Comparison of child and adult vibrotactile thresholds as a function of frequency and duration

Psychophysical thresholds for the detection of sinusoidal vibration of the thenar eminence of the hand were determined for children and adults. The subjects in the child group were between 8 and 11 years old, and the adults were between 20 and 39 years old. Measurements were made for vibration frequencies ranging from 18 to 700 Hz and stimulus durations ranging from 28 to 1,000 msec. For both children and adults, thresholds were a Il-shaped function of stimulus frequency. However, the exact form of the function was influenced by the age of the subjects. At frequencies above 200 Hz, thresholds were virtually identical for children and adults, but below this frequency children were more sensitive than adults. This finding, in combination with known changes in the anatomy of the Pacinian corpuscle with age, is in agreement with a filter model of this cutaneous receptor. Furthermore, variation of stimulus duration resulted in data in agreement with the theory that two classes of mechanoreceptors, Pacinian and non-Pacinian, mediate the perception of vibration.     

Imposed vibration influences perceived tactile smoothness

According to the duplex theory of tactile texture perception, detection of cutaneous vibrations produced when the exploring finger moves across a surface contributes importantly to the perception of fine textures. If this is true, a vibrating surface should feel different from a stationary one. To test this prediction, experiments were conducted in which subjects examined two identical surfaces, one of which was surreptitiously made to vibrate, and judged which of the two was smoother. In experiment 1, the vibrating surface was less and less often judged smoother as the amplitude of (150 Hz) vibration increased. The effect was comparable in subjects who realized the surface was vibrating and those who did not. Experiment 2 showed that different frequencies (150-400 Hz) were equally effective in eliciting the effect when equated in sensation level (dB SL). The results suggest that vibrotaction contributes to texture perception, and that, at least within the Pacinian channel, it does so by means of an intensity code.     

Tactile sensitivity of children: effects of frequency, masking, and the non-Pacinian I psychophysical channel

Tactile perception depends on the contributions of four psychophysical tactile channels mediated by four corresponding receptor systems. The sensitivity of the tactile channels is determined by detection thresholds that vary as a function of the stimulus frequency. It has been widely reported that tactile thresholds increase (i.e., sensitivity decreases) as a function of age. However, there is controversial evidence with regard to the progressive loss of sensitivity starting from childhood. In this study, the tactile thresholds of children (n=9, ages 7-11 years) were measured and compared with the thresholds of young adults (n=11, ages 21-27 years). The stimuli consisted of sinusoidal bursts of mechanical displacements, which were applied to the left index fingertips of the participants by using a cylindrical probe (base area=0.126 cm2) without a contactor surround. Absolute thresholds were measured at frequencies of 2, 10, 40, 100, 250, and 500 Hz without masking. The absolute thresholds decreased at high frequencies and were similar to data from the literature except for some discrepancy because of methodological differences. In addition, the threshold of the non-Pacinian I channel was measured at 40 Hz by elevating the thresholds of the Pacinian channel by forward masking. The effects of forward masking in children were similar to results in young adults. In conclusion, there were no significant differences between the tactile thresholds of children and those of young adults at key frequencies: 40 Hz for the Pacinian and non-Pacinian I channels and 250 Hz for the Pacinian channel. These findings contradict the hypothesis that there is gradual loss of tactile sensitivity starting from childhood to early adulthood. The loss of sensitivity due to aging probably is more abrupt and occurs at a later age.     

Ipsi-and bilateral interactions in taste

In two experiments, the integration over spatial extent in taste was investigated for threshold sensitivity to NaCl and for suprathreshold intensity perception of saltiness. The area of stimulation was doubled by adding either an ipsilateral or a bilateral stimulus. The two stimuli could be of equal or unequal intensity. The data showed that at threshold level a probability summation model applied to all bilateral and most of the ipsilateral stimulus combinations. Probability summation failed to predict detection probability when two stimuli with different intensities were presented at the same tongue side. For suprathreshold stimuli, the magnitude of the saltiness sensation as estimated by a line-length method depended on the level of stimulation. The possible peripheral interaction mechanisms and central factors contributing to the taste response were discussed.     

Inhibition of acoustic startle using different mechanoreceptive channels

In this experiment, we investigated the impact of vibrotactile prepulse frequency and intensity on the acoustically elicited startle response in humans. Mechanoreceptive channels differing in their sensitivity to transient stimulation have been identified in the skin. The Pacinian channel is optimally sensitive to vibrations at approximately 300 Hz and is specialized for the detection of stimulus transients, whereas the non-Pacinian I and III channels are optimally sensitive to vibrations at approximately 30 Hz. Vibrotactile prepulses with frequencies of 30 and 300 Hz and intensities of 95 and 130 mV were presented for 50 msec to the dominant hand of college students (N = 31), followed on some trials by a 95-dB broadband acoustic startle stimulus. The 300-Hz prepulses resulted in significantly more pronounced inhibition of startle magnitude, amplitude, and probability, whereas only the 30-Hz prepulses significantly facilitated blink latency. These results support the idea that the inhibition of acoustic startle is determined more by transient than by sustained aspects of vibrotactile prepulse stimuli. This study also demonstrates that different aspects of the startle response differentially reflect stimulus characteristics of the prepulse.     

