Abstract:

Typically developing (TD) infants show an inborn predisposition to pay attention to faces from birth—that TD infants detect more quickly and fixate longer on faces compared with objects. This innate facial attention bias steadily exists in different stimulus situations at different developmental stages, and shows a rapid growth tendency after a short-term decline between the 4th and 6th weeks in the first year of life.The short-term decline may reflect the inhibitory effect of the initial function from the cortical network on the innate sub-cortical system during the critical period wherein TD infants’ visual attention transit from sub-cortical control to cortical control. After this critical transition, with the gradually maturation of the function of the domain-general frontal-parietal attention control cortical network, TD infants’ ability to suppress interference information and selectively pay attention to specific visual targets gradually enhances. Therefore, the role of visual salience in TD infants’ visual attention patterns is gradually declining with increasing age. With the continuous accumulation of face visual experience, the gradually formed face-specific cortical network strengthens TD infants’ preferentially selective response to faces, the role of the social salience on TD infants’ visual attention patterns continues to increase with increasing age. The two factors mentioned before work together to promote facial attention bias in TD infants. Taking the developmental trajectory of TD infants’ facial attention bias as a reference, Autism Spectrum Disorder (ASD) infants possess an initial innate predisposition to facial attention, but they gradually deviate from the normal track during the critical period of facial cortex development, and ultimately exhibit facial attention impairments around 1 year old. After infancy, there exist still disputes with regard to whether ASD individuals show facial attention impairments in simple stimulus arrays, but they exhibit less facial attention in complex social scenes than TD individuals. This is probably due to the fact that congenital perceptual attention impairments cause ASD individuals not to flexibly switch their attention between different stimuli. They are more likely to “lock” or “fixate” their attention on non-social stimuli with more salient perceptual characteristics in the visual environment. At the same time, due to the abnormal function of the social reward system, ASD individuals fail to recognize the social reward value of faces and lack social motivation to pay attention on faces. As a result, the innate predisposition to pay attention to faces cannot be reinforced promptly. For ASD infants at a critical period of facial cortical development, these two impairments both cause atypical early visual perception learning, which reduce the input of facial visual experience and hinder the professional development of face-selective areas. As a result, in the allocation of visual attention resources in ASD individuals, the role of the visual salience fail to decrease with increasing age, while the role of the social salience fail to increase with increasing age. Future research should explore the origin of the congenital predisposition of facial attention in neonates by using genetic methods and near-infrared brain imaging technology, and systematically investigate the influence of perceptual and social characteristics on the development track of face attention in high-risk infants with ASD to identify the potential mechanism of facial attention impairments.

Key words: infant and toddler, autism spectrum disorder, attention bias to faces, inborn predisposition, developmental change