Perception Of Tactile Stimuli Research Articles

Tactile Vision and Othering: Ethnographic Engagements and Racial Differentiations in 19th Century Travelogues

The transmission, emergence, and dissemination of features of racial differentiation are based on the interplay of different sensory perceptions, as this contribution will illustrate. For this purpose, examples from ethnographic travelogues from German East Africa and from the time of German colonial rule were selected to examine the functioning of tactile perception by means of the descriptions of skin colors and skin decorations. The source material reveals multisensuality in the form of synesthesia of the sense of sight with the sense of touch, in that the perception of tactile stimuli is determined less by direct touch and more by the visual representation of haptic properties.

Content representation of tactile mental imagery in primary somatosensory cortex.

The imagination of tactile stimulation has been shown to activate primary somatosensory cortex (SI) with a somatotopic specificity akin to that seen during the perception of tactile stimuli. Using fMRI and MVPA, we investigate if this recruitment of sensory regions also reflects content-specific activation, i.e. whether the activation in SI is specific to the mental content participants imagined. To this end, healthy volunteers (n=21) either perceived or imagined three types of vibrotactile stimuli (mental content) while fMRI data was acquired. Independent of the content, during tactile mental imagery we found activation of fronto-parietal regions, supplemented with activation in the contralateral BA2 subregion of SI, replicating previous reports. While the imagery of the three different stimuli did not reveal univariate activation differences, using multivariate pattern classification we were able to decode the imagined stimulus type from BA2. Moreover, cross-classification revealed that tactile imagery elicits activation patterns similar to those evoked by the perception of the respective stimuli. These findings promote that mental tactile imagery involves the recruitment of content-specific activation patterns in sensory cortices, namely in SI.Significance StatementIt has been shown previously that mental imagery of sensations in different modalities can activate respective primary sensory cortices (visual/auditory/tactile). However, a relation of such activation to the imagined mental content was mainly shown for the visual system. Here, we generalize this concept to the somatosensory domain by showing that content-specific activation during tactile mental imagery can be found in primary somatosensory cortex subarea BA2. Most importantly, we show that tactile imagery elicits activation patterns similar to those evoked by sensory stimulation. Our results provide further evidence that sensory recruitment is among the brain processes that allow conscious information representation.

Effect of Remote Masking on Tactile Perception of Electrovibration.

Masking has been used to study human perception of tactile stimuli, including those created by electrovibration on touch screens. Earlier studies have investigated the effect of on-site masking on tactile perception of electrovibration. In this article, we investigated whether it is possible to change the absolute detection threshold and intensity difference threshold of electrovibration at the fingertip of index finger via remote masking, i.e., by applying a (mechanical) vibrotactile stimulus on the proximal phalanx of the same finger. The masking stimuli were generated by a voice coil (the Haptuator). For 16 participants, we first measured the detection thresholds for electrovibration at the fingertip and for vibrotactile stimuli at the proximal phalanx. Then, the vibrations on the skin were measured at four different locations on the index finger of subjects to investigate how the mechanical masking stimulus propagated as the masking level was varied. Later, masked absolute thresholds of eight participants were measured. Finally, for another group of eight participants, intensity difference thresholds were measured in the presence/absence of vibrotactile masking stimuli. Our results show that vibrotactile masking stimuli generated sub-threshold vibrations around the fingertip, and hence, probably did not mechanically interfere with the electrovibration stimulus. However, there was a clear psychophysical masking effect due to central neural processes. We measured the effect of masking stimuli, up to 40 dB SL, on the difference threshold at four different intensity standards of electrovibration. We proposed two models based on hypothetical neural signals for prediction of the masking effect on intensity difference thresholds for electrovibration: amplitude and energy models. The energy model was able to predict the effect of masking more accurately, especially at high intensity masking levels.

Temporal patterns in electrical nerve stimulation: Burst gap code shapes tactile frequency perception.

