The Hands Have It: Variation in the Latency of Neural Activity during Beat Gesture-Speech Integration in ASD

Background: Ineffective communication via speech and gesture is a primary diagnostic characteristic of Autism Spectrum Disorder (ASD). Beat gestures, which convey emphasis in conjunction with speech, are particularly likely to be interpreted abnormally in ASD. Abnormal processing of beat gestures in ASD is associated with greater activity in high-level visual cortex and less activity in planum temporale, which is active during beat gesture and speech integration in typically developing (TD) individuals (Hubbard et al., 2012). At present, however, the time course of the neural activity underlying beat gesture and speech integration in ASD is unclear.

Objectives: The objectives of this research were (1) to determine the time course of gesture-speech processing in ASD and (2) to examine how neural activity is affected by the temporal asynchrony of beat gesture. It was predicted that individuals with ASD would be less sensitive to temporal asynchrony of beat gesture and speech than their TD peers. Furthermore, it was predicted that the time course of neural activity in TD would reflect gesture-speech synchrony, whereas that the time course of neural activity in ASD would not reflect it.

Methods: Participants in Study 1 included 18 high-functioning ASD and 23 TD individuals matched in age, gender, and verbal IQ (all ps < .05). In this study, participants viewed a brief cartoon video and retold its events to an experimenter while being tacitly video recorded. Gestures and speech were transcribed and coded by two raters unaware of the experimental design and predictions (ICC=.79 for speech onset; .89 for gesture onset). Participants in Study 2 included 15 TD individuals. In this study, participants viewed clips excerpted from a longer video of a speech, such that a beat gesture always occurred at 1.5 s. Accompanying audio clips were presented either simultaneously with or 500 ms preceding video clips. Data was collected continuously using magnetoencepholagraphy (MEG), a neurophysiological method with high spatiotemporal accuracy, and was temporally synched to gesture onset for analysis.

Results: In Study 1, individuals with ASD produced more temporally asynchronous beat gestures than TD individuals (see Fig. 1). In Study 2, activity was observed in inferior frontal gyrus (IFG) and proximal regions between 150-300 ms after first stimulus onset (see Fig. 2). Additionally, activity was observed in posterior temporal cortex (pSTC) between 500-650 ms after first stimulus onset. Notably, this activity varied on the basis of both latency and laterality, such that greater activation in response to temporally asynchronous beat gesture and speech was associated with shorter latencies and left hemisphere. By contrast, greater activation in response to temporally synchronous beat gesture and speech was associated with longer latencies and right hemisphere.

Conclusions: Together, the results show that the latency of neural activity reflects sensitivity to temporal beat gesture-speech asynchrony and that that integration of temporally asynchronous beat gesture and speech is atypical in ASD. These results form the basis of future research examining the latency of neural activity during beat gesture-speech integration in ASD, providing insight into the neural bases of abnormal gesture-speech integration in ASD.