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.