Localization Of Tactile Stimuli Research Articles

Tactile localization on stretched skin.

The ability to localize touch on the skin is an important aspect of tactile perception. As our limbs move, the skin stretches flexibly, and research has found that signals specifying stretch affect perception of limb posture. Skin stretch also distorts the relative spatial position of different locations on the skin, posing potential problems for tactile localization. Here, we investigated the effects of skin stretch using an established test of tactile localization on the hand. Twenty participants completed a tactile localization task in no-stretch and stretched conditions, respectively, after giving informed consent. The current study found a clear distal and radial bias in both the no-stretch condition and the stretched condition. Indeed, the distal bias was even larger in the stretched condition than at baseline. Critically, however, this change in distal bias was entirely accounted for by changes in the actual location of stimulus as a result of skin stretch, with no corresponding change in the judged location. Thus, the somatosensory system appears to disregard stretch when calculating the location of tactile stimuli. These results mirror recent findings showing that tactile distance perception also fails to take skin stretch into account. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Alpha Oscillations Are Involved in Localizing Touch on Handheld Tools.

The sense of touch is not restricted to the body but can also extend to external objects. When we use a handheld tool to contact an object, we feel the touch on the tool and not in the hand holding the tool. The ability to perceive touch on a tool actually extends along its entire surface, allowing the user to accurately localize where it is touched similarly as they would on their body. Although the neural mechanisms underlying the ability to localize touch on the body have been largely investigated, those allowing to localize touch on a tool are still unknown. We aimed to fill this gap by recording the electroencephalography signal of participants while they localized tactile stimuli on a handheld rod. We focused on oscillatory activity in the alpha (7-14 Hz) and beta (15-30 Hz) ranges, as they have been previously linked to distinct spatial codes used to localize touch on the body. Beta activity reflects the mapping of touch in skin-based coordinates, whereas alpha activity reflects the mapping of touch in external space. We found that alpha activity was solely modulated by the location of tactile stimuli applied on a handheld rod. Source reconstruction suggested that this alpha power modulation was localized in a network of fronto-parietal regions previously implicated in higher-order tactile and spatial processing. These findings are the first to implicate alpha oscillations in tool-extended sensing and suggest an important role for processing touch in external space when localizing touch on a tool.

Mind the Gap: The Effects of Temporal and Spatial Separation in Localization of Dual Touches on the Hand.

In this study, we aimed to relate the findings from two predominantly separate streams of literature, one reporting on the localization of single touches on the skin, and the other on the distance perception of dual touches. Participants were touched with two points, delivered either simultaneously or separated by a short delay to various locations on their left hand dorsum. They then indicated on a size-matched hand silhouette the perceived locations of tactile stimuli. We quantified the deviations between the actual stimulus grid and the corresponding perceptual map which was constructed from the perceived tactile locations, and we calculated the precision of tactile localization (i.e., the variability across localization attempts). The evidence showed that the dual touches, akin to single touch stimulations, were mislocalized distally and that their variable localization error was reduced near joints, particularly near knuckles. However, contrary to single-touch localization literature, we observed for the dual touches to be mislocalized towards the ulnar side of the hand, particularly when they were presented sequentially. Further, the touches presented in a sequential order were slightly “repelled” from each other and their perceived distance increased, while the simultaneous tactile pairs were localized closer to each other and their distance was compressed. Whereas the sequential touches may have been localized with reference to the body, the compression of tactile perceptual space for simultaneous touches was related in the previous literature to signal summation and inhibition and the low-level factors, including the innervation density and properties of receptive fields (RFs) of somatosensory neurons.

Improvement of Praxis Skills in Children with Hemiplegic Cerebral Palsy by Using New Trend of Augmented Visual and Auditory Feedback Training: A Case Report

