Comparison of Vowel and Sentence Intelligibility in People With Dysarthria Secondary to Amyotrophic Lateral Sclerosis.

PURPOSE: In this study, we examined the utility of vowel intelligibility testing for assessing the impact of dysarthria on speech characteristics in people with amyotrophic lateral sclerosis (ALS). We tested the sensitivity and specificity of overall vowel identification, as well as that of vowel-specific identification, to dysarthria presence and severity. We additionally examined the relationship between vowel intelligibility and sentence intelligibility. METHOD: Twenty-three people with ALS and 22 age- and sex-matched control speakers produced sentences from the Speech Intelligibility Test (SIT), as well as 10 American English monophthongs in /h/-vowel-/d/ words for the vowel intelligibility test (VIT). Data for SIT and VIT scores came from 135 listeners. Diagnostic accuracy of VIT measures was evaluated using the area under the curve of receiver operator characteristics. We then examined differences between control speakers, speakers with mild dysarthria, and speakers with severe dysarthria in their relationship between SIT and VIT scores. RESULTS: The results suggest that the overall vowel intelligibility score showed high sensitivity and specificity in differentiating between speakers with and without dysarthria, even those with milder symptoms. In addition, single-vowel identification scores showed at least acceptable group differentiation between the mild and severe dysarthria groups, though fewer single vowels were acceptable discriminators between the control group and the group with mild dysarthria. Identification accuracy of /ɪ/ in particular showed excellent discrimination across all groups. Examination of the relationship between SIT and VIT scores suggests a severity-specific relationship. Speakers with SIT scores above 70% generally had higher SIT than VIT scores, whereas speakers with SIT below 70% generally had higher VIT than SIT scores. DISCUSSION: Vowel intelligibility testing can detect speech impairments in speakers with mild dysarthria and residual articulatory function in speakers with severe dysarthria. Vowel intelligibility testing may, therefore, be a useful addition to intelligibility testing for individuals with dysarthria.

Does hand proximity enhance letter identification?

Adam et al. (2012) found that letters were identified more accurately when presented near, compared to away from, the hands. Participants performed the task in two conditions: with their hands held stationary and with their hands moving towards and away from the target letters. The near-hands effect included the contribution of both static and dynamic trials. Further studies showed that accuracy in letter discrimination was higher when hands were away from a target (a far-hands effect) and moving toward it, suggesting an interaction between hand position and movement direction. The present study aimed to test whether hand proximity affects letter identification when the hands are stationary, as it remains unclear if this effect can be reliably observed. Participants viewed strings of three consonants, briefly presented and masked, and had to verbally report their identity. Stimuli were presented under two different hand conditions: proximal and distal. The predicted effects of letter position and stimulus duration were all statistically significant and robust; however, we did not observe a hand proximity effect.

Perceptual Learning of Altered Vowel Space Improves Identification of Vowels Produced by Individuals With Dysarthria Secondary to Amyotrophic Lateral Sclerosis.

PURPOSE: This study examines the efficacy of perceptual training for improving typical listeners' identification of vowels produced by individuals with dysarthria. We examined whether training on a subset of vowels can generalize to (a) untrained vowels and (b) other speakers with similar overall intelligibility. METHOD: Sixty naive listeners completed a pretest/posttest perceptual learning task. In the pretraining test and posttraining test, participants identified nine American English monophthongs produced by two speakers with dysarthria secondary to amyotrophic lateral sclerosis (ALS). In the 20-min training task, a two-alternative forced choice (2AFC) task with feedback trained listeners on a subset of the vowels and speakers presented in the pretraining test. RESULTS: Vowel identification accuracy improved overall as a function of training. However, patterns of generalization between speakers and vowel types were not symmetric. Specifically, listeners generalized training from front vowels to back vowels but not vice versa. Likewise, listeners generalized from one speaker to another but not in the opposite direction. Examination of confusion matrices for the pretraining and posttraining revealed complex patterns of vowel-specific improvement. CONCLUSIONS: This study demonstrates that listeners benefit from a very simple training paradigm targeting vowels. Additionally, error patterns revealed that vowels are both resistant to and responsive to perceptual learning. Implications for future research and clinical training paradigms are discussed.

Perceptual learning alters effects of foreign language backgrounds in speech-in-speech recognition.

