(975): Individual differences scaling (INDSCAL) of noth noxious electrical stimuli and pain descriptors: A super approach to fitting Steven’s power law

Abstract

The purpose of this study is to quantify jointly the subjective intensities of physical stimuli and verbal descriptors on a single scale at the interval scale level of measurement. Volunteers made similarity judgments to all pairings (120) of 8 electrical stimuli ranging from non-noxious to noxious intensities and 8 related pain and affect descriptors. INDSCAL yielded a one-dimensional group stimulus space with the physical and verbal stimulus objects interdigitated and ordered with respect to subjective intensity. These 16 stimulus objects (ordinate) were plotted against the physical intensity scale in milliwatts (mW) (abscissa). Because the scale is at the interval scale level of measurement it is possible to quantify the perceived intensities of the descriptors. A log-log transformation of the data yielded two linear functions. The lower intensity function ranged from 3 mW and the descriptor “Slight Sensation” to 63 mW and the descriptor “Moderate Sensation”. The higher intensity function, with a different slope and intercept, ranged from 88 mW and “Upsetting” to 235 mW and “Severe Pain”. These two functions represent separate neurosensory systems that mediate non-painful and painful sensations. The results also demonstrate the superiority of theINDSCAL approach over the standard magnitude estimation procedures; for, in contrast to Stevens’s finding of a single function, we found two functions over a comparable range of electrical intensities. The INDSCAL approach is superior to Stevens’s method because it also can be used to construct quantitative pain rating scales. Supported by NIDCR and the Wharton Fund for Research in Brain and Behavior.