(I have been meaning to post this for about two weeks, so if it is a bit dated forgive me.)
Dyslexia is a learning disability characterized by slower reading skills acquisition, and it is associated with certain structural abnormalities in the brain. However, it turns out that different areas of the brain are affected depending on whether your language is alphabetic (like English) or symbolic (like Chinese).
Siok et al. present evidence in PNAS that English and Chinese languages utilize different brain systems and that as a consequence dyslexia presents differently in English and Chinese speakers.
Lots of research has gone into figuring out what parts of the brain look different in people who have dyslexia, and these studies have found that some brain areas associated with language do not activate in dyslexics as much as normal controls. Activation in these studies is measured using a technique called functional MRI -- a technique that measures brain activity by looking at the ratio of oxygenated to deoxygenated blood in a particular brain region.
Mostly, the areas of hypoactivation associated with dyslexia are in the back of the brain near the temporoparietal junction. However, most of these studies in dyslexics have had subjects who use alphabetic languages like English. Alphabetic languages show slightly different areas of activation than symbolic languages, so it is an interesting question to ask whether dyslexia affects the same regions in Chinese speakers.
To answer this question, Siok et al. put Chinese-speaking controls and Chinese-speaking dyslexics in the fMRI scanner. They tested the subjects on a task where they had to determine whether two simultaneously presented characters rhymed or not. The authors looked at the regions of the brain that were activated in both groups with an eye for regions that were not activated as much in the dyslexic group.
As expected, the controls performed better than the dyslexics in the rhyming task. In addition, the dyslexics showed regions of their brain that did not activate in the task as much as the control group.
The interesting part was that the regions of hypoactivation were different than those of English-speaking dyslexics. Below is a sample of their data. (Figure 2 from the paper).
(a) shows the averaged activation in red of the control group. (b) shows the averaged activation of the dyslexic group. See how the level of activation is substantially less. (c) shows the regions where the level of activation significantly different between the two groups.
The interesting part is that these are not the areas generally associated with hypoactivation in alphabetic language speakers. For comparison, I have altered the last panel of this figure below.
The red circle indicates the general area where hypoactivation is seen in English-speaking dyslexics. This is called the temporo-parietal junction. (The exact region varies between the studies I looked at.) Incidentally, it is also only on the left side of the brain. This is because language is lateralized in the brain, and it is generally in the left hemisphere. (To account for this issue -- right-handers have more predictably left-lateralized language functions -- most imaging studies of this nature exclude left-handers. This study is one of them.)
Before talking about the significance, it is important to discuss the following caveat: why did the activation differ? Was it because on average these areas in the dyslexic group were smaller than in the control group? The answer in this case is yes. The authors compared the gray matter volume of the left middle frontal gyrus -- the area showing the most hypoactivation in the Chinese dyslexics -- in both groups. They found that the level of activation postively correlates with gray matter volume. This suggests that this brain regions is less developed in the Chinese dyslexics, and it would account for the hypoactivation.
So why is this study significant? I think it is interesting for a couple reasons.
The first is that if you are going to treat dyslexia, these findings suggest that Chinese- and English-speaking dyslexics may require different types of training.
Much more interesting is what this results says about the existence of a "language module." From time to time, individuals observing the relative uniqueness of language to the human species have suggested that human possess a special language module in our brains that allows us to speak, read, etc. (Never mind that several animal species possess language-like behaviors.) This language module is posited to be specially evolved for the purpose of language.
This result suggests that if a single language module exists, it is significantly more subdivided and complicated than previously anticipated. You could even argue that these results suggest there are two somewhat separable modules, one for symbolic and one for alphabetic languages. Maybe if your native language isn't symbolic, you just don't use that area or use it for something else.
I think these results provide another reason to be skeptical of universal grammar. If a grammar is truly being enforced by the way the brain is structured, why would we expect two different brain structures to apply the same rules? The fact that symbolic and alphabetic languages possess similar grammars may be a consequence of utility rather than because they are biologically circumscribed to be that way.
Anyway, here is my crazy experiment idea to really confirm that there are two system for alphabetic and symbolic languages. Can someone who is fluent in both English and Chinese be dyslexic in only one language? I don't know enough about dyslexia to say for certain, but it would be really interesting to find out.
Siok, W.T., Niu, Z., Jin, Z., Perfetti, C.A., Tan, L.H. (2008). From the Cover: A structural-functional basis for dyslexia in the cortex of Chinese readers. Proceedings of the National Academy of Sciences, 105(14), 5561-5566. DOI: 10.1073/pnas.0801750105
- Log in to post comments
I am no expert on linguistics, but I don't like the expressions like "alphabetic language" and "symbolic language." I feel that the writing system is only a small part and very plastic part of a language. For example, you don't conclude that the Mongolian language is close to Russian simply because they both use the Cyrillic alphabet.
