Orienting Response to Social Versus Physical Audiovisual Synchrony Does Not Differ in Toddlers with ASD

Background: Preferential orienting to biological motion, a skill thought to be critical for early social development, is disrupted in 24-month-old toddlers with autism (Klin et al., 2009). Instead of orienting to biological motion, toddlers with ASD attend to audio-visual synchrony (AVS), suggesting that their attention is guided by physical rather than social contingencies. Despite this apparent dichotomy, it should be noted that while AVS is indeed characterized by physical contingencies (the simultaneous presentation of light and sound), high AVS signals can also contain critical social information, as in the case of speech or co-speech gestures. This raises important questions about the adaptive value of orienting to AVS in typical development, and whether attention to AVS observed in ASD is driven primarily by preferences for physical or socially-meaningful contingencies.

Objectives: Investigate whether toddlers with and without ASD attend differently to high-AVS signals generated by socially-meaningful versus physical contingencies.

Methods: 58 toddlers (21 ASD, 37 TD) were shown point-light biological motion animations. An upright animation was presented on one half of the screen with the soundtrack of the actor’s vocalizations. On the other screen half, the inverted version of the same animation played in reverse order. Levels of AVS were quantified for the upright and inverted figure by measuring synchronous change in motion and sound at each frame. High-AVS moments were defined a priori as frames with AVS values exceeding the 90th percentile threshold. High-AVS moments generated by the upright figure were classified as socially-meaningful AVS in that they were generated by the movements and vocalizations of a biological figure. Conversely, high-AVS moments generated by the inverted figure were classified as physical AVSin that they were generated by the coincident alignment of two disparate signals of light and sound.  Peristimulus time histograms were created to assess the probability of looking at the upright/inverted figure, 1500ms before and after a high-AVS event. If toddlers orient to both socially-meaningful and physical AVS, then they should show similar orienting towards high-AVS moments generated by the upright and inverted figure. If toddlers distinguish between socially meaningful and physical AVS, then they should orient differently to AVS generated by the upright versus inverted figure. 

Results:   Intra-class correlations revealed that while ASD toddlers showed remarkably similar orienting to AVS on the upright and inverted side at all time-points (r=0.89, p<10^-13), this relationship was weaker for TD toddlers (r=0.14, p<10^-6) (Figure 2a). TD toddlers’ orienting to AVS on the upright and inverted side differed in two ways: They showed anticipatory looking towards the upright figure before socially meaningful high-AVS events, and demonstrated sustained looking after socially meaningful high-AVS events. Anticipatory and sustained looking were not observed for physical high-AVS events (Figure 2b). 

Conclusions: While TD toddlers differentially orient to socially-meaningful and physical AVS, ASD toddlers’ attention is indiscriminately biased by these two synchrony types. These findings support and expand on findings that ASD toddlers’ preferentially attend to physical rather than social contingencies, while highlighting the important role that orienting to socially-meaningful AVS may play in typical development.