The visual brain of bilingual readers processes Latin and Chinese letters differently.

More than one language is spoken by almost half of the world’s population, and many adults are fluent readers and writers of multiple scripts. By examining the brains of 31 bilingual individuals, Stanislas Dehaene’s Unicog team at CEA’s NeuroSpin and Laurent Cohen at the Paris Brain Institute were able to determine how the visual cortex adjusts to the recognition of words written in various characters.

The Visual Word Form Area (VWFA) is made up of tiny cortical areas sensitive to word perception, according to research using high-resolution 7T fMRI. Reading in both English and French has no discernible effect on these regions. However, in bilinguals of English and Chinese, specific cortical regions respond to Chinese ideograms specifically and appear to be involved in face recognition.

Therefore, exposure to multiple writing systems may alter the visual cortex to the point where specific neuronal populations become specialized in reading a single alphabet. In the magazine Science Advances, these findings have been reported.

“It is part of a vast mosaic of visual cortex areas specialized in visual identification of objects such as faces, silhouettes, tools, or locations. When this region is destroyed, people become alexic, which means they lose the capacity to distinguish words or even basic letters.”

Laurent Cohen, a neurologist at Paris Brain Institute.

People who regularly read in two languages have developed a remarkable ability to transition from one linguistic universe to another, similar to musicians who can play multiple instruments and read various types of musical notation. This ability is even more fascinating in people who are proficient in multiple writing systems, such as the Hebrew, Georgian, and Roman alphabets, Japanese kanji, Chinese ideograms, and Arabic diacritical marks. The way sounds and meanings are transcribed varies among languages. But how does the brain develop its reading agility?

According to Laurent Cohen, a neurologist at the Paris Brain Institute, “The recognition of written words activates a specific area called the Visual Word Form Area (VWFA), which is formed during the acquisition of reading.”. It is a component of a sizable mosaic of visual cortex regions with expertise in the visual recognition of objects, such as faces, silhouettes, tools, or locations. Affected individuals become alexic, which means they are unable to recognize words or even basic letters.

Because of the low spatial resolution of the frequently used MRI scans in research, this region—which is crucial for reading acquisition—has previously received little attention. Researchers now ponder how learning, experience, culture, and education affect the VWFA’s neural architecture as it develops.

Minye Zhan, the study’s lead author and a post-doctoral fellow in the Cognitive Neuroimaging Research Unit (Unicog) at NeuroSpin, CEA’s neuroimaging facility, explains, “We wanted to see if it is divided into smaller areas that are specialized in one or more languages. Does writing that uses logograms—graphic symbols that represent words—process alphabetic writing in the same way?

High literacy for high resolution.
The team of Laurent Cohen and Stanislas Dehaene used the 7T NeuroSpin MRI, whose accuracy is much greater than that of conventional MRIs, to test the reading comprehension of 10 English-Chinese and 21 English-French bilinguals. The characters on the screen during the MRI test included faces, numbers, houses, and other objects, along with characters that might or might not make up actual French, Chinese, or English words.

The researchers were able to examine each participant’s VWFA using this protocol. They discovered that this area is divided into a number of tiny cortical areas that are highly specialized for word perception but are invisible using conventional imaging methods. All of these regions were equally active for both languages among bilinguals who spoke English and French.

However, some areas in bilingual English-Chinese individuals were only activated when Chinese logograms were recognized. Finally, none of the participants responded as strongly to real, well-known words as they did to fictitious words or poorly drawn characters in these small cortical zones.

Despite having very different spelling rules, Minye Zhan says that the fact that English and French share an alphabet helps to explain why these two languages use the same cortical resources. On the other hand, specialized groups of neurons appear in writing systems where the contour, shape, and complexity of the used signs vary greatly.

Even more intriguing, in English-Chinese bilinguals, cortical regions that responded specifically to reading Chinese words were also strongly activated by faces. We can infer that the mechanisms used to decipher logograms and facial features are similar. Stanislas Dehaene, director of NeuroSpin and professor at Collège de France, adds, “Faces, like Chinese characters, are compact shapes that can only be recognized and distinguished by analyzing the position of their parts in relation to each other.

Now that the specialized areas of the VFWA have been identified, researchers must examine other language pairs to see if they can be found in other linguistic contexts. For instance, bilinguals who are fluent in two different alphabets (Russian and English), who read in the opposite direction from each other (English and Arabic), or who have very different statistical traits like vowel and consonant frequency (French and Polish)

Stanislas Dehaene says, “Future studies will enable us to make sure that the visual processing of Chinese logograms is not an exception in the linguistic landscape.” Since the VFWA overlaps with regions devoted to recognizing faces, objects, and other components of our environment, we can assume that its impressive plasticity permits the emergence of traits typical of large groups of speakers. These are all ways to eventually comprehend the challenges of learning to read.

More information: Minye Zhan et al, Does the visual word form area split in bilingual readers? A millimeter-scale 7-T fMRI study, Science Advances (2023). DOI: 10.1126/sciadv.adf6140

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