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Psychophysical and electrophysiological techniques were used to study the encoding and processing of information about the frequency content of vibrational stimuli applied to glabrous skin in humans and cats. Trained human subjects were asked to discriminate changes in stimulus frequency and harmonic content for pairs of mono- and diharmonic sinusoidal vibrations applied to the fingertips. These psychophysical tests supplied data on what information is available to the central nervous system about the frequency components of vibratory stimuli. Electrophysiological recordings from nerves innervating the glabrous skin of the paw in cats during presentation of the same stimuli used in the psychophysical study provided data on how the peripheral nervous system encodes information about the physical parameters of cutaneous vibratory stimuli. The two sets of data indicated that the subjects derived information about the frequency of vibrotactile stimuli from the mean interval between action potentials in afferent nerve fibers activated by the stimulus.

An apparatus for automated testing of vibrotactile responses of a patient is disclosed. The embodiment of the invention comprises a component to apply indentations and vibrations to the patient's skin to test the patient's response to vibrotactile stimuli. In the preferred embodiment of the invention, a general purpose computer functions to control the operation of the system and to record and store the patient's responses. Indentations and vibrations are produced by off-axis rotational movement of a stimulation probe. A frequency modulated signal generated by the computer is used to control the motor which drives the stimulation probe. The embodiment of the present invention is able to reliably repeat each test so that the tests are reproducible and are carried out in an objective manner.

An automatic apparatus for testing tactile responses of a patient is disclosed. The embodiments of the invention variously include components for: applying a nonambient temperature to the patient's skin to test the patient's response to thermal stimuli; pricking the patient's skin to test the patient's response to pain; indenting the patient's skin to test the patient's response to touch; vibrating the patient's skin to test the patient's response to vibration; and for making two spaced apart contacts with the patient's skin to test the patient's two point discrimination response. A general purpose computer and dedicated control circuits function to control the operation of the system and record the responses of the patient. The embodiments of the present invention are able to repeatedly reproduce each test so that the tests carried out are reproducible and accomplished in a minimum of time.

An automatic apparatus for testing tactile responses of a patient is disclosed. The embodiments of the invention variously include components for: applying a nonambient temperature to the patient's skin to test the patient's response to thermal stimuli; pricking the patient's skin to test the patient's response to pain; indenting the patient's skin to test the patient's response to touch; vibrating the patient's skin to test the patient's response to vibration; and for making two spaced apart contacts with the patient's skin to test the patient's two point discrimination response. A general purpose computer and dedicated control circuits function to control the operation of the system and record the responses of the patient. The embodiments of the present invention are able to repeatedly reproduce each test so that the tests carried out are reproducible and accomplished in a minimum of time.

Psychophysical and physiological experiments using low amplitude, high‐frequency vibrations which selectively activate Pacinian corpuscle mechano‐receptors have been employed to address the question: Can the vibrotactile system distinguish between pure and polyharmonic sinusoidal stimuli applied to the glabrous skin in the presence of concomitant changes in fundamental frequency and amplitude? Human subjects are presented with stimulus pairs in which a pure tone is paired with a tone having a significant second harmonic component. The fundamental frequency and amplitude of each member of the pair are varied independently so they typically differ in peak‐to‐peak amplitude and frequency composition as well as harmonic content. In addition, different phase relations between the fundamental and harmonic of the diharmonic tone are used. The subjects are asked to identify which member of the pair is diharmonic. Responses of Pacinian corpuscles to the same tone pairs are recorded from afferent fibers in the forelimb of the cat, using both on‐center and off‐center stimulation. The eventual goal is to collect similar data in primates in order to be able to describe the neural basis for the discrimination ability observed in the psychophysical tests.