This is something I also commented on Greg Laden's post on the same paper, but I think this result makes a lot of sense if you compare this to studies on Japanese patients with alexia. Japanese uses combination of phonetic (syllabic, rather than alphabetic) characters ("hiragana" and "katakana", and collectively called "kana") and the logographic Chinese characters (called "kanji" in Japanese).
I will quote below a paragraph from Essentials of Neural Science and Behavior by Kandel, Schwartz, and Jessell:
"Because of these differences, one might expect that certain focal lesions would affect reading or writing in one system but not others. This is in fact the case. Both system rely on language centers in the left hemisphere, but each is processed by a different mechanism. Lesions of the angular gyrus of the parietal-temporal-occipital association cortex severely disrupt reading of katakana (phonetic writing) but leave comprehension of kanji (ideographic writing) largely intact. Such lesions can disrupt reading of kanji to some degree, but the disruption entails primarily phonetic processing; patients may be unable to read aloud the kanji word but can accurately explain its meaning. In contrast, these patients are unable to understand the same idea expressed in katakana."
I don't think this will necessarily threat the idea of universal grammar, because only reading and writing are affected.
Nice post. I find it interesting that we worry that something is out of date if it is a few weeks old! Why, back in the old days, they came up with something really new about every two thousand years...
A universal grammer works at the grammatical level - why would grammer be involved in dyslexia, which works at the grapheme level? I've never heard that dyslexics have any grammatical deficits, what they have are deficits in the formation of single words as graphical objects.
Maybe what this implies is that Chinese and Western dyslexia are not the same disease, but just syndromes produced by different diseases. Or that dyslexia is a more wide-spread disturbance of graphical processing than previously thought - other symptoms are much smaller so unnoticed.
Maybe this is the right blog and thread to ask:
What's "sheanut oil"?
http://www2.kelloggs.com/Product/ProductDetail.aspx?product=9270
"... Ingredients
WHEAT FLOUR, SUGAR, VEGETABLE OIL (PALM, SHEANUT, AND COTTONSEED OILS), MALTODEXTRIN, ...."
Argh.
http://en.wikipedia.org/wiki/Shea_butter
I was just being dysgooglic.
Now I wonder about dyscalculia, being dyslexic with numbers, what happenes to these people in relationship with their language.
I wonder if "alphabetic language" dyslexics compensate by acquiring reading skills that are more "symbolic." My son (who is dyslexic) reads wholes words and is confounded by sounding out. This might explain that phenomenon.
To add to my previous comment, I think reading involves figuring out how it sounds and what it means. I am guessing that, when reading Chinese characters, a reader processes the meaning somewhat independently of processing how the characters are pronounced. And that processing is carried out in a region of brain different from where phonetic characters (such as Roman alphabet or Japanese kana) are processed.
So, pxcampbell's comment is interesting.
Good point (though it doesn't really detract from the main results). The relationship between writing system and language is a pretty weak one, if at all. The Dungan language, which is closely related to Mandarin Chinese, is written in Cyrillic characters. Vietnamese used to be written in Chinese-like characters (Chữ-nôm) until Westerners came along.
So what happens if you teach an English-speaking dyslexic Chinese, or if a Chinese-English bilingual person has dyslexia? Would someone in this situation be dyslexic in one language but not the other?
I find this entire conversation fascinating. I had never thought about a left-handed vs. right-handed differential in a dyslexia/language-comprehension issue. Have there been any studies to find out if left-handers possess any language processing functions that might be beneficial to right-handers?
This is really interesting. As a student of the Chinese language and current resident of Beijing, I'd heard from a few people that there were no dyslexics in China, since, if you have a problem decoding them as linguistic symbols, the image center of your brain can pick up the slack. (Or something. My Chinese is OK, but not good enough to understand the details of the explanation.) So, it's really interesting to see that there is Chinese dyslexia, but it's clearly different.
Fascinating topic. Reminding me of a study (not dyslexia; not even reading/writing) I read about in the news maybe 30 years ago - wondering if any of you have heard of it. (These are my 30 year old, not very scientific memories of it.) Japanese-Americans were studied in two groups, those who were bilingual from before the age of 18 and those who learned English after that age. Two adjacent areas in the brain were identified, one for the Japanese language and one for English. The two areas overlapped in the subjects who'd been bilingual from a young age, but were separate in those who'd learned English later.