Aims: The aim of the study is to investigate if the new method of auditory and visual biofeedback as Upper Limb Exercise may improve praxis skills alone without any traditional physical therapy treatment or not and within three successive months of treatment in children with hemiplegic cerebral palsy. Methods: A 6-year-old hemiplegic cerebral palsied child was treated with Upper-Limb Exerciser as one of augmented visual and auditory feedback devices. Sensory Integration and Praxis test was used to measure a child’s ability to integrate sensory input for perception, motor planning, and spatial actions in; Space Visualization, Figure-Ground Perception, Standing and Walking Balance, Design Copying, Postural Praxis, Bilateral Motor Coordination, Constructional Praxis, Postrotary Nystagmus, Motor Accuracy, Sequencing Praxis, Oral Praxis, Manual Form Perception, Kinesthesia, Finger Identification, Graphethesia, Localization of Tactile Stimuli, and Praxis on Verbal Command. Results: The results revealed improvement of the major standard score for each of the 17 subtests of Sensory Integration and Praxis Test when compared after three successive treatment. Conclusion: The using upper limb exerciser as one method of augmented visual and auditory feedback can be used as one of the physical and occupational therapy programs aiming to improve praxis skills in hemiplegic cerebral palsied children.

Afferent motor feedback determines the perceived location of tactile stimuli in the external space presented to the moving arm.

People make systematic errors when localizing a brief tactile stimulus in the external space presented on the index finger while moving the arm. Although these errors likely arise in the spatiotemporal integration of the tactile input and information about arm position, the underlying arm position information used in this process is not known. In this study, we tested the contributions of afferent proprioceptive feedback and predictive arm position signals by comparing localization errors during passive vs. active arm movements. In the active trials, participants were instructed to localize a tactile stimulus in the external space that was presented to the index finger near the time of a self-generated arm movement. In the passive trials, each of the active trials was passively replayed in randomized order, using a robotic device. Our results provide evidence that the localization error patterns of the passive trials are similar to the active trials and, moreover, did not lag but rather led the active trials, which suggests that proprioceptive feedback makes an important contribution to tactile localization. To further test which kinematic property of this afferent feedback signal drives the underlying computations, we examined the localization errors with movements that had differently skewed velocity profiles but overall the same displacement. This revealed a difference in the localization patterns, which we explain by a probabilistic model in which temporal uncertainty about the stimulus is converted into a spatial likelihood, depending on the actual velocity of the arm rather than involving an efferent, preprogrammed movement.NEW & NOTEWORTHY We show that proprioceptive feedback of arm motion rather than efferent motor signals contributes to tactile localization during an arm movement. Data further show that localization errors depend on arm velocity, not displacement per se, suggesting that instantaneous velocity feedback plays a role in the underlying computations. Model simulation using Bayesian inference suggests that these errors depend not only on spatial but also on temporal uncertainties of sensory and motor signals.

Encoding of Tactile Stimuli by Mechanoreceptors and Interneurons of the Medicinal Leech.

For many animals processing of tactile information is a crucial task in behavioral contexts like exploration, foraging, and stimulus avoidance. The leech, having infrequent access to food, developed an energy efficient reaction to tactile stimuli, avoiding unnecessary muscle movements: The local bend behavior moves only a small part of the body wall away from an object touching the skin, while the rest of the animal remains stationary. Amazingly, the precision of this localized behavioral response is similar to the spatial discrimination threshold of the human fingertip, although the leech skin is innervated by an order of magnitude fewer mechanoreceptors and each midbody ganglion contains only 400 individually identified neurons in total. Prior studies suggested that this behavior is controlled by a three-layered feed-forward network, consisting of four mechanoreceptors (P cells), approximately 20 interneurons and 10 individually characterized motor neurons, all of which encode tactile stimulus location by overlapping, symmetrical tuning curves. Additionally, encoding of mechanical force was attributed to three types of mechanoreceptors reacting to distinct intensity ranges: T cells for touch, P cells for pressure, and N cells for strong, noxious skin stimulation. In this study, we provide evidences that tactile stimulus encoding in the leech is more complex than previously thought. Combined electrophysiological, anatomical, and voltage sensitive dye approaches indicate that P and T cells both play a major role in tactile information processing resulting in local bending. Our results indicate that tactile encoding neither relies on distinct force intensity ranges of different cell types, nor location encoding is restricted to spike count tuning. Instead, we propose that P and T cells form a mixed type population, which simultaneously employs temporal response features and spike counts for multiplexed encoding of touch location and force intensity. This hypothesis is supported by our finding that previously identified local bend interneurons receive input from both P and T cells. Some of these interneurons seem to integrate mechanoreceptor inputs, while others appear to use temporal response cues, presumably acting as coincidence detectors. Further voltage sensitive dye studies can test these hypotheses how a tiny nervous system performs highly precise stimulus processing.

