19258
Sex Differences in Visual Attention to the Mouth in Infancy: Implications for Language Development and ASD
Objectives: The current study seeks to elucidate the importance of increased mouth-fixation for language development, and to explore apparent sex differences among TD infants for their importance to the male-bias in ASD diagnosis. In keeping with these goals, this study tests the extent to which increased mouth-fixation correlates with increases in communicative abilities and in specific indices of language acquisition.
Methods: Eye-tracking data were collected longitudinally at 10 time-points from 2 to 24 months of life in TD-infants (26 male, 24 female), and high-risk infants later diagnosed with ASD (13 male). The Mullen Scales of Early Learning (Mullen) and the MacArthur-Bates Communicative Development Inventory (CDI) were administered longitudinally, assessing cognitive and communicative functioning.
Results: Results indicate a phase-shift in mouth-fixation, from increasing with age to decreasing with age, early in the second year of life. The mouth-fixation shift is evident in TD-females at 13.5 months of age, in TD-males at 15 months, and in ASD-males between 15 and 16 months. Concurrent sex differences in trajectories of scores on clinical measures of expressive vocabulary (F(2,47)=7.214, p<0.01), gesture (F(2,47)=5.230, p<0.01), and language-related cognitive abilities (F(3,46)=9.452, p<0.01), indicate that TD-females are precocious in these areas, and support a relationship between mouth-fixation and language development. Spearman’s rho was used to quantify the relationship between mouth-fixation and measures of communicative development before and after mouth-fixation phase-shift, for each sex and for ASD-males (Table 1).
Conclusions: Measures of communicative development were correlated with age and not with mouth-fixation prior to mouth-fixation phase-shift. After the phase-shift, vocabulary measures and mouth-fixation were negatively correlated in females, during their period of decline in mouth-fixation. As such, vocabulary growth was greatest just after the peak in mouth-fixation. Similar relationships existed for TD-males and ASD-males. Results suggest that sex-dimorphic chronologies of developmental events in typical-development are present in both language and in an apparent behavioral correlate, and can inform our understanding of developmental trajectories that deviate from those of TD-infants in ASD, as TD-females appear chronologically advanced.