ABSTRACT
S. S. Stevens discovered, in the summer of 1953, that if you ask individuals to give direct numerical estimates of the relative magnitudes of their sensory experiences, reliable empirical relationships obtain between their judgments and the physical magnitudes of the stimuli that produce them. As a sound or light varies in intensity, observers can easily describe the perceived changes in loudness or brightness (or in any other attribute they might discern) in numerical terms—just as they can use numbers to estimate the lengths of lines, the heaviness of lifted objects, or the duration of a timed event. Such judgments, of course, are fallible in that judgments of the same event repeated over time tend to be variable and they tend to be idiosyncratically influenced by contextual and procedural variables. Nevertheless, when averaged over trials or observers, numerical judgments of subjective magnitudes enter into highly reliable functional relationships with objective measures of stimulus magnitude and, although magnitude judgments are not actual measurements of sensations or perceptions, they can be relatively reliable indicators of how the experiences of these events are related conceptually for the individual experiencing them.