Nonspatial Cueing of Tactile STM Causes Shift of Spatial Attention

The focus of attention can be flexibly altered in mnemonic representations of past sensory events. We investigated the neural mechanisms of selection in tactile STM by applying vibrotactile sample stimuli of different intensities to both hands, followed by a symmetrically shaped visual retro-cue. The retro-cue indicated whether the weak or strong sample was relevant for subsequent comparison with a single tactile test stimulus. Locations of tactile stimuli were randomized, and the required response did not depend upon the spatial relation between cued sample and test stimulus. Selection between spatially segregated items in tactile STM was mirrored in lateralized activity following visual retro-cues (N2pc) and influenced encoding of task-irrelevant tactile probe stimuli (N140). Our findings support four major conclusions. First, retrospective selection results in transient shifts of spatial attention. Second, retrospective selection is functionally dissociable from attention-based rehearsal of locations. Third, selection mechanisms are linked across processing stages, as attention shifts in STM influence encoding of sensory signals. Fourth, selection in tactile STM recruits attentional control mechanisms that are, at least partially, supramodal.

Analysis on Influence of Visual Stimuli on Localization of Tactile Stimuli in Augmented Reality

Analysis on Influence of Visual Stimuli on Localization of Tactile Stimuli in Augmented Reality

Sensory integration and activities of daily living in children with developmental coordination disorder

ObjectiveThe aim of our study was to evaluate sensory integration and activities of daily living in children with developmental coordination disorderSubjects and methods37 cases with developmental coordination disorder and 35 healthy age-matched peers were included in this study. Ayres Southern California Sensory Integration Test was used for evaluating the sensory integration and Functional Independence Measure for Children (WeeFIM) was used for evaluating the activities of daily living.ResultsSignificant differences were found in the visual shape perception, position in space, and design copying (p < 0.05). According to the results of somatosensory perception tests, significant differences were found in kinesthesia, manual form perception, finger identification, figure-ground perception, localization of tactile stimuli, double tactile stimuli perception (p < 0.05). Control group was better in motor planning (p < 0.05). Comprehension, expression, social communication, problem solving, and memory skills were significant in favor of the control group (p < 0.05). Graphestesia and self-care domain was found to be correlated (r = 0,491, p = 0.002) between the groups.DiscussionSpecial education and rehabilitation programs including sensory integration therapy and motor performance will increase independence in the activities of daily living in children with developmental coordination disorder.

Integration of hand and finger location in external spatial coordinates for tactile localization.

Tactile stimulus location is automatically transformed from somatotopic into external spatial coordinates, rendering information about the location of touch in three-dimensional space. This process is referred to as tactile remapping. Whereas remapping seems to occur automatically for the hands and feet, the fingers may constitute an exception in that some studies have implied purely somatotopic coding of touch to the fingers. When participants judge the order of two tactile stimuli, they often err when the stimulated body parts (usually the two hands) are crossed, presumably because somatotopic and external coordinates are in conflict in crossed postures. Using this task, we investigated, first, whether the fingers are unlike other limbs with regard to spatial coding, by testing whether crossing effects, indicative of external coding, were observable when stimulating two fingers, either on the same or on different hands. Second, we investigated the interaction of hand and finger posture in tactile localization of finger stimuli. Crossing effects emerged when fingers and hands were crossed, suggesting external coding for all body parts. Crossing effects were larger when both hand and finger were located in the hemifield opposite to their body side, and smaller when only hand or finger lay in the opposite hemifield. We suggest that tactile location is estimated by integrating the external location of all relevant body parts, here of a finger and its belonging hand, and that such integrative coding may represent a general principle for body part processing as well as for tool use.

Multisensory hand representations in early life

Research into perceptual and cognitive development has, with notable exceptions, neglected both multisensory processes, and embodied representations. In an attempt to address these issues, I will describe our programme of research tracing the early development of multisensory representations of the hand. I will mention several studies currently being conducted in our lab, including investigations of: (i) the emergence of multisensory processes in hand localisation and ownership in early childhood, (ii) the development of categorical representation of the hand as a discrete body part, (iii) the representation of the location of tactile stimuli on the hand. I will focus mainly on the last of these investigations, relating both behavioural and physiological measures of infants’ and young children’s emerging abilities to use multisensory information to locate the hand and stimuli applied to it across changes in arm posture.