We have previously described a novel temporal encoding mechanism in the somatosensory system, where mechanical pulses grouped into periodic bursts create a perceived tactile frequency based on the duration of the silent gap between bursts, rather than the mean rate or the periodicity. This coding strategy may offer new opportunities for transmitting information to the brain using various sensory neural prostheses and haptic interfaces. However, it was not known whether the same coding mechanisms apply when using electrical stimulation, which recruits a different spectrum of afferents. Here, we demonstrate that the predictions of the burst gap coding model for frequency perception apply to burst stimuli delivered with electrical pulses, re-emphasising the importance of the temporal structure of spike patterns in neural processing and perception of tactile stimuli. Reciprocally, the electrical stimulation data confirm that the results observed with mechanical stimulation do indeed depend on neural processing mechanisms in the central nervous system, and are not due to skin mechanical factors and resulting patterns of afferent activation.

A Review of Surface Haptics: Enabling Tactile Effects on Touch Surfaces.

In this article, we review the current technology underlying surface haptics that converts passive touch surfaces to active ones (machine haptics), our perception of tactile stimuli displayed through active touch surfaces (human haptics), their potential applications (human-machine interaction), and finally, the challenges ahead of us in making them available through commercial systems. This article primarily covers the tactile interactions of human fingers or hands with surface-haptics displays by focusing on the three most popular actuation methods: vibrotactile, electrostatic, and ultrasonic.

Perception of Time-Discrete Haptic Feedback on the Waist is Invariant With Gait Events.

The effectiveness of haptic feedback devices highly depends on the perception of tactile stimuli, which differs across body parts and can be affected by movement. In this study, a novel wearable sensory feedback apparatus made of a pair of pressure-sensitive insoles and a belt equipped with vibrotactile units is presented; the device provides time-discrete vibrations around the waist, synchronized with biomechanically-relevant gait events during walking. Experiments with fifteen healthy volunteers were carried out to investigate users' tactile perception on the waist. Stimuli of different intensities were provided at twelve locations, each time synchronously with one pre-defined gait event (i.e. heel strike, flat foot or toe off), following a pseudo-random stimulation sequence. Reaction time, detection rate and localization accuracy were analyzed as functions of the stimulation level and site and the effect of gait events on perception was investigated. Results revealed that above-threshold stimuli (i.e. vibrations characterized by acceleration amplitudes of 1.92g and 2.13g and frequencies of 100 Hz and 150 Hz, respectively) can be effectively perceived in all the sites and successfully localized when the intertactor spacing is set to 10 cm. Moreover, it was found that perception of time-discrete vibrations was not affected by phase-related gating mechanisms, suggesting that the waist could be considered as a preferred body region for delivering haptic feedback during walking.

Сравнение стратегий восприятия тактильных стимулов в норме и у больных шизофренией

The article presents the results of a study of tactile perception. The phenomena of hypersensitivity and hypensensitivity in mental pathology are associated with chenges of reaction rate, thresholds of perception of tactile stimuli, or with physiological characteristics — a change in the tactile receptor system (McGlone F., 2014). This study was performed as an attempt to identify cognitive perception strategies (styles) for the tactile system, as well as their changes in patients with a hallucinatory-paranoid form of schizophrenia. The method, which we called the “tactile pictogram”, was developed to identify tactile perception features. Stimuli: eight textile samples (different fabrics), the same size and shape (A5), but different in structure, density, color and texture. Instruction: We allow the patient to touch the fabtic with closed eyes to feel it (fabrics presented one by one) and tell any words to memorize this fabric. After that, as a test it was necessary to find out the fabric according to your description. Subjects was 45 students (department of psychology), age 20 to 50 years. 24 patients with a hallucinatory-paranoid form of schizophrenia and schizotypic disorder (F20.0, F21.0 in ICD-10) aged 14 to 40 years. Patients at the time of the study were medicated, pathological symptoms persisted. All the received characteristics were combined into categories: “image”, “symbol”, “color and pattern”, “function”, “subjective evaluation”, “affiliation”, “objective evaluation”, “associations by place”, “character”. The answers of the subjects were coded according to the categories, expert assessments were used. The values of the U-test for the intergroup differences p = 0.05 for the categories “image”, “symbol”, “color and pattern”. In general, both healthy and schizophrenics used no more than three perception strategies. Some samples have recognizable features (cotton) and do not differ in characteristics in patients and healthy. Conclusions: 1. For tissue samples: cotton, fine viscose and thin felt for both groups, no differences between groups are revealed; 2. Intergroup differences in other samples showed a predominance of associative strategies in patients with schizophrenia (compared to healthy ones).

