Algebraic models for integration of painful and nonpainful electric shocks

Subjects rated the average intensity of two sequentially presented electric shocks, which were either painful (intensity range from 1 to 4 mA, Experiment 1) or nonpainful (intensity range from .6 to .9 mA). In both experiments, stimuli were presented in a 4 by 4 factorial design to allow tests of algebraic models of the integration process under analysis of variance (Anderson, 1970, 1974). Both sets of data were fit by the equation R_{i j}=w₁s₁+w₂+s₂, (w₁+w₂=1), where R_{i j}is the rating scale response, s₁ and s₂ the scale values for the first and second stimuli, respectively, and w₁ and w₂ associated weights. When stimuli were painful, w₁=w₂, and when stimuli were nonpainful, w₁< w₂. Subjective scale values as a function of stimulus intensity appear to increase nonlinearly for painful stimuli and linearly for nonpainful stimuli. Some implications of the results for pain research are discussed.