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- Published 16.09.13
Those who are born blind but have their vision restored later in life may have problems in recognising people, a study conducted in Hyderabad has shown.
The study, carried out by researchers from the Hyderabad-based L.V. Prasad Eye Institute and the University of Hamburg in Germany, has established that the brain’s ability to process faces requires early visual experience.
Scientists know that there is a period in the first few months of life when a baby develops the proficiency to process human faces. The new study shows that humans are born with the basic neural circuitry to process faces but the brain relies on visual experiences early in life to fine tune these circuits in a way that enhances visual processing. The paper appeared in the latest issue of the Proceedings of National Academy of Sciences.
“We know from earlier research that individuals whose vision was restored show some lower face processing skills and have problems in recognising people from different perspectives, say, under different lighting conditions or if the emotional expression of the faces changes,” says Brigitte Roeder, neuropsychologist at Hamburg University and lead author of the study.
|Brigitte Roeder (top) and Ramesh Kekunnaya|
“We know from experience that people with congenital blindness who have their vision restored through treatment cannot figure out human faces. They may be able to identify a shape (such as a triangle) or a house but they cannot say a particular face belongs to a particular person when the image of the face is shown to them,” says Ramesh Kekunnaya of Jasti Ramanamma Children’s Eye Care Centre at LVPEI and a co-author of the paper.
The scientists studied 11 children who had been blind from birth (usually because of dense cataract) and whose sight had been restored up to 14 years later, along with matched healthy participants and those with partial eyesight.
To understand whether these children can actually recognise human faces, the scientists recorded electroencephalography (EEG) — recording of electrical activity along the scalp — of the participants when they were shown intact and scrambled images of human faces and houses. The researchers particularly looked for an electrical potential called N170, which is typically produced in response to human faces.
While all participants could identify the pictures, individuals who had been blind from birth experienced N170 regardless of whether they were shown pictures of faces or houses. Healthy and partial-sighted participants, however, experienced N170 only in response to human faces.
“The multiple facial features seem to be perceived as a configuration, that is, in parallel rather than being sequentially scanned and put together,” says Roeder. “The fact that this system [N170] is active to all types of visual stimuli in people born blind suggests that the its functional specialisation did not take place,” she says.
This means that these individuals “see” faces not at a glance but by a process that needs more conscious effort. According to Roeder, there are two things that emerge from the study. It is important to remove congenital blindness as early as possible. At the same time, it doesn’t mean that later surgery does not make sense.
“This is like learning a language. It would be best to learn a second language like English from birth. However, if you did not have the chance to do it, it is better to learn it to some degree later in life than not at all,” quips Roeder.
S.P. Arun, a faculty at the Centre for Neuroscience at the Indian Institute of Science Bangalore, says: “This is an interesting study. But there is a contradiction between the almost-normal performance of the patients with recovered vision and the deficit seen in their brain signals. It is also not clear whether these patients exhibit a problem with faces in particular or with objects in general”.
“This study underscores the benefits of early blindness treatment,” says Pawan Sinha, professor of vision and computational neuroscience at the Massachusetts Institute of Technology in the US. “If visual deprivation is allowed to linger, it can have long-lasting adverse consequences on a person’s ability to analyse images of faces and possibly other objects,” says Sinha, whose earlier studies with blind Indian children have shown that people born blind need to be taught to correlate the visual images of objects that they earlier knew only by touching.