What is Absolute About Absolute Magnitude Estimation?

A fundamental problem in psychophysics is the measurement of the magnitude of sensations. There are no techniques for directly measuring the magnitudes of private sensations. The available methods are indirect, at best. The magnitude of asensation must be inferred from the subject&s;s responses to stimuli. To redefine sensation in terms of observable neural activity does not solve the problem, because to do so requires that we know the neural code for stimulus intensity, and presently no widespread agreement exists on this matter. The problem is further illustrated by the two-stage model of psychophysical scaling (e.g., Attneave, 1962; Curtis, Attneave, & Harrington, 1968; Shepard, 1981) in which sensation magnitude (rp) and its relation to stimulus intensity (», known as the psychophysicallaw [rp = F I (»], must be inferred from the relationship between the stimulus and the observable response [R = F3 (»]. To do this, however,the relationship between the response and the sensation [R = F2 (rp)] must be known. Unfortunately, the relationship between response and sensation is as inaccessible to direct observation and therefore is just as elusive as the relationship between stimulus and sensation. In spite of these difficulties, psychophysical scales of sensory magnitude have been constructed, and claims for their validity have been made.