1. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison1 The eyes receivers of information Shaping and transforming light into sensory perceptions for nearly 600 million years.

2. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison2 Why are we talking about eyes today?

3. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison3 Approaches to perception and cognition Philosophy (BC 600 - early 1800s) Early Psychology (early 1800s - early 1900s) “Classic” Psychology (early 1990s - 1950s) Modern Psychology (1950s - ) –information in light -> ecological optics –information used to choose best hypothesis -> cognitive psychology (symbolic manipulation) –information coded, recoded and decoded (rewoven) -> eg, intelligent eye

4. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison4 Light - carrier of information 1.Travels in straight lines Assumption: optical density unchanging 2.Reflects off of surfaces (  i =  r ) 3.Refracts when travelling into new medium n i sin (  i ) = n r sin (  r ) 4.Has various frequencies (colours) 5.Has various amplitudes (intensities)

5. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison5 Refraction review n1n1 n2n2 n 1 <n 2

6. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison6 Refraction quiz A B C 1 2 3 n1n1 n2n2

7. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison7 Seeing physical recording of the pattern of light energy received from the world that consists of: 1.Selective gathering of the light 2.Projection or focusing of the light on a photosensitive surface 3.Conversion of the light into a pattern of chemical or electrical activity

8. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison8 The eye - receiver of information Light sources: sun, light bulbs, candles, moon Light reflects off of objects in environment

9. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison9 The eye - receiver of information Light sources: sun, light bulbs, candles, moon Light reflects off of objects in environment objects effectively become light sources

10. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison10 Implications for vision Does not matter if an object is a source or a reflector of light Strength of reflection is a function of: –color of object –smoothness of object –relative orientation between light rays, surface normal, and observer

11. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison11 What do eyes do? why do most creatures have them? how do they do their work? what do they pass on to the brain?

12. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison12 Photoreceptor “receptor of light [photons]” photoreceptor cell transforms light into nerve impulses

13. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison13 Photoreceptor “receptor of light [photons]” photoreceptor cell transforms light into nerve impulses

14. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison14 Photoreceptor “receptor of light [photons]” photoreceptor cell transforms light into nerve impulses more light == higher frequency of impulses

15. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison15 Photoreceptor transducer of light into neural signal process: transduction object: transducer action: transducing

16. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison16 What good is a single photoreceptor? How can the utility of single photoreceptor be improved? Assumption: small creature

17. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison17 Directional sensitivity if photoreceptor responds to light from any direction –cannot determine direction of light –can only determine overall amount of light

18. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison18 Directional sensitivity if photoreceptor responds to light from any direction –cannot determine direction of light –can only determine overall amount of light

19. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison19 Directional sensitivity if photoreceptor responds to light from any direction –cannot determine direction of light –can only determine overall amount of light

20. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison20 Directional sensitivity: eye cups Need to exclude all light, except rays which come from a particular direction pigmented cells behind eye cups: Cambrian period, 570–500 million years ago

21. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison21 From http://www.sfu.ca/biology/faculty/burr/ Directional sensitivity in a parasitic worm Mermis nigrescens Photoreceptor Pigment

22. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison22 Directional sensitivity: ommatidium Need to exclude all light, except rays which come from a particular direction pigmented cells around: extend eye cup into a tube

23. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison23 Ommatidium long narrow light conductor (tube) –selects light traveling in direction along axis

24. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison24 Image formation array of ommatidia: compound eye From http://ebiomedia.com/gall/eyes/octopus-insect.html

25. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison25 Compound eyes insects trilobites (300 million years ago) very near sighted: wide field microscopic vision very poor far vision average human vision requires array 1m diameter

26. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison26 Array of ommatidium…

27. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison27 Array of photoreceptors

28. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison28 How to form an image?

29. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison29 Pinhole eye array of photo receptors along cavity pinhole selects light traveling in direction between it and photoreceptor

30. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison30 Pinhole eye result is a complete image on photoreceptor array image represented by set of outputs

31. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison31 Nautilus: squid that lives in a shell http://www.paleobase.com/gallery/gallery2.html http://platea.pntic.mec.es/~rmartini/ciencias.htm

32. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison32 Drawbacks of a pinhole eye…

33. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison33 Lens eye vertebrates, octopus Lens focuses and selects light rays instead of a single ray through a narrow pinhole

34. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison34 Lens eye vertebrates, octopus beam of light focused onto each photoreceptor

35. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison35 Human eye Fovea Optic nerve fibers Retina Vitreous humor Lens Iris Pupil Cornea Aqueous humor

36. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison36 Human Eye lens eye array of photoreceptors: retina –rods and cones focusing: cornea plus crystalline lens photoreceptors are “backwards” –axons (nerves) leave through blind spot

37. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison37 Retina Retina covered with light-sensitive receptors: –rods primarily for night vision & perceiving movement sensitive to broad spectrum of light can’t discriminate between colors sense intensity or shades of gray –cones used to sense color

38. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison38 Retina Center of retina has most of the cones –allows for high acuity of objects focused at center –cones packed very tightly in fovea “depression” Edge of retina is dominated by rods –allows detecting motion of threats in periphery

39. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison39 Edge detection Photoreceptor array “copies” incoming light –lens forms an image on the retina –photoreceptors fire at a rate “proportional” to intensity of light But, absolute intensity is not that useful –changes when light level changes –for example? Better to represent objects via changes of intensity over space: edges

40. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison40 For example, consider pattern of light rays from an object with a patch of black paint on it

41. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison41 However, changes (edges) are still in same place. If incoming light is twice as strong, twice as much will get reflected…

42. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison42

43. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison43

44. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison44 Representing objects by edges Very efficient compression 100 million axons from photo receptors per eye 1 million axons from ganglion cells per eye Reduction by a factor of 100!!

45. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison45 Finally What was the purpose of this presentation? Which question remains unanswered?

46. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison46 Copepod picture From http://www.nmnh.si.edu/iz/copepod/

47. 2002/01/14PSCY202-005, Term 2, Copyright 2002 Jason Harrison47 Copepod picture From Gregory, Ross, Moray http://www.richardgregory.org/papers/copilia/curious-eye-copilia.pdf