The effect of skin temperature on vibrotactile sensitivity

The effect of skin temperature on detection of vibrotactile stimuli was measured for vibrations of 30 and 250 Hz. Data for the 250-Hz stimulus supported the results of Weitz (1941), who found that thresholds for 100-, 256-, and 900-Hz vibration varied as a If-shape function of skin temperature with a minimum at about 37°C. Temperature had a negligible effect on sensitivity at 30 Hz. A second experiment examined a range of frequencies between 30 and 250 Hz. Cooling greatly lowered sensitivity only to 150- and 250-Hz stimuli. Warming reduced sensitivity less, but more uniformly across frequencies. It was concluded that cooling may affect vibrotactile thresholds by decreasing the sensitivity of Pacinian corpuscles; the reason for the decrease in sensitivity due to warming is unclear.     

Changes in excitability in motor cortex (representation of foreleg) of the dog depending on signal signification of flexor reaction during elaboration of trans switching

Excitability in a cortical representation of a foreleg was determined during elaboration of transswitching in dogs in three variations depending upon the stimulus used as a Conditioned stimulus (CS). If the flexor reaction to direct stimulation of the motor cortex was used as a CS, excitability changes of opposite signs appeared in the cortical representation of the foreleg, the threshold of flexion decreased in the alimentary situation and increased in the defense situation. Such changes in excitability were observed during instrumental conditioned transswitching. If subthreshold stimulation of the motor cortex was used as the CS, the threshold of flexion increased in both situations in approximately equal degree.     

Tactile sensitivity in Asperger syndrome

People with autism and Asperger syndrome are anecdotally said to be hypersensitive to touch. In two experiments, we measured tactile thresholds and suprathreshold tactile sensitivity in a group of adults with Asperger syndrome. In the first experiment, tactile perceptual thresholds were measured. Two frequencies of vibrotactile stimulation were used: 30 and 200 Hz. The results demonstrated significantly lower tactile perceptual thresholds in the Asperger group at 200 Hz but not at 30 Hz, thus confirming tactile hypersensitivity but only for one class of stimulus. A second experiment investigated whether self-produced movement affected the perception of touch in a group of adults with Asperger syndrome. A suprathreshold tactile stimulus was produced either by the participant (self-produced condition) or by the experimenter (externally produced condition) and participants were asked to rate the perception of the tactile stimulation. The results demonstrated that, while both Asperger and control groups rated self-produced touch as less tickly than external touch, the Asperger group rated both types of tactile stimulus as significantly more tickly and intense than did the control group. This experiment confirms the finding of tactile hypersensitivity, but shows that the perceptual consequences of self-produced touch are attenuated in the normal way in people with Asperger syndrome. An abnormality in this process cannot therefore account for their tactile hypersensitivity.     

Depth motion sensitivity functions

Functions reliably describing perception of motion in depth have been established experimentally by using psychophysical methods of size and distance estimations and threshold measurements. The stimuli were generated with a new hybrid technique yielding an image refresh rate of 1667 Hz. In this way it was possible to generate rapid expansions and contractions of the moving checkerboard pattern constituting the stimulus for depth motion perception. The results showed that perceived size constancy as well as depth impression varied with oscillation frequency. Under the conditions of slow motions (oscillation frequencies around 2 Hz), perfect size constancy was obtained. Above that limit, size constancy systematically decreased, and with oscillation frequencies of about 5 Hz the perceived size constancy was close to zero when small-sized patterns were used. Under the conditions of wide field stimulation (when the pattern subtended 66 degrees of visual angle), the cut-off limit increased to 16 Hz. Since the perception of depth motion amplitudes as well as perceived velocities of the visual object are related to perceived size constancy, the findings have certain implications for theoretical explanations of depth motion perception. Received: 15 December 1997 / Accepted: 21 December 1998     

The coding of roughness.

This review examines the way information about textures is captured, encoded, and processed by the somatosensory system to produce sensations of roughness/smoothness. Textures with spatial periods exceeding about 200 microm are encoded spatially, so roughness is nearly independent of the speed and direction of their movement across the skin. The information consists of spatial variations in activity among slowly adapting (SA1) mechanoreceptors, and appears to be extracted by specialized cortical neurons. Perception of the roughness of finer surfaces is mediated by detection, primarily by Pacinian afferents, of cutaneous vibrations generated when textures move across the skin. Movement is necessary to the perception of these textures, and vibrotactile adaptation interferes with it. The code is an intensitive one (i.e., the amount of activity in Pacinian afferents).     

