This is a pretty incredible documentary about Daniel Tammet. He is smarter than you.
It seems to say that he “suffers” from the fairly recently discovered disorder of synesthesia in which senses wiring becomes crossed within the brain. It was rumoured that Pharrell had this in which his vision and hearing were linked, i.e. “Seeing Sounds“. However, this isn’t on wikipedia anymore so who really knows.
A dumb and jealous cake