ERPs in language acquisition Judith Rispens 25 September 2009 J.E.Rispens@uva.nl

Contents of presentation Introduction to EEG and ERP Designing an experiment ERP technique: what does it take to get an ERP component? ERPs and language acquisition: what components are there to investigate? Do’s and don’ts

EEG / ERP EEG: Electroencephalogram ERP: Event-related potential Neuro-imaging method for investigating neurophysiological correlates of language processing Different from fMRI and PET: high temporal resolution (but poor spatial resolution) Non-invasive technique Relatively cheap Can be used with infants, older children and adults

Electroencephalogram Record of electrical brain activity over time EEG constituted by neurons that polarise or depolarise simultaneously Activity measured at the scalp

Event-related potential: response to specific external stimulus Difference in voltage small, so many trials (+/- 50 trials) needed Signal is amplified These are averaged and extracted from the background noise of the ongoing EEG Event-related brain potential An estimate of the time-locked neural activity evoked by an external stimulus

Event Related brain Potentials Properties of ERPs Time-locked to external stimulus Negative or positive peak High temporal resolution (in ms) Measured at different positions at the scalp Scalp distribution of ERP components, but inverse problem: do not know the origin of the measured activity at the scalp fMRI research related to ERP components gives insight into localisation Techniques for spatial modelling (e.g. LORETA)

Event-Related brain Potentials Different linguistic stimuli elicit different ERP components Named after the polarity (negative / positive), latency, appearance at the scalp, or its function N400, P600, Early left anterior negativity (ELAN), mismatch negativity (MMN) etc.

Event-Related brain Potentials Properties of ERPs: Latency (in milliseconds) Onset of ERP component Peak latency Amplitude (in microvolt) Strength of component: indication of processing load Distribution At the scalp (but be aware of inverse problem)

Tools ± 50.000 € What does it take to get an ERP component? ERP software, e.g. Neuroscan Software to present stimuli, e.g. E-Prime Cap with electrodes (e.g. Easycap) Amplifiers Computers Subjects Stimuli Response box Headphones / speakers ± 50.000 €

Tools How does it work? Prepare scalp Takes around 15-30 minutes ‘scrub’ it with alcohol Put on cap Apply gel for conduction Apply electrodes Electrodes to measure eye movements / blinks Try to keep impedance less than 5 kohm Takes around 15-30 minutes

Experimental design Presentation of stimuli: Code the conditions, items and critical sections within your items so that you can track in the ongoing EEG the different responses to the different stimuli Carry out the experiment and record the ongoing EEG After the experiment you remove responses containing artefacts like eye-movements, blinks and head movements as this gives noise in your data Average stimuli of a similar condition May apply a filter to ‘clean up’ your data

Designing an experiment Think about: Auditory or visual presentation of stimuli Do you need a response to your stimuli (e.g. judgements)? If yes, make sure that the behavioural response does not interfere with the EEG recording Position of condition label within a word/ sentence * Hij heeft een gelezen Filler stimuli Around 20-50 items per condition Appropriate items for children (e.g. check age of acquisition) Position of target word in context: wrap up’ effect at sentence end may interfere with ERP component, better to have target mid-sentence

Designing an experiment Subject selection Minimum of 20 subjects Are demands on subjects feasible? Children are less able to sit still and trials with muscular movement need to be removed. Control for age, sex and handedness (in infants parent’s handedness) Children: standardised language tests to check language level in case of suspicion (> 2 years old) Children: screen family background for genetic risk of developing language impairment such as developmental dyslexia and SLI Spend time on subject recruitment: more difficult than behavioural experiments

ERPs and language acquisition Language related ERP components Mismatch negativity ELAN N400 P600 Keep in mind: Properties of ERP components may differ between adults and children due to physiological differences Makes it difficult to make comparisons between adult and child studies

ERPs and language acquisition Mismatch negativity (auditory perception) Index of the detection of a change in an acoustic signal. Can be used with non-speech and speech sounds Presented in ‘oddball’ paradigm: frequent and infrequent stimuli presented in a 9 : 1 ratio The deviant stimulus elicits the mismatch with the neuronal memory trace Between 150-200 ms after stimulus onset negativity at frontal sites Elicited without attention at stimulus No behavioural response is needed thus suitable for infant studies

ERPs and language acquisition MMN F2 electrode

ERPs and language acquisition Why would you study MMN? Investigate phoneme boundaries, auditory perception of sound qualities such as duration, pitch etc. Manipulate difference between sounds Present 90% of cases stimulus 1 and 10% stimulus 2 If infant discriminates between the two sounds, MMN is visible For infant and child studies: the MMN is different from that of adults. MMN preceded by an early positivity

ERPs and language acquisition Mismatch negativity Example of bak-dak experiment NWO project: investigating early precursors of developmental dyslexia Goal: investigate phoneme boundaries in infants of 8 weeks old at genetic risk of dyslexia. Hypothesis: auditory processing is compromised in developmental dyslexia

bak: - b-a dak: \ d \ a Van Beinum et al. (2005).

