Preferential looking to eyes versus mouth in early infancy: heritability and link to concurrent and later development

Abstract

Background: From birth, infants orient preferentially to faces, and when looking at the face, they attend primarily to eyes and mouth. These areas convey different types of information, and earlier research suggests that genetic factors influence the preference for one or the other in young children. Methods: In a sample of 535 5-month-old infant twins, we assessed eye (relative to mouth) preference in early infancy, i.e., before neural systems for social communication and language are fully developed. We investigated the contribution of genetic and environmental factors to the preference for looking at eyes, and the association with concurrent traits and follow-up measures. Results: Eye preference was independent from all other concurrent traits measured, and had a moderate-to-high contribution from genetic influences (A = 0.57; 95% CI: 0.45, 0.66). Preference for eyes at 5 months was associated with higher parent ratings of receptive vocabulary at 14 months. No statistically significant association with later autistic traits was found. Preference for eyes was strikingly stable across different stimulus types (e.g., dynamic vs. still), suggesting that infants' preference at this age does not reflect sensitivity to low-level visual cues. Conclusions: These results suggest that individual differences in infants' preferential looking to eyes versus mouth to a substantial degree reflect genetic variation. The findings provide new leads on both the perceptual basis and the developmental consequences of these attentional biases.

Sustained looking at faces at 5 months of age is associated with socio‐communicative skills in the second year of life

“…The same specificity has been found for the tendency to look at either the eyes or the mouth, another social attention phenotype that has been found to be highly heritable in both toddlerhood (Constantino et al., 2017) and infancy (Viktorsson et al., 2023). A preference for looking at eyes (vs. the mouth) at 5 months is independent from concurrent development and specifically related to later language comprehension (Viktorsson et al., 2023). These findings suggest that social looking in infancy consists of multiple distinct mechanisms that may be, at least partially, heritable and linked to specific outcomes.…”

“…Another study of infant twins found that face preference at 5 months was heritable and linked specifically to verbal competence at 14 months (Portugal et al, 2023). The same specificity has been found for the tendency to look at either the eyes or the mouth, another social attention phenotype that has been found to be highly heritable in both toddlerhood (Constantino et al, 2017) and infancy (Viktorsson et al, 2023). A preference for looking at eyes (vs. the mouth) at 5 months is independent from concurrent development and specifically related to later language comprehension (Viktorsson et al, 2023).…”

Genetic and environmental contributions to gaze lateralization across social and non-social stimuli in human infants

“…The stimuli used in this study (Non-social condition 36 ; Social condition 37 ; Mixed condition 38 ) were not purposefully designed to measure gaze lateralization, but were used for this purpose as we believe they fulfil the characteristics necessary to answer our research questions. In all three conditions, the sample is based on the same set of infants from BATSS 35 , although the sample varies slightly in each condition due to stimuli-specific exclusion criteria (see specifications in each condition section).…”

“…1 ). The primary goal of these stimuli was to measure eye versus mouth looking (already published data 37 ). The videos were shown in a pseudo-random order, unique to each participant.…”

“…The length of the videos ranged from 4 to 12 s (total duration was 153 s). Further details are provided elsewhere 37 . A dynamic area of interest (AOI) was created for each frame of the videos (Fig.…”