Handedness, hemispheric asymmetries, and joke comprehension

Seana Coulson, Christopher Lovett

Marianna’s questionMy questions this week concern the tests administered to the participants in

order to classify them into groups.First, regarding the handedness assessment test, the authors mention that the handedness scale ranges from -100 to +100 (completely left-handed to completely right-handed respectively). Their groups of participants seem to be unbalanced along this scale (left-handers: -51, right-handers: +71). Is this an important difference? Could this affect the results in any way? At some point, in the results discussion, they mention that some of the left-handed women had left-handed relatives. Is this included in this handedness assessment test?

I was also interested in knowing more about the semantic relation test they used to determine participants' verbal ability. What does this test consist in? Is it a typical test administered to determine verbal ability scores? Why do women perform so poorly?

Lynn’s question

• The experimenters presented a comprehension question at the end of each stimuli sentence. They do not report (or perhaps did not record) the reaction time it took the participants to answer the comprehension questions. If they had reported reaction times to the questions would speed of processing diffferences been revealed between right and left handers, or males and females or between the high and low vocabulary groups? It would be helpful to see if some kind of behavioral measure correlated to the ERP results they report.

Albert’s question• Understanding jokes is as easy as understanding the N400 component.

I quote from page 281-282, "Typical of ERPs to visually presented words, all stimuli elicited N1, P2, and N400." I might be misunderstanding this but this seems to say that all words elicit an N400. What I am missing?

Our general understanding of the N400 component is that there is a large negativity around 300-500 ms in response to a word which is syntactically appropriate but not semantically appropriate. I think that their stimuli was trying to elicit the N400 on the Joke set and the Straight set but not the Expected set of sentences. The graphs seem to indicate that there is a N400 for most of the Jokes and Straights. The authors seem to be surprised that the N400 was larger for the Joke set only for subjects with low verbal ability (Previous research suggested so).

Pawel’s question• The authors say that a possible reason for the differences for

handedness and sex are due to unequal corpus callosal areas. Might ahalf-field ERP study be a good way to test this claim? The sentence finalword that determines if a sentence is a joke or not could be lateralized andthen the responses for LVF/RH and RVF/LH for each each type ofhandedness/sex could be compared to each other. So, could this flesh outwhether the differences observed were due to inter-hemispheric transfer orinherent hemispheric asymmetry?

Israel’s question• Hi everyone,

Here are my questions/comments on this week's article:

In the data analysis, the authors say that they rejected artifacts such as ?excessive muscle activity?. Does this "activity" refer to laughter, since we are dealing with joke comprehension? In the same line, isn't laughter such a big artifact that it could potentially ruin a large proportion of the trials? Another issue related to joke comprehension is that there may be variability among participants regarding what they find funny. That is, they may understand that the sentence they are presented with is a joke, yet they may not find it funny. Would we expect a different reaction to jokes that are perceived as funny and those that aren't?

Finally, I had trouble understanding how they decided, from the comprehension questions, whether people understood the jokes or not. The example they gave is:

??Every time I wear my spring coat in the rain, it damages the springs.??Comprehension sentence: ??Water isn?t good for my coat.?? Correct response: YES.

I don't see how they need to understand the joke in order to answer this question, they could simply be relying on general world knowledge (e.g. Rain is not good for coats).

See you on Tuesday!Israel

Introduction• Lateralization: despite anatomical similarity,

hemispheres play different roles in language production and comprehension.

• Evidence from aphasics & experimental studies: – LH: basic aspects of production and comprehension– RH: social appropriateness monitoring, tangential

speech, nonverbal cues, overly literal interpretation, sarcasm, inference in joke comprehension

Handedness and hemispheric asymmetry for language

• This pattern presupposes right-handedness (90%)• Broca assumed pattern would be reversed in LH• In reality, LH more likely to display “atypicality”. • Wada test

– RH: 92 – 99% LH dominant for language– LH: 85% LH, 15% RH/Bilateral

• fMRI– RH: 96% LH, 4% RH– LH: 76% LH, 10% RH, 14% Bilateral

• rTMS– RH: 87.5% LH 4.2% RH, 8.2% Bilateral– LH: 73.7% LH, 10.5% RH, 15.8 Bilateral

Knecht et al (2000) found near linear relationship between the degree of handedness (Edinburgh Inventory) and language lateralization (transcranial Doppler sonography) during a word generation task. RH dominance more likely in LH, and those with at least one LH parent.

