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John Wann, Jac Billington, David Field, Richard Wilkie; Optic flow and steering: beyond MT+. Journal of Vision 2009;9(8):826. doi: 10.1167/9.8.826.
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© ARVO (1962-2015); The Authors (2016-present)
Field, Wilkie & Wann (2007) identified an area bordering, but distinct from the Parietal Eye-Fields (PEF) that was responsive to future path information during forward locomotion. We tested the function of this area using stimuli related to Land & Horwood (1995). Participants travelled on a sinusoidal trajectory at 8m/s across a textured ground plane, either forwards or backwards. In some conditions a distal roadway was presented 12m ahead, that indicated their direction of travel in 1.5s time, but not their current direction of travel. The task was to move a joystick to match their instantaneous direction of travel using the flow field information (passive_steering). The joystick motion was open-loop and did not change their actual direction of travel. We localized MT, MST and PEF in each participant and recorded eye-movements for each condition. Forwards and backwards locomotion produced equivalent activation MT+ (both with and without road). When travelling forwards or backwards without a road, there was lag of up to 1.16s in passive_steering but this lag was reduced to 0.5s when the road was present for forward motion, but not for backwards motion. This supports the idea that p’ were able to buffer the information from a distant section of the road and use that in their steering response some 1.5s later. Forward road produced focal activation in the superior parietal lobule (SPL) equivalent to our previous findings. There were no systematic differences in eye-movements that would explain the differential activations. Visual area MT+ is differentially responsive to flow patterns (Morrone et al, 2000) , the homologue of VIP is responsive to global egomotion signals (Wall & Smith, 2008 ), but this egocentric heading information only becomes useful when it is related to external goals for locomotor steering and focal areas of SPL appear to be processing those components.
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