Brain Asymmetry and the Processing of Native, Second, and...
Transcript of Brain Asymmetry and the Processing of Native, Second, and...
Brain Asymmetry and the Processing ofNative, Second, and Artificial Languages
Chuansheng ChenDepartment of Psychology and Social Behavior
University of California, Irvine
UCSD Cognitive Sciences 200, 11/13/2006
An International CollaborativeResearch Team
Prof. Qi Dong, BNU Dr . Gui Xue, UCLA
Li u Li , Li Ti an, Xue Feng
Ji ang Ti ng, Mei Lei l ei ,
He Qi nghua, BNU
Guo Yi , Hust on U.
Zhao Li bo, U. I owa
Dr . Kewei Chen, ASU
Dr . Yapeng Wang, BNU
Dr . Xi nl i n Zhou, BNU
Dr . Hongchuan Zhang,UCSD
Pr of . Zhen Ji n, B 306
Pr of . Danl i ng Peng,BNU
Zhang Lei , Zeng Yawei Zhen Dong, Li Ke, B 306
Outline I. Left-hemisphere dominance in language processing
– Two likely exceptions: Chinese, second languages
II. Special features of Chinese language and the righthemisphere– Reading (Study 1) and tone processing (Study 2)
III. Right brain and second-lang. (English) processing– Working memory (Study 3) and language switching (Study 4)
IV. Brain asymmetry and artificial language learning:– Visual words and phonological learning (Studies 5-8)
V. Overall conclusions and implications for theunderstanding of neural basis of language learning– Specifically, language-specificity, neural compensation, and
individual differences.
I. Hemispheric Lateralization of Language
About 95% of the total (Western) populationshows left hemispheric specialization forlanguage:– Almost all right-handed people– About 1/3 of the left-handed people
Left dominance may have resulted from theright-handed gestural system ofcommunication that preceded the origin oflanguage.
Two likely exceptions
Chinese language, because of itsspecial features
Second language, because ofcompensation?
II. What is special about Chineselanguage?
Pictographic Origins Tonal Addressed phonology
商 代 甲 骨 文 上 的 象 形 文 字
House Crossing Woods Eye
Cup set Tongue Hand Elephant
鼠牛 虎 兔
龙蛇
马羊
猴鸡 狗 猪
Mouse Ox Tiger Rabbit
Dragon Snake Horse Ram
Monkey Chicken Dog Pig
Neural Substrates for Reading
Fiez & Petersen, 1998
Left fusiform (labeledas Visual Word Form Area(VWFA))
– Words– Pseudowords (e.g.,
Joki)
Right fusiform– Faces– Pictures of objects
Hemispheric specialization:Words on the left, faces/pictures on the right
Tark
iain
en e
t al.,
200
2
What about (pictographic) Chinese then?
Stress vs. Tonal Languages
Two phonological units:– Segmental units (vowels, consonants)– Suprasegmental units (pitch, tone, stress)
English is a stress language: Stress does notprovide much lexical information. Tomato:toMAto, but no TOmato, tomaTO. (with a fewexceptions such as, CONtent, conTENT).
In contrast
Chinese is a tonal language. For example, 20 characters are pronounced
“ma”, with 4-6 characters for each of the fourtones.
Thus, tone is essential to the lexicalprocessing.
“Tones, like consonants, are listed in thelexicon as unit phonemes.” (Packard, 1986)
Separate neural systems for segmentaland suprasegmental units? If separate,does the processing of Chinese tonesrely more on right hemisphere fortone/music processing?
Addressed vs. assembled phonology Alphabetic languages typically have
assembled phonology, but some (e.g.,Italian,called shallow orthographies, Paulesu et
al.) are easier to assemble than others (e.g.,English, called deep orthographies).
Some logographic languages (i.e., Korean)use assembled phonology.
Chinese mostly uses addressed phonology-------------------------------- Assembled phonology: One can read/sound it
out a word without understanding it. Addressed phonology: One can understand a
word without being able to sound it out.
