1. EYES!

8. l.m. of embryonic eye
Vitreous humour forming
Choroid (pigmented) layer forming
conjunctiva
cornea
Retina forming
lens
Iris forming

9. Embryonic eye development
Spherical lens
retina
cornea

10. External anatomy of the eye
Pigmented iris – circular and longitudinal muscles
sclerotic
Pupil – diameter controlled by iris muscles
Curved transparent cornea – responsible for refraction of light

11. Figure 6.2 Cross section of the vertebrate eye
Note how an object in the visual field produces an inverted image on the retina.

12. Label the following: j a i b h c d g e f

13. Perception of contours where there really
Subjective Contours
Subjective
Necker
Cube
Is it
really
there?
Perception of contours where there really
are none.

14. Form Perception & Feature Analysis
Bottom-Up Processing
Based upon properties
of the stimulus (e.g.,
patterns of light & dark
areas
Top-Down Processing
Based upon higher-order
information (e.g., prior
knowledge & context)
What is this picture?

15. Figure 6.18 An illustration of lateral inhibition
Do you see dark diamonds at the “crossroads”?

16. Dark & Light Adaptation
Adaptation - process by which the eye becomes
more or less sensitive to light

17. Cones and Colour

18. NO! Colour Vision Do objects possess colour? Is a lemon “yellow”?
Light has no colour
Is a chili pepper “red”?

19. Trichromatic Theory of Colour Vision
Human eye has 3 types of cone
receptors sensitive to different
wavelengths of light.
Helmholtz 1852
Short
Medium
Long
People see colours because the
eye does its own “colour mixing”
by varying ratio of cone
neural activity

21. Bleaching
Bleaching occurs when you have looked at a red picture too long the red iodopsin has being bleached so when you look at white paper the red iodopsin is temporally out of order.

22. Transduction
Both Rods and Cones contain photopigments (chemicals that release energy when struck by light)
11-cis-retinal is transformed into all-trans-retinal in light conditions
this results in hyperpolarization of the photoreceptor
the normal message from the photoreceptor is inhibitory…
Light inhibits the inhibitory photoreceptors and results in depolarization of bipolar and ganglion cells

25. Cones Rods Retina Several layers of cells in inner surface of choroid
Contains photoreceptors - Rods & Cones
Daytime
Night Vision
High resolution
Poor definition
Color
Black & White
Center of
retina
Periphery of retina
Less abundant
More abundant
Cones
Rods

26. Rods & Cones: Distibution
Rod density high away from the center
The more sensitive rods (~100_rods-1_neuron map) help track peripheral image motion
~120 million rods in retina
Cone density high near the center
The 0.3 mm dia fovea has only high density of cones (1_cone-1_neuron map) helps form sharp brilliantly colored images
~6-7 million cones in retina

27. A rod cell (upper) and a cone cell
From which direction would light come?

28. The Photo-receptors: Rods & Cones
Phototopic
Chromatic
Fast
Foveal
Rods
Scotopic
Achromatic
Slow
Peripheral vision

29. A rod cell
Direction of light

30. Figure 6.4 Visual path within the eyeball
The receptors send their messages to bipolar and horizontal cells, which in turn send messages to the amacrine and ganglion cells. The axons of the ganglion cells loop together to exit the eye at the blind spot. They form the optic nerve, which continues to the brain.

31. Rods & Cones: Fovea & Blind Spot
Fovea a 0.3 mm spot with cone-only distribution: highest acuity and color rendition
Blind spot where optic nerve leaves the retina

32. retina
Rod cells
B-P Cells
G-cells
LIGHT

33. Retinal signal processing
Integrator neurons
Horizontal cells
Bipolar cells
Amacrine cells
Ganglion cells
Cones
Cone > Bipolar cell > Ganglion cell
Rods
Rod > Bipolar cell > Amacrine cell > Ganglion cell

36. Rods & Cones
Photosensitive protein is rhodopsin, membrane protein, that modulates membrane ion conductivity via a biochemical cascade once it absorbs a photon, with the cell getting hyperpolarized as a function of light
Different amino-acid sequences in the ‘opsin’ segments of rhodopsin give the different color sensitivities of rods & cones

37. Bipolar Cells
Many Rod cells are connected to one bipolar cell which means that when only one of the Rod cells are activated an impulse is sent to the brain.
One Cone cells is connected to one bipolar cell which means that the light needs activate each Cone cell to send an impulse. This is why the Cone cells have a higher acuity and why they cant function in the dark.

43. Link to brain: Primary pathway
Optic nerve
Optic chiasm
Lateral geniculate body
Optic radiation
Visual cortex