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We do not have a veridical representation of our body in our mind. For instance, tactile distances of equal measure along the medial-lateral axis of our limbs are generally perceived as larger than those running along the proximal-distal axis. This anisotropy in tactile distances reflects distortions in body-shape representation, such that the body parts are perceived as wider than they are. While the origin of such anisotropy remains unknown, it has been suggested that visual experience could partially play a role in its manifestation. To causally test the role of visual experience on body shape representation, we investigated tactile distance perception in sighted and early blind individuals comparing medial-lateral and proximal-distal tactile distances of stimuli presented on the ventral and dorsal part of the forearm, wrist, and hand. Overestimation of distances in the medial-lateral over proximal-distal body axes were found in both sighted and blind people, but the magnitude of the anisotropy was significantly reduced in the forearms of blind people. We conclude that vision does not drive the emergence of tactile distance anisotropies, but visual experience can however modulate its expression on some specific body parts., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Research on media's effects on body perception has mainly focused on the role of vision of extreme body types. However, haptics is a major part of the way children experience bodies. Playing with unrealistically thin dolls has been linked to the emergence of body image concerns, but the perceptual mechanisms remain unknown. We explore the effects of haptic experience of extreme body types on body perception, using adaptation aftereffects. Blindfolded participants judged whether the doll-like stimuli explored haptically were thinner or fatter than the average body before and after adaptation to an underweight or overweight doll. In a second experiment, participants underwent a traditional visual adaptation paradigm to extreme bodies, using stimuli matched to those in Experiment 1. For both modalities, after adaptation to an underweight body test bodies were judged as fatter. Adaptation to an overweight body produced opposite results. For the first time, we show adiposity aftereffects in haptic modality, analogous to those established in vision, using matched stimuli across visual and haptic paradigms., Competing Interests: Declaration of Conflicting InterestsThe authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

When we interact with objects using our hands, we derive their size through our skin. Prolonged exposure to an object leads to a perceptual size aftereffect: adapting to a larger/smaller object makes a subsequently perceived object to appear smaller/larger than its actual size. This phenomenon has been described as haptic as tactile sensations with kinesthetic feedback are involved. However, the exact role of different haptic components in generating this aftereffect remains largely underexplored. Here, we investigated how different aspects of haptic touch influence size perception. After adaptation to a large sphere with one hand and a small sphere with the other, participants touched two test spheres of equal or different sizes and judged which one felt larger. Similar haptic size adaption aftereffects were observed (a) when participants repeatedly grasped on and off the adapters, (b) when they simply continued to grasp the adapters without further hand movements, and (c) when the adapters were grasped without involving the fingers. All these conditions produced stronger aftereffects than a condition where the palms were simply resting on the adapter. Our findings suggest that the inclusion of grasp markedly increased the aftereffects, highlighting the pivotal role of haptic interactions in determining perceptual size adaptation. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Visual working memory content is commonly thought to be composed of a precise visual representation of stimulus information (e.g., color, shape). Nevertheless, previous research has shown that individuals represent this visual information in different formats, historically dichotomized into "verbal" and "visual" formats. With growing popular knowledge of aphantasia, or the absence of sensory mental imagery, recent studies have demonstrated that individuals with aphantasia perform similarly to individuals with typical imagery on visual working memory tasks. This suggest that the use of non-visual strategies may be sufficient to perform visual working memory tasks, which were previously thought to be strictly visual. To investigate the effects of different strategies on performance in a visual working memory task, we recruited individuals across the visual imagery spectrum and tested their ability to identify relatively small (3°), medium (6°), or large (10°) changes in the degree of orientation of gratings held in working memory. Subsequently, participants indicated the extent to which they used five different strategies: visual, spatial, verbal, semantic, and sensorimotor. Results revealed that individuals with aphantasia and typical imagery performed similarly to each other across all task difficulty levels. Individuals with typical imagery dominantly used visuospatial strategies, but surprisingly, individuals with aphantasia overwhelmingly preferred the use of non-visual spatial and sensorimotor strategies over verbal strategies. These results suggest that non-visual spatial and sensorimotor strategies can be adopted in visual working memory tasks and these strategies are equally effective as visuospatial strategies. This calls for a rethinking of the "visual" versus "verbal" dichotomy, and provides evidence for the use of other non-visual mental representations in working memory tasks., Competing Interests: Declaration of competing interest None to declare., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

