Análisis de resultados

To evaluate the protective value of social attention I conducted two types of exploratory analyses:

a) Assuming that the attentive brain state factor reflected the extent to which early risk factors impacted the brain affecting processing during social and non-social attention, I tested whether HR infants with more atypical attentive brain state who did not receive diagnosis of ASD at age 3 showed enhanced visual attention skills at 14 months (protective value of looking behaviour against neural vulnerability);

b) I compared behavioural correlates of social attention in LR and HR boys and girls who did not develop core ASD symptoms in early childhood (sex-specific protective effect of looking behaviour against familial/genetic risk). This analysis allowed me to see whether HR children who have high familial/genetic burden for ASD but have a ‘better than expected outcome’ (Szatmari, 2018) showed unusually higher social attention at 14 months. If so, this would suggest that early social attention skills might have a protective value against familial/genetic risk. Moreover, this analysis allowed me to test whether such an effect was observed to the same extent in males and females. If exceptionally enhanced social attention was observed in HR females only, this would have confirmed the role of sex-specific effects in boosting social

attention. If higher social attention was observed in both HR males and females, this looking behaviour might have been interpreted as protective against risk independently from sex factors.

Protective effect of looking behaviour during social attention against neural vulnerability

For this analysis, I aimed to identify infants with inefficient engagement with social stimuli in the first year of life. The mean Nc amplitude and Ms duration difference between FD and Noise condition were selected as neural correlates of social attention because they were the two variables which mainly contributed to the attentive brain state factor in the SEMs (see section

3.3.1). As a first step, these two variables were scaled such that they both had mean=0 and

s.d.=1. Of note, more negative values of Nc amplitude indicated more enhanced attention engagement. Consequently, more negative scores in the mean Nc amplitude difference between the face and the Noise condition indicated more engagement with the face stimulus. Thus, the mean Nc amplitude score were multiplied by -1 and a composite score for “neural vulnerability” was obtained by summing up the transformed Nc values with the Ms duration difference values. Subsequently, infants were divided into quartiles obtained by ranking all the scores and clustering them into four chunks. More negative values of the neural vulnerability composite score indicated enhanced (stronger and/or prolonged) neural response to the Noise than to the FD stimulus. Therefore, infants in the first two quartiles showed lower attention engagement to the FD than to Noise, while infants in the third and fourth quartiles showed higher attention engagement to the FD than to Noise.

To assess whether differences in looking behaviour were observed in infants at high brain vulnerability, only the HR infants were considered. HR infants in the top two quartiles were considered at “low neural vulnerability”, while HR infants in the lower two quartiles were considered as “high neural vulnerability”. Because I was interested in evaluating the protective role of social attention against ASD, the HR infants were divided into two ASD outcome groups: HR-ASD and HR-noASD, including infants from both the HR-TD and the HR-Aty group.

A two- (high versus low neural vulnerability) by-two (HR-noASD versus HR-ASD) ANOVA was performed to evaluate group and interaction effects for each of the two social attention looking behaviour measures: peak look at the face in the face pop-out task, and looking time at the gazed-at object in the gaze following task. Phase was added as covariate in all analyses. Table

Table 3.1 Number of participants for the ANOVAs testing the protective value of looking behaviour

by neural vulnerability (low versus high) and outcome group (HR infants without a diagnosis of

ASD at three years, i.e. HR-noASD, versus HR-ASD). Vulnerability groups Outcome

groups

Peak look at the face

Looking time at the gazed-at object Low neural vulnerability quartiles HR-noASD 32 34 HR-ASD 5 5 High neural vulnerability quartiles HR-noASD 32 31 HR-ASD 10 8 Total 79 78

Sex-specific protective effect of looking behaviour during social attention against familial/genetic risk

To test whether atypical performance in social attention behaviour at 15 months could have a protective effect against ASD, I compared the three groups of infants with a non-ASD outcome, that is LR, HR-TD and HR-Aty. If any or both these HR groups showed significantly enhanced social attention compared to LR group, this would have pointed towards its possible protective effect against the risk of ASD. Because previous studies argued that such protective effect could be sex-specific (Bedford et al., 2016; Chawarska et al., 2016), I tested for a significant effect of sex in interaction with group. Thus, two 2-way ANOVAs were used to evaluate the effect of group (LR, HR-TD and HR-Aty), sex (males and females) and their interaction on the social attention eye-tracking measures: peak look duration at the face and proportion of looking time at the gazed-at object, respectively. Tukey’s HSD method was used to correct of multiple comparisons in post-hoc analyses investigating significant main effects. As I was interested in the protective value of social attention specifically, disengagement was not investigated. Phase was used as a covariate in both ANOVAs. Number of participants per group for these analyses are shown in Table 3.2.

Table 3.2 Number of participants for the ANOVAs testing the protective value of looking behaviour

by familial/genetic risk, assessing differences in peak look duration at the face from the face pop-

out task and proportion of looking time at the gazed-at object from the gaze following task by group (LR, HR-TD and HR-Aty) and sex (males and females).

Outcome group

Sex Peak look at the face Looking time at the gazed-at object LR Males 27 26 Females 37 28 HR-TD Males 31 32 Females 45 48 HR-Aty Males 18 20 Females 19 16 Total 177 170 3.3 RESULTS