AbstractThis article presents the results of an experiment whose purpose was to investigate the mechanisms of simple addition among native speakers of Russian. The means of storage and retrieval of numerical data in and from the mind and the concrete mechanisms used to perform arithmetic operations are highly cultural specific, and to a great extent dependent on a concrete language, as has been shown in many works previously. The link between number concepts and some cultural features, like reading direction or educational methods, is now being researched intensively. Our experiment tested the hypothesis that the mechanism of simple addition is based on a mental number line, at least for Russian native speakers, so far as Russian is read from left to right and a number line is a widely used method to visualize number relationships in Russian schools. The results of the experiment showed that the proposed hypothesis was not correct, and that arithmetic processing is rather more complicated than linear. Many new questions have arisen because of this and possible directions for future investigations are discussed here.