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Sensation & Perception

Ψ. Sensation & Perception. Ψ. Motion Vision I: Basic Motion Vision. Why care?. Most animals have some form of motion vision (vs. Color). A large part of the brain is devoted to motion processing in these animals. Motion processing in the brain. Why motion?.

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Sensation & Perception

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  1. Ψ Sensation & Perception

  2. Ψ Motion Vision I: Basic Motion Vision

  3. Why care?

  4. Most animals have some form of motion vision (vs. Color) • A large part of the brain is devoted to motion processing in these animals

  5. Motion processing in the brain

  6. Why motion?

  7. Motion as a rich source of survival-relevant information : • Ecologically relevant information • Breaks camouflage • Heading perception, time to collision • Image segmentation, figure/ground • Object perception, structure from motion • Depth perception • Attention guidance

  8. Some demonstrations...

  9. Motion = Change of position over time?

  10. Motion as a separate perceptual dimension • The motion aftereffect (MAE) • Apparent motion • Motion illusions, induced movement

  11. How hard can it be?

  12. Challenges • Relation between movement of luminance on retina and object movement in world is weak. • Apparent motion, flicker, correspondence problem • Image segmentation

  13. Basic principles • Reichardt detectors in V1 integrate luminance signals from the LGN. Retina  LGN  V1

  14. V1 response Hz * LGN cells (input) 1 * 2 * * 3 4 X 5 V1 cell (integrator) t 6 t Reichardt detector

  15. Review: Orientation tuning in V1 • V1 neurons have orientation preferences. • These can be understood by analyzing the receptive field properties of the respective cell.

  16. - - - y y y + + + Hz Hz Hz - - - x x x Review: Orientation tuning in V1

  17. x t x x t t • Motion as orientation/tilt in space-time Space-time plots

  18. t t - - - - + + + + - - - - x x t t x x Motion as a tilt in space-time • V1 neurons tuned for orientation in space time  Extracting motion information by Direction, speed selectivity.

  19. So computationally, motion detection is essentially the same as edge detection. The RFs are just oriented in different dimensions. • How to construct a space-time receptive field?

  20. A B C D E Delay decreases from A to E x t Hz X (A, B, C, D, E) t Constructing the Space-Time RF

  21. Summary • Motion perception is very common among animals. It´s evolutionary survival value is high. • Motion detection is an inference made by the brain about the dynamics of objects in the world

  22. Summary • The perception of motion is a fundamental perceptual quality. It is not derived from other qualities. • Motion extraction in V1 can be understood by the concepts of Reichardt detectors and Orientation tuning in space-time.

  23. There is much more...

  24. Multi-step model of motion perception 1: Local measurement of motion information (direction, speed), esp. V1 2: Constrained integration of local motion information (particularly in MT) 3: Utilizing motion information for action guidance (e.g. MST, FEF, etc.)

  25. Higher upward: • Perception of biological motion • Perception of structure from motion • Perception of heading (optic flow), taking eye movements into account, etc.

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