05d eye movement control

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05d eye movement control

  1. 1. Visual Tracking and Fixing
  2. 2. Visual Tracking • Why Visual Tracking ? – To keep the image in the Fovea which is less than 1mm size and detect visual field of less than diameter of full moon. – It keeps the eye still when the image is still and stabilizes the image when the object moves in the world or when the head itself moves. • How Visual Tracking? – Oculomotor system: moves the eye in the orbit – Head movement which moves the orbit in the space – Information of head motion processed by the vestibular system
  3. 3. Three Axes of Eye Rotations 1. Ductions refer to monocular movements of each eye 2. Versions refer to binocular conjugate movements of both eyes 3. Vergences refer to binocular disjunctive movements
  4. 4. Extra Ocular Muscles
  5. 5. Extra-ocular muscles nerve supply
  6. 6. Actions of Extra-ocular muscles
  7. 7. Laws of Ocular Motor Control 1. Sherrington's law of reciprocal innervation 2. Hering's law of equal innervation
  8. 8. Six Cardinal Position
  9. 9. "Visual Accessing Cues" Richard Bandler and John Grinder "Frogs into Princes: Neuro Linguistic Programming (NLP) "
  10. 10. Up and to the Left Indicates: Visually Constructed Images (Vc) If you asked someone to "Imagine a purple buffalo", this would be the direction their eyes moved in while thinking about the question as they "Visually Constructed" a purple buffalo in their mind.
  11. 11. Up and to the Right indicates: Visually Remembered Images (Vr) If you asked someone to "What color was the first house you lived in?", this would be the direction their eyes moved in while thinking about the question as they "Visually Remembered" the color of their childhood home.
  12. 12. To the Left Indicates: Auditory Constructed (Ac) If you asked someone to "Try and create the highest the sound of the pitch possible in your head", this would be the direction their eyes moved in while thinking about the question as they "Auditorily Constructed" this this sound that they have never heard of.
  13. 13. To the Right Indicates: Auditory Remembered (Ar) If you asked someone to "Remember what their mother's voice sounds like ", this would be the direction their eyes moved in while thinking about the question as they "Auditorily Remembered " this sound.
  14. 14. Down and to the Left Indicates: Feeling / Kinesthetic (F) If you asked someone to "Can you remember the smell of a campfire? ", this would be the direction their eyes moved in while thinking about the question as they used recalled a smell, feeling, or taste.
  15. 15. Down and To the Right Indicates: Internal Dialog (Ai) This is the direction of someone eyes as they "talk to themselves".
  16. 16. Brain area participate in Visual Fixation The cerebral structures involved in fixation are: Parietal eye field (lateral interparietal area and area 7a in monkeys) V5 and V5A (MT and MST in monkeys) Supplementary eye field Dorsolateral prefrontal cortex The brainstem structures involved in fixation are: Substantia nigra pars reticulata in the basal ganglia Rostral pole of the superior colliculus
  17. 17. An Active Fixation System Keeps the Eyes on a Stationary Target
  18. 18. The Visual Fixation System •The fixation system holds the image of a stationary object on the fovea when the head is immobile. •Steady fixation is actually an illusion. •Normal fixation consists of three distinct types of physiological miniature movements that are not detectable by the naked eye
  19. 19. Eye Movement Function of Eye Type of Eye Movement Movement "Version" (Conjugate) "Vergence" (Disjunctive) "Holding" (slow) •Smooth Pursuit •Optokinetic Nystagmus •Convergence (slow phase) •Divergence •Vestibular Nystagmus •Accommodative Vergence "Catching" (fast) •Saccades •Optokinetic Nystagmus (quick phase) "Sustaining" (miniature) •Microsaccades •Tremor •Drift voluntary eye movement; involuntary eye movement
  20. 20. The Vestibular and Optokinetic Systems • The vestibulo-ocular and optokinetic reflexes are the earliest eye movements to appear phylogenetically • The vestibulo-ocular reflex (VOR) stabilizes retinal images during head motion by counter-rotating the eyes at the same speed as the head but in the opposite direction • Optokinetic eye movements stabilize the eyes during tracking of a large moving visual scene, which causes an illusionary sensation of self rotation (circularvection) in the opposite direction
  21. 21. Types of Head Motion 1. Rotation : A change in orientation 2. Translation: A change in position
  22. 22. Characteristics of the VOR The VOR stabilizes retinal images during brief head movements by counter-rotating the eyes at the same speed as the head but in the opposite direction
  23. 23. The Horizontal VOR Pathway
  24. 24. The Vertical and Torsional VOR Pathway
  25. 25. The Otolith-Ocular Pathway
  26. 26. VOR Adaptation and the Cerebellum
  27. 27. The Optokinetic System •Optokinetic nystagmus is induced reflexively by motion of a large visual scene, which causes an illusionary sensation of self- rotation (circularvection) in the opposite direction •Whereas the angular VOR responds best to brief, high- frequency head rotation, the optokinetic system maintains retinal image stability during sustained, low-frequency rotation
  28. 28. The Saccadic System Points the Fovea Toward Objects of Interest
  29. 29. Saccads during reading
  30. 30. Pulse-Step of Innervation for Saccadic Eye Movement
  31. 31. Extraocular Motor Signal Eye Position and Velocity
  32. 32. Central control of Horizontal Saccad
  33. 33. Brainstem Generation of Vertical and Torsional Saccades
  34. 34. Cortical Pathway for Saccades
  35. 35. Summary of Central Control of Saccades
  36. 36. The Smooth Pursuit System Keeps Moving Targets on the Fovea
  37. 37. Gaze Involves Combined Head and Eye Movements
  38. 38. Cortical control of Pursuit Eye movement
  39. 39. Summary of Central Control of Pursuit Eye Movement
  40. 40. Vergence Eye movment
  41. 41. Neural Substrate of Vergence Eye Movements
  42. 42. Thank You

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