In 1931 Pritchard1 showed that localization of stimuli is more accurate when the skin is touched with a von Frey hair than when a warm sensation is elicited without involving the contact of a stimulator with the skin. From these experiments he concluded:
Accurate localization of cutaneous stimulation is possible when the sensibility to touch is present and is in abeyance when this form of sensibility is absent.
As the experiments to be described show, there is a significant difference in the accuracy of localization between experiments involving and those excluding stimulation of sensory endings in the skin by direct contact. In Pritchard's experiments, however, two types of sense organs were involved. In the first group of his experiments, in which von Frey hairs were used, the pressure end-organs which elicit touch sensation were stimulated, and in the second group the end-organs for the warmth sense. Moreover, in none
GELLHORN E, MEHLMAN J, KAPLAN M. CONTRIBUTION TO PROBLEM OF CUTANEOUS LOCALIZATION IN MAN. Arch NeurPsych. 1938;39(2):327-332. doi:10.1001/archneurpsyc.1938.02270020117009