Spatial Summation in the Warmth Sense

Abstract

The warmth sense is characterized by generous spatial summation: perceived strength of warmth sensation increases with increasing areal extent of stimulation as well as with increasing stimulus intensity. When intensity is low, area exerts its greatest effect, in that warmth depends on the product of stimulus area and intensity - i.e., on total power in watts. Response to integrated heat input at low intensity enables the warmth sense to help maintain constant body temperature. As stimulus intensity increases, area’s relative influence on warmth diminishes until the pain threshold is reached, whereupon spatial summation vanishes. Lack of summation at high intensity enables the warmth sense to help protect the skin from potentially damaging heat. The level-dependence of spatial summation is reflected in the way stimulus size influences the psychophysical power functions that relate warmth sensation to stimulus intensity: the larger the areal extent of the stimulus, the smaller the exponent of the power function.