1. Vision Psychology 2606

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

3. Vision Like any sensory process, vision converts some energy to neural messages Like any sensory process, vision converts some energy to neural messages In this case, light In this case, light Light is just a form of electromagnetic radiation Light is just a form of electromagnetic radiation So are x rays, micro waves, infra red, UV cosmic rays etc 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 Wavelength of light determines hue Intensity determines brightness Intensity determines brightness Light enters the eye through the cornea and the pupil Light enters the eye through the cornea and the pupil Pupil size regulated by iris Pupil size regulated by iris Behind pupil, lens, which accommodates Behind pupil, lens, which accommodates Light hits the retina Light hits the retina Oh ya, it is upside down…. Oh ya, it is upside down….

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

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

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

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

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

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

14. Occipital lobe V1 – V5 V1 – V5 Blobs and interblobs in V1 Blobs and interblobs in V1 Blobs do colour, interblobs do motion and form Blobs do colour, interblobs do motion and form Info goes on to V2 Info goes on to V2 Now the dorsal and ventral streams are produced 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 The region of the retina that when stimulated will cause a cell to fire This is coded on to layers in V1 This is coded on to layers in V1 So top is top layer, etc So top is top layer, etc Cortical cells have receptive fields too Cortical cells have receptive fields too Receptive field in cortex relates to much bigger area that receptive field in retina, so, many ganglion cells 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 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 So, for example, we can see shape by the nervous system analyzing luminance contrast between receptive fields Simple cells, orientation Simple cells, orientation Complex cells, orientation and movement Complex cells, orientation and movement Hypercomplex cells, orientation, movement and inhibition on one side 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 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) Connections from blobs in V1 to V4 (so V4 does some things with colour) V4 does some stuff about form too V4 does some stuff about form too V5 only does motion V5 only does motion V3 does ‘dynamic form’ (shape in 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 V4 -> only see shades of grey Damage to V5 -> motion detection is gone Damage to V5 -> motion detection is gone V1 damage, blind, yet they can see! V1 damage, blind, yet they can see! So V1 probably is where the brain makes sense of visual input So V1 probably is where the brain makes sense of visual input

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

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