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2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 20021 The Brain from retina to extrastriate cortex.

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Presentation on theme: "2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 20021 The Brain from retina to extrastriate cortex."— Presentation transcript:

1 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 20021 The Brain from retina to extrastriate cortex

2 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 20022 Neural processing responsible for vision photoreceptors retina –bipolar and horizontal cells –ganglion cells (optic nerve) optic nerves optic chiasma (X) lateral geniculate body striate cortex extrastriate cortex

3 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 20023 Lateral inhibition Edge detection and contrast enhancement Bipolar, Horizontal and Ganglion cells

4 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 20024 Lateral inhibition If no activity in neighboring photoreceptors, output = output of photoreceptor

5 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 20025 Lateral inhibition if activity in neighboring photoreceptors, –output is decreased, possibly absent

6 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 20026 Lateral inhibition via addition and negative weights

7 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 20027 Another example

8 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 20028 Different kinds of ganglion cells == different sets of weights

9 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 20029 Optic nerve axons of the ganglion cells –1 million optic nerves –120 million photoreceptors

10 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200210 brains From http://www.marymt.edu/~psychol/cortex.html

11 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200211 From light to vision Lateral Geniculate Nucleus (LGN) Striate Cortex Geniculo-Striate Pathway

12 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200212 (LGN) Striate Cortex Striate cortex (primary visual centre) Neurons are edge detectors fires when an edge of a particular orientation is present

13 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200213 (LGN) Striate Cortex Striate cortex (primary visual centre) Neurons are edge detectors fires when an edge of a particular orientation is present frequent output vertical bar

14 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200214 (LGN) Striate Cortex Striate cortex (primary visual centre) Neurons are edge detectors fires when an edge of a particular orientation is present infrequent output diagonal bar

15 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200215 Edge detection each cell “tuned” to particular orientation –vertical –horizontal –diagonal cats: only horizontal and vertical humans: 10 degree steps edges at particular orientations and positions

16 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200216 Extrastriate cortex (beyond the striate cortex) V1

17 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200217 Extrastriate cortex Each area handles separate aspect of visual analysis –“V1-V2 complex”: Map for edges –V3: Map for form and local movement –V4: Map for colour –V5: Map for global motion Each is a visual module –connects to other areas –operates largely independently

18 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200218 Finally What was the purpose of this presentation? Which question remains unanswered?

19 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200219 Slides after this point review neuron function and vocabulary. We did not cover them in lecture, but you may find them useful. Gregory covers this pp 68-74 Coren, Ward, Enns in an appendix

20 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200220 The brain - processor of information Eyes are actually a part of the brain Ganglion cells are a special type of neuron:

21 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200221 The brain - processor of information Eyes are actually a part of the brain Ganglion cells are a special type of neuron:

22 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200222 The brain - processor of information Eyes are actually a part of the brain Ganglion cells are a special type of neuron:

23 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200223 The brain - processor of information Eyes are actually a part of the brain Ganglion cells are a special type of neuron:

24 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200224 The brain - processor of information Eyes are actually a part of the brain Ganglion cells are a special type of neuron:

25 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200225 The brain - processor of information Eyes are actually a part of the brain Ganglion cells are a special type of neuron:

26 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200226 The brain - processor of information Eyes are actually a part of the brain Ganglion cells are a special type of neuron:

27 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200227 Input signals on dendrites affect voltage on cell body -action potentials (spikes) sent along axon, towards terminals -speed ≈1 m/sec (narrow) to 100 m/sec (wide) -when voltage change is sufficiently high, cell begins to fire

28 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200228 Input signals on dendrites affect voltage on cell body -action potentials (spikes) sent along axon, towards terminals -speed ≈1 m/sec (narrow) to 100 m/sec (wide) -when voltage change is sufficiently high, cell begins to fire

29 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200229 Input signals on dendrites affect voltage on cell body -action potentials (spikes) sent along axon, towards terminals -speed ≈1 m/sec (narrow) to 100 m/sec (wide) -when voltage change is sufficiently high, cell begins to fire

30 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200230 Input signals on dendrites affect voltage on cell body -action potentials (spikes) sent along axon, towards terminals -speed ≈1 m/sec (narrow) to 100 m/sec (wide) -when voltage change is sufficiently high, cell begins to fire

31 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200231 Output strength represented by rate of firing along axon of neuron Typical rates: 200-1000 spikes per second

32 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200232 Output strength represented by rate of firing along axon of neuron Typical rates: 200-1000 spikes per second

33 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200233 Output strength represented by rate of firing along axon of neuron Typical rates: 200-1000 spikes per second

34 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200234 Output strength represented by rate of firing along axon of neuron Typical rates: 200-1000 spikes per second

35 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200235 Output strength represented by rate of firing along axon of neuron Typical rates: 200-1000 spikes per second

36 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200236 Information processed by neurons activating each other in sequence -output of one neuron = input of next -connection = synapse

37 2002/01/21PSCY202-005, Term 2, Copyright Jason Harrison, 200237 But excitation is not the only way that neurons interact…

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