The goal of our research is to uncover the cortical computations that support the functions of the extrastriate visual areas of the cerebral cortex. Our approach is to create functional models of cortical processing, and fit them to data recorded from single neurons. Functional models are designed to account for the visual response properties of neurons as economically as possible. These models do not necessarily reflect the details of neuronal circuitry, but have an overall organization that seeks to be consistent with known structures and neuronal connections. We will focus on an important area in the extrastriate cortex, MT (or V5). MT contains a high concentration of directionally selective neurons and is specialized for the analysis of visual motion. To study processing in MT, we need to know the properties of the neurons that transmit information to it, how that information is integrated, and how that integration is affected by the context in which the information is presented. MT is heavily dependent on input from V1 for its visual responsiveness, and receives direct inputs from directionally selective neurons in V1. Information can also reach MT through several indirect relays, and there is evidence that these different relays carry different sorts of visual information. First, we will identify and characterize the V1 and V2 neurons that provide the major specific functional input to MT, to provide a more complete account of the information reaching MT. Second, we will incorporate this knowledge into an existing but limited functional model of MT, which we will challenge with a set of novel multi-component stimuli. Our goal is to extend the model so that it can explain such essential features of neuronal responses as their dependence on the integration of motion information over space and time. The development and elaboration of this model will motivate the development of new mathematical techniques for model fitting, and will also form the basis for the subsequent development of models for visual responses in other extrastriate areas. Finally, we will use the knowledge gained in elaborating the functional model of MT to explore the role of the contextual modulations of MT activity that can be evoked by stimuli delivered to the region surrounding the classical receptive field. The work proposed will advance the overall goal of understanding cortical computation in the visual system by bringing to bear on the extrastriate cortex a set of tools and methods that have had many signal successes in probing primary visual cortex function.
Disorders of the visual nervous system are a major cause of visual disability. Damage to the primary visual processing area of cortex (V1) causes a loss of conscious vision over part or all of the visual field. This profound disability is considered irremediable. Parts of the visual cortex outside V1 may, however, be able to substitute for some lost functions after V1 damage, a phenomenon known as "blindsight". Other disorders affect these same areas outside V1, and cause other forms of visual loss such as akinetopsia (motion blindness) and agnosia (form blindness). Our research seeks to understand the organization and function of the cortical visual areas beyond primary cortex, both because of their potential as substrates for visual loss and recovery after brain damage, and because they are where sensory data are transformed into signals that form decisions, guide actions, and create enduring memories of evanescent events.
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|Levi, Dennis M; McKee, Suzanne P; Movshon, J Anthony (2011) Visual deficits in anisometropia. Vision Res 51:48-57|
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|Tailby, Chris; Majaj, Najib J; Movshon, J Anthony (2010) Binocular integration of pattern motion signals by MT neurons and by human observers. J Neurosci 30:7344-9|
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