Experiments for Extra Credit

1. Experiments for Extra Credit • Still available • Go to www.tatalab.ca to sign up

2. Next Tuesday • Read article by Anne Treisman

3. Information Theory • Donald Broadbent - earliest systematic investigations of selective attention • First principle of human information processing: capacity is limited

4. Information Theory • Donald Broadbent - earliest systematic investigations of selective attention Second principle of human information processing: information sources can be selected

5. Shadowing • Many early studies employed variations on a paradigm called “shadowing” “Four score and seven years ago…” “Four score and seven years ago…” “It was the best of times, it was the worst of times…”

6. Stages of Selection • Broadbent: Early Selection - a bottleneck exists early in the course of sensory processing that filters out all but the attended channel • Alternative theory: Late Selection - the bottleneck exists not at the lowest stages, but at the highest - such as response planning, memory and consciousness

7. Stages of Selection

8. Stages of Selection • Testing Early Selection Theory - what prediction can be made?

9. Stages of Selection • Testing Early Selection Theory - what prediction can be made? • Information (such as words) in unattended channel shouldn’t be processed for meaning

10. Stages of Selection • Testing Early Selection Theory - what prediction can be made? • Information (such as words) in unattended channel shouldn’t be processed for meaning • Demonstrates that Early Selection Theory is not entirely correct

11. Stages of Selection • Testing Early Selection Theory - what is another prediction that can be made?

12. Stages of Selection • Testing Early Selection Theory - what is another prediction that can be made? • Should be able to find differences in brain activity in primary sensory areas (A1, V1)

13. Stages of Selection • Electrical activity recorded at scalp (EEG) shows differences between attended and unattended stimuli in A1 within 90 ms Hansen & Hillyard (1980)

14. Stages of Selection • Evidence exists for both early and late selection mechanisms • One interpretation: early reduction in “sensory gain” followed by late suppression of unselected information

15. Capacity Limitations in Vision • A limit on the amount of information you can process at once shows up in visual perception • “Cluttered” or dense scenes

16. Visual Search: finding a single item in a cluttered visual scene

17. Visual Search • Visual Search: finding a single item in a cluttered visual scene

18. Visual Search • Is there a green square?

19. Visual Search • Is there a green square?

20. Visual Search • Parallel search: like many independent spotlights

21. Visual Search • Serial search: each item is selected until target is found

22. Visual Search • Serial search: each item is selected until target is found

23. Visual Search • Serial search: each item is selected until target is found

24. Visual Search • Serial search: each item is selected until target is found

25. Visual Search • How could you test which kind of search was happening?

26. Visual Search • Search Slope: How long per item?

27. Visual Search • Search Slope: How long per item?

28. Visual Search • Search Slope: How long per item?

29. Visual Search • Parallel search - search time is independent of distracter number

30. Visual Search • Conjunction search: NOT FLAT!

31. Visual Search • Serial Search - linear increase in search time with number of distractors

32. Visual Search • Search slope for shape singletons is flat. What does this tell us about shape and attention?

33. Visual Search • Search slope for color singletons is flat. What does this tell us about color and attention?

34. Visual Search • Search Slopes can be flat for targets defined by: • color • orientation • curvature • motion • depth • What does this imply about these features ? • What does it tell us about conjunctions of features ?