Peripheral neural basis of tactile sensations in man: I. Effect of frequency and probe area on sensations elicited by single mechanical pulses on hairy and glabrous skin of the hand

Hand-Feel Touch Cues and Their Influences on Consumer Perception and Behavior with Respect to Food Products: A Review

There has been a great deal of research investigating intrinsic/extrinsic cues and their influences on consumer perception and purchasing decisions at points of sale, product usage, and consumption. Consumers create expectations toward a food product through sensory information extracted from its surface (intrinsic cues) or packaging (extrinsic cues) at retail stores. Packaging is one of the important extrinsic cues that can modulate consumer perception, liking, and decision making of a product. For example, handling a product packaging during consumption, even just touching the packaging while opening or holding it during consumption, may result in a consumer expectation of the package content. Although hand-feel touch cues are an integral part of the food consumption experience, as can be observed in such an instance, little has been known about their influences on consumer perception, acceptability, and purchase behavior of food products. This review therefore provided a better understanding about hand-feel touch cues and their influences in the context of food and beverage experience with a focus on (1) an overview of touch as a sensory modality, (2) factors influencing hand-feel perception, (3) influences of hand-feel touch cues on the perception of other sensory modalities, and (4) the effects of hand-feel touch cues on emotional responses and purchase behavior.

Differential temporal coding of the vibratory sense in the hand and foot in man

OBJECTIVE

We studied the difference in the temporal tuning function of the vibratory senses between the hand and foot in man by using steady-state somatosensory evoked potentials (S-SEPs) to vibratory stimulation.

METHODS

Vibratory stimuli were applied to the palm and sole, and the S-SEPs were then recorded in 8 normal subjects. A total of 200 responses were recorded from 4 electrodes including the ipsi-and contralateral somatosensory areas of the hand and foot. The amplitude of the first harmonic component (1F) was obtained by a Fourier analysis. The effect of modulation frequency (17-30 Hz) on the 1F at a stimulus intensity of 0.05 N was studied.

RESULTS

The amplitudes of the S-SEPs were the greatest in the contralateral hand and foot areas. The mean 1F amplitudes of the palm S-SEPs as a function of the modulation frequency showed a narrow tuning curve with a peak near 21 Hz while those of the sole demonstrated a broad tuning curve.

CONCLUSION

Our results suggest the differential temporal coding of the vibratory sense in the hand and foot areas of the somatosensory cortex in man. This is probably caused by the different characteristics in the receptors situated in the hand and foot.

The perception of tactile distance: influences of body site, space, and time

Vibrotactile prostheses for deaf or blind persons have been applied to any number of different locations on the body, including the finger, wrist, forearm, abdomen, back, and nape of the neck. The discriminability of patterns presented by such devices can be affected by the acuity of the site of application and the resolution of the display. In addition, the mutual influences among stimuli close together in both space and time can affect percepts within a broad range of parameters. For example, consideration must be given to a variety of tactile illusions often associated with the spatial separations and the range of temporal intervals typically used in cutaneous communication displays. Experiments are reported in which magnitude estimates and cross-modality matches of perceived extent produced by pairs of vibrotactile taps presented to separate loci were obtained on three different body sites. Perceived distance was directly related both to the timing between the taps and to their physical separation. The findings show a consistent relationship to cortical magnification across body sites.

Spatial features of vibrotactile masking effects on airpuff-elicited sensations in the human hand

It was recently shown that the cutaneous sensitivity to airpuffs is decreased by a low-frequency vibrotactile masker in the hairy skin, and by a low-frequency but especially by a high-frequency masker in the glabrous skin. In the current study, the spatial features of this masking effect were determined in four healthy human subjects, using a reaction time paradigm. The masking effect decreased monotonically with increasing interstimulus distance, and identically in longitudinal and transverse (i.e., lateral) directions in the palm or dorsal surface of the hand. The masking effect was stronger in the glabrous than in the hairy skin, especially in the fingers. In the glabrous skin, the spread of masking effect produced by a high-frequency masker was more extensive than that produced by a low-frequency masker. The mechanical spread of high-frequency vibration was less extensive than that of low-frequency vibration in the skin. In the glabrous skin, a masker applied to the tip of the finger produced a stronger masking effect on sensations in the base of the finger than when the masker was located at the base and the test stimulus was located at the tip. It is concluded that mechanical spread of vibration in the skin is of minor importance in explaining the masking effects. Different peripheral neural mechanisms underlie the airpuff-elicited sensations in the hairy and glabrous skin. The afferent inhibitory mechanisms are stronger for signals coming from the glabrous skin of the fingers than for signals coming from the hairy skin. Furthermore, the peripheral innervation density and size of the cortical representational areas may be of importance in determining the magnitude of the masking effect.

