Weber Fractions for Weight and Mass as a Function of Stimulus Intensity

Laboratory simulations of weightlessness have shown that the Weber fraction for mass is higher than that for weight in the range 1000–7000 g. Experiments in the weightless conditions of orbital and parabolic flight have found the same at the 50 g level. To obtain measures at intermediate intensities, the Weber fractions for weight and mass were measured for 15 subjects at 50, 200 and 400 g. The stimuli were canisters suspended on strings. The subjects lifted them for the weight condition and swung them firmly sideways for the mass condition. The Weber fraction was higher for mass than for weight at all intensities, and increased at 50 g for both conditions. In a second mass condition, in which the subjects shook the cylinders within a loosely clenched hand, the Weber fraction remained almost constant at all intensities and was significantly smaller than for the firm swing method at 50 g. The differences in performance between conditions may be related to the continuity or intermittency of pressure information. Other explanations are discussed.