1. The visual system Chapter 10

2. The physical stimulus Light is a wave… …and a particle

3. Psychological dimensions of light Hue Saturation Brightness

4. The eye Cornea – the main focusing element Lens – adjustable focusing Iris – adjust sensitivity and depth of focus Retina – photosensitivity and much, much more

5. Structure of the retina

6. Visual transduction Photons produce electrical events in photoreceptors (hyperpolarization)

7. In darkness, there’s a continuous current in the outer segment caused by the circulation of sodium. In light, sodium circulation slows down and receptors hyperpolarize

8. Disks in outer segments called lamellae contain a photopigment

9. Rhodopsin -- the magic photopigment

10. Through the wizardry of biochemistry, sodium channels close

11. Photoreceptors come in different flavours

12. Spectral absorption curves

13. Lateral interactions in the retina help with several problems 1. Contour sharpening 2. Enhancing sensitivity

14. Mach bands

15. A slightly misleading illustration We understand the neural basis of lateral inhibition because of work on the horseshoe crab that is not feasible in mammals

16. The duplex retina

17. The cost of the duplex retina

18. Central visual pathways The lateral geniculate nucleus of the thalamus

19. Primate lateral geniculate nucleus

20. Centre-surround antagonism is the mammalian analogue of lateral inhibition.

22. Hubel and Wiesel’s simple hierarchical model of visual cortical processing Simple cells Complex cells

23. Columnar organization of VI

24. Ocular dominance

25. The hypercolumn

27. Optical imaging of ocular dominance columns

28. Optical imaging of orientation tuning

29. Correlation between optical imaging and electrophysiological results for orientation tuning

30. Margaret Wong-Riley and the cytochrome oxidase story autoradiography and activity cytochrome oxidase and activity intrinsic variability in cyo

31. Cytochrome oxidase in monkey VI and VII -blobs and stripes of every stripe

32. V2 and cytochrome oxidase stripes

33. Multiple visual representations in cortex

34. Visual agnosias Motion blindness Prosopagnosia Cortical colour blindness Visual object agnosia

35. Visual processing streams I Schneider’s Experiment Tectal undercutCortical ablation

36. Visual processing streams II Gordon Holmes –single patient studies -- it was obvious that people without conscious vision were not ‘blind’

37. In a preliminary test, Weiskrantz positioned a stick in D.B.s blind spot, either sideways or straight up and down. He asked D.B. what he saw. The patient said, "I see nothing." Weiskrantz persisted. "Am I holding the stick sideways, or vertically?" D.B.: "I don't know -- I don't see a stick." Weiskrantz: "Guess." D.B.: "Sideways." Weiskrantz: "Now which way am I holding it?" D.B. "I don't see a stick." Weiskrantz: "Guess." This continued for 20 trials in which D.B.'s performance was perfect. Visual processing streams III –Weiskrantz and blindsight

38. Weiskrantz recounts: "In the interview that followed, and which was recorded, D.B. expressed considerable surprise. 'Did you know how well you had done?', he was asked. 'No,' he replied, 'I didn't -- because I couldn't see anything; I couldn't see a darn thing.' 'Can you say how you guessed -- what it was that allowed you to say whether it was vertical or horizontal?' 'No, I could not because I did not see anything; I just don't know.' (p 24)."

39. Pohl’s Experiment

40. Ungerleider and Mishkin’s Two visual cortical streams

41. Milner and Goodale’s “Posting” experiment