Abstract
Global motion and global form sensitivity can provide a developmental indicator of extra-striate processing in the dorsal and ventral streams respectively, and measures of spatial cognition, visuo-motor co-ordination and control of attention offer higher level indicators of the integrity of the dorsal cortical stream. We will provide an overview of our own work and others using these measures to show that ‘dorsal stream vulnerability’ is a feature of many neurodevelopmental disorders, both genetic (Williams syndrome, fragile-X, and probably autism and dyslexia) and acquired (perinatal brain injury, prematurity, congenital cataract). Follow up of prematurely born infants at 6-7 years allows the distinct impacts of white matter injury, weeks gestation, and prematurity per se on different visuo-cognitive measures to be assessed.
Since both genetic and acquired disorders show differential effects on dorsal stream processing, this vulnerability cannot be considered either a direct effect of gene expression or of specific environmental impact. Rather, the unfolding programme by which the visual system is built, with genetic control in an environmental context, appears to make dorsal stream function vulnerable either to interaction with other genetic effects, or to various environmental disruptions. We will consider the developmental demands on dorsal stream function that may be responsible for this vulnerability. We will also review our findings, using novel high-density VERP measures, on the normal development of global motion processing and the reorganization of its cerebral basis between infancy and adulthood, which may help to understand the period(s) of development when the system is vulnerable to disruption.