1. The Retina has layers of cells
photoreceptors transduce incoming light
ganglion cells send signals along to the brain

2. Two kinds of Photoreceptors
2 types of photoreceptors: rods and cones
rods are very sensitive - useful in dim light
cones are less sensitive but work even in very bright light

3. The Retina
Rods and cones are distributed differently across the retina

4. The Retina
visual acuity (ability to see detail) depends on cones - thus acuity varies across the visual field

5. The Retina
Why don’t you notice your blind spot?

6. The Retina Why don’t you notice your blind spot?
Blindspots don’t overlap!
Your brain “fills in” the missing information
The specific information in the blindspot isn’t much more missing than the rest of the periphery!

7. The Retina three types of cones: short, medium, and long
different absorptions enable color vision

8. Neurons “collect” information
each ganglion cell integrates information from a particular spot on the retina called its receptive field

9. Receptive Fields Stimulus is in receptive field
Action potentials
Stimulus is in receptive field
Stimulus is near receptive field
Stimulus is outside receptive field

10. Visual Pathways
Ganglion cells project to the brain via the optic nerve
information is projected to contralateral cortex!

11. Visual Pathways the retina is mapped onto primary visual cortex
called a retinotopic or spatiotopic map
Stimulus
Cortical Activity

12. Visual Pathways
signals are separated according to the type of information
Dorsal “Where” Pathway: Motion and Location
Primary Visual Cortex (V1)
Ventral “What” Pathway: Color and Form

13. Seeing

14. Seeing
Discussion of Gregory’s Article on Visual Illusions - Tuesday Oct 23

15. Seeing
Seeing is the process of converting electromagnetic radiation into a conscious mental event

16. Seeing visual system faces many challenges too much information
too little information
conflicting information
ambiguous information

17. Seeing
too much information

18. Seeing
too little information

19. Seeing
Conflicting Information

20. Seeing
Ambiguous information

21. Seeing
We will consider two aspects of vision to explore how the brain overcomes these challenges:
Seeing depth
Seeing in color