Ability to read aloud words
lower grade level grade level beyond grade level
Chinese
American
Lee,
Utta
l, C
hen,
199
5
The addressed vs. assembled phonology, however,is not expected to vary by hemispheres .
So is there evidence of a specialrole of the right hemisphere inthe processing of Chinese?
Past Research on Chinese
Hemifield Experiments– Some found right hemispheric dominance
(Cheng & Yang, 1986, Brain Lang.; Tzeng et al., 1979,Nature)
– Some found left hemispheric dominance(Besner et al., 1982, Brit. J. Psych.)
– Some found bilaterality (Fang, 1997, J. Exp Psych;Leong et al., 1997, Brain Lang.)
– Gender differences (with the foveal splitting method,Hsiao & Shillcock, 2005)
– There is a need to localize possible hemispheric asymmetry
Past Research (Cont’d)
ERP and fMRI Experiments
– All 20 studies found left hemispheric dominance inthe frontal region
– But with bilaterality or rightward lateralization inthe occipital and occipito-temporal regions.
Direct comparisons between the twohemispheres are needed to pinpoint thelocation of Chinese-specific processing
Study 1: Reading Chinese Characters Question: Which is Chinese-specific area in
the visual cortex? Hypothesis: Bilaterality or rightward laterality
occurs at the primary visual cortex, but wholeword processing is left lateralized.
Rationale: The visual cortex is hierarchicallyorganized:– Primary visual cortext (BA 17 and 18)
visuospatial tasks visual features of words– Higher-level visual cortex (BA 19 and 37) object
processing whole word recognition– Chinese is no longer a pictographic language.
Xue, Dong, Chen, Jin, Chen, Zeng, Reiman, 2005, Cog. Brain Res.
Hierarchical organization ofvisual cortex
Source: Riesenhuber & Piggo, 1999
Tasks
a “black [hei(1)]” and “white [bai(2)]” for thesemantic task
b “ticket [piao(4)] “ and “jump [tiao(4)]” for thephonological task.
Semantic Task vs. Fixation
Phonological Task vs. Fixation
Voxel-wise comparison
Original Flipped
Subtraction
Brain Asymmetry: Semantic Tasks
Brain Asymmetry: Phonological Task
Summary of Study 1 Our hypothesis was confirmed: significant
leftward asymmetry in the fusiform region(like alphabetical languages) but bilaterality inthe primary visual cortex (unlike alphabeticallanguages) for Chinese processing.
The right hemisphere appears to be importantfor the initial visual processing of the complexspatial features of Chinese characters.
Study 2: Chinese Tone processing Question: Where in the brain does Chinese
tone processing (suprasegmental) vary fromvowel processing (segmental)?
Hypothesis: Right hemisphere, possibly areasin the inferior frontal gyrus
Rationale: Tone processing resembles musicprocessing, which is right lateralized.
Previous research showed mixed results,perhaps due to single task and lack of directcomparisons between the two hemispheres.
Liu, Peng, Ding, Jin, Zhang, Li, Chen., 2005, NeuroImage
We used an adaptation paradigm (i.e.,keeping the tone constant but varyingthe vowel, or keeping the vowelconstant but varying the tone) and twotasks (pinyin and Chinese characters)to study the neural overlap ordissociation between tones and vowels.
Vowels Tones
Clear leftward laterality, but…
Differences between tones and vowels
Crosshair marks right inferior frontal gyrus.
Conclusion of Study 2
Left dominance in both vowel and toneprocessing.
Neural dissociation in tones and vowels forChinese, suggesting special neural bases(especially right IFG)for tonal languageprocessing (also see Gandour et al. Wang et al.).