I've always wondered if this would be true also for two more similar languages, for instance two germanic languages.
Okay, so here's the thing. Logographic Dyslexia and Alphabetic Dyslexia - not only might they have different underlying brain structural abnormalities, but they may really be different disorders with somewhat similar behavioral patterns.
The core deficit in developmental dyslexia (alphabetic) seems to be phonological - that is, dyslexics have trouble converting the visual code to an auditory code at the level of the phoneme. Also, this impairment is characterized as "unexpected", in that the dyslexic individual has an average or above-average IQ. If they ALSO have language impairments, you're talking about a whole different story.
I'm not a reader of any logographic language, but my understanding is that the smallest "units" of written language are not at the level of phonemes, but are somehow larger. It may be an analogous disorder, in that there is trouble converting the written code to the auditory code, but it may be that it is not "phonological".
But it gets more complicated because there are even significant differences among alphabetic languages. German dyslexics typically have problems with automatic word recognition and reading speed, whereas English-language dyslexics typically have problems with decoding - even well compensated dyslexics have trouble decoding novel words (like crenidmoke or bufty).
Further, "dyslexic" is a sort of catch-all phrase to describe anyone who has trouble reading - but the fact is there are likely to be a number of "subtypes" (see Pennington (2006) in the journal Cognition) - and not merely defined by the reader's first language.
And we haven't even gotten into environmental effects yet (which just so happens to be the theme of my current research - environmental effects on brain structural development in good and poor readers).
Since logographic readers and alphabetic readers rely on different underlying subskills, it is not surprising to me that different brain regions would be recruited for the task. Whether or not different children would end up being qualified as dyslexic in different regions remains to be seen, I think. I think there are environmental factors at play which serve to amplify the underlying abnormalities, which would prove important in either type of language.
Also, if there is a phonological core deficit for alphabetic dyslexia, then logographic dyslexia (which may have a different core deficit) may indeed be a different learning disability altogether, with a different neurobiological characterization, and just similar behavioral presentation.
This somewhat disjointed comment is all to say that the picture is significantly more complicated than simply "logographic versus alphabetic dyslexia."
I'm a Chinese and English speaker, english is my second language though (I'm 20, been in US for 9 months now). I want to make the argument that it's NOT necessary that the brain regions connected to diff languages are different, but rather it's the regions connected to the ideas,which are better associated with our language are diff.
Well, I always felt that the way I learn english as a foreign language is actually from - reading chinese - the translated version of english text (surprise~, you can actually learn spanish from reading english translated text faster and easier). So languages are always more than just languages. Languages influence how you think and what you think. For example, I always felt my need to learn English is not that I want to, so I can come to U.S. and earn dollars (dollars suck these days anyway); but rather it's because I need to. A certain part of my growing experience, say, some childhood readings that influence my way of thinking , if not "in" english, is in English ideology, it's wearing the skin of chinese (NOT the real chinese, the flavor is changed), but it's a foreigner.
As a result, a certain part of my ideas can't be conveyed effectively, fully and natually without being conveyed in the language that I learned the ideas from. Language is not part of the culture, neither does the relation works the other way - it's rather that they reinforce each other to get to a point that they are co-exsisting in an optimal state. A certain school of ancient chinese philosophy can't be even explained in a introductory level in English, while I find the chinese version of high school physics are simply dull to reach the students (I become a physics major now that I'm here in U.S., which I NEVER could imagine because I used to hate science so much in high school, a little part of it is the mandatory way they are teaching it, big part is that I can't absorb the information originally as where they came from. I mean you learn theories, and then apply them to the problems at the back of the chapter, but how are you going to face a problem and use your own theory to explain them if you are just applying and not thinking...oops...where was I...oh, right, language)
anyway, I just got an A on my english paper (which is super hard, not the class, we are talking about a really hard grader), part of it is that I have limited amount of vocab pool, and actually many times I got the feedback saying my language is obscure, too ambiguous, not clear enough, devide this sentence into four sentences, my original paper is usually 2 to 3 pages, consistent with the concise and symbolic character of chinese. But actually in chinese literature, the ambiguity of language is like the medium grey tonality in chinese painting, a kind of eastern beauty describing the ambiguity of the real world itself, and my chinses teachers usually appreciate this kind of language, so whenever I have an idea, first of what I do is that I'll find the most BEAUTIFUL way to put it down, NOT the shortest way, nor the most quantitative way, nor the most economic way, northe most exciting, nor popular way - it's "high up there". chinese poem analysis always including a certain essay question surrounding the "mental scenery" of teh poem. it's like impressionism, in a very metaphysical way. And the highest level of the chinese literature is that the poem can express it in such a surprising fashion, seemingly unbelievable mental phenomenon occurs, but if the readers put themselves in the situation they would notice that it's the only reasonable way the poet could respond. I would say to english translated chn poems, they are not poems, they are half-blood weirdoes.
