The first link below includes a description by Daniel Tammet, a math 'genius' with autism who describes his rage to think mathematically, and how he has visual images associated with numbers that help him arrive at correct answers. His descriptions seem similar to descriptions of mathematical manipulations by synesthetes like Richard Feynman: "When I see equations, I see the letters in colors- I don't know why. As I'm talking, i see vague pictures of Bessel functions...with light tan J's, slightly violet-bluish n's, and dark brown x's flying around.
Synesthesia is a mingling of senses whereby sight, sounds, tastes, or smells may be mixed into different sensory impressions and associations. Synesthesia has been noted to occur in highly creative people and individuals with extraordinary memory. Synesthesia may occur 'naturally', run in families, or be associated with nervous system reorganization.
Tammet's description should also be a reminder that autistic people should not be written off as 'concrete' thinkers. We often don't get detailed verbal descriptions of the experience of autism, so we probably know very little of their perceptual experience.
In the figure below, see how for synesthetes, words activate many more brain areas (emotional and associational sensory areas)than for controls.
Autistic Math Genius
Synesthesia and fMRI