The effect of training on linguistic release from masking (LRM) was examined. In a pre-test and post-test, English monolingual listeners transcribed sentences presented with English and Dutch maskers. During training, participants transcribed sentences with either Dutch, English, or white noise maskers and received feedback. LRM was evident in the pre-test (performance was better with Dutch maskers) but was eliminated after training (masker conditions did not differ). Thus, the informational masking driving LRM can be ameliorated through training. This study is a basis for future research examining the specific aspects of informational masking that change as a function of experience.

Is semantic processing impaired near the hands?

In a sentence decision task, Davoli et al. (2010) found that the semantic analysis of sentences differed depending on whether the participants' hands were close to or far from the computer screen. According to the authors, the findings reflected an impoverishment of semantic processing near the hands. In the current study, we examine this explanation by asking whether hand position affects 1) other aspects of sentence processing, such as syntactic analysis, 2) semantic processing at the individual word level, and 3) performance in a picture naming task that requires access to meaning. In Experiment 1, participants judged the acceptability of sentences, half of which included semantic or syntactic violations. In Experiment 2, only semantically acceptable or nonacceptable sentences were presented. In Experiment 3, participants performed a go/nogo semantic categorization task on individual words. In Experiment 4, participants performed a picture naming task. Participants performed these tasks both with their hands near to and far from the computer screen. Regardless of the task, we found no evidence of impoverished semantic processing near the hands.

The Role of the Speaker, the Listener, and Their Joint Contributions During Communicative Interactions: A Tripartite View of Intelligibility in Individuals With Dysarthria.

Purpose We present a tripartite view of intelligibility in which the contributions of both the speaker and listener, as well as their joint effort during interaction, are considered. While considerable research has examined communicative interactions in situ, there is a critical gap in current knowledge on how speech intelligibility unfolds during such interactions. Here, we argue that research examining speech intelligibility in communicative interactions may provide important groundwork for advancement in clinical interventions for individuals with dysarthria. Method First, we describe the view and argue for its consideration as a powerful way of thinking about speech intelligibility. We then briefly situate the view in the relevant literature on speech intelligibility and existing theoretical frameworks. We then identify suitable methodological paradigms for studying joint contributions to intelligibility and, lastly, discuss the clinical application and potential impact of this tripartite view. Conclusions Speech communication occurs through interaction; however, in the laboratory and clinic, emphasis is usually placed on individual speakers and listeners. We have proposed that it is critical to consider how the joint contributions of speakers and listeners affect speech intelligibility in communicative interaction. This conceptualization is well aligned with the International Classification of Functioning, Disability and Health, and the findings from such an approach will allow us to better understand how to maximize available resources to enhance speech intelligibility.

The Use of Vowel Length in Making Voicing Judgments by Native Listeners of English and Spanish: Implications for Rate Normalization.

Among other characteristics, voiced and voiceless consonants differ in voice onset time (VOT; Lisker & Abramson, 1964). In addition, in English, voiced consonants are typically followed by longer vowels than their unvoiced counterparts (Allen & Miller, 1999). In Spanish, this relationship is less systematic (Zimmerman & Sapon, 1958). In two experiments, we investigated perceptual sensitivities of English and Spanish native speakers to following vowel length (VL) in categorizing syllables that ranged from a prevoiced bilabial stop [ba] to a long-lag bilabial stop [pa]. According to our results, English speakers show sensitivity to following vowels with VLs falling within an English-typical range (Experiment 1), but not when vowels are shorter and in a Spanish-typical range (Experiment 2). Interestingly, Spanish native speakers do not show sensitivity to following VL in either condition. These results suggest that VOT-VL tradeoffs in perception reflect phonological sensitivities of listeners and are not reducible to speech rate compensation.

Lexical exposure to native language dialects can improve non-native phonetic discrimination.

Nonnative phonetic learning is an area of great interest for language researchers, learners, and educators alike. In two studies, we examined whether nonnative phonetic discrimination of Hindi dental and retroflex stops can be improved by exposure to lexical items bearing the critical nonnative stops. We extend the lexical retuning paradigm of Norris, McQueen, and Cutler (Cognitive Psychology, 47, 204-238, 2003) by having naive American English (AE)-speaking participants perform a pretest-training-posttest procedure. They performed an AXB discrimination task with the Hindi retroflex and dental stops before and after transcribing naturally produced words from an Indian English speaker that either contained these tokens or not. Only those participants who heard words with the critical nonnative phones improved in their posttest discrimination. This finding suggests that exposure to nonnative phones in native lexical contexts supports learning of difficult nonnative phonetic discrimination.