Vibration sensitivity of slowly and rapidly adapting cutaneous mechanoreceptors in the human foot and leg

The activities of 30 rapidly adapting cutaneous receptors (FA) and 23 slowly adapting cutaneous receptors (SA) were recorded from the lateral peroneal nerve using the microneurographic method. Their sensitivity to mechanical vibrations with constant amplitude applied at various frequencies to the center of the receptive field was studied. These two populations of cutaneous receptors were found to be very sensitive to this stimulus: they could be driven in a one to one manner up to between 100 and 200 Hz. The difference lay in the response observed when the vibration frequency was increased to above this critical value: the FA receptors sharply stopped firing, whereas the SA receptors became progressively unlinked from the stimulus. The effects of vibration on the physiological messages were also studied. The results showed that the messages coding the properties of tactile stimuli were either completely or partly masked by the receptor response to vibration. These vibration-induced modifications of cutaneous sensory messages might be at least partly responsible for the sensorimotor alterations observed when subjects are exposed to vibration.

Cutaneous pain and detection thresholds to short CO2 laser pulses in humans: evidence on afferent mechanisms and the influence of varying stimulus conditions

Pain and detection thresholds to short CO2 laser pulses were studied in healthy human subjects. Pain thresholds were significantly higher than detection thresholds in both hairy and glabrous skin; in the glabrous skin both thresholds were higher in the hairy skin. The range from detection threshold to pain threshold was larger in the glabrous skin. The minimal energy per surface area needed to produce any sensation (detection) or pain sensation decreased with increasing stimulus surface, and this spatial summation effect was to equal magnitude in the hairy and the glabrous skin. With decreasing stimulus pulse duration (from 45 to 15 msec) the detection and pain thresholds were elevated: this effect was stronger on pain thresholds. With increasing adapting skin temperature, less energy was needed to produce any sensation (detection) or pain sensation. The effect of adapting skin temperature was equal on pain and detection thresholds. The conduction velocity of fibers mediating laser evoked first sensations was in the thin fiber range (less than 10 msec), according to a reaction time study. The results suggest that short CO2 laser pulses produce both non-pain and pain sensations, but that both these sensations are based on the activation of the same primary afferent fiber population of slowly conducting nociceptive fibers. Central summation of primary afferent impulses is needed to elicit a liminal non-painful sensation, and an increased number of impulses in the same fibers produces pain.

Tactile detection threshold determined with single sinusoidal mechanical pulses in the monkey skin

Tactile detection thresholds for single sinusoidal mechanical pulses increased with decreases in the frequency of the stimulus pulse (from 150 to 20 Hz) in a monkey's skin. The results correspond with those of similar electrophysiological studies.

Response characteristics of peripheral mechanoreceptive units in man: relation to the sensation magnitude and to the subject's task

The characteristics of responses of 23 peripheral mechanoreceptive units to tactile pulses of varying amplitude (50-950 micron) were studied by means of human microneurography during two different tasks. The simultaneously recorded unit responses were related to estimates of sensation magnitude in order to study the coding properties of units. The possible effects of the tasks were studied by comparing the response to identical stimulus pulses during the two tasks. The S-R functions of single units had smaller exponents than the magnitude estimation functions, but the relation between the number of impulses/frequency of impulses and the simultaneously given magnitude estimate was well described by linear functions for 74% of units. Thus both of these parameters may serve as codes for stimulus amplitude. For 18 units differences were obtained between the two task situations when thresholds, latency of the first impulse, mean frequency of impulses, or number of impulses in responses were compared. The differences were partly due to a continuous decrease of sensitivity of units with time. However, the results indicate also that the sensitivity of the units was higher during the magnitude estimation than during the counting task. The effect of the task of the subject on the sensitivity of the peripheral mechanoreceptive units may be mediated through direct neural connections. The results indicate that the reorganization of the neural processes according to the task of the subject is not limited to the central nervous system, but involves also the periphery.

