Event Related Potentials (ERPs):Event Related Potentials (ERPs):

What can they tell us about What can they tell us about

how we think?how we think?

Kim SweeneyKim Sweeney

COGS1COGS1-- Introduction to Cognitive ScienceIntroduction to Cognitive Science

October 23, 2008October 23, 2008

With thanks to Seana Coulson!

OverviewOverview

�� What are ERPs?What are ERPs?

�� ERP components:ERP components:

–– P300P300

–– N400N400

–– P600P600

�� What are they? When do they occur?What are they? When do they occur?

�� How can we use these components to How can we use these components to

investigate the workings of the mind?investigate the workings of the mind?

Event Related Potentials (ERPs)Event Related Potentials (ERPs)

Electroencephalogram (EEG) invented 1928Electroencephalogram (EEG) invented 1928

Early recording set-up Human Subject

Hans Berger

Electroencephalogram (EEG)Electroencephalogram (EEG)

�� We record the EEG by We record the EEG by

placing placing

electrodes on electrodes on

the headthe head

Info in raw EEG…Info in raw EEG…

Could that work?Could that work?

Neurons communicate with electrical signalsNeurons communicate with electrical signals

Summates Cancels outSummates Cancels out

EEG monitors alertnessEEG monitors alertness

Event Related Potentials (ERPs)Event Related Potentials (ERPs)

Characteristics of ERP componentsCharacteristics of ERP components

�� PolarityPolarity

–– Is it a positive wave or a negative one?Is it a positive wave or a negative one?

�� LatencyLatency

–– How long after stimulus presentation does it peak?How long after stimulus presentation does it peak?

�� AmplitudeAmplitude

–– How big is it?How big is it?

�� Functional SignificanceFunctional Significance

–– What cognitive (or perceptual) activity is it sensitive What cognitive (or perceptual) activity is it sensitive

to?to?

–– What makes it bigger or smaller?What makes it bigger or smaller?

What do ERPs reflect?What do ERPs reflect?

�� Sensory, motor, and/or cognitive events in Sensory, motor, and/or cognitive events in

the brainthe brain

�� SynchronousSynchronous activity of large populations activity of large populations

of neurons engaged in information of neurons engaged in information

processingprocessing

What are ERPs?What are ERPs?

�� ERPs are formed by averaging EEG timeERPs are formed by averaging EEG time--locked locked

to the onset of stimuli that require cognitive to the onset of stimuli that require cognitive

processingprocessing

�� ERPs represent electrical activity associated with ERPs represent electrical activity associated with

the processing of the stimulithe processing of the stimuli

�� ERPs can be related to different kinds of ERPs can be related to different kinds of

cognitive tasks, e.g. attention, memory, & cognitive tasks, e.g. attention, memory, &

language comprehensionlanguage comprehension

fMRIfMRI ERPsERPsfunctional Magnetic Resonance Imaging functional Magnetic Resonance Imaging

fMRIfMRI like timelike time--lapse photographylapse photography

fMRIfMRI ERPsERPs

�� Low Spatial ResolutionLow Spatial Resolution

�� High Temporal High Temporal

ResolutionResolution

�� Sensitive to what sorts Sensitive to what sorts

of cognitive processes of cognitive processes

activeactive

�� Good for studying Good for studying

cognitive processes cognitive processes

that unfold rapidly in that unfold rapidly in

timetime

�� High Spatial ResolutionHigh Spatial Resolution

�� Low Temporal Low Temporal

ResolutionResolution

�� Sensitive to what sorts Sensitive to what sorts

of cognitive processes of cognitive processes

activeactive

�� Good for mapping the Good for mapping the

brainbrain

fMRIfMRI ERPsERPs

�� Low Spatial ResolutionLow Spatial Resolution

�� High Temporal High Temporal

ResolutionResolution

�� Sensitive to what sorts Sensitive to what sorts

of cognitive processes of cognitive processes

activeactive

�� Good for studying Good for studying

cognitive processes cognitive processes

that unfold rapidly in that unfold rapidly in

timetime

�� High Spatial ResolutionHigh Spatial Resolution

�� Low Temporal Low Temporal

ResolutionResolution

�� Sensitive to what sorts Sensitive to what sorts

of cognitive processes of cognitive processes

activeactive

�� Good for mapping the Good for mapping the

brainbrain

P300P300-- The Oddball ParadigmThe Oddball Paradigm

Beep.

P300P300-- Amplitude. Surprise! Amplitude. Surprise!

Beep.Beep.Beep.BOOP. Beep.Beep.

