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Chapter 9

Chapter 9. Action and the Perception of Events. Structure from Motion. Structure from motion (SFM) refers to our ability to derive information about three-dimensional shape from motion. Perception of SFM can be created using dynamic arrays of random dots generated on a video monitor.

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Chapter 9

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  1. Chapter 9 Action and the Perception of Events

  2. Structure from Motion • Structure from motion (SFM) refers to our ability to derive information about three-dimensional shape from motion. • Perception of SFM can be created using dynamic arrays of random dots generated on a video monitor.

  3. Biological Motion • Biological motion is a special type of SFM that allows us to distinguish between animate and inanimate objects • Biological events generate unique patterns and individually characteristic motions.

  4. Biological Motion • The perception of biological motion from just a few points of moving light is called point-light motion. • Neural mirroring may play a central role in our ability to observe and imitate the behavior of others or infer another person’s intentions.

  5. Biological Motion

  6. Visual Guidance of Locomotion • Visual expansion is a type of optic flow (changing pattern of stimulation) that signals the approach of an object. • The relationship between the rate of retinal image expansion and time of impact with an object enables us to avoid collision.

  7. Visual Guidance of Locomotion

  8. Eye Movements: Aims & Consequences • Saccades are rapid, jerky eye movements that occur between fixations. • Saccadic suppression is the dampening of vision that occurs during a saccade.

  9. Eye Movements: Aims & Consequences • Unlike saccades, pursuit (smooth) eye movements are not jerky or ballistic. • Speed and direction of pursuit eye movements are constantly modified to remain on target.

  10. Space-Time Receptive Fields • Direction-selective cells respond most strongly to one preferred direction but little (if at all) to motion in the opposite direction. • Motion defined by luminance variations over space/time is called first-order motion. • Second-order motion is defined by other cues, such as texture differences.

  11. Apparent Motion • We experience apparent motion when the visual system takes discrete inputs and makes them continuous. • Motion perception (real and apparent) involves direction-sensitive neurons.

  12. Correspondence Problem in Motion Perception • How does the visual system register that an object seen at one moment corresponds to the same object seen at another moment? • The visual system is biased against unnatural solutions to the correspondence problem and favors solutions that are consistent with the properties of real-world objects.

  13. Aperture Problem • Aperture problem: DS neurons are ambiguous because each one responds only to events within its own receptive field. • This is resolved by integrating local measurements to produce a global response.

  14. Aperture Problem • Ambiguous early responses are channeled to a second stage of visual processing involving higher-order neurons. • An array of spatially distributed V1 neurons contribute to individual MT receptive fields.

  15. Area MT’s Special in Motion Processing • MT neurons contribute motion information that is qualitatively different from the information provided by V1 neurons. • Area MT is important in the detection of correlated motion.

  16. Area MT

  17. Correlated Motion

  18. Common Fate • Global motion is a general tendency to perceive motion in a given direction. • Motion capture: array of dots moving in random directions can appear to move in a single direction when those dots are superimposed on a large object moving in that direction.

  19. Motion Adaptation • Neural adaptation to motion leads to illusory motion aftereffects (MAEs), or the waterfall illusion. • MAE probably results from a biased distribution of responses in direction-selective neurons, including neurons in MT.

  20. Motion Adaptation

  21. Tracking Multiple Objects • Multiple object tracking • Target designation: presentation of 10 targets scattered on a computer display • Movement: targets move in various directions • Probe: one of discs is highlighted

  22. Tracking Multiple Objects • In multiple object tracking, an observer may group the random movement of targets by tracking a virtual object. • Multiple object tracking is mediated by frontal and parietal regions, and area MT.

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