The yawning videos elicited more yawning in TD children than in children with ASD (Mann–Whitney test: z=−2.80, p=0.01), but the control movies showed no difference between groups in the number of yawns (Mann–Whitney test: z=−1.28, p>0.1; ). Within-group analyses also revealed that in TD children, yawning videos elicited more yawning than control videos (Wilcoxon signed-rank test: z=−2.07, p=0.038, one-tailed). However, children with ASD did not show any difference between yawning and control videos (Wilcoxon signed-rank test: z=−0.43, p>0.1).
Average frequency of yawns of participants during or after the observation of yawn and control conditions. TD, typically developing children; ASD, children with autism spectrum disorder; **p<0.01; *p<0.05.
In both children with ASD and TD children, the number of yawns did not correlate with age, IQ or scores of ASQ-J (Spearman: all ρ<0.31, p>0.1). The effect of gender on the frequency of yawning in the yawn and control conditions was examined both in ASD and TD group, and no significant effect of gender was found. In addition, group differences in the yawning condition remained significant when only male participants were compared (Mann–Whitney test: z=−2.01, p=0.044, one-tailed). Again, the control condition did not show a significant group effect in this subgroup (Mann–Whitney test: z=−1.69, p>0.1).
To further examine the effect of IQ, an additional group comparison was conducted with the IQ-matched subgroups of 16 TD children (7 females) and 16 children with ASD (3 females; see table in the electronic supplementary material). Results confirmed the main findings: TD children elicited more yawns than children with ASD in the yawning condition (Mann–Whitney test: z=−2.39, p=0.034), but not in the control condition (Mann–Whitney test: z=−0.79, p>0.1).
Note that Bonferroni corrections were applied to all multiple comparisons.