Sex differences in the development of visual processing in infancy

The first months of life are a sensitive period for the development of visual processing, and face processing in particular. The main goal of this thesis is to examine the influence of infant sex on the development of visual processing. The overarching hypothesis was that 5-month-olds would differ in performance on tasks related to the higher levels of the ventral processing stream, with females showing more advanced ventral visual processing. To begin tracing the developmental trajectory of these differences, another group was tested at 7 to 8 months, after major changes in face processing abilities occur. An exploratory look was taken throughout at two factors that may influence face processing development – the size of the social environment, and locomotion level. In Chapter 2, 5-month-olds were tested on detection of an eye expression change, from smiling to neutral, following infant-controlled habituation. As predicted, females outperformed males in evidencing a novelty preference. In Chapter 3, 7- to 8-month-olds were tested on the same task. For females, a developmental change from novelty to familiarity preference was found. For males no indication of eye expression discrimination at either age was found. In Chapter 4, both age groups were tested on discriminating a featural change in internal features (eyes, nose, mouth). A female advantage was found in 5-month-olds, but disappeared by 7 to 8 months. Chapter 5 replicated the Chapter 2 findings of female superiority in eye expression discrimination at 5 months. Contrary to prediction, females did not show greater mirror image confusion. Laterality effects for both eye expression and mirror image discrimination were found in females, and a negative relation between mirror image and eye expression discrimination was found in males. Finally, effects of the social environment on male face processing and of locomotion level on female face processing were found. The results support the hypothesis of a sex difference in the development of ventral stream processing. They inform the fields of visual/face processing development and of sex differences, showing a sex difference in infant development of processing of internal facial features and identifying additional factors involved, and have implications for studies of autism.Medicine, Faculty ofGraduat