Effects of Speaking Rate Changes on Speech Motor Variability in Adults.

The relationship between speaking rate and speech motor variability was examined in three groups of neurotypical adults, n = 40; 15 young adults (18-30 years), 13 adults (31-40 years), and 12 middle-aged adults (41-50 years). Participants completed a connected speech task at three speaking rates (habitual, fast, and slow) where kinematic (lower lip movement) and acoustic data were obtained. Duration and variability were measured at each speaking rate. Findings revealed a complex relationship between speaking rate and variability. Adults from the middle age range (31-40 years) demonstrated shorter acoustic and kinematic durations compared with the oldest age group (41-50 years) during the habitual speaking rate condition. All adults demonstrated the greatest variability in the slow speaking rate condition, with no significant differences in variability between habitual and fast speaking rates. Interestingly, lip aperture variability was significantly lower in the youngest age group (18-30 years) compared with the two older groups during the fast speaking rate condition. Differences in measures of acoustic variability were not observed across the age levels. Strong negative correlations between kinematic/acoustic duration and lip aperture/acoustic variability in the youngest age group were revealed. Therefore, while a slow speaking rate does result in greater variability compared with habitual and fast speaking rates, longer durations of productions by the different age groups were not linked to higher spatiotemporal index (STI) values, suggesting that timing influences speech motor variability, but is not the sole contributor.

Naive Listener Ratings of Speech Intelligibility Over the Course of Motor-Based Intervention in Children With Childhood Apraxia of Speech.

PURPOSE: The aim of this study was to describe changes in speech intelligibility and interrater and intrarater reliability of naive listeners' ratings of words produced by young children diagnosed with childhood apraxia of speech (CAS) over a period of motor-based intervention (dynamic temporal and tactile cueing [DTTC]). METHOD: A total of 120 naive listeners (i.e., listeners without experience listening to children with speech and/or language impairments; age range: 18-45 years) orthographically transcribed single-word productions by five children (age range: 2;6-3;11 [years;months]) across three time points over an intervention period (baseline, post-treatment, maintenance). Changes in intelligibility and interrater and intrarater reliability were examined within and across time points. RESULTS: Speech intelligibility significantly increased in children with CAS over the course of treatment, and these gains were also maintained at 6 weeks posttreatment. There was poor-to-fair consistency between listeners (interrater reliability) and excellent consistency within listeners (intrarater reliability) in ratings of speech intelligibility within and across time points. CONCLUSIONS: Motor-based intervention increases speech intelligibility following a period of DTTC treatment. Variability among naive listeners of speech intelligibility was also present, with intrarater reliability (within listeners) yielding greater consistency than interrater reliability (between listeners). The implications for including naive listeners as raters of speech intelligibility for research and clinical purposes are discussed.

The Multilevel Word Accuracy Composite Scale: A Novel Measure of Speech Production in Childhood Apraxia of Speech.

PURPOSE: The Multilevel word Accuracy Composite Scale (MACS) is a novel whole-word measure of speech production accuracy designed to evaluate behaviors commonly targeted in motor-based intervention for childhood apraxia of speech (CAS). The MACS yields a composite score generated through ratings of segmental accuracy, word structure maintenance, prosody, and movement transition. This study examined the validity of the MACS through comparison to established measures of speech accuracy. Reliability was also examined within and between practicing speech-language pathologists (SLPs). METHOD: The MACS was used to rate 117 tokens produced by children with severe CAS. Ratings were performed in the laboratory setting by two expert raters and by practicing SLPs (N = 19). Concurrent validity was estimated through comparison of expert MACS ratings (i.e., MACS score and each component rating) to measures of speech accuracy (percent phoneme correct and the 3-point scale) using correlational analyses. Reliability was examined between expert raters and across SLP raters using the intraclass correlation coefficient to examine interrater reliability of expert ratings, in addition to inter- and intrarater reliability of SLP ratings. RESULTS: Correlation analyses between MACS ratings (i.e., MACS score and component ratings) and existing measures of speech accuracy revealed small to large positive correlations between measures. Reliability analyses revealed moderate to excellent reliability for MACS ratings performed by expert raters and between (interrater) and within (intrarater) SLP raters. CONCLUSIONS: Analyses of concurrent validity indicate that the MACS aligns with established measures, yet contributes novel elements for rating speech accuracy. Results further support the MACS as a reliable measure for rating speech accuracy in children with severe speech impairment for ratings performed by expert raters and practicing clinicians.