Summarizing Studies 1 and 2 andstudies by others In general leftward lateralization for Chinese
processing (both visual words and sounds). Chinese tones and initial visual processing
showed right-hemisphere involvement (IFGand BA 17 and 18)
Thus, in all there are three main differencesbetween neural bases of Chinese and Englishprocessing: Right primary visual cortex, rightinferior frontal gyrus, and left dorsal lateralfrontal region (see next slide)
Based on meta images From: Bolger et al. (2005). Cross-cultural effect on the brain revisited. Hum. Brain Mapp
Green circles: occipitotemporal boundary: All languages [VWFA]Blue circles: dorsal inferior frontal area: all languages [motor/speech]Yellow circles: ventral inferior frontal region (more lateral for Japanese): alllanguages [speech]Red circles: superior posterior temporal and inferior parietal region: English andKana, but not Chinese and Kanji [graphophoneme conversion]Pink circles: Dorsal lateral frontal region: Chinese (and Kanji) [addressedphonology, not assembled phonology]Brown circle: Right primary visual cortex and right IFG: Chinese
rOTBSum
mar
y da
ta
rIFG
III: Right Brain and Second-Language Processing
There is much evidence that the rightbrain is involved in second languageprocessing, especially at the earlystages (e.g., nonfluent bilinguals).
But why is it important? Compensation?
Study 3: Second languageprocessing Working memory task:
Xue, Dong, Jin, Chen, 2004, NeuroImage
Red: Chinese
Green: English
Conclusions: Study 3 Similar working memory systems for native
and nonfluent second languages Greater activation in both hemispheres, but
especially the right hemisphere for thenonfluent second language.
Suggesting compensation?– Maybe, but with fluency confounded with L1 and
L2, it is not clear whether it is compensation orlanguage differences (L2 in the right hemisphere).A training paradigm is needed.
Other cognitive functions such as thoseinvolved in inhibiting L1? (especially theprefrontal areas for executive functions?)
Study 4: Language switching
ER design. Naming drawings of objects. Conditions:
– Switching: ChineseEng; EngChinese– Non-switching: Chi Chi; Eng Eng.
Wang, Xue, Chen, Dong, Xue. in press, NeuroImage.
Brain Region BA Coordinates z p
x y z
Frontal _Mid_R BA10 36 59 5 3.47 0.000
Frontal _Mid_R BA46
39 50 9 3.57 0.000
Frontal _Mid_Orb_R BA46
45 52 0 3.01 0.001
Frontal _Mid_Orb_R BA11
3 43 -12 3.45 0.000
Cingulum_Ant_R BA32
6 50 17 3.19 0.001
Occipital_Sup_R BA18
18 -89 27 3.36 0.000
Precentral _R BA 6 39 2 50 3.97 0.000
Frontal_Sup_Medial_L
0 29 46 3.72 0.000
Parietal_Sup_L BA 2 -33 -47 60 3.12 0.001
supraMarginal _ L BA40
-62 -36 35 3.15 0.001
Angular_L BA39
-42 -56 39 3.09 0.001
Temporal_Mid_L BA21
-62 -29 1 3.71 0.000
Brain regions activated by forward switching (Chinese English) relative tobackward switching (English Chinese).
Brain Region BA Coordinates z p
x y z
Occipital_ Inf_ R BA19 33 -85 -3 4.17 0.000
Lingual_R BA17 3 -73 -4 3.46 0.000
Cerebellum_L BA37 -24 -48 -23 4.21 0.000
Cerebellum_L BA19 -30 -62 -20 3.24 0.001
Fusiform_L BA37 -36 -59 -10 3.27 0.001
Precentral_L BA6 -33 5 36 3.29 0.001
Brain regions activated by backward switching relative to forward switching.
Study 4: Conclusions
When switching between Chinese andEnglish, executive control areas areespecially important. Much right hemisphereaction is due to that reason. Perhaps thatexplains to some extent the role of righthemisphere for second language processing
This study also confirmed some language-specific areas: Right occipital for switching toChinese reading and left temporo-parietalregion for English (assembled phonology)
IV: Brain asymmetry and learning anartificial language
To study the effects of language experienceon the neural bases of language processing--neural plasticity, especially the righthemisphere.
