CS 182 Midterm review

Transcription

1 CS 182 Midterm review

2 Near far Image schemas What is a schema? a pattern capturing structure in the world What is an image schema? a schema about interaction with the world Can you name some? Containment Source Path Goal Part whole

3 Image schemas Think of image schemas as the basic categories of interaction with world Image schemas have basis in interaction with world and with neural structures Of course, neural structures should capture regularities in interaction with world Not linked to a specific neural area Instead, linked to a neural CIRCUIT

4 English AROUND ON OVER IN Bowerman & Pederson

5 Dutch OP OM AAN BOVEN IN Bowerman & Pederson

6 Chinese ZHOU LI SHANG Bowerman & Pederson

7 The collection of image schemas Trajector / Landmark (asymmetric) The bike is near the house TR LM? The house is near the bike Boundary / Bounded Region boundary bounded region a bounded region has a closed boundary Topological Relations Separation, Contact, Overlap, Inclusion, Surround Orientation Vertical (up/down), Horizontal (left/right, front/back)

8 Learning System dynamic relations (e.g. into) structured connectionist network (based on visual system) We ll look at the details next lecture

9 Outline 1/3 Biology Neuron mechanics spiking, neurotransmitters, ion channels, Na+ Development growth cones, chemical gradients, activity dependent pruning Models McCullough Pitts model backpropagation: minimize error by slow steps triangle node recruitment learning

10 Outline 2/3 Psych experiments Stroop task, priming, spreading activation Brain study PET, fmri, EEG, MEG, TMS, lesion, single unit Learning backprop, Hebbian, LTP, calcium, retrograde, blank slate (not) Colors language variations and invariants; intermediate representations

11 Outline 3/3 Categories basic categories: functional distinction & effects category structure Schemas Image schemas FrameNet Regier's model hand built feature extraction, learned mapping

12 different types of ions for different receptors/transmitters Neurobiology Ion pumps polarized resting potential ions: Na+, K+, Cl Neurotransmitters voltage admits Ca+, vesicles to release transmitters bind to ionotropic receptors allow ions into postsynaptic cell

13 Neurobiology 2 Action potential threshold all or nothing voltage gated channels refractory period Myelin electrical transmission only in mammals

14 Neural development Neurons migrate to correct positions Grow axons with growth cones on tips Axons follow chemical gradients in increasing or decreasing directions, attracting or repelling them brain areas grow axons generally together Axons meet other neurons, form synapses overconnect prune based on activity humans not blank slate!

15 The McCullough Pitts Neuron y j w ij x i f y i t i : target x i = j w ij y j y i = f(x i ) y j : output from unit j W ij : weight on connection from j to i x i : weighted sum of input to unit i

16 Backpropagation Minimize squared error gradient descent use momentum (constant times previous change) Minimum error on training set may not be minimum error on all data! overfitting memorize training data at expense of generalization reduce it by checking against a validation set or just stopping early

17 Triangle nodes Triangle nodes Reciprocal connections to three other units Activates whenever 2 units activate Activates all 3 units Can be implemented as group of McCullough Pitts neurons Recruitment learning Intermediate units activated by multiple sources strengthen connections to sources Now intermediate unit represents conjunction

18 Hebbian learning Neurons that fire together, wire together If presynaptic neuron helps cause postsynaptic neuron to fire, synapse strengthened Biology Ca2+ enters postsynaptic cell when synapse active and cell fires Temporarily makes receptors more sensitive; also slowly adds new receptors releases nitrous oxide (NO) retrograde messenger causes changes in presynaptic neuron, too releases more neurotransmitter

19 Psych experiments Measure behavioral differences that indicate processing differences Stroop task difficulty in reading words in other color indicates topic specific interference in language processing Word priming related words make recognizing words faster timing dependent effects opposite words speed up without time to process; slow down processing with more time explained by slower onset inhibition

20 Brain study PET fmri lesion EEG single unit recording TMS

21 Biology Colors 3 input signals neural representations of sums & differences e.g. yellow = green + red blue Psychophysics quantitative measurements of psychological quantities e.g. find out how small a color difference subjects can discern Language different languages have different groups certain groupings maintained: no one groups red + green certain central concepts maintained: no one says turquoise is a good example of grue (green blue color group)

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