Guest 4

Lecture 16 - February 10th, 2017

Guest Lecture

By Alona Fyshe

My research question:

How doees the brain encode (represent) the meaning of words? How does it combine word meaning to represent more complex concepts?

Siri and the Long tail:

Outline

• Brain imaging
• Word meaning in the brain
• Words in context

Brain imaging technology:

• Functional Magnetic Resonance Imaging (fMRI)
  • Measuers changes in blood oxygenation (BOLD)
    • Good spatial resolution
    • Poor time resolution
• MEG
  • Magnetoecephalography (magnet / brain / graph)
  • Magneted sheeted room -> because earth
    • 102 sensor position
    • 3 sensors / position
    • Poorer spatial resolution than fMRI
    • Great time resolution
    • Great for language studies

Meaning in the brain:

• What would it mean to have a model of meaning representation in the brain?
  • Which brain areas acKvate for parKcular words
  • Predict the word a person is reading from their brain acKvaKon

How to build a model?

Show a computer algorithm many examples.
Training
Find Patterns
Test

Predict unseen words
Find Patterns

You can't build model for every word
    Solution: Word Features (eg. edible, alive)

Ex. The Brain Data

• 9 subjects fMRI , 9 subjecy MEG
• 60 concrete noun w/ pictures

Word Features

Co-occurence with verbs: (MRI)

• Accuracy: 77%

20 Questions: (MEG)

• Array of numbers = Identifier of the Word

• Visual Features (Of the Word and the Image)
  • Posterior Regions
    • Detected in 150ms-250ms
• Word Meaning
  • Distrubuted throughout the brain
    • Detected in 200-600ms