Abstract
There is a large body of research implicating structures within the right hemisphere (RH) are critical for face processing. Developmental research has shown that early in life retinal sensitivity is best in the nasal portion of the retina, which sends crossed projections from each eye to the opposite hemisphere. However, sensitivity in the temporal retina, which sends the uncrossed projections to ipsilateral cortex, develops closer to age two (Lewis & Maurer, 1990). Early visual experience is critical for normal maturation of visual function. People with early-onset congenital cataract have shown face processing deficits (Le Grand et al., 2003). Specifically, left-eye cataracts (RH deprivation), but not right-eye cataracts (left hemisphere deprivation) are related to impairments in face discrimination, showing that visual input to the RH is critical for establishing the neural substrates for face processing. Another ideal method for assessing the role of crossed connections in developing RH structures required for face processing is studying the effects of removing one eye (enucleation) shortly after birth, disconnecting that eye from the brain. As a result, left eye enucleation early in life eliminates input to the RH. We tested individuals with either left or right eye enucleation compared to binocularly and monocularly viewing controls on face discrimination and emotional expression recognition tasks. This included tests of configural, featural, contour and composite face discrimination and intensity of emotional expression recognition. Unlike congenital cataract, left-eye enucleation does not appear to disrupt face discrimination or emotional expression discrimination. Previous research has shown that unilateral enucleation actually facilitates some aspects of spatial vision compared to controls (e.g. Steeves et al., 2004). It is possible that any enhancement in spatial vision in one-eyed observers reverses potential face-processing deficits in these observers with early visual deprivation.
JKES is supported by grants from the Banting Research Foundation and the Natural Sciences and Engineering Research Council. KRK is supported by the Canadian Institutes for Health Research.