P300 amplitude is greater when stimuli are P300 amplitude is greater when stimuli are

important to the subjectimportant to the subject

___ counting

----- reaction time

….. feedback

P300P300-- LatencyLatency

Synonyms of “prod” (20%) vs. other words(80%)“David” (20%) vs. “Nancy” (80%)

Male names (20%) vs. Female names (80%)

�� The harder it is The harder it is

to categorize a to categorize a

stimulus, the stimulus, the

longer the longer the

latency of the latency of the

P300P300

P300P300-- more than a “reaction time”?more than a “reaction time”?

�� RT very useful in RT very useful in

psychological researchpsychological research

�� RT includes (at least!)RT includes (at least!)

–– stimulus evaluationstimulus evaluation

–– response selection/executionresponse selection/execution

�� RT delayed by task difficulty, RT delayed by task difficulty,

e.g.e.g.

–– ‘noise’ in stimulus‘noise’ in stimulus

–– response incompatibilityresponse incompatibility

�� P300 latency affected by P300 latency affected by

noise, but noise, but notnot response response

incompatibility!incompatibility!

P300 ComponentP300 Component

�� ERP component sensitive to probability ERP component sensitive to probability

and importance (or personal relevance) of and importance (or personal relevance) of

a stimulus.a stimulus.

�� May reflect the updating of a ‘schema’ May reflect the updating of a ‘schema’

(model) of the world, incorporating novel (model) of the world, incorporating novel

information.information.

Hesocksspreadthewarmbreadwith

What about unexpected language?What about unexpected language?

P300 to incongruous (nonsense) endings?P300 to incongruous (nonsense) endings?

Surprising stimulusSurprising stimulus

N400N400

Professor Kutas

Professor Hillyard

Kutas & Hillyard, 1980words, pictures, sounds

N400 measures processing difficultyN400 measures processing difficulty

�� a) N400 to anomalies in the middle a) N400 to anomalies in the middle of sentence as well as the endof sentence as well as the end

�� b) sensitive to typicalityb) sensitive to typicality

�� c) to written & spoken words, and c) to written & spoken words, and to picturesto pictures

�� d) smaller if a word is repeated (or d) smaller if a word is repeated (or if it’s primed)if it’s primed)

�� e) smaller for frequent words than e) smaller for frequent words than for rarefor rare

�� f) In sensible sentences, N400 big f) In sensible sentences, N400 big for first words, smaller for later for first words, smaller for later onesones

Is N400 languageIs N400 language--specific?specific?

�� I take my coffee with I take my coffee with

cream and…cream and…

sugar.

dog.

N400 to words vs. picturesN400 to words vs. pictures

�� Similar type of ERP Similar type of ERP

responseresponse

�� Different topography Different topography

suggests slightly suggests slightly

different brain areas different brain areas

activeactive

How does the brain “do” language?How does the brain “do” language?

I like to eat frosting. Iliketoeatfrosting.

How does the brain “do” language?How does the brain “do” language?

I like to eat frosting.

IliketoI like to eat frosting.

How does the brain “do” language?How does the brain “do” language?

DeLong, Urbach and Kutas, 2005

Is music like language?Is music like language?

�� Familiar vs. Unfamiliar MelodiesFamiliar vs. Unfamiliar Melodies

�� End with…End with…

–– Congruent NoteCongruent Note

–– Diatonic Note Diatonic Note (wrong note, same key)(wrong note, same key)

–– NonNon--Diatonic Note Diatonic Note (out (out

of key)of key)

�� P300 sensitive to P300 sensitive to

–– How ‘bad’ the note isHow ‘bad’ the note is

–– How ‘good’ the listener is How ‘good’ the listener is

Besson & Faita, 1995

Familiar Unfamiliar

Musicians

Non Musicians

Besson et al., 2002

Is the P600 languageIs the P600 language--specific?specific?

�� YesYes

�� Language is innateLanguage is innate

–– Dedicated brain Dedicated brain

mechanisms for mechanisms for

learning grammarlearning grammar

�� Dedicated brain Dedicated brain

regions are devoted regions are devoted

to processingto processing

–– Semantics (meaning)Semantics (meaning)

–– Syntax (grammar)Syntax (grammar)

�� NoNo

�� Ability to learn Ability to learn language derives from language derives from generalgeneral learning learning mechanismsmechanisms

�� Brain response to Brain response to grammatical errors is grammatical errors is a subset of the brain a subset of the brain response to response to improbable eventsimprobable events

P300P300

Is the P600 languageIs the P600 language--specific?specific?

