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Even the simplest action must involve linkage between memory, vision, eye movements, and body movements. from Land et a

The nervous system, vision, and motor control. Even the simplest action must involve linkage between memory, vision, eye movements, and body movements. from Land et al, 1999. Perception Cognition Action. Studying the integrated system. 500 msec. Levels of analysis

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Even the simplest action must involve linkage between memory, vision, eye movements, and body movements. from Land et a

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  1. The nervous system, vision, and motor control Even the simplest action must involve linkage between memory, vision, eye movements, and body movements. from Land et al, 1999

  2. Perception Cognition Action

  3. Studying the integrated system 500 msec

  4. Levels of analysis • Behavior: What are we trying to explain? • Performance limits, loss of information • Analytical vs. Ecological (Gibson) • Neurophysiology & Anatomy: Structure and function of nervous system. What are the neural processes underlying behavior? • Theory: Computer vision, Robotics, Artificial Intelligence. What are the principles governing brains/sensory systems?

  5. Need for all levels of analysis.

  6. What image information is needed for the things we do? How is vision used to acquire information from the world?

  7. Why do we move our eyes? - Image stabilization - Information acquisition

  8. The Eye and Retina

  9. Cone Photoreceptors are densely packed in the central fovea

  10. Visual Acuity matches photoreceptor density Relative visual acuity Receptor density

  11. Scaled for equal visibility

  12. Why do we move our eyes? 1. To bring objects of interest onto high acuity region in fovea.

  13. Visual Projections

  14. Cortical Magnification Primary Visual Cortex: V1 The brain uses more physical space for signals from the fovea than periphery

  15. Why do we move our eyes? 1. To bring objects of interest onto high acuity region in fovea. 2. Cortical magnification suggests enhanced processing of image in the central visual field.

  16. Muscles that Move the Eye

  17. Visual Angle x a d tan(a/2) = x/d a = 2 tan-1 x/d Why eye movements are hard to measure. A small eye rotation translates into a big change in visual angle 18mm 1 diopter = 1/focal length in meters 55 diopters = 1/.018 0.3mm = 1 deg visual angle

  18. Types of Eye Movement Information GatheringStabilizing Voluntary (attention) Reflexive Saccades vestibular ocular reflex (vor) new location, high velocity, ballistic body movements Smooth pursuit optokinetic nystagmus (okn) object moves, velocity, slow whole field image motion Vergence change point of fixation in depth slow, disjunctive (eyes rotate in opposite directions) (all others are conjunctive) Fixation: period when eye is relatively stationary between saccades.

  19. Demonstration of “miniature” eye movements It is almost impossible to hold the eyes still.

  20. Stereotyped fixation patterns arise in different natural tasks Examples: Making tea or sandwiches Playing cricket, table tennis Driving Note: Real world activities almost always have some combination of saccades, smooth pursuit, VOR, & vergence

  21. Driving: fixate tangent point while driving around a curve Fixation density

  22. Eye movements in cricket bowler Bounce point batsman Land & MacLeod, 2000

  23. Batsman anticipate bounce point Better batsman arrive earlier saccade pursuit Vision is Predictive Eye movements in cricket: bounce Land & MacLeod, 2000

  24. Making tea: object oriented actions Land et al 1999

  25. Specialized fixation patterns

  26. Main Insights from Natural Tasks Vision is active not passive. Specific information is usually acquired at the fixation point. Information is acquired “just-in-time”.

  27. TO DO: Read Land chapter on class website.

  28. Cortical specialization

  29. Imaging Jargon High Spatial Frequency/Resolution -Sharp/ In Focus- Low Spatial Frequency/Resolution -Blurry/ Out of Focus-

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