S. R. D., born with cataracts, only perceived light until age 12 when surgery allowed for limited vision at 20/200. Despite this improvement, her ability to understand visual information remained impaired due to childhood blindness that hindered the development of brain areas linked to pattern vision. Clinicians have largely believed that without early intervention before six years of age, such vision deficits might become permanent. Research on kittens suggested critical periods for visual development, leading to further studies on the implications for humans, particularly in correcting congenital blindness.
"Pattern vision" is the set of visual processes that combine perceptions of an object into a coherent and distinct whole. Without pattern vision, visual experiences become a chaotic parade of disjointed sensations.
Clinicians have often assumed that unless blindness is reversed before the end of early childhood, a permanent deficit in pattern vision will occur.
Two Harvard neurobiologists, David Hubel and Torsten Wiesel, found that depriving kittens of visual experience soon after birth disrupted visual development, resulting in permanent blindness under some conditions.
Pawan Sinha initiated a research program in 2004 to test the critical-period theory in humans as part of Project Prakash, aimed at treating congenital blindness."
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