Behavioural and biological predictors of flow parsing performance across the adult lifespan

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Humans are primarily active, moving through the environment to interact with objects of interest while avoiding static and moving obstacles. Activity, however, creates a problem for the brain: retinal motion could arise from movement of either the observer or other objects in the scene. How, then, do we parse the incoming visual flow to work out which parts of the scene are moving and if so where they are going? These problems are ubiquitous and important; Without rapid and accurate processing of visual motion to solve them the likelihood of colliding with obstacles and associated injury is increased. In the last decade evidence has emerged for a new, purely visual solution to this parsing problem. The flow parsing hypothesis [1] suggests that humans selectively filter (or parse out) the structured patterns of global motion that arise from observer movement (termed optic flow). Currently, little is known about neural implementation of this mechanism. To address this we will examine individual differences in flow parsing performance across the adult lifespan and consider both biological and lower-level visual psychophysics predictors of flow parsing performance. In particular, it is already known that older individuals are impaired across a wide range of motion processing tasks (e.g. see [2]). We anticipate that flow parsing and hence object movement detection will also be compromised for this group. Such impairments could contribute to increased fall risk and/or motoring accidents in ageing.In this project we will use a multi-disciplinary approach involving behavioural experiments and neuroimaging approaches to:1. Measure speed and strength of flow parsing across a wide age range of healthy participants and investigate the effects of ageing on flow parsing 2. Shed light on the underpinning mechanisms of flow parsing by considering how performance is predicted by individual differences in lower-level visual motion processing tasks. 3. Investigate the relationship between speed of flow parsing (thought to be initiated only 10-15 ms [3] after onset of self-movement) and demyelination which is known to occur in older participants [4] and thought to slow cognitive processing [5]. As the first study to examine: i) impairments in flow parsing in older observers; ii) the relationship between flow parsing and lower level motion processing and iii) biological correlates of flow parsing, the project will be well placed to make important contributions to the visual neuroscience literature.