High- and Low-Risk Six-Month-Olds' Visual Attention to Smiling and Neutral Faces: Effects of Smile Intensity and Infant Risk-Status

Background: Individuals with autism demonstrate atypical attention to facial expressions (Pelphrey et al., 2002).  Investigations of the early autism phenotype find signs of atypical socio-emotional reciprocity emerge as early as 12 months (Ozonoff et al., 2010).  It remains unclear whether high risk (HR) infants who have an older sibling with autism and low risk (LR) infants who do not have an older sibling with autism differ in how they visually attend to facial expressions (Merin, Young, Ozonoff, & Rogers, 2007).   

Objectives: To determine the effect of smile intensity and infants’ risk-status on their visual attention to smiling versus neutral faces. 

Methods:  Six-month-old HR (n = 12) and LR (n = 18) infants’ visual attention to pairings of neutral and smiling static faces was examined using eye-tracking technology.  Risk groups were matched on verbal and nonverbal DQ.  Infants viewed three levels of face pairings with each level distinguished by variation in smile intensity: neutral/closed-mouth smile (low intensity), neutral/open-mouth smile (moderate intensity), and neutral/exaggerated smile (high intensity).  The dependent variable for analyses was the proportion of time spent looking at the smiling face (S ratio) relative to total looking at both the smiling and neutral faces.

Results: A 3 (smile intensity) X 2 (risk-status) repeated measures ANOVA was conducted to investigate the effect of these factors on the S ratio.  An S ratio over 0.50 indicates more looking to the smiling than neutral face.  There was a significant interaction of smile intensity and risk-status, F(2, 27) = 5.78, p = 0.008.  Follow-up analyses indicate: 

• Closed-Mouth Smiles: Six-month-old HR (M = 0.48, SD = 0.16) and LR (M = 0.52, SD = 0.10) infants did not differ in visual attention to closed-mouth smiles, t(28) = 0.77, p = 0.45.   
• Open-Mouth Smiles: Six-month-old HR infants (M = 0.44, SD = 0.23), t(28) = 2.27, p = 0.03 looked significantly less to open-mouth smiling faces than LR infants (M = 0.59, SD = 0.13) .
• Exaggerated Smiles: Six-month-old HR infants (M = 0.63, SD = 0.09) looked significantly more to exaggerated smiling faces than LR infants (M = 0.48, SD = 0.13), t(28) = 3.35, p = 0.002.

Conclusions: HR and LR group differences in looking emerged only for moderate and high-intensity smile/neutral pairings.  LR 6-month-olds looked more to open-mouth smiles than HR 6-month-olds.  In contrast, HR 6-month-olds looked significantly more than LR 6-month-olds to high-intensity, exaggerated smiles.  These data suggest HR and LR group differences in looking to smile versus neutral faces emerge as early as 6 months.  Results suggest HR infants may need more exaggerated expressions in order to elicit a preference.