A Prospective Study of the Impact of Transcranial Alternating Current Stimulation on EEG Correlates of Somatosensory Perception.

The (8–12 Hz) neocortical alpha rhythm is associated with shifts in attention across sensory systems, and is thought to represent a sensory gating mechanism for the inhibitory control of cortical processing. The present preliminary study sought to explore whether alpha frequency transcranial alternating current stimulation (tACS) could modulate endogenous alpha power in the somatosensory system, and whether the hypothesized modulation would causally impact perception of tactile stimuli at perceptual threshold. We combined electroencephalography (EEG) with simultaneous brief and intermittent tACS applied over primary somatosensory cortex at individuals’ endogenous alpha frequency during a tactile detection task (n = 12 for EEG, n = 20 for behavior). EEG-measured pre-stimulus alpha power was higher on non-perceived than perceived trials, and analogous perceptual correlates emerged in early components of the tactile evoked response. Further, baseline normalized tactile detection performance was significantly lower during alpha than sham tACS, but the effect did not last into the post-tACS time period. Pre- to post-tACS changes in alpha power were linearly dependent upon baseline state, such that alpha power tended to increase when pre-tACS alpha power was low, and decrease when it was high. However, these observations were comparable in both groups, and not associated with evidence of tACS-induced alpha power modulation. Nevertheless, the tactile stimulus evoked response potential (ERP) revealed a potentially lasting impact of alpha tACS on circuit dynamics. The post-tACS ERP was marked by the emergence of a prominent peak ∼70 ms post-stimulus, which was not discernible post-sham, or in either pre-stimulation condition. Computational neural modeling designed to simulate macroscale EEG signals supported the hypothesis that the emergence of this peak could reflect synaptic plasticity mechanisms induced by tACS. The primary lesson learned in this study, which commanded a small sample size, was that while our experimental paradigm provided some evidence of an influence of tACS on behavior and circuit dynamics, it was not sufficient to induce observable causal effects of tACS on EEG-measured alpha oscillations. We discuss limitations and suggest improvements that may help further delineate a causal influence of tACS on cortical dynamics and perception in future studies.

Altered tactile localization and spatiotemporal integration in complex regional pain syndrome patients

In complex regional pain syndrome (CRPS), altered perception of the affected hand and neglect-like symptoms of the affected body side are common features. In this study, we presented tactile stimuli to the affected hands in CRPS patients and matched healthy controls. The participants' task was to point at the perceived positions of the stimuli using a tracking device. The spatial coordinates of the perceived positions were analysed for accuracy and consistency. We also presented patterns consisting of two stimuli at distinct positions with a delay of 100ms. These patterns are known to induce spatiotemporal integration ("sensory saltation"). CRPS patients were less accurate and less consistent in the spatial perception of tactile stimuli on their hands. Furthermore, they showed increased spatiotemporal integration, although these effects were smaller than expected. These deficiencies were related to the clinically assessed intensity of recurrent pain episodes. Surprisingly, the intensity of clinically assessed ongoing pain was associated with increased precision. In line with earlier reports, our findings indicate that the representation of the affected hands in CRPS patients is less accurate than in healthy people, probably reflecting reorganization in somatosensory cortices. The exact relationships between these findings and other aspects of CRPS remain to be elucidated. CRPS patients performed poorly in localizing positions on their affected hands via pointing and exhibited increased spatiotemporal integration. The presented method may prove useful in diagnostics as well as psychophysical and neurofunctional research on CRPS and other chronic pain disorders.

