A friend emailed me to ask about the topic, and I thot it might be of interest to some here. I built my answer on “top of” the Wikipedia entry on SS.
Savant syndrome is a condition in which a person demonstrates profound and prodigious capacities or abilities far in excess of what would be considered normal.[1][2][3] People with savant syndrome may have neuro-developmental disorders, notably autism spectrum disorders, or brain injuries. The most dramatic examples of savant syndrome occur in individuals who score very low on IQ tests, while demonstrating exceptional skills or brilliance in specific areas, such as rapid calculation, art, memory, or musical ability.[4][5][6][7]
Savant skills are usually found in one or more of five major areas: art, musical abilities, calendar calculation, mathematics, and spatial skills.[1] The most common kind of autistic savants are calendrical savants,[10][11] “human calendars” who can calculate the day of the week with speed and accuracy. Memory feats are the second most common savant skill in a survey.[10]
Approximately half of savants are autistic; the other half often have some form of central nervous system injury or disease.[1] Among those with autism, it is estimated that 10% have some form of savant abilities.[1][12][13]
No widely accepted cognitive theory explains savants’ combination of talent and deficit.[14] It has been suggested that individuals with autism are biased towards left-hemispheric dominance to the almost total exclusion of new input from the right once they are done perceiving, and as a result, extremely “re-presentational” detail-focused processing and that this cognitive style predisposes individuals either with or without autism to savant talents.[15] We know that autistics are typically so sensitive to detail on one or more sensory tracks (mostly auditory, then tactilte, then visual, in that order) that they have to block out what they can no longer “put up with.” The limited material “taken in” through the right hemisphere is =so= detailed that it can provide enormous “grist” for the left hemisphere to work work, including simply “regurgitate” as “facts” or musical notes or visual artwork.
Another hypothesis is that savants hyper-systemize, thereby giving an impression of talent. Hyper-systemizing is an extreme state in the empathizing–systemizing theory that classifies people based on their skills in empathizing with others versus systemizing facts about the external world.[16] Hyper-systemizing is precisely the same thing as what I just described above. These people are so “locked” into left-hemispheric exclusion of new sensory data (for whatever reasons, including avoidance of sensory experience they find “intolerable,” which is exactly what autistics do) that they can do very remarkable things with words and symbols.
Also, the attention to detail of savants is a consequence of enhanced perception or sensory hypersensitivity in these unique individuals.[16][17] This describes my experience with autistics. But once the detail crosses the corpus callosum from the right hemisphere to the left for interpretation / analysis / assessment / evaluation / attribution of meaning, it is held “prisoner” there and never allowed back to the right hemisphere for “confirmation” or dis-confirmation. The right hemisphere is allowed to “show and tell,” but never to comment on the ideas, opinions and reactions of the left. It has also been confirmed that some savants operate by directly accessing low-level, less-processed information that exists in all human brains that is not normally available to conscious awareness.[18]
This holds water for me because of the way autistics are able to just shut out so much they do not want to deal with. The savants I have observed (all in clinical contexts) do exactly the same thing. Further, everything that is described here is =very= similar to what we see in “positive affect schizophrenia,” wherein the pt. is almost always extremely intelligent and hyper-sensitive to sensory stimulation.