Brain Asymmetry and the Processing of Native, Second, and Artificial - PowerPoint PPT Presentation

Brain Asymmetry and the Processing of Native, Second, and Artificial Languages Chuansheng Chen Department of Psychology and Social Behavior University of California, Irvine UCSD Cognitive Sciences 200, 11/13/2006

An International Collaborative Research Team Prof. Qi Dong, BNU Dr . G ui Xue, UC LA Zhang Lei , Zeng Yawei Pr of . Zhen Ji n, B 306 Pr of . Danl i ng Peng, Zhen Dong, Li Ke, B 306 BNU Li u Li , Li Ti an, Xue Feng Dr . Kewei C hen, ASU Ji ang Ti ng, M ei Lei l ei , Dr . Yapeng W ang, BNU He Q i nghua, BNU Dr . Xi nl i n Zhou, BNU G uo Yi , Hust on U. Dr . Hongchuan Zhang, Zhao Li bo, U. I owa UC SD

Outline  I. Left-hemisphere dominance in language processing – Two likely exceptions: Chinese, second languages  II. Special features of Chinese language and the right hemisphere – 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 the understanding 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) population shows left hemispheric specialization for language: – Almost all right-handed people – About 1/3 of the left-handed people  Left dominance may have resulted from the right-handed gestural system of communication that preceded the origin of language.

Two likely exceptions  Chinese language, because of its special features  Second language, because of compensation?

II. What is special about Chinese language?  Pictographic Origins  Tonal  Addressed phonology

商 代 甲 骨 文 上 的 象 形 文 字 Eye House Crossing Woods Tongue Hand Elephant Cup set

Mouse Ox Tiger Rabbit 牛 虎 兔 鼠 Dragon Snake Horse Ram 马 龙 羊 蛇 Monkey Chicken Dog Pig 猪 狗 鸡 猴

Neural Substrates for Reading Fiez & Petersen, 1998

 Left fusiform (labeled  Right fusiform as Visual Word Form Area – Faces (VWFA)) – Pictures of objects – Words – Pseudowords (e.g., Joki)

Hemispheric specialization: Words on the left, faces/pictures on the right Tarkiainen et al., 2002 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 not provide much lexical information. Tomato: toMAto, but no TOmato, tomaTO. (with a few exceptions 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 four tones.  Thus, tone is essential to the lexical processing.  “Tones, like consonants, are listed in the lexicon as unit phonemes.” (Packard, 1986)

 Separate neural systems for segmental and suprasegmental units? If separate, does the processing of Chinese tones rely more on right hemisphere for tone/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 Chinese American Lee, Uttal, Chen, 1995 lower grade level grade level beyond grade level The addressed vs. assembled phonology, however, is not expected to vary by hemispheres .

So is there evidence of a special role of the right hemisphere in the 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 in the frontal region – But with bilaterality or rightward lateralization in the occipital and occipito-temporal regions.  Direct comparisons between the two hemispheres are needed to pinpoint the location 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 whole word processing is left lateralized.  Rationale: The visual cortex is hierarchically organized: – 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 of visual cortex Source: Riesenhuber & Piggo, 1999

Tasks a “black [hei(1)]” and “white [bai(2)]” for the semantic task b “ticket [piao(4)] “ and “jump [tiao(4)]” for the phonological task.

Semantic Task vs. Fixation

Phonological Task vs. Fixation

Voxel-wise comparison Subtraction Flipped Original

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 in the primary visual cortex (unlike alphabetical languages) for Chinese processing.  The right hemisphere appears to be important for the initial visual processing of the complex spatial features of Chinese characters.

Study 2: Chinese Tone processing  Question: Where in the brain does Chinese tone processing (suprasegmental) vary from vowel processing (segmental)?  Hypothesis: Right hemisphere, possibly areas in the inferior frontal gyrus  Rationale: Tone processing resembles music processing, which is right lateralized.  Previous research showed mixed results, perhaps due to single task and lack of direct comparisons 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 varying the vowel, or keeping the vowel constant but varying the tone) and two tasks (pinyin and Chinese characters) to study the neural overlap or dissociation 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 tone processing.  Neural dissociation in tones and vowels for Chinese, suggesting special neural bases (especially right IFG)for tonal language processing ( also see Gandour et al . Wang et al .).

Summarizing Studies 1 and 2 and studies by others  In general leftward lateralization for Chinese processing (both visual words and sounds).  Chinese tones and initial visual processing showed right-hemisphere involvement (IFG and BA 17 and 18)  Thus, in all there are three main differences between neural bases of Chinese and English processing: Right primary visual cortex, right inferior frontal gyrus, and left dorsal lateral frontal region (see next slide)

Summary data rIFG rOTB 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): all languages [speech] Red circles: superior posterior temporal and inferior parietal region: English and Kana, but not Chinese and Kanji [graphophoneme conversion] Pink circles: Dorsal lateral frontal region: Chinese (and Kanji) [addressed phonology, not assembled phonology] Brown circle: Right primary visual cortex and right IFG: Chinese

III: Right Brain and Second- Language Processing  There is much evidence that the right brain is involved in second language processing, especially at the early stages (e.g., nonfluent bilinguals).  But why is it important? Compensation?

Study 3: Second language processing  Working memory task:  Xue, Dong, Jin, Chen, 2004, NeuroImage

Red: Chinese Green: English