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Announcements

Announcements. a3 is out, due 2/15 11:59pm Please please please start early quiz will be graded in about a week. a1 will be graded shortly—use glookup to see your grade. Where we stand. Last Week Imaging studies Connectionist representation This Week Backprop traditional AI Coming up

merritt-ferrell
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Announcements

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  1. Announcements • a3 is out, due 2/15 11:59pm • Please please please start early • quiz will be graded in about a week. • a1 will be graded shortly—use glookup to see your grade

  2. Where we stand • Last Week • Imaging studies • Connectionist representation • This Week • Backprop • traditional AI • Coming up • Neurophysiology of color

  3. The Big (and complicated) Picture Psycholinguistics Experiments Spatial Relation Motor Control Metaphor Grammar Cognition and Language Computation Chang Model Bailey Model Narayanan Model Structured Connectionism abstraction Neural Net & Learning Regier Model SHRUTI Computational Neurobiology Triangle Nodes Visual System Biology Neural Development Quiz Midterm Finals

  4. Quiz! • How is fMRI used? How is TMS used? • What systems are active when we observe a person picking up a glass? • What is the biological mechanism for short-term memory? Long-term memory? • Why is Hebb’s rule not the complete story for the learning that goes on in the brain?

  5. Quiz! • How is fMRI used? How is TMS used? • What systems are active when we observe a person picking up a glass? • What is the biological mechanism for short-term memory? Long-term memory? • Why is Hebb’s rule not the complete story for the learning that goes on in the brain?

  6. Imaging Techniques • fMRI Measures the magnetic resonance of cranial blood flow, which varies with oxygenation • fMRI has very good spatial resolution (mm-scale) but not-so-great temporal resolution (2-5 seconds) • TMS induces a current in the brain, the movement of which indicates interconnections • TMS can be used with fMRI…

  7. Quiz! • How is fMRI used? How is TMS used? • What systems are active when we observe a person picking up a glass? • What is the biological mechanism for short-term memory? Long-term memory? • Why is Hebb’s rule not the complete story for the learning that goes on in the brain?

  8. The Mirror Circuit in Monkeys • top: monkey sees experimenter grasp an object • bottom: monkey sees experimenter reaches his hand behind a screen to grasp an object this is what we see in a monkey… measuring a neuron in the parietal area

  9. Somatotopy • top: humans watching foot , hand and mouth actions without an object • bottom: humans watching same actions with an object • What can we learn from these two experiments? integrated, multi-modal representation of actions, along with the objects and locations Buccino et al., 2001

  10. Quiz! • How is fMRI used? How is TMS used? • What systems are active when we observe a person picking up a glass? • What is the biological mechanism for short-term memory? Long-term memory? • Why is Hebb’s rule not the complete story for the learning that goes on in the brain?

  11. Memory Declarative Non-Declarative Episodic Semantic Procedural Two ways of looking at memory: facts about a situation general facts skills

  12. Memory Short Term Memory Long Term Memory Two ways of looking at memory: electrical changes structural changes LTP

  13. strengthen weaken LTP and Hebb’s Rule • Hebb’s Rule: neurons that fire together wire together • Long Term Potentiation (LTP) is the biological basis of Hebb’s Rule • Calcium channels is the key mechanism

  14. Quiz! • How is fMRI used? How is TMS used? • What systems are active when we observe a person picking up a glass? • What is the biological mechanism for short-term memory? Long-term memory? • Why is Hebb’s rule not the complete story for the learning that goes on in the brain?

  15. tastebud tastes rotten eats food gets sick drinks water Why is Hebb’s rule incomplete? • here’s a contrived example: • should you “punish” all the connections?

  16. yj wij yi xi f ti : target xi = ∑j wij yj yi = f(xi) The McCullough-Pitts Neuron yj: output from unit j Wij: weight on connection from j to i xi: weighted sum of input to unit i

  17. i1 w01 w02 i2 y0 b=1 w0b x0 f Let’s try an example: the OR function • Assume you have a threshold function centered at the origin • What should you set w01, w02 and w0b to be so that you can get the right answers for y0?

  18. i2 i1 Many answers would work y = f (w01i1 + w02i2 + w0bb) recall the threshold function the separation happens when w01i1 + w02i2 + w0bb = 0 move things around and you get i2 = - (w01/w02)i1 - (w0bb/w02)

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