1. CS 182 Sections 101 - 104 Created by Eva Mok Modified by JGM 2/2/05 Q:What did the hippocampus say during its retirement speech? A:“Thanks for the memories” Q:What happens when a neurotransmitter falls in love with a receptor? A:You get a binding relationship. Q:What did the Hollywood film director say after he finished making a movie about myelin? A:“That’s a wrap!” http://faculty.washington.edu/chudler/jokes.html

2. Announcements a2 is out, due next Monday 11:59pm –play with tlearn –you can either run it on inst machines or download it and run on your pc (though this may give you some headaches…) Quiz on Thursday

3. Where we stand Last Week –Basic idea of learning, Hebb’s rule –Psycholinguistics experiments This Week –Spreading Activation, triangle nodes –Connectionist representations Coming up –Backprop (review your Calculus!)

4. Quiz! What are does the Stroop effect show? What was the point of the eye-tracking experiment? Why is Hebb’s rule not the complete story for the learning that goes on in the brain? What’s a McCullough-Pitts neuron? How does it work? What does the “They all rose” experiment show? How can you explain the results computationally?

5. DeclarativeNon-Declarative EpisodicSemanticProcedural Memory Two ways of looking at memory: facts about a situation general facts skills

6. Stroop effect takes longer to say what color a word is printed in if it names a different color suggests interaction of form and meaning (as opposed to an encapsulated ‘language module’)

7. ‘Word superiority effect’ it’s easier to remember letters if they are seen in the context of a word militates against ‘bottom-up’ model, where word recognition is built up from letters suggestion: there are top-down and bottom-up processes which interact

8. Eye-tracking Experiment Three hypothesis for eye-tracking results: –Cohort theory –Neighborhood activation model –TRACE (McClelland & Elman)

9. Memory Short Term MemoryLong Term Memory Two ways of looking at memory: electrical changes structural changes LTP

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11. 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 LTP and Hebb’s Rule strengthenweaken

12. Why is Hebb’s rule incomplete? here’s a contrived example: should you “punish” all the connections? tastebudtastes rotteneats foodgets sick drinks water

13. The McCullough-Pitts Neuron y j : output from unit j W ij : weight on connection from j to i x i : weighted sum of input to unit i xixi f yjyj w ij yiyi x i = ∑ j w ij y j y i = f(x i ) t i : target

14. Let’s try an example: the OR function Assume you have a threshold function centered at the origin What should you set w 01, w 02 and w 0b to be so that you can get the right answers for y 0 ? i1i1 i2i2 y0y0 000 011 101 111 x0x0 f i1i1 w 01 y0y0 i2i2 b=1 w 02 w 0b

15. Many answers would work y = f (w 01 i 1 + w 02 i 2 + w 0b b) recall the threshold function the separation happens when w 01 i 1 + w 02 i 2 + w 0b b = 0 move things around and you get i 2 = - (w 01/ w 02 )i 1 - (w 0b b/w 02 ) i2i2 i1i1

16. “They all rose” triangle nodes: when two of the neurons fire, the third also fires model of spreading activation

17. How we can model the triangle node with McCullough-Pitts Neurons? BC A ABC

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