Comparison of response properties of dorsal and ventral spinocerebellar tract neurons to a physiological stimulus

The response characteristics of dorsal spinocerebellar tract (DSCT) neurons and ventral spinocerebellar tract (VSCT) neurons to the cutaneous inputs applied to footpads were studied in the cat. Three different wave forms were used: step displacement of varying amplitudes (0.1-3.5 mm); constant amplitude ramps with different slopes (5-120 mm/s); and constant amplitude sinusoidal displacements of varying frequencies (1-20 Hz). Both DSCT and VSCT neurons responded phasically to cutaneous stimuli of different wave forms. The phasic responses were related to both the amplitude and velocity of the peripheral stimulus. However, the responses of DSCT neurons were graded over only a very narrow, low range of stimulus intensities, whereas the responses of VSCT neurons were graded over a larger range of skin indentation up to 3 mm. Only the DSCT neurons exhibited some length sensitivity to ramp stimuli, and only DSCT neurons were activated repetitively by periodic stimuli. These results suggest both DSCT and VSCT can transmit exteroceptive information but respond selectively to different features of these stimuli.

Effect of tourniquet-induced ischemia on magnitude scaling of tactile stimuli applied to the human hand

The effect of tourniquet-induced ischemia was tested on magnitude scaling of supraliminal tactile stimuli (single-cycle sine waves) applied to the human hand contra- or ipsilaterally to the cuff. Magnitude estimations were not influenced on the contralateral side. In the ischemic hand there was a reduction of magnitude estimates beginning 12 min. after inflation of the cuff, independent of the stimulus intensity. The results indicate that peripheral noxious stimulation does not produce a nonsegmental reduction of tactile sensitivity. Moreover, it is suggested that the thickest afferent mechanoreceptive fibers (A-beta) have a major role in the mediation of tactile signals both at liminal and supraliminal levels.

Vibrotactile atonal interval correlated with activity in peripheral mechanoreceptive units innervating the human hand

The quality of sensations and the vibrotactile atonal interval-the gap between detection and vibration thresholds-were studied with vibratory stimuli of varying frequency (20, 80 and 160 Hz) and duration (100, 400 and 800 ms) applied to the hairy and glabrous skin of the hand. Detection and vibration thresholds were also determined while simultaneously recording single unit activity from the radial nerve innervating the hairy skin of the hand. Both thresholds were lower on the glabrous than the hairy skin, and the thresholds decreased on both skin areas with increasing vibration frequency. A sensation of short duration was elicited at detection threshold only with a 20-Hz stimulus of 100-ms duration; with other frequency-duration combinations sensations of longer duration were reported. Considerably larger vibration amplitudes were needed on both skin areas for the sensations to be unequivocal with respect to duration and pitch (vibration threshold). There was no significant effect of stimulus duration on vibrotactile thresholds. The width of the average atonal intervals was above 10 dB on both skin areas, and with increasing vibration frequency, decreasing values of atonal intervals were obtained on the hairy skin, whereas considerably increasing values were obtained on the glabrous skin. Recording of single unit activity indicates that on the hairy skin detection of the stimulus at 20 Hz is correlated with activation of slowly adapting (SA) type II and the most sensitive rapidly adapting (RA) units, while distinct vibratory sensations involve entrainment of RA units. Also at 80 Hz, non-pacinian units could contribute to the mechanism of vibrotactile thresholds, whereas at 160 Hz only pacinian (PC) units are involved.