1 2 3 4 5 6 7 8 9 10 From BAK to DAK bak 1 bak 2 bak 3 bak 4 bak 5

ERPs and language acquisition Child listens for +/- 45 minutes to stimuli while sleeping

8 weeks old Control babies At-risk babies Van Leeuwen et al. 2006

ERPs and language acquisition Early Left Anterior Negativity (syntax) Around 150 ms after violation onset Violation of syntactic phrase structure elicits ELAN *Het meisje heeft in de geslapen *The girl has in the slept Automatic process (independent of task demands and attention) ELAN reflects highly automatic phrase structure building process

ERPs and language acquisition ELAN Example of experiment (Hahne et al., 2004) Goal investigate developmental pattern of ELAN Subjects: 6, 7, 8, 10 and 13 year old children Materials: a phrase structure error * the goose was in the fed (incomplete PP) The goose was fed

Results 6 year olds: no ELAN 7-10 year olds: sustained ELAN 13 year olds: ELAN comparable to adults

ERPs and language acquisition Conclusion: Conclusions Automatic adult-like structure building established quite late (13 years) in development and absent in early development (until 6 years) Question: sustained negativity a precursor of ELAN or does it reflect different processing mechanism?

ERPs and language acquisition N400 (lexical semantics) Negative wave after 400 ms of stimulus presentation most prominent at centro-parietal sites An index of semantic processing (e.g., Kutas & Hillyard, 1980) Semantically incongruous stimuli elicit greater N400 amplitudes than semantically congruous stimuli This reflects a greater effort at semantic integration for unexpected than expected stimuli The pizza was too hot to read

ERPs and language acquisition Example of experiment Friedrich & Friederici (2005) Goal: To investigate whether adult-like mechanisms of semantic integration, as indexed by N400, are present in 19-month-olds Task: picture-word-matching Congruous condition: picture-word match Incongruous condition: picture-word mismatch Subjects: 55 19 month-old German children

ERPs and language acquisition “ball” (congruous) “duck” (incongruous) “A…” Picture onset Indef. article Target word 0 ms 1000 ms 2000 ms 3000 ms 4000 ms

ERPs and language acquisition Results A broadly distributed long-lasting semantic incongruity effect 700-1400ms: incongruous words more negative than congruous words At centro-parietal & frontal sites Possibly more contribution from the left hemisphere The spatio-temporal distribution of the semantic incongruity in 19-month-olds differs from that in adults.

ERPs and Language acquisition Associated with syntactic reanalysis or revision Is triggered by (morpho-)syntactic violations and garden-path sentences Is affected by task demands, attention and frequency of violation: keep in mind when designing your experiment!! Centro-parietal distribution

P600

P600 Example of experiment Oberecker, Friedrich & Friederici (2005) Are the properties of the P600 component of 32 month old children comparable to those of adults? Latency, amplitude, distribution Experimental conditions: The lion roars (control) The lion in the roars (violation)

P600 Experiment failed…. Too many sentences (250) Too many blinks/movements Delayed response interfered with interpreting the behavioural data

P600 Experiment failed…. Too many sentences (250) Too many blinks/movements Delayed response interfered with interpreting the behavioural data

P600 Results: Conclusions: Different from adults as young children show very early positivity P600 present but with delayed latency Conclusions: 2.8 year old children comprehend simple sentences with a neural system similar to adults. The delayed latencies is taken to reflect a developing system

Some points of attention ERP infant research troubled by different sleep stages, sucking movements etc. ERP infant research troubled by movements, blinks etc. ERP children research challenged by the demands of sitting still Reliability of judgement data Infant skull is still growing and changing, makes it difficult to interpret data longitudinally ERP data in general unreliable at the individual level

Practical tips Ask parents to measure their children’s head before coming to the lab, so you can prepare the right size cap Ask children not to wear fleece sweaters Ask participants to have washed their hair before coming (no gel etc.) Ask participants not to wear expensive clothes as conduction gel may stain Let children watch cartoons during cap preparation Make a picture with a digital camera and give a print-out before leaving

Goodluck with your experiments!!!!!!! J.E.Rispens@uva.nl