Quantifying the Use of Gestures in Autism Spectrum Disorder

Background:  Autism Spectrum Disorder (ASD) is characterized by difficulties in communication and social interaction. In the absence of a biomarker, a diagnosis of Autism Spectrum Disorder (ASD) is reached in settings such as the ADOS (Lord et al., 2000) by observing disturbances of social interaction such as abnormalities in the use of gestures or flow of conversation. These observations rely exclusively on clinical judgement and are thus prone to error and inconsistency across contexts and clinicians. While studies in children show that co-speech gestures are fewer (e.g. Wetherby et al., 1998, Sowden et al., 2013) and for different use (Camaioni et al., 2003), de Marchena and Eigsti (2010) found that in adults some gestures are used with similar frequency in ASD and TD populations, but that their timing and their beneficial impact on the quality of communication are impaired. This may indicate that abnormal temporal processes contribute to impaired social skills in ASD (Allman, 2011).

Objectives:  

-          Quantify the production of gestures in ASD in naturally occurring language

-          Characterise the temporal dynamics of speech and gesture coordination in ASD using two acoustic indices; pitch and volume

Methods:  

The context of a previously published study of memory in ASD (Maras et al., 2013) provided the opportunity to examine video recordings of 17 ASD and 17 TD adults attempting to recall  details of a standardised event they had participated in (a first aid scenario). The videos were segmented to identify single gestures and their timing and linguistic type (iconic, metaphoric, deictic, beat) were documented. In addition the quantity of movement as well as the pitch and volume of speech over time were extracted. Recurrence quantification analysis was then used to examine whether gestures were time-locked to speech similarly in ASD and TD individuals and whether patterns of recurring behaviour would emerge similarly in both groups.

Results:  Overall, our results indicated no main group difference in the use and coordination of speech and gesture: both groups produced the same quantity of movement over time (t(33)=-0.165, p>.8), and gestures were produced within the same time window and with a temporally similar distribution by ASD and TD individuals (η²_p=.042). However we found that the recurrence rate of quantity of movement and intensity of speech was marginally higher in the TD group than in the ASD group (t(34,2)=2.075, p=.052), which indicates that changes in movement and intensity of speech were more often time-locked in typical then ASD individuals.

Conclusions:  

The current data suggest that ASD adults use conversational gestures as often as TD individuals, and when they do so the temporal coordination of speech and gesture is on average no different. However, typical individuals demonstrate a stronger temporal synchronisation of their speech volume and co-speech movements. The somewhat looser coordination of speech and co-speech movement in ASD could contribute to the clinical observation of abnormal flow of conversation and use of gesture.