“Everyone knows what attention is… William James, 1890

1. What is visual attention? ... It is the taking possession by the mind, in clear and vivid form, of one out of what seem several simultaneously possible objects” “Everyone knows what attention is… William James, 1890 • Levels of analysis: • 1. Subjective (W. James) 2. Functional - cognitive (joke) 3. Neurological

2. Subjective level (phenomenology) - if you don’t pay attention to it, you don’t see* it * perceptual awareness In normal subjects Go mist Change blindness In patients with hemispatial neglect

3. Try to find the difference between these two pictures move your eyes (& your attention) you ‘see’ the change -- you are ‘perceptually aware’-- at the attended location You are unaware at the unattended locations

5. Look for waldo

6. Fixate attention • Decide: Is that him? • Disengage attention • Move attention • Fixate onto a new location • These are the Cognitive processes Steps to find Waldo

7. T T L L T T 2. Cognitive Processes: Visual Search Anne Treisman Find the letter T

8. 2. Cognitive processes: How to study visual attention? • Visual search (Treisman) • Overt movement (i.e., moves eyes) • It’s difficult to isolate specific steps (e.g. disengage) • Covert orienting task (Posner) (aka spatial cueing task) • No eye movements • Isolates each step of the process

9. + + Covert orienting task Mike Posner time

10. + RT (ms) + + invalid 20% Covert orienting task Mike Posner 1 sec 0.5 sec Valid 80%

11. Covert orienting task Arrow Onset . Voluntary engagement of attention Target onset at opposite location (invalid trial) . Detect surprising event . Disengage attention from initial site . Move it to the opposite location

12. Attention at the cued location <- <- 15 sec delay Detect stimulus at unattended location Automatic attentional system (ventral) Corbetta et al, nature neuroscience Voluntary Attentional System (dorsal). *

13. Modulated by expectations Alerted by Unexpected stimulus Interaction between the two systems Left IPS Right IPS. Right TPJ balance

14. Hemispatial Neglect Anatomy Temporo-parietal junction (right) TPJ, horizontal cut Lesion can extend toward frontal lobe

15. Alert by unexpected stimulus Greatly reduced Interaction between the two systems post-stroke LESION SPI izq. SPI der. UTP der IMBALANCE Sintoms:?? Covert orienting task

16. Hemispatial neglect, clinical • eye gaze: right side bias • neglects stimulus in left visual field • (bumps wall, misses food on that side of tray) • low arousal (sleepy) • Muscular weakness (hemiparesis): unrelated

17. Clinical assessment Cancelation task Line bisection Star crossing

18. drawings

19. Bias in writing

20. Clinical evaluation (cont’d) - Extincion

21. normal neglect • Does the disordered attentional mechanisms associated with visuospatial neglect alter patient’s representation of space ?

22. 1 2 Before After 3 4 Drawings by Tom Greenshields pre- and post-stroke Self portrait by Anton Raderscheidt, at different stages of recovery

23. Visual search: Eye movements