The role of the inferior frontal gyrus in vicarious social touch: A transcranial direct current stimulation (tDCS) study

The neural mechanisms facilitating the experience of vicarious social touch are largely unknown. The right inferior frontal gyrus (rIFG) has been suggested as part of a simulation observation-execution neural network that plays a key role in the perception of tactile stimuli. Considering that vicarious social touch involves vicarious sharing of emotions, we hypothesized that emotional empathy, i.e., the ability to feel what another individual is feeling, modulates the neural responses to vicarious touch. To examine the role of the rIFG in vicarious touch and its modulation by levels of emotional empathy, we used anodal transcranial direct current stimulation (tDCS) on forty participants who observed photos depicting social touch, nonsocial touch or no touch during tDCS or sham stimulation. The results show that while participants with high levels of emotional empathy exhibited no change in ratings of vicarious social touch, participants with low levels of emotional empathy rate human touch as more emotional following anodal stimulation of the rIFG than following sham stimulation. These findings indicate that emotional responses to vicarious social touch are associated with rIFG activity and are modulated by levels of emotional empathy. This result has major therapeutic potential for individuals with low empathic abilities, such as those with ASD.

Do patients with chronic unilateral orofacial pain due to a temporomandibular disorder show increased attending to somatosensory input at the painful side of the jaw?

BackgroundPatients with chronic orofacial pain due to temporomandibular disorders (TMD) display alterations in somatosensory processing at the jaw, such as amplified perception of tactile stimuli, but the underlying mechanisms remain unclear. This study investigated one possible explanation, namely hypervigilance, and tested if TMD patients with unilateral pain showed increased attending to somatosensory input at the painful side of the jaw.MethodsTMD patients with chronic unilateral orofacial pain (n = 20) and matched healthy volunteers (n = 20) performed a temporal order judgment (TOJ) task indicated which one of two tactile stimuli, presented on each side of the jaw, they had perceived first. TOJ methodology allows examining spatial bias in somatosensory processing speed. Furthermore, after each block of trials, the participants rated the perceived intensity of tactile stimuli separately for both sides of the jaw. Finally, questionnaires assessing pain catastrophizing, fear-avoidance beliefs, and pain vigilance, were completed.ResultsTMD patients tended to perceive tactile stimuli at the painful jaw side as occurring earlier in time than stimuli at the non-painful side but this effect did not reach conventional levels of significance (p = .07). In the control group, tactile stimuli were perceived as occurring simultaneously. Secondary analyses indicated that the magnitude of spatial bias in the TMD group is positively associated with the extent of fear-avoidance beliefs. Overall, intensity ratings of tactile stimuli were significantly higher in the TMD group than in the control group, but there was no significant difference between the painful and non-painful jaw side in the TMD patients.DiscussionThe hypothesis that TMD patients with chronic unilateral orofacial pain preferentially attend to somatosensory information at the painful side of the jaw was not statistically supported, although lack of power could not be ruled out as a reason for this. The findings are discussed within recent theories of pain-related attention.

Enhancement and suppression of tactile signals during reaching.

The perception of tactile stimuli presented on a moving hand is systematically suppressed. Such suppression has been attributed to the limited capacity of the brain to process task-irrelevant sensory information. Here, we examined whether humans do not only suppress movement-irrelevant but also enhance in parallel movement-relevant tactile signals when performing a goal-directed reaching movement. Participants reached to either a visual (LED) or somatosensory target (thumb or index finger of their unseen static hand) and discriminated 2 simultaneously presented tactile stimuli: a reference stimulus on the little finger of their static hand and a comparison stimulus on the index finger of their moving hand. Thus, during somatosensory reaching the location of the reference stimulus was task-relevant. Tactile suppression, as reflected by the increased points-of-subjective-equality (PSE) and just-noticeable-differences (JND), was stronger during reaching to somatosensory than visual targets. In Experiment 2, we presented the reference stimulus at a task-irrelevant location (sternum) and found similar suppression for somatosensory and visual reaching. This suggests that participants enhanced the sensation of the reference stimulus at the target hand during somatosensory reaching in Experiment 1. This suggestion was confirmed in Experiment 3 using a detection task in which we found lower detection thresholds on the target hand during somatosensory but not during visual reaching. We postulate that humans can flexibly modulate their tactile sensitivity by suppressing movement-irrelevant and enhancing movement-relevant signals in parallel when executing a reaching movement. (PsycINFO Database Record