�� In one part of experiment, In one part of experiment,

80% of sentences 80% of sentences

grammatical, 20% grammatical, 20%

ungrammaticalungrammatical

–– Ungrammatical surprisingUngrammatical surprising

�� In another, 80% of In another, 80% of

sentences ungrammatical, sentences ungrammatical,

20% grammatical20% grammatical

–– Grammatical surprisingGrammatical surprising

Coulson, King, & Kutas, 1998

Language ERP ComponentsLanguage ERP Components

�� N400N400

�� Sensitive to the Sensitive to the

difficulty of difficulty of

understanding the understanding the

meaningmeaning of a wordof a word

�� P600P600

�� Sensitive to the Sensitive to the

grammaticality of grammaticality of

words in sentenceswords in sentences

P600 related to P300P600 related to P300

�� Brain areas sensitive Brain areas sensitive

to to grammaticalitygrammaticalitysimilar to those similar to those

sensitive to sensitive to

probabilityprobability

�� P600 related to P300P600 related to P300

�� Unusual grammatical Unusual grammatical

events dealt with like events dealt with like

other sorts of other sorts of

surprising eventssurprising events

The brain is a complicated placeThe brain is a complicated place

�� ““baba……dada……gaga……vava……thatha””

�� ““beep”beep”

�� “beep beep”“beep beep”

McGurk Effect

Sound-Induced Illusory Flash

what you hear what you perceivewhat you see

�� If what you hear can influence what you see…If what you hear can influence what you see…

�� And what you see can influence what you hear…And what you see can influence what you hear…

�� Perhaps what you Perhaps what you feelfeel might influence some might influence some

other aspect of cognition?other aspect of cognition?

Some effects of mood on behaviorSome effects of mood on behavior

�� People in a positive mood…People in a positive mood…

–– Greater life satisfaction Greater life satisfaction (Schwarz & (Schwarz & CloreClore, 1983), 1983)

–– More likely to help, more generous More likely to help, more generous ((IsenIsen, 1970), 1970)

–– Better judgments of neutral possessions Better judgments of neutral possessions ((IsenIsen, 1978), 1978)

–– More likely to ‘think outside the box’ More likely to ‘think outside the box’ ((IsenIsen, 1987), 1987)

–– More likely to focus on global rather than local More likely to focus on global rather than local

featuresfeatures ((Fredrickson & Branigan, 2005)

Some effects of mood on behaviorSome effects of mood on behavior

�� People in a positive mood…People in a positive mood…

–– More words from longer word More words from longer word (Smith & Larsen, 1989)(Smith & Larsen, 1989)

–– More (unusual) associations More (unusual) associations ((IsenIsen, 1985), 1985)

–– Broader, more inclusive categories Broader, more inclusive categories ((IsenIsen, , ‘92‘92, Murray, ‘90) , Murray, ‘90)

–– Better at Remote Associates Task Better at Remote Associates Task ((IsenIsen, 1987), 1987)

�� worm, shelf, end… BOOKworm, shelf, end… BOOK

Thinking when feeling “positive”Thinking when feeling “positive”

Fredrickson & Branigan, 2005

�� Sensitive to semantic processingSensitive to semantic processing

�� Sensitive to semantic categorizationSensitive to semantic categorization

“apple”

“kiwi”

“desk”

_

+

0 200 400 600 800 ms

Semantic Relationships and the N400Semantic Relationships and the N400

FRUITFRUIT

Apple

OrangeBanana

Kiwi

Pineapple

TomatoDesk

Eagle

The N400 is sensitive to semantic CATEGORIZATION

Mood affectsCATEGORIZATION

The amplitude of the N400 reflects the degree of difficultyof the integration process

In CATEGORIZATIONIn CATEGORIZATION

we would expect to we would expect to

see effects of mood see effects of mood

on the amplitude of on the amplitude of

the N400the N400

Semantic Relationships and the N400Semantic Relationships and the N400

“apple”

A kind of fruit…

“kiwi”

“desk”

_

+

�� 10 female participants10 female participants

�� Musical mood inductionMusical mood induction

�� Participants read sentences and performed Participants read sentences and performed

a category judgment taska category judgment task

A kind of fruit: pineapple

10 Female Participants10 Female Participants-- Positive MoodPositive Mood

10 Female Participants10 Female Participants-- Negative MoodNegative Mood

Context MattersContext Matters

SummarySummary

�� ERPs ERPs –– electrical brain electrical brain activity associated with activity associated with processing particular types of processing particular types of stimulistimuli

�� ERPs reflect postERPs reflect post--synaptic synaptic potentialspotentials

�� ERPs sensitive to different ERPs sensitive to different kinds of cognitive processeskinds of cognitive processes

�� P300 componentP300 component–– Elicited by surprising eventsElicited by surprising events

–– Related to updating model of Related to updating model of world in memoryworld in memory

�� N400 componentN400 component–– Elicited by meaningful stimuliElicited by meaningful stimuli

–– Measures processing difficultyMeasures processing difficulty

�� P600 componentP600 component–– Elicited by ungrammatical Elicited by ungrammatical

stimulistimuli

–– Related to P300 componentRelated to P300 component

Behavioral products- including ERPs- are interesting because they tell us something about the underlying processes!

Thank you!