The processing of binocular sensory cues for scene layout and observer motion is inextricably intertwined with motor control of the pointing direction of the eyes. It is of great importance to understand the neural mechanisms underlying this relationship in order to understand developmental failures that can lead to strabismus and the loss of functional binocularity. The normal developmental sequence for sensory binocularity is poorly understood and it has only recently been appreciated that 3D-specific motion signals also contribute to depth perception. It is shown here for the first time, that these 3D motion cues provide an important input to vergence eye movements. The normal developmental sequence for sensitivity to these motion cues is currently unknown. Neither is it known how these signals interact with disparity cues to control eye movements or how they are affected in strabismus. Therefore, each Aim of the proposal is organized around the inter-relationship between, and parallel processing of, horizontal disparity and 3D motion cues.
The first Aim will use high-density EEG recordings to determine the developmental sequences for disparity and motion processing systems in normally developing infants and children. The working hypotheses that sensitivity to relative motion and disparity both depend on the development of domain-specific spatial interactions, that these interactions develop earlier in the motion system than they do in the disparity system and that motion-cues augment stereo cues for motion-in-depth early in development will be tested.
The second Aim will combine fMRI and high-density EEG recordings in normal adults to determine the timing and pattern of spatial interactions that underlie the processing of relative motion and disparity cues across identified visual areas. The hypotheses that relative motion stimuli more effectively activate lower-level visual areas than do relative disparity stimuli and that manifestations of domain-specific surround organization will be more apparent in early retinotopic cortex for relative motion stimuli will be tested.
The third Aim will follow up on pilot data indicating that 3D motion cues provide an independent and largely involuntary velocity input to vergence eye movements.
The fourth Aim will test the hypothesis that developmental asymmetries of motion processing that are common in early onset strabismus are related to a more general developmental failure of 3D motion processing mechanisms. The proposed studies will provide a detailed understanding of both normal and abnormal binocular vision and its development, both by testing of novel hypotheses about sensory processing and motor control, but also through the use of powerful new approaches to EEG recording that will be readily transferable to studies of the effects of treatment for binocula vision and other disorders of visual processing during the developmental critical period.
Amblyopia and strabismus are common disorders of visual development. The proposed work will provide new information about how binocular vision, motion processing and oculomotor control are affected by abnormal visual experience during development. Understanding how visual deprivation affects the neural mechanisms of perception and motor control is an important step in the design of successful treatment programs for strabismus. The dynamic neuroimaging protocols developed in this protocol may also be applicable to the study of other developmental disorders including autism, dyslexia and cortical visual impairment. The methods are also relevant for studies of visual processing in low-vision populations, such as patients with macular degeneration.
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