Two models for psychophysical judgment: Scale invariance with changes in stimulus range

Two scaling models are investigated, each of which includes parameters which reflect variation in the use of judgmental categories. In one model, response categories are represented as successive intervals on an underlying sensory continuum. In the other, they are represented as points. Psychophysical scales based upon either of these models are invariant up to a linear transformation when the range of stimulus magnitudes is manipulated. Successive intervals scale values obtained from magnitude estimates are also linearly invariant with changes in stimulus range. Similarities in the proximity functions for the two judgment models are examined.