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Stephan Tschechne, Heiko Neumann; Ordinal depth from occlusion using optical flow: A neural model. Journal of Vision 2011;11(11):716. doi: 10.1167/11.11.716.
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© ARVO (1962-2015); The Authors (2016-present)
Problem. An occluding surface boundary is created by the spatio_temporal pattern of deletion and accretion of visual structure in which ordinal depth relations along the edge are defined by the arrangement of occluding and occluded surface regions (Gibson et al., Perception & Psychophysics 5, 1969). What are the neural computational mechanisms underlying the motion_based segregation of figure from ground based on occlusion boundary information?
Method. We propose a biologically inspired model of cortical motion detection and integration. Local motion signals are detected in model V1 which are spatially integrated over a larger neighborhood in model MT. Top_down feedback signals from MT to V1 disambiguate and stabilize the local measurements. The presence of temporal occlusions generated by surfaces hovering at different depths is evidenced by a transition from high motion energy when coherent motion is measured to low motion energy in cases of failure to find coherent spatio_temporal structure. In cases of temporal dis_occlusions low motion energy responses change into high motion energy response patterns. We propose an opponent scheme of temporal on/off interactions in which local motion energy signals from model V1 are spatially integrated by the temporally offset on/off subfields. This mechanism is gated by direction selective model MT cells to make the spatio_temporal occlusion detection selective to different motion directions.
Results. The model was probed with artificial scenes of moving and mutually occluding object surfaces. Motion is estimated by the model and activities at the stage of occlusion detection correctly indicate the foreground objects when they partially occlude the background. The occlusion/dis_occlusion boundary responses together with directional motion signals determine the border-ownership direction of an occluding surface. This demonstrates that spatio-temporal figure-ground separation can be achieved by local mechanisms at early and intermediate stages of the dorsal visual pathway.
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