The rubber hand illusion and the tactile Simon effect

We examined the effects of the rubber hand illusion on representing tactile stimuli using the Simon effect. In a tactile Simon effect task, participants are instructed to make intensity judgments (using foot pedal responses) to tactile stimuli presented to the hands. Participants are faster when the tactile stimulus and response foot are on the same versus opposite side of the body, regardless of whether the limbs are crossed or uncrossed. Furthermore, participants are faster overall when the hands are crossed versus uncrossed. In this study, participants engaged in a tactile Simon effect experiment with rubber hands positioned directly above the participants’ hidden hands, and with real and rubber hands stroked before each experimental block. Each participant was tested in four blocks, manipulating real and rubber hand position (crossed or uncrossed). First, we found that participants responded faster with real or rubber hands crossed, demonstrating that crossing the hands (real or rubber) can hasten tactile intensity judgments. Furthermore, on trials when the rubber hands were crossed, high ownership ratings for the rubber hand were significantly correlated with faster reaction times. Finally, we found a significantly more robust Simon effect when the rubber hands (but not real hands) were crossed. We discuss these findings with reference to how integration of rubber hands into the body schema influences how we represent the location of tactile stimuli.

Encoding of tactile stimulus parameters by mechanosensory P cells of the medicinal leech Hirudo medicinalis

Some nervous systems achieve precise behavioral responses to sensory stimuli with surprisingly few neurons. The medicinal leech possesses one of the smallest central nervous systems with ~10.000 neurons with ganglia containing up to 400 neurons. Individual ganglia are able to elicit behavioral responses to sensory stimuli, e.g. bending away from pressure applied to the skin, even if they are dissected from the rest of the CNS. The local bend reflex [1] is initiated by activation of the mechanosensory P (‘pressure’) cells, processed by one layer of interneurons and one layer of motorneurons, which cause muscle contraction and elongation. This behavioral response of the leech was shown to depend on stimulus location and intensity [2]. Based on responses of only two P cells with overlapping receptive fields, the leech can discriminate locations of tactile stimuli which are only 9° of the body circumference apart [3]. In order to investigate how P cells of the medicinal leech encode information about tactile stimuli, we have recorded intracellularly from P cells while stimulating the skin mechanically with tactile stimuli of varied intensity and duration. The neuronal responses were analyzed with respect to their features latency, spike count and interspike intervals by performing stimulus estimation based on the maximum likelihood method. We found that the intensity of tactile stimuli influenced all response features considered in this study. With rising intensity the spike count increased, whereas the latency and the interspike intervals (in particular the 1st ISI) decreased. Longer stimulus duration led to a greater spike count, while the other response features were basically unaffected. When estimating seven different pressure intensities between 5mN and 60mN based on the spike count, the latency, or the 1st ISI of individual P cell responses, all three response features led on average to similar estimation performances (~34% correct estimations, chance level 14.3%, 10 P cells). The 2nd and 3rd interspike intervals yielded slightly lower performances (~28% correct estimations). Combinations of two response features did not improve the estimation performances. Since stimulus duration strongly affected spike count, combinations of three stimulus durations and two pressure intensities could be estimated much better based on spike counts (~61% correct estimations, chance level 16.7%, 12 P cells) than on the other response features or their combinations (between ~22% and ~35% correct estimations). These findings suggest that stimulus duration is encoded by spike count, while spike count, interspike intervals and latency of single P cells provide at least to some extend redundant information about stimulus intensity. However, a related study (Kappel, Pirschel, Kretzberg, this issue) revealed that interneuron EPSPs are more strongly influenced by the 1st ISI than by spike count of P cell responses. Most probably, the leech CNS combines the responses of the two P cells with overlapping receptive fields and the responses of two T (‘touch’) cells to reliably estimate stimulus intensity, as it was found for stimulus location [3].

