Intelligibility of Clear Speech: Effect of Instruction

Abstract

Purpose The authors investigated how clear speech instructions influence sentence intelligibility. Method Twelve speakers produced sentences in habitual, clear, hearing impaired, and overenunciate conditions. Stimuli were amplitude normalized and mixed with multitalker babble for orthographic transcription by 40 listeners. The main analysis investigated percentage-correct intelligibility scores as a function of the 4 conditions and speaker sex. Additional analyses included listener response variability, individual speaker trends, and an alternate intelligibility measure: proportion of content words correct. Results Relative to the habitual condition, the overenunciate condition was associated with the greatest intelligibility benefit, followed by the hearing impaired and clear conditions. Ten speakers followed this trend. The results indicated different patterns of clear speech benefit for male and female speakers. Greater listener variability was observed for speakers with inherently low habitual intelligibility compared to speakers with inherently high habitual intelligibility. Stable proportions of content words were observed across conditions. Conclusions Clear speech instructions affected the magnitude of the intelligibility benefit. The instruction to overenunciate may be most effective in clear speech training programs. The findings may help explain the range of clear speech intelligibility benefit previously reported. Listener variability analyses suggested the importance of obtaining multiple listener judgments of intelligibility, especially for speakers with inherently low habitual intelligibility.

Clear Speech Variants: An Acoustic Study in Parkinson's Disease

“…Further research is needed to investigate the impact of instruction when using a clear speech training program. Previous studies have reported that different clear speech instructions also vary in the amount of clear speech benefit or intelligibility increase in young healthy adults (Lam & Tjaden, 2013a). It is unknown whether this relationship holds for speakers with PD.…”

“…However, the instructions used to elicit clear speech vary widely across studies. In our previous research with young healthy adult speakers, three variants of clear speech instruction-including "Overenunciate each word," "Speak to someone with a hearing impairment," and "Speak clearly"-differentially affected the magnitude of acoustic adjustments and, in turn, positively correlated to the amount of clear speech intelligibility benefit (Lam & Tjaden, 2013a, 2013bLam, Tjaden, & Wilding, 2012). In the current study, we extend this line of inquiry to speakers with PD and a group of age-and sex-matched controls.…”

Impact of Clear, Loud, and Slow Speech on Scaled Intelligibility and Speech Severity in Parkinson's Disease and Multiple Sclerosis

“…Whether certain cues for eliciting clear or loud speech serve to maximize intelligibility is worthy of study in the future, perhaps especially in light of research suggesting that the cue for stimulating an increased vocal intensity affects the nature of the speech production adjustments in PD (Darling & Huber, 2011). Clear speech instructions also have been shown to impact the magnitude of acoustic adjustments made by neurologically healthy talkers (Lam et al, 2012), as well as the magnitude of the improvement in intelligibility (Lam & Tjaden, 2013). …”

Variability and Diagnostic Accuracy of Speech Intelligibility Scores in Children

“…One observation that seems to be common among studies of intelligibility involving both children and adults across disorder populations is that there is considerable variability in the performance of different listeners who hear the same speaker (interlistener variability; see Hustad & Cahill, 2003;Hustad et al, 2012;Lam & Tjaden, 2013;Montag, AuBuchon, Pisoni, & Kronenberger, 2014;Pennington et al, 2013). In fact, studies report standard deviations within a given speaker across listeners of up to 17% for individuals with the most severe dysarthria and slightly lower for those speakers with less severe dysarthria (Hustad & Cahill, 2003).…”