Brain mechanisms underlying human motion perception

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The ability to see objects in motion is a fundamental aspect of vision in all species. It is rare for a person to totally lack the ability to perceive motion, but certain disorders of vision and certain types of brain damage affect the ability to perceive specific types of motion. In addition, the development of motion perception in children differs across different types of motion. The overall goal of this research is to understand how the perception of motion is normally achieved by the human brain. The specific goal of this proposal is to determine the role of two subdivisions of the visual pathway (referred to as M/dorsal and P/ventral) in our perception of motion. This work will focus on global motion and motion-defined form perception. Although these two types of motion are similar in many ways, the fact that only one or the other tends to be disrupted in neural disorders such as dyslexia, lazy eye or multiple sclerosis, suggests that different pathways may be involved. Motion perception is traditionally considered to be a function of the M/dorsal pathway, but more recent evidence implicates the P/ventral pathway, particularly at slower speeds of motion. Global motion and motion-defined form perception at different speeds will be studied in: (1) adults with temporary disruption of the M/dorsal pathway, (2) individuals with permanent damage to the M/dorsal or P/ventral pathway, and (3) children with developing visual systems. Two different non-invasive techniques will be used. With a behavioural technique called psychophysics, computer "games" will be used to measure a person's ability to perceive different types of motion. With functional magnetic resonance imaging, changes in brain activity while a person watches different types of motion will be used to determine the visual pathways involved. Our approach is unique in linking psychophysical and functional MRI data from adults, children and individuals with brain lesions. This work will provide new challenges for existing models of motion perception and help resolve some current controversies. There will also be practical implications for the treatment and rehabilitation of children and adults with visual problems caused by neural disorders or brain injury.