MOTION PERCEPTION

1. MOTION PERCEPTION • Types of Motion Perception • Corollary Discharge Theory • Movement Detectors • Motion Perception and Object Perception • Ecological Perception • Vestibular System

2. Types of Motion Perception • Real Movement occurs when an object actually moves • Apparent Movement is a perception of motion caused by the appearance of two stationary stimuli at different times

3. Types of Motion Perception • Induced Movement occurs when movement of one object causes a perception of motion in another object • Movement After-Effects occur when a perception of motion is caused by viewing real movement in the opposite direction

4. Corollary Discharge Theory • When the brain sends a message to move the eyes, it sends a copy (corollary discharge) to a comparator • Information about image movement is also sent to the comparator

5. Corollary Discharge Theory • If the comparator receives information that the image is moving but the eyes are not moving, motion is perceived • If the comparator receives information that the image is not moving but the eyes are moving, motion is perceived

6. Corollary Discharge Theory • If the comparator receives information that the image is moving and the eyes are also moving, motion is not perceived

7. Movement Detectors • Real Movement Detectors in V3 respond only when the stimulus actually moves, whether the eyes are moving or not • Neurons in the Middle Temporal (MT) cortex respond to movement in a particular direction

8. Motion and Object Perception • Recognition of patterns affects perception of movement • shortest path constraint - movement appears to occur on the shortest possible path • When the shortest path violates knowledge about objects, a longer path is perceived

9. Motion and Object Perception • Recognition of motion affects perception of objects • Kinetic Depth Effect • Biological Motion

10. Motion and Object Perception • The “What” and “How” streams communicate with each other

11. Ecological Perception • How do we use perception to guide our actions in the environment? • Invariant information - information that remains constant during observer movement

12. Ecological Approach (Gibson) • We can perceive motion by using information from the environment • Optic array - surfaces, textures, and contours in the environment • Local disturbance - one object moves relative to the environment, deleting and accreting

13. Optic Flow • Optic flow - movement of elements relative to the observer • Focus of Expansion(FOE) - point in the distance at which there is no flow

14. Navigation Neurons • Collision-sensitive neurons - respond only when an object is on a collision course; found in pigeon brain • Neurons in the human Medial Superior Temporal (MST) area respond to flow patterns; have large receptive fields

15. Mirror Neurons • Located in Premotor Area (PM) in frontal lobes • Respond when the monkey grasps an object OR when the monkey sees someone grasp an object

16. Vestibular System • This system provides information to the brain on orientation and movement of body • The sensory organs are the semicircular canals and vestibular sacs in the inner ear

17. Semicircular Canals • three tubes at right angles • fluid filled • hair cells at the base of each canal • detect rotation in three dimensions

18. Vestibular Sacs • two sacs at the base of semicircular canals • detect linear motion • motion causes movement of statolith which bends hair cells

19. Vestibular Pathway • 8th Cranial nerve carries information from hair cells • brain stem • cerebellum (movement and balance) • thalamus • cortex

20. Interaction with Vision • Vestibulo-ocular Reflex - stabilizes visual field by coordinating eye movements with head movements • Motion sickness - mismatch between visual and vestibular information

21. Interaction with Vision • Visual cues can affect balance, overcoming influence of vestibular information • Swinging room experiment (Lee & Aronson)