More specifically, to examine whether the roleof the right hemisphere is compensatory
Finally, to explore whether the left-right shiftcould be neurofunctional predictors oflanguage learning efficiency
Logographic artificial language (LAL) :Korean Hangul characters (in different fonts)
Mismatched sounds (those different from Chinese and English)
Arbitrary meanings (Chinese translation, picture)
Training
Study 5: Fusiform and visual wordlearning
Xue, Chen, Jin, Dong, 2006a. J. Cog. Neuro. Xue, Chen, Jin, Dong, 2006b. NeuroImage
Pre-Training Results: Fusiform AreaAsymmetry Index:
Chinese: .55
Korean: .21
(-1 = 100% right lateralization;
0 = bilaterality
1 = 100% left lateralization)
Preliminary conclusions:
Evidence of compensation (both right and left hemisphere)
Second-language is more bilateral
However, two challenges to these preliminary conclusions…..
Challenge #1
If the right hemisphere plays only acompensatory role, post-training resultsshould no longer show activation in theright hemisphere (provided that trainingis effective behaviorally as well asneurally).
Training Effects: BehavioralResults
70%
75%
80%
85%
90%
95%
100%
Before After
Corr
ect
Rati
o
Chinese
Korean
400
450
500
550
600
650
700
750
800
Before After
Rea
ctio
n t
ime
(ms)
Chinese
Korean
Training effects at the neural level
It appears that the right hemisphere may not simply play acompensatory role when processing a new language.
Why bilateral then?
Challenge #2: Individual Results
It appears thatbilaterality wasonly at the grouplevel. Mostindividuals werenot bilateral.
Furthermore, individual differences in AIwere stable across training sessions.
r =. 778; p < .005
If right hemisphere hadplayed a compensatoryrole, training shouldhave resulted inleftward laterality.
Leftward lateralization facilitated learning
Pretraining AI Post-training AI
Post
-trai
ning
per
form
ance
Also: A caution against interpreting correlation betweenbrain activation and learning as evidence of brain plasticity.
Regression Analysis: Predicting post-trainingperformance
Note: RT = reaction time, AI = asymmetry index, R2 = .75
Predictors B (s.e.) β t p
Pre-training RT .12 (.12) .17 .97 .36
Pre-training AI -100.3 (22.4) -.79 -4.47 .002
Summary of Study 5
The right hemisphere perhaps plays acompensatory role (as does the left hemisphere)initially, but its sustained activation may havemore to do with individual differences in learninga new language.
Individual differences in the brain asymmetryduring the initial processing of second languagepredicted later learning. In this case, the use ofthe left fusiform seems to facilitate the learningof visual forms of words.
Studies 6 - 8: Does Sex Matter?
Much evidence that in languageprocessing males show more leftlaterality, whereas females show morebilaterality (e.g., Hsiao & Shillcock, 2006; Kansaku et
al., 2000; Shaywitz et al., 1995). Does that affect the learning of a new
language?
Chen, Xue, Dong, Jin, Li, Xue, Zhao, Guo, 2006. Neuropsychologia
-1
-0.8
-0.6
-0.4
-0.2
0
D6 D7 D8 D9 D10
!"##$%&'(")*+"$,,(+($)'-
.
/
Male
Female
Similarly, in phonological training:
He, Li, Xue, Chen, Dong, under reviewMei, Chen, Xue, et al. in preparation
Individual differences in left middle temporal gyrus predicted listening comprehension
Six months later
Dong, Mei, Xue, Chen, under review
V. Overall Conclusions andimplications The processing of Chinese shows
mainly left-hemispheric dominance, justas that of alphabetic languages. Tworegions of the right hemisphere play aspecial role in Chinese processing: theprimary visual cortex for visual wordsand the inferior frontal gyrus forChinese tones.
Overall Conclusions cont’d The sustained right-hemisphere involvement
in second-language processing may haveless to do with compensation, more to do withlanguage switching and with individualtendencies to use one side of the brain whenlearning a new language.
Native-language-tuned brain facilitates theacquisition of a new language. Because ofsex differences in native language tuning (leftlaterality for males, and bilaterality forfemales), brain asymmetry differentiallypredicted learning for males and females.
Thank you for yourcomments & suggestions