Figure 3. A) Proportion of synchrony judgments per group as a function of SOA for congruent and incongruent trials. Here, negative SOAs indicate that the voice was leading the lip movements, and vice versa. B) Proportion of synchrony judgments (collapsed across SOAs) as a function of age and congruency for each group (bins of 10 years). The error-bars reflect the standard error of the mean.
We conducted a repeated measures ANOVA on the mean proportion of synchrony responses with SOA and congruency as within subjects variables, group as a between subjects variable, and age as a continuous covariate. This yielded a significant main effect of SOA (F (1,866)=208.845, p <.001). The rate of synchrony responses across the SOAs formed a typical Gaussian distribution with a slight visual leading offset (see Figure 3a). Additionally, the proportion of synchrony responses was much higher when the stimuli were congruent than incongruent (F (1,866)=377.547,p <.001). Congruency also interacted with SOA, such that its effect was most pronounced when stimuli occurred simultaneously or with a slight visual lead (F (1,866)=48.803,p <.001), and with group (F (1,866)=17.004,p <.001). A follow up t-test comparing the difference between mean simultaneity judgment response rates for congruent and incongruent trials according to group revealed that the effect of congruency was greater for non-autistic participants than autistic ones (t (867)=6.76, p <.001; see Figure 3a). SOA also interacted with group, with the differences between autistic and non-autistic participants emerging at the mid-range SOAs (F (1,866)=7.204, p <.001), which is logical given that the longer SOAs were much more obvious to both groups. Both congruency (F (1,866)=31.101, p <.001) and SOA (F (1,866)=55.233, p <.001) also significantly interacted with age. Finally, we detected a significant three way interaction between congruency × SOA × age (F (1,866)=6.792,p <.001). The difference between congruent and incongruent trials was greater at younger ages. Because SOA interacts with all significant factors due to the nature of simultaneity judgment tasks, these effects were not explored further.
Window of Perceived Synchrony. We fitted a Gaussian distribution to the synchrony distribution for each individual by using the curve_fit function from the scipy Python module to estimate a WPS, amplitude and PSS. Figure 3b illustrates the mean WPS as a function of age (bin size = 10 years) for participants with and without autism. Note that for one participant, the fitting procedure was not successful, resulting in exclusion from further analyses.