The localization of low- and high-frequency vibrotactile stimuli

Four experiments were conducted to determine whether spatial localization on the skin varied in acuity as a function of frequency of vibratory stimulation. The glabrous skin of the palm over the hypothenar eminence was selected as the site for stimulation by two frequencies, one at 25 Hz to stimulate non-Pacinian receptors, and one at 250 Hz to excite Pacinian receptors. Because the Pacinian receptors have larger receptive fields than the non-Pacinians, it was thought that the subjects' ability to localize would be poorer when the Pacinians were the class of receptor stimulated. In addition to frequency of vibration, the presence of a surround, the site of stimulation, the separation of the stimulator pair used in the 2AFC method, and the use of an impulse stimulus were all conditions varied to determine whether a simple direct correlation exists between receptor category and spatial acuity for vibratory stimuli. A significant difference in acuity was found as a function of vibration frequency at a proximal locus on the palm, but this vanished at a distal locus. The results have been interpreted to suggest that receptor density and its gradient across the skin areas involved may be as important as receptor type in the determination of spatial acuity.