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Howard Hock, Oliver Layton, Adar Pelah; Slowed optic flow is used to perceive object motion during active locomotion. Journal of Vision 2017;17(10):711. doi: 10.1167/17.10.711.
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© ARVO (1962-2015); The Authors (2016-present)
Although locomotion generates complex optic flow patterns across the retina, sighted animals simultaneously perceive their self-motion and the motion of independently moving objects, while retaining a stable percept of the environment. A perceptually stable reference frame could be established by discounting the optic flow component due to self-motion, a mechanism that is consistent with observed underestimation of optic flow speed during open-loop treadmill walking (Thurrell, Pelah & Distler 1998; Thurrell & Pelah 2005; the slowing effect of Pelah, Barbur, Thurrell & Hock 2015). A world-centric reference frame is critically important for perceiving object motion during object interception and other locomotor tasks (Fajen 2013), which may also rely on the discounting of the observer's self-motion to recover the object motion through the world (Warren & Rushton 2009; Layton & Fajen 2016). We investigated whether a common mechanism could account for the world-centric reference frame established during both self-motion and object motion perception. In each trial, subjects either walked on a treadmill or remained stationary while viewing a simulated self-motion optic flow display, which contained a moving object that glided along the ground plane towards the observer. Subjects then adjusted, while stationary, the trajectory of an identical object to match the just-perceived (walking or stationary) object trajectory. Results showed that object motion judgments while walking, compared to while stationary, were biased toward the locomotor path. This finding would be expected had subjects experienced the slowing effect, which we confirmed in a separate experiment. We conclude that the visual system may use a slowed version of the global optic flow field, combined with non-visual signals during active locomotion, to recover world-centric object motion. The flow immediately surrounding the object also impacted judgments, which suggests that a local mechanism interacts with the global motion discounting process that occurs to maintain perceptual stability during locomotion.
Meeting abstract presented at VSS 2017
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