Event Related Potentials (ERPs): A window onto the timing of cognition Kim Sweeney COGS1- Introduction to Cognitive Science November 19, 2009 With thanks to Seana Coulson and Katherine De Long!
Overview What are ERPs? How can ERPs be uniquely 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?
How does the brain make mind?
Neurons communicate with electrical signals
Electroencephalogram (EEG) invented 1928 Early recording set-up Hans Berger Human Subject
Could that really work?
Summates Cancels out
Electroencephalogram (EEG) We record the EEG by placing electrodes on the head Info in raw EEG
EEG monitors alertness
Event Related Potentials (ERPs) voltage Time
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. sensation, perception, attention, memory, language comprehension
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/smaller? Earlier/later?
What do ERPs reflect? Sensory, motor, and/or cognitive events in the brain Synchronous activity of large populations of neurons engaged in information processing
fmri functional Magnetic Resonance Imaging ERPs
fmri like time-lapse photography
fmri ERPs High Spatial Resolution Low Temporal Resolution Sensitive to what sorts of cognitive processes active Good for mapping the brain Low Spatial Resolution High Temporal Resolution Sensitive to what sorts of cognitive processes active Good for studying cognitive processes that unfold rapidly in time
fmri ERPs High Spatial Resolution Low Temporal Resolution Sensitive to what sorts of cognitive processes active Good for mapping the brain Low Spatial Resolution High Temporal Resolution Sensitive to what sorts of cognitive processes active Good for studying cognitive processes that unfold rapidly in time
P300- The Oddball Paradigm
P300- Amplitude. Surprise! Beep. Beep.Beep.Beep.BOOP. Beep.Beep.
P300 amplitude is greater when stimuli are important to the subject counting ----- reaction time.. feedback
P300- Latency The harder it is to categorize a stimulus, the longer the latency of the P300 David (20%) vs. Nancy (80%) Male names (20%) vs. Female names (80%) Synonyms of prod (20%) vs. other words(80%)
P300- more than a reaction time!! RT very useful in psychological research RT includes (at least!) stimulus evaluation response selection/execution RT delayed by task difficulty, e.g. noise in stimulus response incompatibility P300 latency affected by noise, but not response incompatibility!
P300 Component ERP component sensitive to probability and importance (or personal relevance) of a stimulus. May reflect the updating of a schema (model) of the world, incorporating novel information.
What about unexpected language? He spread the warm bread with socks. P300 to incongruous (nonsense) endings? Surprising stimulus
N400 Professor Hillyard Professor Kutas words, pictures, sounds Kutas & Hillyard, 1980
N400 measures processing difficulty a) N400 to anomalies in the middle of sentence as well as the end b) sensitive to typicality c) to written & spoken words, and to pictures d) smaller if a word is repeated (or if it s primed) e) smaller for frequent words than for rare f) In sensible sentences, N400 big for first words, smaller for later ones
Is N400 specific to words? I take my coffee with cream and dog. sugar. Ganis, Kutas, Sereno, 1996
Similar type of ERP response Different topography suggests slightly different brain areas active Ganis, Kutas, Sereno, 1996
How does the brain do language? I like to eat frosting. frosting. eat like toi
How does the brain do language? I like to eat frosting. I like to eat frosting. like toi
Prediction is important in many aspects of life
Is prediction important in language? A matter of timing- normal speech is ~3 words/sec! Benefits/risks of predictive language processing In sentence processing, what does it mean to predict? What exactly gets pre-activated? A phoneme? a part of speech? a meaning? a word?
The cat chased an orange butterfly.
English indefinite articles (a, an) Vowel-sound initial nouns an airplane an eagle an hour Consonant-sound initial nouns a kite a robin a watch
Experimental stimuli Because it frequently rains in London, Nigel always carries with him. an umbrella (high cloze) a newspaper (low cloze) DeLong, Urbach & Kutas, 2005
Experimental stimuli The day was breezy so the boy went outside to fly in the park. a kite (high cloze) an airplane (low cloze) If people are predicting a specific upcoming noun, then their expectations should be violated when they get the unexpected article! DeLong, Urbach & Kutas, 2005
e.g., The day was breezy so the boy went outside to fly Articles Nouns an airplane airplane < 50% Article Cloze < 50% Noun Cloze < 50% Noun Cloze
The brain predicts language Subjects anticipated the phonological form of a particular noun and therefore had expectations for a particular article type! Functional similarity of ERP effect at article and canonical (noun) N400
Is music like language? Familiar vs. Unfamiliar Melodies End with Congruent Note Diatonic Note (wrong note, same key) Non-Diatonic Note (out (off key) P300 sensitive to How bad the note is How good the listener is Familiar Musicians Non Musicians Unfamiliar Besson & Faita, 1995
What if note AND word are wrong? Besson et al., 2002
Osterhout & Nicol, 1997
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
P300
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
Language ERP Components N400 Sensitive to the difficulty of understanding the meaning of a word P600 Sensitive to the grammaticality (syntax) of words in sentences (among other things)
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
The brain is a complicated place McGurk Effect ba da ga va tha Sound-Induced Illusory Flash what you see what you hear beep what you perceive beep beep
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?
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)
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, (Isen, 92,, Murray, 90) Better at Remote Associates Task (Isen, 1987) worm, shelf, end BOOK
Thinking when feeling positive Fredrickson & Branigan, 2005
Semantic Relationships and the N400 Sensitive to semantic processing Sensitive to semantic categorization desk _ kiwi + apple 0 200 400 600 800 ms
Pineapple Eagle Banana Apple FRUIT Orange Desk Tomato Kiwi
Mood affects CATEGORIZATION The N400 is sensitive to semantic CATEGORIZATION The amplitude of the N400 reflects the degree of difficulty of the integration process
In CATEGORIZATION we would expect to see effects of mood on the amplitude of the N400
Semantic Relationships and the N400 A kind of fruit desk _ kiwi + apple
10 female participants Musical mood induction Participants read sentences and performed a category judgment task
The A Yes pineapple opposite kind out or of No? fruit of in
10 Female Participants- Positive Mood
10 Female Participants- Negative Mood
Context Matters
Summary ERPs electrical brain activity associated with processing particular types of stimuli ERPs reflect post-synaptic 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 Behavioral products- including ERPs- are interesting because they tell us something about the underlying processes!
The cat chased an enormous mouse.
Thank you!