The visual system

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 IVisual perception

5. Speed

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

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

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

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

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

18. Invariance

19. Top-Down controlof perceptual judgements M.C. Escher

20. Top-Down controlof perceptual judgements Kandel et al. (2000)

21. Top-Down controlof perceptual judgements Kay & Kempton, 1984 Blue Green Siyoname

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

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

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

30. Luck & Vogel, 1997 Set size 10 0 t c e r r o C Gap 75 t Size n e Orientation c r Colour e P Conjunction 50 2 4 6 Study Test Conclusion: the capacity of visual WM is about four objects, while every object can consist of multiple features. - WM similar to attention.

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

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