Proceedings of the Annual Meeting of the Cognitive Science Society

In numerosity comparison, performance is faster, more accurate, and less noisy with the ratio of compared numbers.Whereas the ratio-dependency has been intensively studied in relation to internal noise, processes of numerosity com-parison that may increase internal noise have not been fully understood. In this paper, we propose a process theory thataccounts for non-numerical, visuo-spatial processes in numerosity comparison. Consistent with the theory, we found thatas required processes decreased, performance improved significantly, to the extent that there were no differences betweennon-symbolic and symbolic number comparison in reaction time, accuracy, and internal noise. The findings suggest thatcomparing numerosities requires multiple processes homogenizing ancillary stimulus dimensions and that the homoge-nization processes are the major source of fuzziness in approximate number comparison.