1. The visual system Martha Nari Havenith MPI for Brain Research Aug. 5th 2008 FIAS Summer School

2. Receptive field What and Where pathway Change blindness Bipolar cell Striate cortex Orientation column Grandmother (Halle Berry) cell Fusiform face area

3. Outline Stuff we see – visual perception Eye and retina Tectum and thalamus The visual cortices Neuronal codes in the visual system What I won’t really talk about: Depth, colour and motion perception; subcortical structures of the visual system, visual WM and attention

4. The visual system I Visual perception

5. Speed

6. → 150 ms Thorpe & Fabre-Thorpe (2001) Speed

7. Thorpe & Fabre-Thorpe (2001) 20-40 ms 30-50 ms 40-50 ms 50-70 ms 70-90 ms 80-100 ms Speed

8. Acuity Two-point acuity: 25 arc seconds = 3-4 mm at 50 cm distance = diameter of a retinal photoreceptor Vernier acuity: 8 arc seconds ~= 1 mm at 50 cm distance From Krauskopf & Forte (2002)

9. Context sensitivity

10. Figure segregation

11. From Schiffman (2000) Figure segregation – Gestalt principles Proximity

12. From Schiffman (2000) Figure segregation – Gestalt principles Similarity

13. From Schiffman (2000) Figure segregation – Gestalt principles Common fate

14. Figure segregation – Gestalt principles From Schiffman (2000) Closure

15. Figure segregation – What we can do

16. Figure segregation- What Windows cannot do

17. Invariance

19. M.C. Escher Top-Down control of perceptual judgements

20. Kandel et al. (2000)

21. Top-Down control of perceptual judgements Kay & Kempton, 1984 BlueGreen Siyoname

22. Some limitations of visual perception - Awareness Monkey: 77% correct - His V1: 96% correct! Chen et al., 2008 Ideal observer Monkey

23. Some limitations of visual perception - Priming HAPPINESS

24. Some limitations of visual perception - Priming HAPPINESS

25. Some limitations of visual perception - Priming HAPPINESS

26. Some limitations of visual perception - Priming HAPPINESS

27. Some limitations of visual perception – Parallel processing

28. Adapted from Anne Treisman Pop-out Stimulus size Automatic processing Search time Focused attention No pop-out Pop-out Automatic No Pop-out Attentive Some limitations of visual perception – Parallel processing

29. Visual memory The modal model Sensory memory (iconic memory) Short-term memory (working memory) Long-term memory 200-300 ms Several seconds or while rehearsing Up to life long

30. Luck & Vogel, 1997 Conclusion: the capacity of visual WM is about four objects, while every object can consist of multiple features. - WM similar to attention. StudyTest

31. Wheeler & Treisman, 2002 StudyTest Conclusions: - Feature dimensions are independent. - Only four features per feature dimension. - Attention binds features within WM. - Proof: With distractors memory for conjunctions impaired. Performance drops for conjunctions but not for features.

32. Some limitations of visual perception – Change blindness

33. Some limitations of visual perception Impossible objects

34. Summary I – Visual perception is… Fast and precise Highly specialized for extraction of contours Designed for detecting invariant features Modulated by top-down processes Limited by the capacity of attention and visual WM