Integration of object motion across apertures during tracking eye movements: perceptual and oculomotor measures D Souto1, D Kerzel1, A Johnston2 |
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1University of Geneva, Switzerland |
| Local motion signals need to be integrated across space to recover objects’ direction of motion. We investigated previously reported directional asymmetries in perceiving global motion during pursuit eye movements [Souto D and Johnston A 2011 ECVP]. Observers had to track or fixate a dot surrounded by a ring of randomly oriented Gabors and discriminate the direction (±10°) of a brief episode of global motion. Higher signal to noise ratios were required for direction discrimination with motion opposite to the eye movement as compared to motion in the same direction, or with a stationary display. Oculometric measures were derived from horizontal eye velocity change induced by global motion. In contrast to perception, eye movements indicated lower or similar thresholds for motion opposite to the pursuit direction compared to same direction or fixation. We propose that higher perceptual thresholds for opposite motion arise from a deficit in parsing signal from noise, since it is specifically required for the perceptual task but not for generating a horizontal ocular response. Relatively better perceptual integration for same direction motion signals might have a functional role, since a rigid object’ contours move in the direction it is tracked, unlike background or occluding features. |
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