependent sensory processing as well as deeper linguistic processing abstracted from the input speech. These clear speech findings have implications for our understanding of perceptual mechanisms that underlie improved speech perception, including the use of cognitive resources and listening effort.

Speech signals are acoustically redundant, which could explain why sentence intelligibility is fairly robust even when sentences are acoustically degraded. We investigated the contributions to sentence intelligibility of clear speech redundancy encoded as patterns of spectrotemporal covariation between frequency channels. Participants (N = 16) transcribed 120 clear-speech English sentences acoustically degraded to 5, 8, or 15 frequency bands derived from an ERB-scaled filter bank. Before the acoustic degradation, each sentence was expressed as a linear combination of principal component eigenvectors representing different patterns of covariation between channels. Half of the sentences preserved the channels providing larger score magnitudes for the eigenvector accounting for more spectral covariance (high-covariance condition). These channels represented the spectral covariation patterns that were more dominant in each sentence. The other half of the sentences preserved the bands conveying larger score magnitudes for the eigenvector accounting forless spectral covariance (low-covariance condition). These bands represented the spectral covariation patterns that were less dominant. Participants yielded significantly better transcription accuracy in the high-covariance condition (mixed-effects, ps

Listener-oriented hyperarticulated clear speech facilitates linguistic processing and cognitive functioning associated with speech perception under various listening conditions. Using the visual-world eye-tracking paradigm, we investigated whether clear speech also aids speech segmentation, or the discovery of word boundaries, and examined the dynamic time course of its effect. Native American English speakers (N = 77) heard sentences in which the target word (e.g., ham) was temporarily ambiguous with a longer unintended competitor (e.g., hamster) across a word boundary (e.g., She saw the ham starting…) while viewing images depicting the target, competitor, and unrelated distractors. Clear and conversational sentences were presented in quiet or in speech-shaped noise at +3 dB signal-to-noise ratio. Analysis of eye fixations to the images over time revealed that compared with conversational speech, clear speech facilitated the disambiguation of the target from the competitor even before the disambiguation point was reached. The facilitation was found in both listening conditions but was relatively delayed in noise. These findings suggest that speaking clearly improves word segmentation and reduces lexical competition especially in optimal listening conditions. The speech segmentation facilitation may partly underlie the clear speech benefits observed for other signal-dependent and relatively signal-independent linguistic and cognitive processes.

Talkers dynamically modify their coarticulatory patterns when producing listener-oriented hyperarticulated clear speeches. This study examined how the use of protective face masks interacts with the production of intelligibility-enhancing clear speech to impact coarticulation. A native and a non-native speaker of English read sentences in a clear and conversational speaking style with and without a surgical mask. Coarticulation between word-internal adjacent segments was analyzed with a whole-spectrum analysis including spectral distance and segment overlap duration. Both speakers coarticulated less in clear than in conversational speaking style as indicated by the larger spectral distance and shorter overlap duration between adjacent segments. Coarticulation was further reduced when clear speech was produced with a mask by the native speaker but not by the non-native speaker. The findings showed that producing hyperarticulated intelligibility-enhancing clear speech also involves reducing coarticulatory overlap across adjacent segments. Coarticulatory resistance was adaptively reinforced in the presence of the additional communicative barrier, face mask, particularly for the speaker with extensive experience with the target language. Such cumulative reduction of coarticulation may in part underlie the larger perception-in-noise benefit for clear speech produced with a mask for the native compared to the non-native talker.

We analyzed the degree and time course of coarticulatory vowel nasalization in hyperarticulated clear speech produced in real and imagined communicatively challenging conditions from the LUCID corpus (Baker & Hazan, 2011). Southern British English speakers completed an interactive spot-the-difference task in pairs when there was no overt communication barrier (NB), when the partner was non-native (L2), and when one speaker’s speech was vocoded (VOC) or mixed with talker babble (BABBLE). They also read sentences conversationally (READ-CO) and clearly (READ-CL). The results showed significantly greater overall keyword vowel nasalization in the BABBLE and L2 conditions than in NB, READ-CO, and READ-CL, as well as in VOC than in NB and READ-CO. READ-CL and READ-CO did not differ significantly. Examining vowel nasalization over time revealed that the significant differences emerged, on average, at 7.4% into the vowel. Speakers increased coarticulatory nasalization early in the vowel when producing hyperarticulated speech in response to a real communicative barrier, consistent with the idea that nasal coarticulation facilitates speech processing by cueing upcoming segments. It remains to be determined why nasal coarticulation is increased while coarticulation for other consonant-vowel sequences is decreased during the production of hyperarticulated listener-oriented speaking styles (Guo and Smiljanic, 2021).