Handedness and ‘right hemisphere’ language processes

• Handedness impacts fundamental processes such as production and comprehension.

• What about high level language processing? – Joke processing requires constructing mental model and then “frame-shifting” to

undergo a semantic reanalysis– Difficulty with joke comprehension associated with RH damage

• Kutas & Coulson (2001) found left lateralized sustained negativity (500-900 ms), N400, and later posterior positivity in people who got most of the jokes. – If N400 reflects processing difficulty, why not found in the people who didn’t get the

jokes? • People with poor comprehension: only right frontal negativity (300-700 ms) to

jokes. ERP effects tended to be lateralized, suggesting contributions of one hemisphere

more important

Present study

• Investigate the consequences of bilateral language representation in processing of jokes (thought to recruit right hemisphere in RH)

• Record ERPs as left & right handers read one-line jokes • Hypothesis: – If LH brains are more laterally symmetric than RH brains,

might expect to see less lateral asymmetry in LH’s brainwaves. If joke comprehension is unrelated to language lateralization, we might expect similar ERP effects in both LH and RH subjects.

Participants32 UCSD Undergrads (16 F) Received cash or experimental credit16 Left-handed (LH) (8 F) 6 LH participants had a LH immediate family16 Right-handed (RH) (8 F) member (4 F).

Handedness assessed via Edinburgh InventoryAverage Laterality Quotient: LH = -51, RH = 71Monolingual native English speakersNormal vision, no history of reading or neurological difficulties

Battery of verbal ability tests used to divide participants into groups of high and low verbal ability within each handedness group

Marianna’s questions:Familial sinistrality, Semantic Relations Test, Laterality Quotients

Methods• Each participant read 240 sentences

– 80 jokes (e.g., A replacement player hit a homerun with my girl)– 80 straights (e.g., “A replacement player hit a homerun with my

ball”)– 80 expecteds (e.g., “My green car blocked the narrow driveway”)– Each participant read 240 sentences

All participants saw the same fillers, but the 160 pairs of experimental sentences were in 2 different lists, so one group saw the straight versions of the other group’s jokes and vice versa.

Published word association norms: joke and straight endings equally surprising

Sample experimental stimuli

Israel’s questions:

• Excessive muscle activity = laughter = artifact?• Variability in sense of humor – differences in waveforms?

Procedure• Electrically shield, sound attenuated chamber• Rapid serial visual presentation (200 ms/word)• Asked to read for comprehension• After each sentence, a comprehension sentence presented and

asked to judge whether (Y/N) consistent with previous item• Items preceded by fixation cross • Inter-stimulus interval varied as function of world-length (i.e.,

200 ms + 32 ms/character)• Blank screen for 2500 ms between target sentence and

comprehension sentence• Comprehension sentence (4 s), then blank screen (2 s) before

next trial

EEG Recording

• 29 tin electrodes in Electro-Cap• Referenced to left mastoid• 10-20 sites: FP1, FPZ, FP2, F7, F3, FZ, F4, F8, FT7, FC3, FCZ, FC4, FT8,

C3, CZ, C4, TP7, CP3, CPZ, CP4, TP8, T5, P3, PZ, P4, T6, O1, OZ, O2. • Eye moments monitored via bipolar montage of electrodes placed

at outer canthi• Blinks monitored via electrode placed on infraorbital ridge of right

eye and referenced to left mastoid• EEG also recorded at right mastoid, and all data were re-referenced

and averaged to the average of the left & right mastoids. • Electrode impedances kept below 5kΏ• EEG processed through SA Instrumentation amplifiefiers set at a

band pass of 0.01-40 Hz, and continuously digitized at 250 Hz.

Data analysis• Visual inspection, trials rejected when contaminated by artifacts

(excessive eye moments, muscle activity, amplifier blocking, drift)• Participants with >40% rejection rates were excluded (4 LH, 3 RH).

• ERPs computed for recording epochs from 100 ms pre-stim onset baseline to 920 ms post-onset.

