1. Seeing Things 1 Eye and Brain
How Your Brain Works - Week 3
Dr. Jan Schnupp
HowYourBrainWorks.net

2. Light Wavelength

3. Optics of the Eye

4. Eye and Retina

5. The Blind Spot

6. Retinotopy
Adapted from drawings by Ramon y Cajal

7. The Optic Pathway: eye, optic nerve, optic chiasm, optic tract, thalamus, optic radiation, visual cortex
Source:

8. Rene Descartes, Retinotopy and the Seat of the Soul

9. Photoreceptors
The human eye has ca. 10 million rods and ca 120 million cones

10. Phototransduction
Immage source: wikipedia
Light activated rhodopsin (R) activates G-protein (G) which in turn activates phosphodiesterase (PDE) which cleaves cGMP which closes cGMP-gated Na+ channel.
What does any of this have to do with carrots?

11. Absorption Spectra
The three different types of cones and the rods have slightly different opsins which are sensitive to different wavelengths.
“Trichromacy” theory.

12. Sensitivity of Receptors

13. Rod and Cone Distribution

14. Retinal Wiring Photoreceptors Horizontal cells Bipolar cells
Amacrine cells
Retinal ganglion cells

15. Centre –Surround Receptive Fields
Photo-
receptors
Horizontal
Cell
Bipolar
Cell
Retinal Ganglion
Cell

16. On-centre and off-centre Receptive Fields
Lateral inhibition provided by photoreceptor ribbon synapses, horizontal cell synapses and amacrine cells

17. Lateral inhibition for contrast (edge) detection

18. RGC receptive fields as “spatial frequency filters”

19. Difference of Gaussians Model of Retinal Ganglion Cells
DoGmodelFigure.m
The centre-surround structure of Retinal Ganglion Cells turns them into “spatial frequency filters”. Larger RGC receptive fields are tuned to “coarsely grained” structure in the visual scene, while smaller RFs are tuned to fine grain structure.

20. Convolving a Penny with DoGs
The picture of an American cent (left) seen through large (middle) or small (right) difference of Gaussian receptive fields.
filterPennies.m

21. The Fovea

22. Eye muscles

23. Eye movements
Eye-movement traces while a subject explores a picture of the bust of Nefertiti.
From "Eye Movements and Vision" by A. L. Yarbus; Plenum Press, New York; 1967

24. Dan Simmons’ visual attention task
Count the number of passes of the white team

25. Colour opponency

26. Colour Opponency

27. The Colour Wheel
Yellow-Blue
Red Green

28. Why Colour Vision Does Not Work Well in Poor Light

29. Cone mosaics Cone mosaics for four different individuals
Source:

30. Colour blindness Red-green channel broken Blue-yellow channel broken

31. M cells and P cells
90% P cells
5% M cells
5% non-M non-P

32. Projections to the Lateral Geniculate Nucleus

33. The Stepping Feet Illusion
What is going on here?
M cells are colour blind, but very sensitive to brightness (luminance) contrast.
P cells are R-G opponent
Non-M non-P cells are Y-B opponent
Only M cells project to the motion processing streams in the brain.