1. Motion detection with movement detectors

2. 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 Requirements on movement detectors a b a+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 v response

6. Relation between temporal and spatial gradients Δx

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

8. Movement detector responsie Δt

9. Movement detector

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

11. The aperture problem

12. Receptive field of movement detector Δx

13. The aperture problem

14. Identical responses for v=v 0 /cosα α v0v0

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. 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