Age-related differences in the pleasantness of chemosensory stimuli

Modest decrements in both taste threshold sensitivity and, more recently, suprathreshold sensitivity have been associated with the aging process. The present study was designed to investigate the existence of changes in preference for various concentrations of single tastes and of the same single tastes in more complex chemosensory mixtures. In this study, 300 participants from three different age groups (18-26, 32-45, over 65) rated for pleasantness four concentrations of sodium chloride, sucrose, and citric acid presented in both aqueous and beverage bases. Results showed significant effects of age, stimulus background, stimulus, concentration, and of several interactions, and they suggest that elderly subjects find salt and sugar pleasanter at higher concentrations than younger subjects do.     

The angle of visual roll motion determines displacement of subjective visual vertical

The effect of full-field sinusoidal visual roll motion stimuli of various frequencies and peak velocities upon the orientation of subjective visual vertical (SV) was studied. The angle of the optokinetically induced displacement of SV was found to be a linear function of the logarithm of the stimulus oscillation angle. Interindividual slopes of this function varied between 2 and 9. The logarithmic function is independent of stimulus frequency within the range of .02 Hz to .5 Hz and of peak stimulus velocity from 7.5°/sec to 170°/sec. It holds for oscillation angles up to 100°–140°. With larger rotational angles, saturation is reached. With small stimulus angles, a surprisingly high threshold (5°-8°) was observed in our experiments. This may reflect the unphysiological combination of visual roll stimuli without corroborating vestibular and proprioceptive inputs normally present when body sway produces visual stimulation. Under natural conditions, the visual feedback about spontaneous sway stabilizes body posture by integrating rotational velocity over stimulus duration which is equal to rotational angle.     

Vibrotactile intensity and frequency information in the pacinian system: a psychophysical model

The objective of the study was to characterize the Pacinian representation of stimulus waveform. Subjects were presented with pairs of high-frequency vibrotactile stimuli that varied in intensity and/or frequency content and made same-different judgments under conditions of low-frequency adaptation designed to minimize the contribution of the RA system. We wished to infer the nature of the information conveyed by the Pacinian system about the stimuli from measured sensitivity (d') to stimulus differences. We first tested the hypothesis that the Pacinian system conveys only intensive information about vibratory stimuli and found that intensive cues could not account for much of the variance in the discrimination data. We then proposed a model characterizing the Pacinian-mediated representation of an arbitrary stimulus as a pattern of activation in a set of frequency-tuned minichannels. The model was shown to predict the discriminability of the stimulus pairs presented in the psychophysical experiments. Furthermore, the model parameters, optimized to fit the discrimination data, were compatible with analogous values obtained in other experimental contexts. One of the assumptions underlying the model is that information about individual spectral components is conveyed in parallel and quasi-independently. By simulating the response of a population of Pacinian afferents to a polyharmonic stimulus, we demonstrated that such a population can simultaneously convey information about multiple frequency components, despite having a homogeneous spectral profile.     

Anchor effects on the discrimination of pitch

Two experiments considered the effects of introducing an extreme stimulus (anchor) upon the differential perception of tonal stimuli. In the first experiment, in which Ss rated series stimuli from 1,000 to 2,000 Hz or from 2,000 to 3,000 Hz, the presence of a 750-Hz anchor apparently disrupted discrimination. A second experiment involved testing for a difference threshold (method of limits) in which the standard was a tone of 1,500 Hz. The uncertainty interval (Iu) was larger when the interval between paired stimulus presentations was filled with a 750-Hz tone, again suggesting that discrimination is impaired by the introduction of a low-frequency anchor. Results are discussed in terms of theories relating range extent and discriminability.     

The effect of refractive error on central and peripheral motion sensitivity at various exposure durations

Pennsylvania State University, University Park, Pennsylvania 16802 The influence of refractive error on movement sensitivity was determined for a range of stimulus durations in the fovea and periphery. At short durations, threshold is determined by a constant displacement of the stimulus. At longer durations, a constant velocity is required. The correction of peripheral refractive error increases movement sensitivity in the displacement (short duration) component, but does not influence sensitivity in the velocity (long duration) component of the motion threshold. Implications concerning the mechanisms underlying motion perception are discussed.     

