Diadochokinetic Rate and Accuracy In Autism Spectrum Disorders

Background:  Several studies have found subtle deficits in diadochokinetic rate as a measure of oromotor functioning for children with ASDs; however, most studies have relied on overall scores and have not examined whether or not there are patterns of behavior as a function of task difficulty. This is important because demands on executive functioning and speech motor programming (oromotor sequencing) increase as the phonetic complexity of the task increases.  

Objectives:  We used acoustic and perceptual measurements of diadochokinetic rate and accuracy to measure the performance of children with ASD during repetition of several increasingly difficult syllable sequences.

Methods:  Participants were 24 children and adolescents with high-functioning ASD and 21 typically-developing peers between the ages of 11-18. Participants were matched on chronological age, IQ, and language abilities, and diagnoses were confirmed using the ADOS, ADI-R, and clinical judgment. Participants completed a series of diadochokinetic test items, which required them to repeat a sequence of sounds multiple times as fast as possible without making any errors.  Critical items included /pə/, /pə-tə/, /tə-kə/, /mə-bə/, /pə-tə-kə/, and /plə-trə-kə/.  The executive demands of oromotor sequencing increase as the number and complexity of the sound sequences increase. We used PRAAT (Boersma & Weeninck, 2009) to acoustically analyze the speech signal. For monosyllable and di-syllable items, we measured the rate of syllable production.  For the more challenging tri-syllables, we measured the percentage of sequencings accurately produced, because rate was confounded by the number of sequencing errors.

Results: There were no differences in diadochokinetic rate for the simple monosyllabic and disyllabic items. However, the group with ASD had a significantly higher percentage of errors than the typically developing comparison group (29% vs. 15%) on the more demanding /pə-tə-kə/ item, F(1,43)=4.62 p<.05, Cohen’s d=.66, and marginally higher percentage of errors on the /plə-trə-kə/ item (43% vs. 29%), F(1,43)=3.47, p=.07, Cohen’s d=.57. 

Conclusions:  Findings from this study are indicative of oromotor sequencing deficits in individuals with high-functioning ASD, even when controlling for general language and IQ functioning. Differences do not appear to be driven by slower speech motor systems, but by a reduced ability to retain the correct phonetic form in short-term memory and/or to accurately sequence the motor movements in complex sequences. Further exploration of speech output in children with ASD is needed, including the relationship between linguistic and motoric processes.