The well-known decrease in finger dexterity during healthy aging leads to a significant reduction in quality of life. Still, the exact patterns of altered finger kinematics of older adults in daily life are fairly unexplored. Finger interdependence is the unintentional comovement of fingers that are not intended to move, and it is known to vary across the lifespan. Nevertheless, the magnitude and direction of age-related differences in finger interdependence are ambiguous across studies and tasks and have not been explored in the context of daily life finger movements. We investigated five different free and daily-life-inspired finger movements of the right, dominant hand as well as a sequential finger tapping task of the thumb against the other fingers, in 17 younger (22-37 yr) and 17 older (62-80 yr) adults using an exoskeleton data glove for data recording. Using inferential statistics, we found that the unintentional comovement of fingers generally decreases with age in all performed daily-life-inspired movements. Finger tapping, however, showed a trend towards higher finger interdependence for older compared with younger adults. Using machine learning, we predicted the age group of a person from finger interdependence features of single movement trials significantly better than chance level for the daily-life-inspired movements, but not for finger tapping. Taken together, we show that for specific tasks, decreased finger interdependence (i.e., less comovement) could potentially act as a marker of human aging that specifically characterizes older adults' complex finger movements in daily life. NEW & NOTEWORTHY Kinematic finger movement data were analyzed with regard to age-related differences. Extensive analyses of complex and daily-life-inspired movements reveal that the direction of age effects is not uniform but task-dependent: Although older adults generally show more finger interdependence than younger adults in a simple finger tapping task, this effect is reversed for daily-life-inspired movement tasks. For these tasks, finger interdependence indices offer potential new markers to predict the age group of an individual using machine learning approaches.

Autosuggestion is a cognitive process where the inner repetition of a thought actively influences one's own perceptual state. In spite of its potential benefits for medical interventions, this technique has gained little scientific attention so far. Here, we took advantage of the known link between intensity and frequency perception in touch ('Békésy effect'). In three separate experiments, participants were asked to modulate the perceived intensity of vibrotactile stimuli at the fingertip through the inner reiteration of the thought that this perception feels very strong (Experiment 1, n = 19) or very weak (Experiments 2, n = 38, and 3, n = 20), while they were asked to report the perceived frequency. We show that the task to change the perceived intensity of a tactile stimulus via the inner reiteration of a thought modulates tactile frequency perception. This constitutes the first experimental demonstration that an experimental design that triggers autosuggestion alters participants' tactile perception using a response orthogonal to the suggested variable. We discuss whether this cognitive process could be used to influence the perception of pain in a clinical context., (© 2024. The Author(s).)

When reproducing the remembered location of dots within a circle, judgments are biased toward the center of imaginary quadrants formed by imaginary vertical and horizontal axes. This effect may result from the heightened precision in the visual system for these orientations in a retinotopic reference frame, or alternately on the internal representation of gravity. We dissociated reference frames defined by the retina and by gravity by having participants locate dots from memory in a circle when their head was upright (aligned with gravity) versus tilted 30° to the left (misaligned with gravity). We mapped the structure of spatial prototypes in a data-driven way using a novel "imaging" procedure. We calculated the rotation of the prototype maps which maximized the similarity between postures, letting us quantify the contribution of each reference frame. Spatial categories are determined by a combination of reference frames, with clear contributions from both gravitational and retinal factors. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Aphantasia is a neurocognitive phenomenon affecting voluntary visual imagery, such that it is either entirely absent, or markedly impaired. Using both the social and medical models of disability, this article discusses the extent to which aphantasia can be understood as a disorder or just a form of neutral neurodivergence, given that imagery plays a central role in thinking and memory for most other people. Preliminary school performance data are presented, showing that low imagery does not necessarily complicate life, especially given compensatory strategies and low societal barriers. In addition, we discuss the consequences of labelling aphantasia a disorder with regard to self- and public stigma, and we provide further data regarding a confidence gap, by which aphantasics perceive themselves as performing worse than they objectively do. We conclude that aphantasia should be understood as neutral neurodivergence and that labelling it a disorder is not only wrong, but potentially harmful., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Adaptation aftereffects for features such as identity and gender have been shown to transfer between faces and bodies, and faces and body parts, i.e. hands. However, no studies have investigated transfer of adaptation aftereffects between whole bodies and body parts. The present study investigated whether visual adaptation aftereffects transfer between hands and whole bodies in the context of adiposity judgements (i.e. how thin or fat a body is). On each trial, participants had to decide whether the body they saw was thinner or fatter than average. Participants performed the task before and after exposure to a thin/fat hand. Consistent with body adaptation studies, after exposure to a slim hand participants judged subsequently presented bodies to be fatter than after adaptation to a fat hand. These results suggest that there may be links between visual representations of body adiposity for whole bodies and body parts., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Orientation information contributes substantially to our tactile perception, such as feeling an object's shape on the skin. For vision, a perceptual adaptation aftereffect (tilt aftereffect; TAE), which is well explained by neural orientation selectivity, has been used to reveal fundamental perceptual properties of orientation processing. Neural orientation selectivity has been reported in somatosensory cortices. However, little research has investigated the perceptual characteristics of the tactile TAE. The aim of the current study was to provide the first demonstration of a tactile TAE on the hand and investigate the perceptual nature of tactile TAE on the hand surface. We used a 2-point stimulation with minimal input for orientation. We found clear TAEs on the hand surface: Adaptation induced shifts in subjective vertical sensation toward the orientation opposite to the adapted orientation. Further, adaptation aftereffects were purely based on orientation processing given that the effects transferred between different lengths across adaptor and test stimuli and type of stimuli. Finally, adaptation aftereffects were anchored to the hand: tactile TAE occurred independently of hand rotation and transferred from palm to dorsum sides of the hand, while the effects did not transfer between hands. Our findings demonstrate the existence of hand-centered perceptual processing for basic tactile orientation information. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Decoding natural hand movements is of interest for human-computer interaction and may constitute a helpful tool in the diagnosis of motor diseases and rehabilitation monitoring. However, the accurate measurement of complex hand movements and the decoding of dynamic movement data remains challenging. Here, we introduce two algorithms, one based on support vector machine (SVM) classification combined with dynamic time warping, and the other based on a long short-term memory (LSTM) neural network, which were designed to discriminate small differences in defined sequences of hand movements. We recorded hand movement data from 17 younger and 17 older adults using an exoskeletal data glove while they were performing six different movement tasks. Accuracy rates in decoding the different movement types were similarly high for SVM and LSTM in across-subject classification, but, for within-subject classification, SVM outperformed LSTM. The SVM-based approach, therefore, appears particularly promising for the development of movement decoding tools, in particular if the goal is to generalize across age groups, for example for detecting specific motor disorders or tracking their progress over time.

