Age- and Experience-Dependent Modulation of Coherent Visual Motion Processing

Abstract

Visual motion processing dysfunction has been observed in developmental dyslexia, but the nature of the relationship between this dorsal stream function and the reading difficulties observed in dyslexia is unclear. This is due to the fact that the typical development of visual motion processing and its dorsal visual substrates has yet to be fully characterized, and as such the relationship between reading experience and dorsal stream development is ambiguous. Similarly, while visual motion processing differences observed in deaf populations have been attributed to the effects of deafness, it is unknown how experience with a visuospatial sign language may be impacting these effects. This dissertation presents two complementary studies addressing these questions. The first investigated the functional development of the neural substrates of coherent visual motion processing (e.g., area V5/MT) using both a cross-sectional and longitudinal approach, and evaluated V5/MT activation in the context of reading ability. From this, we report that the development of V5/MT is characterized by a shift in the location, rather than intensity, of peak response to coherent visual motion, and that children show greater connectivity between V5/MT and local surrounding cortex than adults. Further, our evidence does not support there being a relationship between V5/MT activity and later reading ability in typically reading children. The second study examined the effects of deafness and sign language experience on the neural substrates of coherent motion processing using a factorial analysis of four groups: hearing native users of English, hearing native users of sign language, deaf native users of English, and deaf native users of sign language. When the effects of deafness and experience with sign language were fully disambiguated, we found there to be a main effect of sensory experience in right hemisphere auditory association cortex, and a main effect of language experience in left ventral temporal and right inferior frontal cortices. Together these studies help clarify the age- and experience-dependent effects on visual motion processing and the dorsal visual system.