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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

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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
Where we stand

  • Last Week

    • Imaging studies

    • Connectionist representation

  • This Week

    • Backprop

    • traditional AI

  • Coming up

    • Neurophysiology of color


The big and complicated picture
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


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?


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?


Imaging techniques
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…


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?


The mirror circuit in monkeys
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


Somatotopy
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


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?


Two ways of looking at memory

Memory

Declarative

Non-Declarative

Episodic

Semantic

Procedural

Two ways of looking at memory:

facts about a situation

general facts

skills


Two ways of looking at memory1

Memory

Short Term Memory

Long Term Memory

Two ways of looking at memory:

electrical changes

structural changes

LTP


Ltp and hebb s rule

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


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?


Why is hebb s rule incomplete

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?


The mccullough pitts neuron

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


Let s try an example the or function

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?


Many answers would work

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)


Anonymous feedback lectures
Anonymous Feedback: Lectures

feel free to comment on each instructor seperately

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What will be most helpful to you in getting the most out of lectures?

Any particularly confusing topic?


Anonymous feedback sections
Anonymous Feedback: Sections

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Any other comments?


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