Performance of expert abacus operators

Ten expert abacus operators were given various restrictions and distractions during addition of ten numbers of 3–5 figures. All subjects except one could calculate very rapidly without an abacus, probably relying upon its mental representation. Some of those at an intermediate level of mastery moved their fingers as if they had been manipulating a real abacus, and prohibition of this movement or interfering finger-tapping reduced their performance. All the subjects could answer simple non-mathematical questions during abacus calculation without increasing time or errors, but answering extraneous mathematical questions was very hard.