This is a pop science magazine article about acquired savant syndrome and Jason Padgett, a case who appears to be very much modelled on the story of Daniel Tammet:
Treffert, Darold (2014) Accidental genius. Scientific American. August 2014. P.42-47.
and this is a pop science magazine article about acquired savant syndrome and Derek Amato, a case who appears to be very much modelled on the story of Daniel Tammet:
Piore, Adam (2013) When Brain Damage Unlocks The Genius Within. Popular Science (website) February 19th 2013.
Piore, Adam (2013) The genius within. Popular Science. March 2013. Vol 282 Issue 3 p.46-53.
Both articles appear to describe this 2012 study by Alan Snyder and Richard Chi:
but it is disappointing that neither article gave a proper citation to the paper, so I can only guess.
It is worth noting that Snyder and Chi did a similar study that was published in 2011: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0016655
That study and associated excitable press commentary inspired an interesting article in the Guardian newspaper criticising the media hype and the study itself: http://www.theguardian.com/science/blog/2011/feb/16/thinking-caps-pseudoscience-neuroscience