Hemispheric asymmetries and joke comprehension

1. Hemispheric asymmetries and joke comprehension Coulson, S., & Williams, R. F. (2005) Neuropsychologia, 43, 128-141.

2. Background • Joke comprehension seems to include 2 parts: surprise and updating (frame-shifting) “I asked the bartender for something cold and full of rum, and he recommended …” a daiquiri = expected; fits context of bar and drinks his wife = unexpected; requires reevaluation of sentence context (cold + rum = bartender’s wife)

3. ERPS & Joke ComprehenisonCoulson & Kutas, 2000 • Are there 2 separate stages? • Recorded ERPs while participants read RSVP sentences that ended with either a joke or non-joke word (wife/daiquiri) • Why ERPs? • temporally precise: can examine timecourse of joke comprehension, specifically when surprise and updating stages occur, or if they are even separate

4. ERPS & Joke ComprehenisonCoulson & Kutas, 2000 • Stimuli • Jokes and non-joke controls were identical until final word • Joke and non-joke endings were matched on cloze probability (~3%) • They were further divided by the constraint of the sentence, or cloze probability of the most popular response • High constraint (> 40% cloze prob.) “She read so much about the bad effects of smoking that she decided she’d have to give up reading/thehabit.” • Low constraint (< 40% cloze. Prob.) “Statistics indicate that Americans spend 80 million a year on games of chance, mostly weddings/dice.”

5. ERPS & Joke ComprehenisonCoulson & Kutas, 2000 • Procedure • 200ms per word; 500ms for last word • Sentence followed with true/false comprehension question, to ensure correct interpretation of joke • e.g., “The bartender suggested a frozen drink” “The bartender’s wife was a frigid lush” • Responses were used to divide good comprehenders (avg. 83% correct) and bad comprehenders (avg. 64% correct) • All but one subject scored above 83% on non-jokes, so comprehension problems were only with jokes

6. ERPS & Joke ComprehenisonCoulson & Kutas, 2000 • Enhanced N400 for joke endings • Negative-going wave, peaking ~400ms • Distribution: broad, slightly right-lateralized, stronger over centro-parietal areas • Enhanced N400s typically associated with difficulty of lexical processing/ integration • LAN (left anterior negativity / sustained negativity) • Associated with WM demands and updating sentences

7. ERPS & Joke ComprehenisonCoulson & Kutas, 2000 • Effects varied with comprehension and constraint groupings N400 • Broader N400 distribution for poor comprehenders (distribution for good comprehenders more canonical) • N400 effects only significant for high constraint sentences LAN • Only present for good comprehenders, regardless of constraint

8. ERPS & Joke ComprehenisonCoulson & Kutas, 2000 Conclusions • Joke endings produced an N400 effect only in constraining sentence contexts • This seems to represent the surprise element of the joke ending • But the distribution varied, and the effect was stronger for poor comprehenders • Good comprehenders also showed a LAN • Seems to represent updating the sentence context • However, authors conclude that these 2 components do not support the 2-stage theory, because of temporal overlap

9. Evidence for hemispheric asymmetries? • Studies on unilateral brain damage have shown different deficits in joke comprehension • LHD (left hemisphere brain damage) => problems with recognizing the initial disruption • RHD (right hemisphere brain damage) => problems with updating the sentence context appropriately • Neuroimaging studies (fMRI) have shown increased activation in the RH (right hemisphere) during joke comprehension

10. Visual Half-field Paradigm Stimuli presented in one hemifield are received by contralateral hemisphere RVF (right visual field)[ LH (left hemisphere) LVF (left visual field)[ RH (right hemisphere) Subjects fixate centrally; stimuli are then presented to the left (left visual field: LVF) or to the right (right visual field: RVF) of fixation

11. Coulson & Williams, 2005: Design • Stimuli • Same as 2000 study, but now sentence-final joke word is presented to left or right of fixation • Also included expected filler items for comparison • Procedure • Read sentence word-by-word • When prompted, name final word (only correctly named words were included in analysis) • Answer comprehension question (>90%)

12. Coulson & Williams, 2005: Results • Predictability effects • Enhanced N400s for joke and non-joke endings, relative to fillers • Joke effects • For rvf/LH presentation, larger N400 for jokes than non-jokes • For lvf/RH presentation, no N400 differences

13. Coulson & Williams, 2005: Results • Jokes elicited a LAN – both VFs • Only present at one channel (F7) • Jokes elicited frontal positivity – both VFs

14. Coulson & Williams, 2005: Conclusions • Clear differences in how each hemisphere processes jokes • LH showed N400 differences, reflecting difficulty integrating joke ending • RH showed no difference, suggesting that it has no problem understanding jokes • Consistent with: • Coarse-coding • RH activates a broader array of semantic associates – more prepared for deviation from expected • LH has more fine-grained activation – more disrupted by deviation • Prediction / integration • RH builds a flexible context – able to accept unexpected items if they still make sense • LH rapidly builds context and tries to predict upcoming items – thrown off by contrasting items

15. DISCUSSION • Why are they not getting P600 effects? • Process of joke comprehension seems similar to garden-path processing – why are there differences • If N400 effect reflects recognition that the joke is inconsistent with current interpretation, why does it not show up for the RH at all? • If the LAN represents reevaluation, this must have been signaled by inconsistency

16. DISCUSSION • Given that level of constraint and comprehenders’ status was so important in previous study, why not divide into these groups again?