Positive Affect in Infant Siblings of Children Diagnosed with Autism Spectrum Disorder

Background: Although the literature indicates that children with Autism Spectrum Disorder (ASD) display flatter affect and express less positive emotion than their typically developing peers (Bieberich & Morgan, 1998), little research has examined the early development of expressed emotion in ASD. Preliminary evidence suggests that by one year of age, high-risk infants showing signs of ASD display fewer social smiles than controls (Zwaigenbaum, Bryson, Rogers, et al., 2005). However, additional research is necessary to determine whether smiling distinguishes infant siblings who are and are not diagnosed with ASD, and, if so, when these differences begin to emerge. 
Objectives: To examine smiling behaviour across three time points (6, 12, and 18 months) in high-risk infants with an older sibling with ASD and low-risk control infants. Of particular interest is whether there are group differences among high-risk infants later diagnosed with ASD (ASD sibs), non-ASD sibs, and controls and, if so, when this divergence occurs.

Methods: To date, videos of 45 infants (15 ASD sibs, 15 non-ASD sibs, and 15 typically-developing controls) have been coded for displays of positive affect at 6, 12 and 18 months of age. All of the children (6 females and 9 males per group) were followed to age 3 years, at which time an independent ASD assessment was conducted using the ADOS, ADI-R, DSM-IV, and expert clinical judgement. The video clips were collected while the infants were assessed on the Autism Observation Scale for Infants (AOSI; Bryson, McDermott, Rombough, et al., 2004), a semistructured play schedule designed to measure early signs of ASD. Each 7- to 10-minute clip took place during the same portion of the AOSI assessment. The main dependent variable was the average number of seconds spent smiling per minute.

Results: A 3 x 3 (Group x Time Point) mixed repeated measures analysis of variance revealed a significant effect of Time Point (F (2, 80) = 5.91, p = .004; partial eta² = .13); children spent more time smiling as they grew older. Although preliminary analyses failed to reveal a significant effect for Group (F (2, 40) = 1.84, p = .17), effect size calculations indicate that there is a medium- to large-sized effect of this variable (partial eta² = .084), with the anticipated trend of reduced smiling in ASD sibs relative to controls at 12 and 18 (but not 6) months. No significant interaction was found between the Group and Time Point variables (F (2,40) = .33, p = .86; partial eta² = .02). Data collection is ongoing.
Conclusions: Preliminary findings suggest that by 12 months of age, ASD sibs may spend less time smiling than controls. Discussion will focus on the implications of these findings for subsequent child development and for treatment efforts.