• Averages of artificat-free ERP trials calculated for each type of target word (jokes, straights, expecteds)

• Quantified using mean amplitude of waveforms 300-500, 500-700, and 700-900 ms post onset relative to the baseline.

• RM ANOVA – Between variables: Handedness, verbal ability, and sex – Within variables: Ending, hemisphere, and anterior/posterior scalp site. – Huhyn-Feldt correction

Percent correct on comprehension questions (standard error)

Trials for which comprehension judgment task incorrectly answered not included in ERP data analysis.

Lynn’s QuestionThey do not report (or perhaps did not record) the reaction time it took the participants to answer the comprehension questions. If they had reported reaction times to the questions would speed of processing diffferences been revealed between right and left handers, or males and females or between the high and low vocabulary groups? It would be helpful to see if some kind of behavioral measure correlated to the ERP results they report

Example may be bad one, but even so, what if comprehension question clarifies joke to those who didn’t understand initially – difference between initial reaction and slightly later comprehension

Israel’s QuestionEvery time I wear my spring coat in the rain, it damages the springs.Comprehension sentence: Water isn’t good for my coat. Correct response: YES.

I don't see how they need to understand the joke in order to answer this question, they could simply be relying on general world knowledge (e.g. Rain is not good for coats).

Results • Sustained negativity 500-900 MS Right Handers (RH) • ERPs to jokes slightly more negative than to straights on central & parietal endings among left-handers (C3, C4, P3, P4)

•Left-handers appear more bilaterally symmetrical

Albert’s question: "Typical of ERPs to visually presented words, all stimuli elicited N1, P2, and N400."

-Amplitude sensitive to semantic violation? -Semantic integration-General wrap up & decision making at end of sentence-Not sensitive to negation• “A robin is a bird” vs. “A robin is a tree”• “A robin is NOT a bird” vs. “A robin is NOT

a tree”

• Interaction of ending & anterior-posterior factor: ERPs to jokes slightly more positive than straights of prefrontal sites (FP1 and FP2) and more negative than straights over central & parietal sites. Posterior negativity thought to reflect the N400.

• N400 best seen low verbal ability, left-handers P3 & P4 sites. • Greater bilateral symmetry in left-handers

•Right handers: negative-going ERP effect only over anterior left lateral sites, distinct from N400 effect.

Late Positivities

• Late positivity in males

• Late positivity broader and more bilaterally symmetric in LH females • Larger corpus callosal areas more efficient inter-hemisphere communication?

•Pawel’s question: •Inter-hemisphere communication, or hemisphere asymmetries? •Half-field ERP study

• Coulson & Kutas (2001): larger amplitude N400 to subset of jokesCurrent study• Only observed in low verbal ability left handers. • Right handers: negative-going effect only evident only left lateral electrode

sites – distinct from N400.

Absence of strong N400 joke effect:• Low vs. high constraint jokes

• High: “I asked the hostess if she remembered me from the party last year, and she said she never forgets a face/dress”

• Low: “My husband took all the money we had been saving to buy a new car and blew it at the movies/tables”

• 30% joke stimuli led to a joke “set” that facilitated processing of jokes that may have reduced N400 effects.

DiscussionNegativity: 300 – 500 ms

Discussion:Late Positivity

• Jokes elicited more positive ERPs than straights, but differed as a function of handedness & sex.

• Left-handed women, expected to have largest corpus callosal areas, show most laterally symmetric ERPs, other groups show largest late positivity to jokes over the right hemisphere.

• Sex confounded by familial sinistrality – 4/8 F had LH relative; only 2/8 M

• Remote possibility that ERP effects come from skull thickness, or cranial differences – requires further examination with electrophysiological & radiological techniques

• Coulson & Kutas (2001): jokes elicited sustained anterior negativity 500-900 ms over left lateral electrode sites, argued to index frame-shifting necessary to get a joke because evident in both high and low constraint jokes, and absent in ERPs from poor joke comprehenders.

• Effect found in right handers, but missing from left-handers despite equivalent comprehension performance. Instead, waveforms from left and right anterior sites symmetrical, suggesting different, bilateral processes in left handers.

Discussion:Sustained anterior negativity