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Right hemisphere sensitivity to word & sentence level context: Evidence From Event-Related Brain Potentials. Coulson, S. Federmeier, K.D., Van Petten, C., and Kutas, M. (2005) JEP: Learning, Memory, and Cognition. Gist . Question : Is right hemisphere message blind? Measurement : ERP
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Right hemisphere sensitivity to word & sentence level context: Evidence From Event-Related Brain Potentials. Coulson, S. Federmeier, K.D., Van Petten, C., and Kutas, M. (2005) JEP: Learning, Memory, and Cognition.
Gist • Question: Is right hemisphere message blind? • Measurement: ERP • Paradigm: associate priming without/within sentence context • Answer: RH is not message blind, but there is indeed hemispheric asymmetries in the use of word and sentence contexts
Message-blind RH --the hypothesis • LH has the ability to integrate syntactic, semantic, and pragmatic information to construct a message-level representation of meaning. • RH its language competence extends only to word-level priming mechanisms
Message-blind RH --why people made this claim? • LH • priming in RT to words embedded in normal or scrambled sentences (Faust et al. 1995) • Larger priming effect when the amount of context is increased (Faust et al. 1993) • Longer RT to words in implausible sentence context than plausible context (Faust, 1998) • RH • Contexts do not seem to facilitate or hinder the language process so…RH seems to be blind to these message level information..
Message-blind RH --however….. • LH • RH • Should be sensitive to some message level information, since when RH is damaged • patients cannot understand certain kinds of jokes, metaphoric language, and sarcastic utterances • Some studies did find sentence congruity effect in the RH (Chiarello, Liu, & Faust, 2001; Faust, Bar-lev, & Chiarello, 2003)
Ex1 [word level context effect] • Lexical association • Ex2 [sentence level context effect] • Lexical association • Sentence congruity
Experimental design (EX1) Primes are centrally presented, and targets are lateralized to either visual field (split visual field display).
PROCEDURE 1000~1200ms ++++ 200ms spare 0ms 200ms tire 300ms 2500ms ?
Prediction • Ex1[word level context effect] • Since both hemispheres are sensitive to word level info, similar-sized N400 context effects are expected
EX1 LVF/rh
EX1 LVF/rh N400 LPC
EX1 RVF/lh
Experimental design (EX2) The cloze probability were matched between the two types of congruous sentences (associated & unassociated) and also between the two types of incongruous sentences. This was done to ensure that the message level constraints are similar in the associated and unassociated conditions.
Prediction • Ex1[word level context effect] • Since both hemispheres are sensitive to word level info, similar-sized N400 context effects are expected • Ex2[sentence level context effect] • LH: • A large N400 congruity effect • Negligible effects of association • RH: (if the message blind RH model holds) • A large N400 association effect • Negligible effects of context congruity
EX2 LVF/rh N400 LPC
EX2 RVF/lh N400 LPC
Summary • word level: association effects for both LVF/rh and RVF/lh presentation • sentence level: robust congruity effects for both LVF/rh and RVF/lh presentation the message-blind RH model is not supported • At the sentence level, the congruity effect lead to a dramatic attenuation of the association effect. • Lexical context is less important in sentence contexts
unassociated Association effect associated Association effect unassociated associated 5 µV Congruity effect incongruous congruous
Summary • Although both hemispheres make use of word level as well as sentence level contexts, they seem to use them in different ways. • LH seems to make use of lexical association only when the sentence context is incongruous. • RH shows a smaller lexical association effect at the word level, which suggests that RH might be weaker to use this source of semantic context. • RH shows the association effect in congruous sentences there might be a greater reliance on word level relationships in the lexical integration processes in understanding sentences
Questions • Is the LPC the same thing as the P600? • Do blinks also produce surges that might overshadow brain activity on the EEG? • How common is subject attrition due to excessive artifacts? • Onset or peak? Which point is more interesting? In what situations would one or the other be the focus? • What if they ran their experiments on brain damaged patients ? • Why was a naming paradigm chosen for the target as opposed lexical decision? • Great Britain norms vs. US participants ….isn’t it problematic? • Is the hemispheric asymmetry in reliance on lexical relationships has to do with other abilities commonly associated with RH function (e.g., spatial abilities).