Effects of intelligibility on within- and cross-modal sentence recognition memory for native and non-native listeners

Learning a language with vowelless words

Vowelless words are exceptionally typologically rare, though they are found in some languages, such as Tashlhiyt (e.g., fkt 'give it'). The current study tests whether lexicons containing tri-segmental (CCC) vowelless words are more difficult to acquire than lexicons not containing vowelless words by adult English speakers from brief auditory exposure. The role of acoustic-phonetic form on learning these typologically rare word forms is also explored: In Experiment 1, participants were trained on words produced in either only Clear speech or Casual speech productions of words; Experiment 2 trained participants on lexical items produced in both speech styles. Listeners were able to learn both vowelless and voweled lexicons equally well when speaking style was consistent for participants, but learning was lower for vowelless lexicons when training consisted of variable acoustic-phonetic forms. In both experiments, responses to a post-training wordlikeness ratings task containing novel items revealed that exposure to a vowelless lexicon leads participants to accept new vowelless words as acceptable lexical forms. These results demonstrate that one of the typologically rarest types of lexical forms - words without vowels - can be rapidly acquired by naive adult listeners. Yet, acoustic-phonetic variation modulates learning.

The role of speech style, frequency, and density in recognition memory for spoken words

What determines whether listeners remember a spoken word? The Effortfulness Hypothesis claims that memory is modulated by a word's intelligibility during real-time processing, while the Distinctiveness Hypothesis claims that it is modulated by a word's distinguishing characteristics. We tested these differing predictions using American English words that varied along three dimensions known to affect both intelligibility and distinctiveness: speech style (clear versus casual), frequency (high versus low), and neighborhood density (high versus low). In a recognition memory experiment, participants (n = 66) listened to a set of study words, and then gave yes/no judgments to indicate whether or not they had heard the word earlier. Results showed that those words which exhibited distinctive characteristics - whether due to clear speech style, low frequency, or low density - were remembered better. The finding supports the Distinctiveness Hypothesis, suggesting that our capacity for remembering words relies on their distinctiveness, rather than on our capacity for recognizing them in real time.

An acoustic study of Cantonese alaryngeal speech in different speaking conditions

Esophageal (ES) speech, tracheoesophageal (TE) speech, and the electrolarynx (EL) are common methods of communication following the removal of the larynx. Our recent study demonstrated that intelligibility may increase for Cantonese alaryngeal speakers using clear speech (CS) compared to their everyday "habitual speech" (HS), but the reasoning is still unclear [Hui, Cox, Huang, Chen, and Ng (2022). Folia Phoniatr. Logop. 74, 103-111]. The purpose of this study was to assess the acoustic characteristics of vowels and tones produced by Cantonese alaryngeal speakers using HS and CS. Thirty-one alaryngeal speakers (9 EL, 10 ES, and 12 TE speakers) read The North Wind and the Sun passage in HS and CS. Vowel formants, vowel space area (VSA), speaking rate, pitch, and intensity were examined, and their relationship to intelligibility were evaluated. Statistical models suggest that larger VSAs significantly improved intelligibility, but slower speaking rate did not. Vowel and tonal contrasts did not differ between HS and CS for all three groups, but the amount of information encoded in fundamental frequency and intensity differences between high and low tones positively correlated with intelligibility for TE and ES groups, respectively. Continued research is needed to understand the effects of different speaking conditions toward improving acoustic and perceptual characteristics of Cantonese alaryngeal speech.

Clear Speech Variants: An Investigation of Intelligibility and Speaker Effort in Speakers With Parkinson's Disease

PURPOSE

This study investigated the effects of three clear speech variants on sentence intelligibility and speaking effort for speakers with Parkinson's disease (PD) and age- and sex-matched neurologically healthy controls.

METHOD

Fourteen speakers with PD and 14 neurologically healthy speakers participated. Each speaker was recorded reading 18 sentences from the Speech Intelligibility Test in their habitual speaking style and for three clear speech variants: clear (SC; given instructions to speak clearly), hearing impaired (HI; given instructions to speak with someone with a hearing impairment), and overenunciate (OE; given instructions to overenunciate each word). Speakers rated the amount of physical and mental effort exerted during each speaking condition using visual analog scales (averaged to yield a metric of overall speaking effort). Sentence productions were orthographically transcribed by 50 naive listeners. Linear mixed-effects models were used to compare intelligibility and speaking effort across the clear speech variants.

