Data from a choice reaction time (RT) experiment in which Ss (5 graduate students, 1 faculty member) responded to the larger of a pair of circles were fitted by a 2-stage model previously shown to describe direct magnitude estimates of difference. Results suggest that choice RT is a reciprocal function of the subjective difference between stimuli, where subjective area is a power function of objective area. The exponent of the power function for subjective area obtained from these RT data was very similar to the exponent previously obtained from magnitude estimates of difference. (PsycINFO Database Record (c) 2006 APA, all rights reserved)