Speech Production and Developmental Language Disorder in Children
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Abstract
Developmental language disorder (DLD) is a spoken language disorder in which children have difficulties in learning, understanding, and using spoken language. It is considered a neurodevelopmental disorder, even though no agreed sensory or neural causes have been identified. Research has found that children with DLD have higher thresholds for the acoustic parameters that yield stress patterns in language, which contribute to rhythmicity. Given the abundance of literature connecting stress and rhythm, I hypothesize here that children with DLD will show difficulties in their abilities to produce the rhythm structures of words and phrases. Previous investigations of stress patterning have neglected the importance of the amplitude envelope (AE) and rise time in the perception and production of stress patterns, instead focusing on other parameters. My thesis will fill this gap, focusing on relations between AE processing as measured by 3 psychoacoustic tasks and the production of syllable stress patterns. Additionally, I will also measure pitch contour (PC) processing in the context of stress patterning. The theoretical framework adopted for this investigation is the Temporal Sampling Framework. To identify potential differences in stress production, I will compare the speech production of familiar words by children with Developmental Language Disorder (DLD), age-matched controls (AMC) and younger language (YLC) control children.
To identify the presence of DLD, participants were administered a series of standardized and experimental tests of language, phonology and reading. Experimental measures of the hypothesized rhythm difficulties were a rhythmic motor tapping task, the 3 acoustic threshold measures of AE rise time, 3 further measures of the acoustic correlates of stress (frequency, intensity, and duration), and the novel speech production task.
The core aim of my project is to measure how well the DLD, AMC and YLC participants match their AE and PC production to that of the token stimuli. Second, I explored the presence of learning effects in the speech production task by way of repetition effects. Third, I investigated if word length (2 versus 3 versus 4-syllable words) impacted AE and PC similarity scores, which is possible as the longer words are more phonologically complex. Fourth, item analyses were run to identify if some items presented more challenges for the children. Lastly, I ran correlational analyses to investigate the relationships between the accuracy of syllable stress production and acoustic and rhythmic processing across the three groups.
Results supported the hypothesis that children with DLD present with linguistic and acoustic deficits, and while they can keep tapping to a rhythmic beat, they tap at a different rate than the control groups. Moreover, children with DLD displayed atypical word production patterns in comparison to the control groups in terms of both similarity metrics, with more difficulty with PC than AE. No repetition effects were found. All children showed the highest accuracy for the 3 syllable items and although differences were present in the item analyses, the same items showed difficulty for all the three groups. Moreso, surprisingly, the perceptual acoustic measures of stress did not reveal strong correlations with the rhythmic tapping measures nor with the speech production measures. As predicted, the language tests were correlated with the perceptual measures of stress and the speech production measures.
Using the Temporal Sampling Framework (TSF) as a framework to investigate the underlying causes of DLD was thus a fruitful approach, as atypical word production and linguistic, acoustic, and rhythmic motor tapping tasks provided a comprehensive profile of a child presenting with language deficits. Findings from this experiment could potentially be utilized in the school setting, by carrying out activities designed to improve the perception and production of syllable stress patterns in children exhibiting language deficits, as well as those at-risk for later language deficits.