RESULTS

Intelligibility was reduced for the PD group in comparison to the control group only in the habitual condition. All clear speech variants significantly improved intelligibility above habitual levels for the PD group, with OE maximizing intelligibility, followed by the SC and HI conditions. Both groups rated speaking effort to be significantly higher for both the OE and HI conditions versus the SC and habitual conditions.

DISCUSSION

For speakers with PD, all clear speech variants increased intelligibility to a level comparable to that of healthy controls. All clear speech variants were also associated with higher levels of speaking effort than habitual speech for the speakers with PD. Clinically, findings suggest that clear speech training programs consider using the instruction "overenunciate" for maximizing intelligibility. Future research is needed to identify if high levels of speaking effort elicited by the clear speech variants affect long-term sustainability of the intelligibility benefit.

Reading aloud in clear speech reduces sentence recognition memory and recall for native and non-native talkers

Speaking style variation plays a role in how listeners remember speech. Compared to conversational sentences, clearly spoken sentences were better recalled and identified as previously heard by native and non-native listeners. The present study investigated whether speaking style variation also plays a role in how talkers remember speech that they produce. Although distinctive forms of production (e.g., singing, speaking loudly) can enhance memory, the cognitive and articulatory efforts required to plan and produce listener-oriented hyper-articulated clear speech could detrimentally affect encoding and subsequent retrieval. Native and non-native English talkers' memories for sentences that they read aloud in clear and conversational speaking styles were assessed through a sentence recognition memory task (experiment 1; N = 90) and a recall task (experiment 2; N = 75). The results showed enhanced recognition memory and recall for sentences read aloud conversationally rather than clearly for both talker groups. In line with the "effortfulness" hypothesis, producing clear speech may increase the processing load diverting resources from memory encoding. Implications for the relationship between speech perception and production are discussed.

Face masks and speaking style affect audio-visual word recognition and memory of native and non-native speech

Though necessary, protective mask wearing in response to the COVID-19 pandemic presents communication challenges. The present study examines how signal degradation and loss of visual information due to masks affects intelligibility and memory for native and non-native speech. We also test whether clear speech can alleviate perceptual difficulty for masked speech. One native and one non-native speaker of English recorded video clips in conversational speech without a mask and conversational and clear speech with a mask. Native English listeners watched video clips presented in quiet or mixed with competing speech. The results showed that word recognition and recall of speech produced with a mask can be as accurate as without a mask in optimal listening conditions. Masks affected non-native speech processing at easier noise levels than native speech. Clear speech with a mask significantly improved accuracy in all listening conditions. Speaking clearly, reducing noise, and using surgical masks as well as good signal amplification can help compensate for the loss of intelligibility due to background noise, lack of visual cues, physical distancing, or non-native speech. The findings have implications for communication in classrooms and hospitals where listeners interact with teachers and healthcare providers, oftentimes non-native speakers, through their protective barriers.

The impact of face masks on the recall of spoken sentences

The effect of face covering masks on listeners' recall of spoken sentences was investigated. Thirty-two German native listeners watched video recordings of a native speaker producing German sentences with and without a face mask, and then completed a cued-recall task. Listeners recalled significantly fewer words when the sentences had been spoken with a face mask. This might suggest that face masks increase processing demands, which in turn leaves fewer resources for encoding speech in memory. The result is also informative for policy-makers during the COVID-19 pandemic, regarding the impact of face masks on oral communication.

Clear speech improves listeners' recall

The present study examined the effect of intelligibility-enhancing clear speech on listeners' recall. Native (n = 57) and non-native (n = 31) English listeners heard meaningful sentences produced in clear and conversational speech, and then completed a cued-recall task. Results showed that listeners recalled more words from clearly produced sentences. Sentence-level analysis revealed that listening to clear speech increased the odds of recalling whole sentences and decreased the odds of erroneous and omitted responses. This study showed that the clear speech benefit extends beyond word- and sentence-level recognition memory to include deeper linguistic encoding at the level of syntactic and semantic information.