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The ability is very rare among autistics, according to Dr. Darold Treffert, an expert on savants with autism.
Treffert is author of the forthcoming book, "Islands of Genius." It features Wiltshire's artwork on the cover, and tells about Wiltshire's life
Treffert estimated on "The Early Show" that only about 100 autistic people worldwide have ability levels comparable to Wiltshire's, adding that about one-in-10 autistic people have some savant abilities.
How are savants characterized?
Autistic savants, Treffert explained, are ranked on three levels: People on the first level have what's called "splinter skills," in which people can memorize trivia, among other things. The second level is "talented savant." Talented savants have a more honed, obvious skill. The third level is "prodigious savant."
"A prodigious savant is someone whose skill would be spectacular, even if it were to be seen in a non-disabled person, in which case you would call it a genius," Treffert said.
Wiltshire, Treffert said, is among that "elite," prodigious group.
"Early Show" co-anchor Harry Smith remarked the family's involvement with autistic savants seems very important, especially in Wiltshire's case.
Treffert agreed, saying, "A crucial part of the development of all of these savants is the family -- the cheerleaders -- the people who might not be concerned about what might be a deficit but, 'Hey, look what's there,' and are excited about that."
Treffert added that savants are more than just their ability.
"It really is their language, it's their way of speaking and communicating to us. As they develop, or what I call, 'train the talent,' they have better language ability, better social skills and a move toward independence," he said.
Treffert said Wiltshire's a "prime example" of savant development, particularly marked by what he's achieved, including the establishment of his own art gallery in London.
Read Stephen Wiltshire's "Early Show" blog
Wiltshire will continue drawing his panorama of New York at Pratt Institute in Brooklyn. He is expected to complete the drawing Friday. CBS News correspondent Michelle Gielan reported from Pratt Thursday, showing side-by-side images of Wiltshire's drawing with photos of the city's skyline and remarking about how closely Wiltshire's drawing resembled reality.
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Wiltshire told Gielan his favorite part of New York to draw is Manhattan. He said he enjoys the borough's skyscrapers, huge avenues and taxicabs.