Scale-flee tests of an additive model for the size-weight illusion

Abstract

In two experiments, Ss rated the difference in heaviness between two objects varying in both size and weight. Assumption of the subtractive model and the use of factorial designs allow separation of judgmental effects from psychophysical processes. Difference ratings were rescaled by monotone transformation to fit the subtractive model, yielding scale-free values for the size-weight combinations. The subtractive model provided a good description of the difference ratings, but critical violations of the additive model for the size-weight illusion were obtained. The experiments illustrate how ordinal information can be used to differentiate additive from multiplicative processes. © 1974 Psychonomic Society, Inc.