Common Anatomical and External Coding for Hands and Feet in Tactile Attention: Evidence from Event-related Potentials

Recent studies have suggested that the location of tactile stimuli is automatically recoded from anatomical into external coordinates, independent of the task requirements. However, research has mainly involved the two hands, which may not be representative for the whole body because they are excessively used for the visually guided manipulation of objects and tools. We recorded event-related potentials (ERPs) while participants received tactile stimuli to the hands and feet, but attended only one limb. The hands were placed near the feet either in an uncrossed or a crossed posture, thus varying the spatial distance of each hand from each foot. Centro-parietal ERPs 100-140 msec poststimulus were more positive when stimulating the anatomically same-side hand while attending a foot. They were also more positive when the Euclidean distance between the stimulated hand and the attended foot was small rather than large. When a foot was stimulated and a hand attended, a similar modulation of foot ERPs was observed for the right foot. To assess the spatial distance between two limbs in space, the external location of both must be known. The present ERP results therefore suggest that not only the hands but also other body parts are remapped into external coordinates. The use of both anatomical and external coordinates may facilitate the control of actions toward tactile events and the choice of the most suitable effector.

From maps to form to space: Touch and the body schema

Evidence from patients has shown that primary somatosensory representations are plastic, dynamically changing in response to central or peripheral alterations, as well as experience. Furthermore, recent research has also demonstrated that altering body posture results in changes in the perceived sensation and localization of tactile stimuli. Using evidence from behavioral studies with brain-damaged and healthy subjects, as well as functional imaging, we propose that the traditional concept of the body schema should be divided into three components. First are primary somatosensory representations, which are representations of the skin surface that are typically somatotopically organized, and have been shown to change dynamically due to peripheral (usage, amputation, deafferentation) or central (lesion) modifications. Second, we argue for a mapping from a primary somatosensory representation to a secondary representation of body size and shape ( body form representation). Finally, we review evidence for a third set of representations that encodes limb position and is used to represent the location of tactile stimuli relative to the subject using external, non-somatotopic reference frames ( postural representations).

Tactile discrimination, but not tactile stimulation alone, reduces chronic limb pain

Chronic pain is often associated with reduced tactile acuity. A relationship exists between pain intensity, tactile acuity and cortical reorganisation. When pain resolves, tactile function improves and cortical organisation normalises. Tactile acuity can be improved in healthy controls when tactile stimulation is associated with a behavioural objective. We hypothesised that, in patients with chronic limb pain and decreased tactile acuity, discriminating between tactile stimuli would decrease pain and increase tactile acuity, but tactile stimulation alone would not. Thirteen patients with complex regional pain syndrome (CRPS) of one limb underwent a waiting period and then ∼2 weeks of tactile stimulation under two conditions: stimulation alone or discrimination between stimuli according to their diameter and location. There was no change in pain (100 mm VAS) or two-point discrimination (TPD) during a no-treatment waiting period, nor during the stimulation phase ( p > 0.32 for both). Pain and TPD were lower after the discrimination phase [mean (95% CI) effect size for pain VAS = 27 mm (14–40 mm) and for TPD = 5.7 mm (2.9–8.5 mm), p < 0.015 for both]. These gains were maintained at three-month follow-up. We conclude that tactile stimulation can decrease pain and increase tactile acuity when patients are required to discriminate between the type and location of tactile stimuli.

Head orientation biases tactile localization

Does the perceived location of tactile stimuli presented on the torso depend on the orientation of our heads with respect to our bodies? An experiment is reported that was designed to assess whether the subjective perception of tactile stimuli on the torso changes as people turn their heads in different directions. Our participants used a scale presented on a computer monitor to indicate the perceived position of vibrotactile stimuli presented to one of eight different positions around the frontal side of their waist while they either looked straight ahead, turned their head to the left, or else turned their head to the right. The results showed that the perceived location of tactile stimuli was systematically influenced by head orientation. In particular, the perceived location of the tactile stimuli shifted away from their actual position in the direction opposite to the direction of the participant's head turn. Our results also revealed a systematic decline in the accuracy of tactile localization as a function of the physical distance of the tactile stimuli from the participant's navel. These results echo related findings in the auditory domain where it has been shown that changes in eye position affect auditory lateralization. Our results also have important implications for the design of tactile displays for presenting directional information in a variety of real-world applications.