Long-latency components of somatosensory evoked potentials during passive tactile perception of gratings.

Perception of tactile stimuli elicits Somatosensory Evoked Potentials (SEPs) that can be recorded via non-invasive electroencephalography (EEG). However, it is not yet clear how SEPs localization, shape and latency are modulated by different stimuli during mechanical tactile stimulation of fingertips. The aim of this work is thus to characterize SEPs generated by the tactile perception of gratings during dynamic passive stimulation of the dominant fingertip by means of a mechatronic platform. Results show that a random sequence of stimuli elicited SEPs with two long-latency components: (i) a negative deflection around 140 ms located in the frontal-central-parietal side in the contralateral hemisphere; (ii) a positive deflection around 250 ms located in the frontal-central midline. Time-frequency analysis revealed significant continuous bilateral desynchronization in the alpha band throughout the passive stimulation. These results are a fundamental step towards building a model of brain responses during perception of tactile stimuli for future benchmarking studies.

EEG-Based Perceived Tactile Location Prediction

Previous studies have attempted to investigate the peripheral neural mechanisms implicated in tactile perception, but the neurophysiological data in humans involved in tactile spatial location perception to help the brain orient the body and interact with its surroundings are not well understood. In this paper, we use single-trial electroencephalogram (EEG) measurements to explore the perception of tactile stimuli located on participants’ right forearm, which were approximately equally spaced centered on the body midline, 2 leftward and 2 rightward of midline. An EEG-based signal analysis approach to predict the location of the tactile stimuli is proposed. Offline classification suggests that tactile location can be detected from EEG signals in single trial (four-class classifier for location discriminate can achieve up to 96.76%) with a short response time (600 milliseconds after stimulus presentation). From a human-machine-interaction (HMI) point of view, this could be used to design a real-time reactive control machine for patients, e.g., suffering from hypoesthesia.

The two dimensions of the body representation in women suffering from Anorexia Nervosa

A core symptom of Anorexia Nervosa (AN) is a severe alteration of body representations. Evidence from somatoperception studies point to a generic disturbances of somatosensory components of body representations. Here we have investigated whether AN patients (N=18) and controls differed in the perception of tactile stimuli differently oriented along the body axes. We tested the hypothesis that patients perceive and represent their body selectively larger in only one dimension. To this aim we used elementary tactile measures for tactile acuity (Von Frey's test and two-point discrimination thresholds – 2PD) and tactile discrimination measures. The rationale is based on the assumption that AN patients have a wider body representation, and that tactile body representation tasks (Tactile Distance task) oriented across the bodies (horizontally) are influenced by distorted body representations compared with tactile stimuli oriented along the bodies (vertically) which should not be influenced by body representations. Results showed that patients judged horizontal tactile stimuli significantly wider than the same stimuli oriented vertically.These results suggest that human brain perceives things differently based on body representations and that the beliefs concerning body size influence the specific somatosensory process of tactile experience.

A new paradigm of electrical stimulation to enhance sensory neural function

The ability to improve peripheral neural transmission would have significant therapeutic potential in medicine. A technology of this kind could be used to restore and/or enhance sensory function in individuals with depressed sensory function, such as older adults or patients with peripheral neuropathies. The goal of this study was to investigate if a new paradigm of subsensory electrical noise stimulation enhances somatosensory function. Vibration (50Hz) was applied with a Neurothesiometer to the plantar aspect of the foot in the presence or absence of subsensory electrical noise (1/f type). The noise was applied at a proximal site, on a defined region of the tibial nerve path above the ankle. Vibration perception thresholds (VPT) of younger adults were measured in control and experimental conditions, in the absence or presence of noise respectively. An improvement of ∼16% in VPT was found in the presence of noise. These are the first data to demonstrate that modulation of axonal transmission with externally applied electrical noise improves perception of tactile stimuli in humans.

