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Neuronal Recycling Hypothesis: 4. Letterbox

2010/01/18 at 5:59 pm | Posted in Cognition, Reading, Thought | Leave a comment

Letterbox and the related cortical regions.

Below: The red region is the core of the neural recycle hypothesis - letter box.

At the 2009 X’mas Eve, Hsuan Chih Chen from Hong Kong Chinese University gave a talk to the fellows in the Dong Hwa University. During the dinner with Prof. Chen, I met Peter who is teaching at the department of life science of Dong Hwa University. He shared his astonished experience on learning Chinese which have made him suspect that Chinese ancestor created reading before writing contrary to that Indo-European created writing before reding. Coincidently I have learned Plato’s academy been the landmark that the western societies were beginning to accept the silent reading as a meaningful activity from Steven Fisher’s book “A History of Reading“. At that era, Chinese society have steped into “literatural” world. Until now we still have little clues to answer why did Chinese have the reading ability ealier than the western societies. Dehaene have suggested either Chinese or western readers depend on the same neural circuit for reading their own words.

That the left occipito-temporal region has been identified as “Letterbox” synthesizes the magnetic resonance imaging (MRI) data of the patitents suffered by the pure alexia. This reading deficit causes the readers percieve the string of letters as single visual feature rahter than a “complete” word. Letterbox exchange the information with the visual area, the region analyze the input visual information, and transfer to the meaning pathway and the phonological pathway. In the comparisons among the neuro imaging literatures, Dehaene and his colleagues concluded that the “letterbox” burden the responsibility to initiate the reading pathways across languages. More than the discoriveries on human readers’ brain, he figures out that the apes have the perception to detect the “proto-letters”, the visual stimuli have the shape as similar to strokes of the mordern letters. Many evidence have shown that the neugral circuits sponsering the apes’ perception are close to the letterbox in the human brain. In the summary of the functions and locations of this region across normal readers, reading deficit, and the apes, Dehaene propose his “bold” neural recylcing hypothesis. Our brain adapt the function of the neural circuits for percieving some specoific shapes to the function for reading words.

It is still a “hypothesis” because there are many mysteries amid the pathway between letterbox and visual area and more amid the connections among the other regions distrubited among the reading pathways. In addition, the modular scheme that Dehaene used to speculate his reading pathways is under debate till present and hard to see the end in a expectd future. The following comments will discuss these issues, and my introduction works temporarily stop here. It is joyful to finish this work just two days before Dahaene gave his talk about this book to Taiwan.

Neuronal Recycling Hypothesis: 3. Two Routes in Reading

2010/01/08 at 8:11 am | Posted in Cognition, Reading, Thought | Leave a comment

How amazing you can find the word you are reading in your brain!

Before the end of 2009, The New York Times publshed the book review composed by Alison Gopnik. This book obviously touch the popular thought about reading and the education of reading in the western societies. Now let’s understand what is the “perfect reading” to survive in this mordern civilized society. In other words, what is the nature of reading ability.

The creation of words began from two purposes for human societies: the restore of the speech and the consolidation of meaning. One is the record of communication among people, and the other is the comprehension about this world. Reading is the activity to restore the speech and the meaning the words carry. Traditionally researchers of reading equate both functions and prefer an overall accounting for them in a model. Every model of reading illustrates the route from orthography to phonology and the route from orthography to semantic. The difference between models is the combination and sequence of processing components in one route.

Dehaene certainly suggests that these routes have been “written” in our neural circuits. Our genes which were selected by the neutral selection offer us the limited amount of the raw circuits for the making up of cognitive system supporting our life. Individual learning experience has adjusted the circuits since our birth. In a civilized society, everyone eventually acquire a sound route and a meaning route in brain. According to the summary of Dehaene, the sound route includes the brain areas such as the superior temporal gyrus, middle temporal gyrus, supramarginal gyrus, and the inferior frontal gyrus (pars opercularis); the meaning route includes the brain areas such as the middle temporal gyrus, basal temporal region, and the inferior frontal gyrus (pars triangularis). All of these brain areas locate in our left hemisphere which is consistent with the well known left-hemisphere hypothesis of language. Both routes share a boost mechanism located in the left occipito-temporal region. Dehaene called this region “letterbox”. This region is the core of Dehaene’s theory of reading. I’ll introduce this region and end my summary work in the next article.