Stimulus-dependent effects on tactile spatial acuity

BackgroundPrevious studies have shown that spatio-tactile acuity is influenced by the clarity of the cortical response in primary somatosensory cortex (SI). Stimulus characteristics such as frequency, amplitude, and location of tactile stimuli presented to the skin have been shown to have a significant effect on the response in SI. The present study observes the effect of changing stimulus parameters of 25 Hz sinusoidal vertical skin displacement stimulation ("flutter") on a human subject's ability to discriminate between two adjacent or near-adjacent skin sites. Based on results obtained from recent neurophysiological studies of the SI response to different conditions of vibrotactile stimulation, we predicted that the addition of 200 Hz vibration to the same site that a two-point flutter stimulus was delivered on the skin would improve a subject's spatio-tactile acuity over that measured with flutter alone. Additionally, similar neurophysiological studies predict that the presence of either a 25 Hz flutter or 200 Hz vibration stimulus on the unattended hand (on the opposite side of the body from the site of two-point limen testing – the condition of bilateral stimulation – which has been shown to evoke less SI cortical activity than the contralateral-only stimulus condition) would decrease a subject's ability to discriminate between two points on the skin.ResultsA Bekesy tracking method was employed to track a subject's ability to discriminate between two-point stimuli delivered to the skin. The distance between the two points of stimulation was varied on a trial-by-trial basis, and several different stimulus conditions were examined: (1) The "control" condition, in which 25 Hz flutter stimuli were delivered simultaneously to the two points on the skin of the attended hand, (2) the "complex" condition, in which a combination of 25 Hz flutter and 200 Hz vibration stimuli were delivered to the two points on the attended hand, and (3) a "bilateral" condition, in which 25 Hz flutter was delivered to the two points on the attended hand and a second stimulus (either flutter or vibration) was delivered to the unattended hand. The two-point limen was reduced (i.e., spatial acuity was improved) under the complex stimulus condition when compared to the control stimulus condition. Specifically, whereas adding vibration to the unilateral two-point flutter stimulus improved spatial acuity by 20 to 25%, the two-point limen was not significantly affected by substantial changes in stimulus amplitude (between 100 – 200 μm). In contrast, simultaneous stimulation of the unattended hand (contralateral to the attended site), impaired spatial acuity by 20% with flutter stimulation and by 30% with vibration stimulation.ConclusionIt was found that the addition of 200 Hz vibration to a two-point 25 Hz flutter stimulus significantly improved a subject's ability to discriminate between two points on the skin. Since previous studies showed that 200 Hz vibration preferentially evokes activity in cortical area SII and reduces or inhibits the spatial extent of activity in SI in the same hemisphere, the findings in this paper raise the possibility that although SI activity plays a major role in two-point discrimination on the skin, influences relayed to SI from SII in the same hemisphere may contribute importantly to SI's ability to differentially respond to stimuli applied to closely spaced skin points on the same side of the body midline.

Covert attention in touch: Behavioral and ERP evidence for costs and benefits

To investigate the mechanism underlying tactile spatial attention, reaction times (RTs) and event-related potentials (ERPs) were recorded in response to mechanical stimuli delivered to the hands. At the start of each trial cues indicated either the correct (valid) or incorrect (invalid) tactile stimulus location or were uninformative (neutral). RT costs (suppression of invalid compared to neutral trials) were found to be larger than benefits (enhancement of valid compared to neutral trials). ERPs showed that costs and benefits contribute equally to attentional modulations of the somatosensory N140 component, whereas these were largely due to costs at longer latencies. These results differ from the pattern of attentional ERP modulations previously found for vision and audition, where costs precede benefits, and therefore suggest that the mechanisms of attentional selectivity in touch might be different from attentional processes in other modalities.

Remodeling of somotasensory hand representations following cerebral lesions in humans

There is evidence of reorganization of somatotopic maps following cortical lesions in mammals such as monkeys, raccoons and rats. However, there has been a striking lack of research on somatosensory plasticity following cerebral damage in adult humans. We describe two individuals with left hemisphere damage who misperceive the locations of tactile stimuli whose presence or absence they can readily detect. We find that the mislocalizations preserve the relative topography of pre-lesion experiences, resulting in shifted and compressed representations of the hand surfaces. These results not only provide evidence for systematic remodeling of somatotopic maps in humans, they also reveal that the systematic changes in cortical topography that have been documented using electrophysiological methods may give rise to similarly systematic changes in somatosensory perception itself.