Discriminative and affective touch: sensing and feeling.

The multimodal properties of the human somatosensory system continue to be unravelled. There is mounting evidence that one of these submodalities-touch-has another dimension, providing not only its well-recognized discriminative input to the brain, but also an affective input. It has long been recognized that touch plays an important role in many forms of social communication and a number of theories have been proposed to explain observations and beliefs about the "power of touch." Here, we propose that a class of low-threshold mechanosensitive C fibers that innervate the hairy skin represent the neurobiological substrate for the affective and rewarding properties of touch.

Gating of spontaneous somatic sensations by movement

Movement is known to attenuate the perception of tactile stimuli delivered on the moving part of the body, and this gating diminishes the greater the distance from the moving part. However, does it influence the perception of sensations occurring spontaneously without external triggers? In Experiment 1, participants were asked to focus on one hand while moving or not moving their thumb, and thereafter to map and describe the spatial and qualitative attributes of sensations perceived over the remaining, motionless part of the hand. The results show that movement reduces the frequency, spatial extent, and intensity of sensations, but also participants’ confidence about their spatial characteristics. As expected, gating decreased the greater the distance from the moving thumb. Furthermore, gating was greater for distal than proximal segments of the hand, suggesting a hierarchical proximo-distal suppression. Experiment 2 ruled out the possibility that these effects were due to tactile sensations elicited by movement. Possible mechanisms of gating in the case of spontaneous sensations are discussed.

Turning Body and Self Inside Out

Prominent theories highlight the importance of bodily perception for self-consciousness, but it is currently not known whether bodily perception is based on interoceptive or exteroceptive signals or on integrated signals from these anatomically distinct systems. In the research reported here, we combined both types of signals by surreptitiously providing participants with visual exteroceptive information about their heartbeat: A real-time video image of a periodically illuminated silhouette outlined participants’ (projected, “virtual”) bodies and flashed in synchrony with their heartbeats. We investigated whether these “cardio-visual” signals could modulate bodily self-consciousness and tactile perception. We report two main findings. First, synchronous cardio-visual signals increased self-identification with and self-location toward the virtual body, and second, they altered the perception of tactile stimuli applied to participants’ backs so that touch was mislocalized toward the virtual body. We argue that the integration of signals from the inside and the outside of the human body is a fundamental neurobiological process underlying self-consciousness.

Crossing the arms confuses the clocks: Sensory feedback and the bimanual advantage

The bimanual advantage refers to the finding that tapping with two fingers on opposite hands exhibits reduced timing variability, as compared with tapping with only one finger. Two leading theories propose that the bimanual advantage results from the addition of either sensory (i.e., enhanced feedback) or cognitive (i.e., multiple timekeeper) processes involved in timing. Given that crossing the arms impairs perception of tactile stimuli and modulates cortical activation following tactile stimulation, we investigated the role of crossing the arms in the bimanual advantage. Participants tapped unimanually or bimanually with their arms crossed or uncrossed on a tabletop or in the air. With arms crossed, we expected increased interval timing variance. Similarly, for air tapping, we expected reduced bimanual advantage, due to reduced sensory feedback. A significant bimanual advantage was observed for the uncrossed, but not the crossed posture in tabletop tapping. Furthermore, removing tactile feedback from taps eliminated the bimanual advantage for both postures. Together, these findings suggest that crossing the arms likely impairs integration of internal (i.e., effector-specific) and external (i.e., environment-specific) information and that this multisensory integration is crucial to reducing timing variability during repetitive coordinated bimanual tasks.