Event Related Potentials ERPs:

1
Event Related Potentials (ERPs)

• What can they tell us about
• how we think?
• Kim Sweeney
• Introduction to Cognitive Science
• May 22, 2008

With thanks to Seana Coulson!
2
Overview

• What are ERPs?
• How/why are ERPs useful to cognitive scientists?
• P300, N400 and P600 components
• What are they?
• What is their functional significance?
• How can we use these components to investigate
  the workings of the mind?

3
Event Related Potentials (ERPs)
4
Electroencephalogram (EEG)

• We record the EEG by
  
• placing
• electrodes on the
  head
• Info in raw EEG

5
Event Related Potentials (ERPs)
6
Characteristics of ERP components

• Polarity
• Is it a positive wave or a negative one?
• Latency
• How long after stimulus presentation does it
  peak?
• Functional Significance
• What cognitive (or perceptual) activity is it
  sensitive to?
• What makes it bigger or smaller?

7
What do ERPs reflect?

• Sensory, motor, and/or cognitive events in the
  brain
• Synchronous activity of large populations of
  neurons engaged in information processing

8
What are ERPs?

• ERPs are formed by averaging EEG time-locked to
  the onset of stimuli that require cognitive
  processing
• ERPs represent electrical activity associated
  with the processing of the stimuli
• ERPs can be related to different kinds of
  cognitive tasks, e.g. attention, memory,
  language comprehension

9
fMRI ERPsfunctional Magnetic
Resonance Imaging

10
fMRI like time-lapse photography
11
fMRI ERPs

• Low Spatial Resolution
• High Temporal Resolution
• Sensitive to what sorts of cognitive processes
  active
• Good for studying cognitive processes that unfold
  rapidly in time

• High Spatial Resolution
• Low Temporal Resolution
• Sensitive to what sorts of cognitive processes
  active
• Good for mapping the brain

12
fMRI ERPs

• Low Spatial Resolution
• High Temporal Resolution
• Sensitive to what sorts of cognitive processes
  active
• Good for studying cognitive processes that unfold
  rapidly in time

• High Spatial Resolution
• Low Temporal Resolution
• Sensitive to what sorts of cognitive processes
  active
• Good for mapping the brain

13
Oddball Paradigm
14
P300
Beep.
Beep.
Beep.
Beep.
BOOP.
Beep.
Beep.
15
P300 bigger when stimuli are important to the
subject
16
P300 Component

• ERP component sensitive to probability and
  importance (or personal relevance) of a stimulus.
• Reflects updating of model of world in memory
• Orient to novel or important stimuli
• Keep track of how often such stimuli occur

17
What about unexpected language?
He
socks
spread
the
warm
bread
with
P300 to incongruous (nonsense) endings? Surprisi
ng stimulus
18
N400
Professor Hillyard
Professor Kutas
words, pictures, sounds
Kutas Hillyard, 1980
19
N400 measures processing difficulty

• N400 to anomalies in the middle of sentence as
  well as the end
• N400 smaller if a word is repeated (or if its
  primed)
• N400 smaller for frequent words than for rare
• In sensible sentences, N400 big for first words,
  smaller for later ones

20
Is N400 language-specific?

• I take my coffee with cream and

dog.
sugar.
21
N400 to words vs. pictures

• Similar type of ERP response
• Different topography suggests slightly different
  brain areas active

22
N400 to anomalous music?
Familiar
Unfamiliar

• Familiar vs. Unfamiliar Melodies
• End with Congruent Note, Diatonic Note, or
  Non-Diatonic note
• Bad notes elicit positive-going ERP like P300

Besson Faita, 1995
23
(No Transcript)
24
(No Transcript)
25
Is the P600 language-specific?

• Yes
• Language is innate
• Dedicated brain mechanisms for learning grammar
• Dedicated brain regions are devoted to processing
• Semantics (meaning)
• Syntax (grammar)

• No
• Ability to learn language derives from general
  learning mechanisms
• Brain response to grammatical errors is a subset
  of the brain response to improbable events

26
P300
27
Is the P600 language-specific?

• In one part of experiment, 80 of sentences
  grammatical, 20 ungrammatical
• Ungrammatical surprising
• In another, 80 of sentences ungrammatical, 20
  grammatical
• Grammatical surprising

Coulson, King, Kutas, 1998
28
Language ERP Components

• N400
• Sensitive to the difficulty of understanding the
  meaning of a word

• P600
• Sensitive to the grammaticality of words in
  sentences

29
P600 related to P300

• Brain areas sensitive to grammaticality similar
  to those sensitive to probability
• P600 related to P300
• Unusual grammatical events dealt with like other
  sorts of surprising events

30
Summary

• ERPs electrical brain activity associated with
  processing particular types of stimuli
• ERPs reflect post-synaptic potentials
• ERPs sensitive to different kinds of cognitive
  processes

• P300 component
• Elicited by surprising events
• Related to updating model of world in memory
• N400 component
• Elicited by meaningful stimuli
• Measures processing difficulty
• P600 component
• Elicited by ungrammatical stimuli
• Related to P300 component

31

32
The brain is a complicated place

• badagavatha

McGurk Effect
Sound-Induced Illusory Flash
what you hear
what you perceive
what you see

• beep
• beep beep

33

• If what you hear can influence what you see
• And what you see can influence what you hear
• Perhaps what you feel might influence some other
  aspect of cognition?

34
Some effects of mood on behavior

• People in a positive mood
• Greater life satisfaction (Schwarz Clore, 1983)
• More likely to help, more generous (Isen, 1970)
• Better judgments of neutral possessions (Isen,
  1978)
• More likely to think outside the box (Isen,
  1987)
• More likely to focus on global rather than local
  features (Fredrickson Branigan, 2005)

35
Some effects of mood on behavior

• People in a positive mood
• More words from longer word (Smith Larsen,
  1989)
• More (unusual) associations (Isen, 1985)
• Broader, more inclusive categories (Isen, 92,
  Murray, 90)
• Better at Remote Associates Task (Isen, 1987)
• worm, shelf, end BOOK

36
Thinking when feeling positive
Fredrickson Branigan, 2005
37
Semantic Relationships and the N400

• Sensitive to semantic processing
• Sensitive to semantic categorization

desk
kiwi
_
apple

0 200 400 600 800
ms
38
FRUIT
39
The N400 is sensitive to semantic CATEGORIZATION
Mood affects CATEGORIZATION
The amplitude of the N400 reflects the degree
of difficulty of the integration process
40

In CATEGORIZATION we would expect to see effects
of mood on the amplitude of the N400
41
Semantic Relationships and the N400

A kind of fruit
desk
kiwi
_
apple

42

• 10 female participants
• Musical mood induction
• Participants read sentences and performed a
  category judgment task

43
out
Yes or No?
The opposite of in
Yes or No?
pineapple
A kind of fruit
44
10 Female Participants- Positive Mood
45
10 Female Participants- Negative Mood
46
(No Transcript)
47
Context Matters
48

And now Katherine DeLong