Developing a side bias for conspecific faces during childhood.

Adults preferentially use information from the left side of face images to judge gender, emotion, and identity. In this study, we examined the development of this visual-field bias over middle childhood (5-10 years). Our goal was to both characterize the developmental trajectory of the left-side bias (should one exist) and examine the selectivity of the phenomenon. We used own- versus other-species faces (human and monkey faces) to ask whether the left-side bias was equally strong for categories with which children have vastly different amounts of experience. We found that the left-side bias did show both a developmental trend over the age range we considered and distinct category selectivity; for human faces the preference for the left side of the image increased across the age range tested, but for monkey faces it did not. We discuss our results in the context of experience-dependent perceptual narrowing during development.