Clayton L. Van Doren

Vibrotactile forward masking: Psychophysical evidence for a triplex theory of cutaneous mechanoreception

Threshold shifts for the detection of vibrotactile test stimuli were determined as a function of the intensity of a masker. A 50-ms sinusoidal test stimulus was applied to the thenar eminence of the hand 25 ms after the termination of a 700-ms sinusoidal masker applied to the same site. The frequency of the test stimulus and the frequency of the masker were varied. To eliminate the influence of the Pacinian receptor system, stimuli were delivered through a 0.01-cm2 contactor. The results support the hypothesis that the detection of vibration delivered through a small contactor is determined by two separate populations of non-Pacinian receptors. The study constitutes a psychophysical demonstration of the existence of three receptor systems responsible for the detection of vibration.

Prediction of vibrotactile masking functions

Threshold shifts for the detection of vibrotactile test stimuli were determined as a function of the intensity of a masker. The masking stimulus, narrow‐band noise centered at 275 Hz, and the test stimulus, a 15‐, 50‐, 80‐, or 300‐Hz sinusoidal burst, were applied to the same site on the thenar eminence of the hand. The intensity of the masker was varied over a range of 0 to 52 dB SL. The results support the hypothesis that the detection of vibrotactile stimuli is mediated by at least two receptor systems which do not mask each other.

Vibrotactile masking: Effects of oneand two-site stimulation

Masked vibrotactile thresholds at the index fingertip were measured as a function of masker intensities, which were applied to the thenar eminence of the same hand. Test and masker frequencies were selected so that the Pacinian and non-Pacinian receptor systems were selectively activated. Remote-site masking was effective only when both masker and test stimulus were within the frequency range of the Pacinian system. Cross-channel masking did not occur.

A model of spatiotemporal tactile sensitivity linking psychophysics to tissue mechanics

Sensitivities were measured for tangible spatiotemporal sinusoids applied to the index fingertip. The sinusoids had temporal frequencies of 8 and 128 Hz, in order to selectively activate the non‐Pacinian I (NP I) and Pacinian (P) cutaneous mechanoreceptor systems, respectively, and had spatial frequencies from 0.00–1.03 cycles/mm. The sensitivity of the NP I system increased as the spatial frequency increased, whereas the sensitivity of the P system generally decreased as the spatial frequency increased. A mechanical model of the fingertip was used to calculate the normal and shear strains in the tissue, and a psychophysical linking hypothesis was introduced to predict tactile sensitivities based on the calculated strains. Specifically, the fingertip was modeled as a slab of a linear, isotropic, homogeneous, viscoelastic material. The boundary conditions were imposed by the spatiotemporal sinusoid at the top of the slab and the rigidly attached bone at the bottom of the slab. It was then assumed that the ...

A device for measuring tactile spatiotemporal sensitivity

A tactile stimulator array constructed from 88 piezoelectric ceramic plates is described. The array can produce sinusoidal traveling waves with arbitrary temporal frequency, spatial wavelength, and amplitude. Detection thresholds were measured for five temporal frequencies (1, 4, 16, 64, and 256 Hz) and five spatial wavelengths (1.81, 3.62, 7.23, 14.5, and infinity mm), and were plotted as a three-dimensional, spatiotemporal threshold surface. Detection thresholds were also measured using a conventional vibrator and a large circular contactor simulating the infinite wavelength stimulus produced by the array. The results describe the spatial and temporal frequency sensitivity of the P and NP I cutaneous receptor populations.

The effects of a surround on vibrotactile thresholds: Evidence for spatial and temporal independence in the non‐Pacinian I (NP I) channel

Detection thresholds were measured for sinusoidal vibrations applied to the thenar eminence and volar forearm. Stimuli were applied via a 0.72‐cm2 circular contactor, with and without a rigid surround. At low frequencies, below about 40 Hz, the thresholds were higher without the surround than with the surround. However, in contrast to earlier reports, the shape of the threshold function was the same with and without the surround, suggesting that the temporal and spatial tuning characteristics of the non‐Pacinian I (NP I) channel are independent.

Temporal summation by Pacinian corpuscles precludes entrainment at the detection threshold.

For rapidly adapting mechanoreceptor afferents, entrainment is defined as a response of one spike per stimulus cycle. For Pacinian corpuscles, the entrainment threshold and psychophysical detection threshold are similar. The psychophysical threshold, however, exhibits temporal summation, which proves that the psychophysical threshold and the physiological entrainment threshold cannot be identical.

Independence of spatial and temporal tuning in the NP I cutaneous mechanoreceptor system

Results from a previous study that measured tactile detection thresholds for spatiotemporal sinusoids suggest that the spatial and temporal tuning of the P and NP I cutaneous mechanoreceptor systems are independent. In other words, provided that the spatial configuration of a vibratory stimulus is independent of temporal frequency, changing the spatial configuration should not change the shape of the temporal tuning curve of either system. To test this hypothesis for the NP I system, vibrotactile thresholds were measured as a function of temporal frequency (10, 12, 15, 20, 25, 30, 40, 55, 80, 100, 175, and 250 Hz) for 200‐ms stimuli delivered to the thenar eminence via a 0.75‐cm2 circular contactor, with and without a rigid surround. At frequencies where the threshold was mediated exclusively by the NP I system, the presence of a rigid surround did not significantly alter the shape of the temporal tuning curve, but did change the overall sensitivity. That is, NP I thresholds were uniformly higher without ...

Measurement of tactile spatio‐temporal sensitivity

The perception and discrimination of texture is an important part of cutaneous tactile function, and requires the use of both spatial and temporal information. Earlier studies that have used a variety of stimulators to measure tactile responses to temporal and spatial variations will be reviewed. A stimulus that has been successfully employed in the study of visual pattern perception, but has not been available for tactile research, is the spatio‐temporal sinusoid, where the amplitude of the stimulus varies sinusoidally along one spatial dimension and in time. A new, 88‐element linear stimulator array, constructed to produce tangible spatio‐temporal sinusoids, is described. Each element in the array is a plate of a piezoelectric ceramic. The elements are assembled on 0.38‐mm centers for a total array length of 33.4 mm. Therefore, the spatial wavelengths that can be produced by the array range from 0.76–33.4 mm. The temporal bandwidth of the array is 0.8–1000 Hz, and the maximum stimulus amplitude is 8 μ z...

A triplex model of cutaneous mechanoreception

The technique of heterofrequency forward masking was used to determine thresholds of three cutaneous receptor systems at the thenar eminence of the hand. A 50‐ms sinusoidal test stimulus was presented 25 ms after the termination of a 700‐ms sinusoidal masking stimulus. Both test and masking stimuli were varied over the frequency range of 15–300 Hz. The stimuli were delivered through a 0.01 cm2 contactor eliminating the influence of the Pacinian receptor system and exposing the threshold characteristics of two non‐Pacinian systems, designated as NPI and NPII. The low‐frequency slopes of the NPI and NPII tuning curves are similar to those measured physiologically from SA and RA receptors, respectively.