Scaling is the determination of the relationship between the physical intensity of stimuli such as lights, tones, and temperature and their corresponding psychological intensities. Psychological intensities refer to the experiences described as brightness, loudness, warmth, cold or pain (Snodgrass, Levy-Berger and Haydon, 1985). Two dimensions can be defined in sensation, a prothetic dimension that deals with sensations that differ in quantity and a metathetic dimension that deals with sensations that differ in quality. For stimuli in the prothetic dimension, a change in a particular stimulus results in a change in the intensity of the perception of that stimulus, that is, it is an additive change (bigger/smaller, brighter/darker). For stimuli in the metathetic dimension, a change in particular stimulus results in a non-additive a change in perception (Snodgrass et al., 1985). For visual stimuli then, brightness (which can be darker or brighter) is in the prothetic dimension and hue (which can be red or green) is in the metathetic dimension. In the psychophysical approach and scaling, only prothetic dimensions are relevant because quantitative physical changes need to be related to quantitative psychological changes.

How is scaling done in an experimental setting?