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PPT

  1. 1. Attention - Overview Definition Theories of Attention Neural Correlates of Attention •Human neurophysiology and neuroimaging Change Blindness Deficits of Attention •Unilateral neglect
  2. 2. Stroop Task Blue Green Yellow Red Yellow Yellow Green Blue Red Green Blue Red Green Yellow Blue Green
  3. 3. Stroop Task ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** *****
  4. 4. Stroop Task Blue Green Yellow Red Yellow Yellow Green Blue Red Green Blue Red Green Yellow Blue Green
  5. 5. Stroop • Failure of selective attention • Race model – Word name is processed automatically – Color is not so automatic – Both arrive at the same time, we have a hard time attending to the relevant stimulus attribute – Doesn’t happen upside down
  6. 6. Stroop Task. BlueGreenYellowRed YellowYellowGreenBlue RedGreenBlueRed GreenYellowBlueGreen
  7. 7. Attention – Neurophysiology Hillyard’s experiments – dichotic listening: attention-dependent effect on ERP amplitude. Early or late? Study by Woldorff et al., localization of an early (20-50 ms latency) attention effect using ERP(F)/MRI).
  8. 8. W. W. Norton
  9. 9. W. W. Norton
  10. 10. W. W. Norton
  11. 11. Woodman, G., and Luck, S. (1999). Electrophysiological measurements of rapid shifts of attention during visual search. Nature 400:867.
  12. 12. Figs. 4, 5, and 6, Corbetta et al., “Selective and divided attention during visual discriminations of shape, color and speed: Functional anatomy by positron emission tomography, The Journal of Neuroscience 11: 2383–2402, (1991) Adapted with permission of The Society for Neuroscience. Adapted from Heinze, H.J., Mangun, G.R., Burchert, W., Hinrichs, H., Scholz, M., Münte, T.G., Gös, A., Scherg, M., Johannes, S., Hundeshagen, H., Gazzaniga, M.S. and Hillyard, S.A., Combined spatial and temporal imaging of brain activity during visual selective attention in humans, Nature 372 (1994): 543–546.
  13. 13. Attention – Neuroimaging Previous imaging studies revealed: changes in neural activity related to attentional shifts (parietal lobe) and attention-related specific activation of extrastriate areas (color, form, motion). No changes in V1. Recent fMRI studies (e.g. Somers et al., 1999): - Selective visual attention modulates neural activity in extrastriate cortex, as well as in V1. - Attentional modulations in V1 are spatially specific. - “Window of attention can be spatially complex”, hints at object-selective attention.
  14. 14. Attention – Neuroimaging Flattening of the occipital lobe (Somers et al., 1999)
  15. 15. (a) and (b): Stimulus (c) and (d): Topography (e) and (f): Attentional Modulation
  16. 16. Attention – Top-Down Most “natural” visual scenes are composed of multiple objects. Receptive fields in higher visual areas are large (up to 25 degrees) and typically contain multiple objects at one time. This creates a problem for neurons encoding specific object features…
  17. 17. Attention – Top-Down Ambiguous response
  18. 18. Attention – Top-Down Ambiguity in neural response can be reduced by: a) Referencing spatial (retinal) location b) Attentional modulation of firing rate
  19. 19. Attention – Top-Down Prediction Un-ambiguous response
  20. 20. W. W. Norton
  21. 21. W. W. Norton
  22. 22. Moran and Desimone, 1985 Note: visual input does not change (fixation point), what changes is the focus of covert attention Cellular Basis of Attention
  23. 23. Unilateral Neglect
  24. 24. Unilateral Neglect Eye movements from a patient with left unilateral neglect, during visual exploration
  25. 25. Hemineglect QuickTime™ and a YUV420 codec decompressor are needed to see this picture.
  26. 26. Unilateral Neglect: Frames of Reference “On the side opposite to”: In what frame of reference does neglect occur (space, object, world)? How do we define LEFT? Reference Frame: system for representing locations relative to some standard coordinate system Neglect affects multiple reference frames
  27. 27. Unilateral Neglect: Frames of Reference Neglect patient JM’s copying of a daisy presented in different orientions. Spatial or object-centered?
  28. 28. Unilateral Neglect and Memory Bisiach’s patient (unable to recall half of the piazza del duomo) – representations are affected, not just acute visual input (“unilateral neglect of representational space”)
  29. 29. What Causes Unilateral Neglect? 1. Neglect results from damage to the attentional orienting system. Attention is mostly deployed to the right. 2. Neglect is caused by a failure to construct a complete mental representation of contralesional space.
  30. 30. Change Blindness QuickTime™ and a Sorenson Video decompressor are needed to see this picture.
  31. 31. Change Blindness QuickTime™ and a Sorenson Video decompressor are needed to see this picture.
  32. 32. Change Blindness QuickTime™ and a QuickDraw decompressor are needed to see this picture.
  33. 33. Change Blindness QuickTime™ and a Animation decompressor are needed to see this picture.
  34. 34. Change Blindness Applet Change Blindness Applet
  35. 35. Salience Model QuickTime™ and a YUV420 codec decompressor are needed to see this picture.

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