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Motion detection with movement detectors

Motion detection with movement detectors. Requirements on movement detectors. It is a non-linear device: response to velocity a and velocity b is not equal to velocity a+b

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Motion detection with movement detectors

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  1. Motion detectionwith movement detectors

  2. Requirements on movement detectors • It is a non-linear device: response to velocity a and velocity b is not equal to velocity a+b • movement detection may be asymmetric (response to velocity a is not opposite to response to velocity -a) or symmetric a a+b b

  3. Asymmetric movement detector V = Δx/Δt

  4. Movement detector • V = Δx/Δt • Note: • the same velocity v is detected for various Δx and Δt as long as Δx/Δt = constant

  5. Velocity dependence of movement detector v response v

  6. Relation between temporal and spatial gradients Δx Δx

  7. Movement detector Step-like response functions are not very likely

  8. Movement detector Δt responsie

  9. Movement detector

  10. Movement detector in fly visual system Response to spatial sinewave pattern with wavelength 16o and τ = 50 ms.

  11. The aperture problem

  12. The aperture problem Δx Receptive field of movement detector

  13. The aperture problem

  14. The aperture problem Identical responses for v=v0/cosα α v0

  15. The aperture problem A single cell cannot solve the aperture problem; only an ensemble of cells can under the assumption of a rigid body

  16. Example 1

  17. Example 2

  18. Various types of cells - + End-stop cell - + - + - +

  19. Example 3

  20. Hypothetical solution

  21. Optic/flow detectors

  22. Divergence operator

  23. Rotation operator

  24. Deformation operator

  25. Schematic overview of monkey brain

  26. Responses of neurons in VIP to various optic-flow patterns

  27. Responses of neurons in VIP to various optic-flow patterns Be aware : position of receptive field relative to stimulus !

  28. Retinal motion • Due to object motion • due to eye movements

  29. Schematic overview of monkey brain

  30. Responses of MST neurons to active vs passive optic flow

  31. Perceptual responses to moving stimuli

  32. Movement detector V = Δx/Δt Detectors have all orientations

  33. Transparent motion Percept ?

  34. Movement detector • V = Δx/Δt • Variation in v is achieved by both: • larger Δx • smaller Δt

  35. Transparent motion Percept : two different separately moving patterns

  36. References

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