Effect of Knowledge of Site of Stimulation on the Threshold for Pressure Sensitivity

Abstract

Ordinarily, sensory thresholds are determined under conditions where S knows which part of a sensory surface will be stimulated. The present experiment was done under varying degrees of uncertainty regarding site of stimulation. Modified von Frey hairs were applied in normal adults under the following conditions: (1a) to one palm, (1b) to one thumb, (2) one palm and ipsilateral thumb, (3) both palms, (4) palm and contralateral thumb, (5) both palms and one thumb. Under Conditions 2–5, stimuli were applied successively to the various sites in a randomized sequence, with separate reports required for each stimulation. The thresholds increased from those obtained under the traditional method (single site) to the various multiple-site conditions, in the order indicated (1–4), with the last two conditions (4 and 5) equivalent. Thus, increasing uncertainty as to site decreased sensitivity measures, particularly when both sides of the body were engaged and when the sites of stimulation were nonhomologous.