what gets me real headache is that when we are supposed to write a sonnet, a real strictly metered and rhymed sonnet. Here is what I will do: think of an idea, starts the rhyme, go to dictionary and thesaurus.com, and start to look up words that I want to write down and check spelling. then I will get stuck becase my ideas are in chinese (I learn by far 98% of the greates poems in chinese, sorry, english poems, you guys are sometimes too direct), then I'll go to chn-eng dictionary, and 90% of the chance I CANT find the right word, if I fidn it I need to stick it to the context/phrase and then google it, see if there has been more than 10 people using the whole thing(I have low standard), while typing in oxford eng dic, and look for its REAL meaning (chn-eng is really my lsat choice). So it was a tedious process, but I do learn how to express my chinese ideas in a kind of popular way that can get through. My professor say my poem was "funny", so I guess humor is the universal language? But anyway, the "dividing this sentence into a paragraph" actually sounds very so familiar to me - that's what my high school teachers some time have to alarm me (although they appreciate some remarking ones, but soemtimes I cross the line), that I convey already sophisticated ideas in sophisticated sentence structure.
In terms of reading, I guess I have my own stubborn pace, if I go any faster, I can't understand it, it got carried on to english now, that I can say I passed the process where you go word by word like a foreign speaker/learner, I now know how and when to skip text, just as I can do in chinese. People inserts crappy argument at some pretty universal place in their articles, (I don't know, if it's called the "bs" type of gene in genome). so I felt that I appraoch the symptotes of my reading pace now in english. I sometimes read chinese, although ancient text that I need to work very carefully through.
what really gets me mad is the speaking. most of the time, I know what I was thinking that I just can't find the right way to put it. it's not neccesarily in chinese, because even if I think in chinese, that won't get me the eng expression through. Adn whenever that occurs I felt like a complete outcast, not because I felt like I become antisocial, it's like I'm not appreciated, my argument is not appreciated. And this whole madness is NOT caused by limitation in english, it's my personal problem, I had that before in chinese as well! THE SAME AS READING AND WRITING!
so it's actually not the language that gets in my way. but rather I inherit my weakness or strength in readings, writings, speaking, which I would take as the REAL language skills; but my analytical approaches, philosophical ideas, and understanding of human condition and so forth, are enriched by the broadening of language. So there is actually no surprise that diff parts will be light up, because I would describe how I function from forming an idea to actually spitting it out, in either language: some large proportion of my expression are of memory and events occured (stories, tv shows), they are consist of imageries in my brain. I would then use the language I need to use in the circumstance, to describe the picture as much as I can. When summarize it, based on different emphasize of my feelings, response, and analysis to this certain event, I will prefer to think in a certain language, whichever conveys it in the most natual way, interms of other experience, cultural theme, and other stereotypes which we all have. Then when this notion in this language is formed, I will then either say it in this language if it is allowed in the situation, or I will transform it to another picture, a similar condition, similar process, similar analysis to a similar topic, but I'm sure I learned the scenario in the other language, after confirming the similarity between these two images which correspond to two similar experiences in two languages, is below the accepted limit, I will then use the language that I had experienced the second picture in, to describe what is going on.
quite fascinating, ain't it?
Thanks for this terrifically interesting post and exchange of comments. The work I know of in Japanese, where there are both character-based and pronunciation-based systems working at once, suggest not only different patterns of dyslexia as compared with those who learn only alphabetic languages but different patterns among those who, in the under-70 generation, are allowed to remain lefthanded. There are also very different rates of diagnosis, but this goes to a point made by other commentators here that the issue may be less neuroanatomical than categorical. The term "dyslexia" is a symptom (like "chest pains") and not really a pathology or diagnosis in a strict sense and the term is deployed quite differently (and more circumspectly) in Japan than in the U.S. (where the use is most loosely applied and the rates are highest). It's also interesting what the younger generation texting will do, in Japan, with reading disabilities given that texting is left to right horizontally whereas other forms of reading are right to left vertically. There is much speculation about this esp as five of Japan's bestsellers currently are novels that were originally written for cell phones and are horizontally printed, left to right.