Can a Blind Brain Learn to See?
Learning to see late in life
Posted November 30, 2010
The motivation for this research came from the bleak prospects these children continue to face in India and other parts of the developing world. Blind children rarely receive a complete education, and when they grew up their opportunities for employment are limited. Furthermore, their life expectancy is less than half of children born with sight. 60% of these children never reach adulthood.
To address this dark world, a team of researchers from MIT, led by Pawan Sinha, formed Project Prakash (Sanskrit for ‘light'). Project Prakash teamed up with ophthalmologists in India to perform surgery on children with treatable forms of blindness. Removing cataracts in these children not only elevates their life prospects, but it also informs our understanding of how the brain develops sight.
Sixty years ago, when neuroscientists began exploring how the brain's visual cortex processes the seeable world, they found that by obstructing mammals' eyes early in life, their brains would rewire and the area normally devoted to sight would take on new functions. We are not born with mature brains, but with brains ready to adapt to our surroundings. Early experiences in life are critical for molding the brain to perform the tasks that help us navigate our environment. Based on this finding, scientists and doctors believed that the brain has a critical period for developing vision, and without visual input during this time, the brain would never learn to see.
While irreversible blindness can result if the eye is completely occluded and the world is totally dark, many children born blind can still detect faint visual cues. Their eyes sense light, but the cataracts in their eyes' lens create a cloudy, indistinct world, as if they're enveloped in a heavy fog. The brain is receiving a signal, but it can't make any sense of it until the cataracts are removed and they gain visual acuity.
If the brain were fully mature from birth, you would expect that removing the cataracts would restore vision and these formerly blind children could see as well as someone born with sight. However, Sinha’s research suggests this is not the case.
The first views of the world are hazy and shapeless. The world is filled with colors that blend together and run across each other. Rather than the Mona Lisa, the world looks more like a Jackson Pollock. A triangle overlapping a square looks like one large blob rather than two distinct shapes. The brain must be trained to detect edges of objects, infer depth and find patterns.
Removing the cataracts sets the brain on a path to restoring vision, but that's just the beginning. Learning to see takes time. To better understand the process, Project Prakash took a look at how the brain wires itself to serve specific functions.
One of the extraordinary feats of the human visual system is the exceptional ability to detect faces; there is a specific part of the brain, the Fusiform Face Area or FFA, devoted solely to face recognition. Humans are far better at this than the most sophisticated computer. As past research has shown that newborns stare longer at faces than other objects, neuroscientists believed that the brain came prewired for returning their mother's gaze. However, Project Prakash has provided evidence to the contrary. Using an fMRI, they found that the region of the brain responsible for face recognition develops over a period of months in the children they've operated on. The brain may be more reliant upon learning than previously supposed. The brain isn't exactly a blank slate, because almost everyone's shares the same functions, but when we're born it's a lot closer to a block of raw stone than to Rodin's ‘The Thinker.'
For more information on Project Prakash, visit the homepage.