Differential sensitivity to airpuffs on human hairy and glabrous skin

To compare the relative sensitivities of glabrous and hairy skin, we measured reaction times (RTs) and detectability (d') of airpuffs delivered to the hairy dorsum and glabrous thenar eminence of the hand of six human subjects. In contrast to previous studies with mechanical contact stimuli, airpuffs applied to hairy skin were detected with equal or greater fidelity than airpuffs tested on glabrous skin. Mean RTs to three simultaneously applied airpuffs were significantly shorter (p less than .005) on hairy skin in five of six subjects, and in 74% of paired sessions; no significant difference in mean RTs was observed in 16% of the sessions. The superiority of hairy skin was less evident, however, when single airpuffs were tested, as significantly shorter responses were observed on only 45% of the paired sessions, and nearly identical responses on 38% of the sessions. Detectability of airpuffs (d'), which is independent of the value of RTs, was identical on hairy and glabrous skin at high airpuff intensities (1,600 dyn), and superior (n = 4) or equal (n = 2) on hairy skin with low airpuff intensities (800 dyn). Spatial summation was more pronounced on hairy than on glabrous skin. Three simultaneously presented airpuffs produced significantly shorter RTs than one airpuff in 85% of the paired sessions on hairy skin, but on only half of the sessions on glabrous skin. The spatial distribution of stimulus force was less important on hairy skin, as three low-intensity airpuffs produced the same or shorter RTs than one high-intensity airpuff. By contrast, on glabrous skin, detectability was significantly better when force was concentrated at a single point (1 X 1,600 dyn) than when diffused over a wide skin area (3 X 800 dyn). The enhanced sensitivity of hairy skin to airpuffs appears partially attributable to hair motion in the airstream. After hair removal by chemical depilation, detectability of airpuffs was reduced on hairy skin to a level equal to or below that on glabrous skin. Spatial summation on the depilated skin corresponded to that observed on the intact hairy skin, indicating that depilation did not abolish intensity discrimination, but rather lowered the overall sensitivity of hairy skin. These results show that hair follicle units form a very sensitive detection mechanism on hairy skin of the human hand, similar to that provided by Meissner's and Pacinian afferents in glabrous skin. These findings with airpuffs provide the first example of a tactile stimulus that is less effective for mechanoreceptors in glabrous skin than in hairy skin.(ABSTRACT TRUNCATED AT 400 WORDS)

Somatosensory evoked potentials associated with tactile stimulation at detection threshold in man

Somatosensory evoked potentials elicited by sub- and supraliminal tactile pulses were studied during continuous threshold measurement. Two threshold methods were used: a modified tracking method and a detection method. With both methods threshold estimates of the same order of magnitude were obtained. Stimuli just above the threshold elicited a distinct somatosensory evoked potential with components P50, P100, N190 and P400. No such SEP was associated with the subliminal stimuli. However, in some cases some potential oscillations were obtained, time-locked to the subliminal stimuli; these are suggested to be due to errors in responding. In control experiments detected stimuli elicited a distinct SEP, but no SEP was associated with undetected stimuli of identical amplitude. The results indicate that in the psychophysical threshold determination the neural processing reflected in the SEP is associated only with supraliminal tactile stimulation. The lack of evoked brain activity associated with subliminal tactile stimuli supports the hypothesis derived from human microneurographic studies, stating that the tactile detection threshold may be based on an extremely small peripheral input, perhaps only on a single impulse in a single peripheral fiber.

Ischemic pain nonsegmentally produces a predominant reduction of pain and thermal sensitivity in man: a selective role for endogenous opioids

Ischemic pain was produced by a blood pressure cuff placed to the arm of healthy human subjects for 15 min which produced a mean pain score of 59% (visual analogue scale). Ischemia induced a significant dental pain threshold elevation (mean 67%) and 2 mg of naloxone did not reduce it. Thermal sensitivity of the upper lip had a tendency to reduction during ischemia and 2 mg of naloxone reduced this effect. Tactile thresholds in the forehead or in the contralateral arm were not markedly elevated. Neither ACTH nor prolactin level in the plasma was related to the dental pain threshold elevation during ischemia. The findings of the present study suggest that ischemic pain nonsegmentally produces a predominant inhibition of responses to thin afferents. Endogenous opioids may markedly contribute to the reduction of thermal sensitivity induced by ischemia, but their contribution to dental pain threshold elevations seems to be less important. Stress or other adenohypophyseal mechanisms involving the release of ACTH or prolactin do not explain the effects of ischemia found in the present study.