Mental calculation in an autistic savant: a case study.

We present a detailed investigation of mental calculation in RH, an autistic savant. In Experiment 1 RH performed faster and more accurately than control subjects in mentally solving multi-digit multiplication problems. However, we found no evidence that RH employed short-cut strategies to solve these problems. His response times were consistent with application of a left-to-right computational procedure employed by expert calculators. He also responded extremely quickly to 2-digit squares, suggesting that he may have memorized the answers. In Experiment 2 we taught RH a new computational algorithm for converting temperatures from Celsius to Fahrenheit. RH was able to learn the new algorithm, but required much assistance and made only slight gains with practice. RH did not recognize an easy solution strategy based on inverting steps in the conversion algorithm. We suggest that the inflexible nature of RH's performance may reflect his autistic tendencies coupled with limited intelligence.