Contours of equal perceived amplitude and equal perceived frequency for electrocutaneous stimuli

Previous measurements of equal-sensation contours for electrocutaneous stimuli consisting of repeated bursts of biphasic pulses have shown that stimulus frequency has little effect on perceived amplitude, and that stimulus amplitude has no effect on perceived frequency. These earlier contours, however, were measured over a very restricted range of amplitude and frequency or for a single perceived amplitude or perceived frequency. Contours of equal perceived amplitude and equal perceived frequency were measured in the present study for stimuli covering most of the useable range of amplitudes and frequencies: 3–12 dB SL and 4–64 Hz. Eight naive subjects generated contours of equal perceived amplitude at four reference amplitudes via Békésy tracking, and 8 additional subjects generated contours of equal perceived frequency at three reference frequencies. The contours of equal perceived amplitude declined slightly but significantly with increases in stimulus frequency, consistent with previous results. The shape of the contours was also slightly dependent on the amplitude of the reference stimulus. Contours of equal perceived frequency were unaffected by stimulus amplitude on the average, but the contour shape did vary modestly, though erratically, with reference frequency.     

Motion perception in the ageing visual system: minimum motion, motion coherence, and speed discrimination thresholds

We aimed to address two issues: first, to describe how the perception of motion differs in elderly observers as compared to younger ones; and, second, to see if these changes in motion perception could be accounted for by the known changes in the ability of elderly observers to detect patterns (as indexed via contrast sensitivity). The lower threshold of motion, motion coherence, and speed discrimination were measured, alongside contrast sensitivity, in a group of thirty-two older (mean age 61.5 years) and thirty-two younger (mean age 23.2 years) subjects. The older observers showed losses in their ability to detect slow motions as indexed via the lower threshold of motion for random-dot patterns and for gratings of a range of spatial frequencies. They also were impaired on a test of motion coherence, but only for stimuli of a slow to medium speed, whereas faster speeds showed no decline with age. Finally, at all speeds tested the older observers required greater differences in speed in order to discriminate between patterns moving at different speeds. The pattern of losses on motion perception tasks was not predicted by the deficits of the older groups, such as loss of detection thresholds for high spatial and/or temporal frequencies. It is concluded that these hypotheses do not provide an adequate account of the data, and therefore that the losses occurring with age are complex and probably are a result of the loss of several types of cell.     

Vibrotactile temporal summation for threshold and suprathreshold levels of stimulation

Threshold measurement and matching procedures were used to determine the amount of temporal summation at threshold and suprathreshold levels of vibrotactile stimulation on the thenar eminence of the hand. The frequency of the stimulus was 25, 40, 80, or 200 Hz. At 25 Hz, temporal summation was absent at all intensity levels. Considerable amounts of temporal summation were observed for 80- and 200-Hz stimuli, although the effects decreased as a function of intensity. At 40 Hz, no temporal summation was observed at threshold, but above threshold, a small amount was observed at all intensity levels. The results support a duplex model of mechanoreception in which one of two receptor systems exhibits temporal summation.     

Threshold tracking for assessment of long-term adaptation and sensitization in pain perception

To assess temporal variations in the perception of "phasic" heat pain stimuli a psychophysical tracking procedure was developed that enables repeated assessment of the pain threshold at short intervals. This "double-tracking" procedure produces two tracking curves simultaneously, one that approaches the pain threshold gradually from above, the other from below. The threshold for phasic heat pain was measured in 80 tracking trials with stimuli at temperatures near the pain threshold. Concurrently, the threshold for "tonic" heat pain was determined after every 20 tracking trials with a stimulus adjustment procedure. Eleven healthy subjects (age: 26.4 yr. +/- 6.0) participated in 2 sessions each. Phasic stimulation near the pain threshold did not produce any trends in either of the two threshold measures. Hence there was no long-term adaptation or sensitization. However, there were random variations (random walks) in the tracking curves, which we interpret as resulting from a stochastic relationship between stimulus and sensation. In agreement with other reports, discrimination seemed to be better at painful than at nonpainful temperatures.     

刺激前alpha振荡对视知觉的影响

人类对感觉阈限附近的视觉刺激的知觉不总是一致的。为探究这种视知觉不一致的现象及其神经机制, 一些研究者关注刺激前脑内自发alpha神经振荡(8~13 Hz)对视知觉的影响。近年来的研究发现, 刺激前alpha振荡能量的降低能提高被试的探测击中率, 但不能提高知觉精确度; 而刺激前alpha振荡的相位能预测被试能否成功探测刺激。刺激前alpha能量被认为调控了视皮层的基础活动强度; alpha能量的降低反映了皮层基础活动的增强, 进而提高了对较弱刺激的探测率。刺激前alpha相位则被认为调控了皮层兴奋和抑制的时间; 大脑在刺激呈现时的不同状态(兴奋/抑制)决定了最终的知觉结果。