1. Vision Biology/Psychology 2606

2. Some introductory thoughts Sensory world in general is basically a representation of the real world So, we have a rich visual world, not much of a smelly one Different parts of the brain do different bits of processing This all comes together basically seamlessly to form our visual world

3. Vision Like any sensory process, vision converts some energy to neural messages In this case, light Light is just a form of electromagnetic radiation So are x rays, micro waves, infra red, UV cosmic rays etc

5. I wish to hell I could see better…. Wavelength of light determines hue Intensity determines brightness Light enters the eye through the cornea and the pupil Pupil size regulated by iris Behind pupil, lens, which accommodates Light hits the retina Oh ya, it is upside down….

6. Acuity Acuity is affected by the shape of the eye Nearsighted, eye too long, or cornea too curved So far away stuff is blurry Image is in front of the retina Farsighted, opposite

7. The retina There are two kinds of receptors in the retina, rods and cones Rods for night, brightness Cones for day, colour When a photon hits a receptor it sends a message via the optic nerve to the brain Because of this, we have a blind spot!

8. Gotta love the retina Cones are for fine detail and colour Cones only really work in the light Concentrated in the fovea Rods are more evenly distributed Many rods to one bipolar cell, so you can see in dim light, but only in black and white One cone, one bipolar cell About 130 000 000 receptors per retina

9. Follow the optic nerve Connection is next to the ganglion cells in the optic nerve Cross at the optic chiasm Left visual field to right half of brain, right to left Next the path goes to the LGN Geniculostriate system Some to occipital lobe some to parietal

11. And there is another pathway…. Superior colliculus in the tectum Pulvinar in thalamus Whole thing is called the tectopulvinar system Medial pulvinar, parietal Lateral pulvinar, temporal

12. Dorsal and ventral streams Temporal -> ventral Parietal -> dorsal

14. Occipital lobe V1 – V5 Blobs and interblobs in V1 Blobs do colour, interblobs do motion and form Info goes on to V2 Now the dorsal and ventral streams are produced

15. Receptive Fields The region of the retina that when stimulated will cause a cell to fire This is coded on to layers in V1 So top is top layer, etc Cortical cells have receptive fields too Receptive field in cortex relates to much bigger area that receptive field in retina, so, many ganglion cells Only adjacent areas of visual field in centre have colossal connections

16. So, for example, we can see shape by the nervous system analyzing luminance contrast between receptive fields Simple cells, orientation Complex cells, orientation and movement Hypercomplex cells, orientation, movement and inhibition on one side

17. V1 – V5 V1 and V2 are basically like clearinghouses into which different bits of information are deposited and then routed, post offices if you will Connections from blobs in V1 to V4 (so V4 does some things with colour) V4 does some stuff about form too V5 only does motion V3 does ‘dynamic form’ (shape in motion)

18. V was a bad early 80s sci fi show Damage to V4 -> only see shades of grey Damage to V5 -> motion detection is gone V1 damage, blind, yet they can see! So V1 probably is where the brain makes sense of visual input

19. Case studies can be useful DB -> V1 Damage and blindsight JL -> V4 Damage and colour LM -> V5 Damage and movement perception DF -> General occipital damage and visual agnosia D and T -> Higher level visual processing

20. Conclusions Visual system is way complex It is, frankly, counter intuitive It is not all occipital Vision is clearly important to humans, as much of our brain is devoted to it There MAY be asymmetries