2-POINT DISCRIMINATION OF VIBRATORY PERCEPTION ON THE SOLE OF THE HUMAN FOOT

The capability for discrimination of vibratory stimuli of the sole of the foot was tested on 12 subjects (6 men, 6 women), two vibratory sti muli (sinusoidal impulse: frequency, 200 Hz; amplitude, 0.1 mm; durati on, 2 sec) were applied at different sites to the sole of the foot. Su bjects were asked whether they detected one or two vibratory sensation s. The discrimination threshold was defined as the shortest distance a t which two vibrations can be differentiated at repeated trials. In ad dition, the absolute threshold was measured by one plunger (sinusoidal vibration: frequency, 200 Hz; variable amplitude). The values of the absolute threshold (average value, 1.2 mu m) were in accordance with t he results of other authors. A decrease of discrimination capability w as observed along the longitudinal axis of the foot from distal to pro ximal parts and was about 15 mm at the big toe and 34 mm at the heel. Discrimination at the medial longitudinal arch was inferior to that at the lateral longitudinal arch. This was also true for inverse vibrati on in which all subjects showed lower thresholds. No relationship was found with respect to thickness of the skin (measured by ultrasound), side of foot, or gender. Determining factors for vibratory threshold m ight be the density of the Pacinian corpuscles per cm(2) as well as th eir peripheral and central representation. Anatomical or physical fact ors (e.g., thickness of the skin, impedance of the deeper tissue) can probably be disregarded.