Throughout the somatosensory system, neuronal ensembles generate high-frequency signals in the range of several hundred Hertz in response to sensory input. High-frequency signals have been related to neuronal spiking, and could thus help clarify the functional architecture of sensory processing. Recording high-frequency signals from subcortical regions, however, has been limited to clinical pathology whose treatment allows for invasive recordings. Here, we demonstrate the feasibility to record 200-1200 Hz signals from the human spinal cord non-invasively, and in healthy individuals. Using standard electroencephalography equipment in a cervical electrode montage, we observed high-frequency signals between 200 and 1200 Hz in a time window between 8 and 16 ms after electric median nerve stimulation (n = 15). These signals overlapped in latency, and, partly, in frequency, with signals obtained via invasive, epidural recordings from the spinal cord in a patient with neuropathic pain. Importantly, the observed high-frequency signals were dissociable from classic spinal evoked responses. A spatial filter that optimized the signal-to-noise ratio of high-frequency signals led to submaximal amplitudes of the evoked response, and vice versa, ruling out the possibility that high-frequency signals are merely a spectral representation of the evoked response. Furthermore, we observed spontaneous fluctuations in the amplitude of high-frequency signals over time, in the absence of any concurrent, systematic change to the evoked response. High-frequency, "spike-like" signals from the human spinal cord thus carry information that is complementary to the evoked response. The possibility to assess these signals non-invasively provides a novel window onto the neurophysiology of the human spinal cord, both in a context of top-down control over perception, as well as in pathology., Competing Interests: Declaration of Competing Interest The authors declare no competing financial interests., (Copyright © 2022. Published by Elsevier Inc.)

Objectives: How spinal cord stimulation (SCS) in its different modes suppresses pain is poorly understood. Mechanisms of action may reside locally in the spinal cord, but also involve a larger network including subcortical and cortical brain structures. Tonic, burst, and high-frequency modes of SCS can, in principle, entrain distinct temporal activity patterns in this network, but finally have to yield specific effects on pain suppression. Here, we employ high-density electroencephalography (EEG) and recently developed spatial filtering techniques to reduce SCS artifacts and to enhance EEG signals specifically related to neuromodulation by SCS., Materials and Methods: We recorded high-density resting-state EEGs in patients suffering from pain of various etiologies under different modes of SCS. We established a pipeline for the robust spectral analysis of oscillatory brain activity during SCS, which includes spatial filtering for attenuation of pulse artifacts and enhancement of brain activity potentially modulated by SCS., Results: In sensor regions responsive to SCS, neuromodulation strongly reduced activity in the theta and low alpha range (6-10 Hz) in all SCS modes. Results were consistent in all patients, and in accordance with thalamocortical dysrhythmia hypothesis of pain. Only in the tonic mode showing paresthesia as side effect, SCS also consistently and strongly reduced high-gamma activity (>84 Hz)., Conclusions: EEG spectral analysis combined with spatial filtering allows for a spatially and temporally specific assessment of SCS-related, neuromodulatory EEG activity, and may help to disentangle therapeutic and side effects of SCS., (© 2020 The Authors. Neuromodulation: Technology at the Neural Interface published by Wiley Periodicals LLC on behalf of International Neuromodulation Society.)

Background: Systematic perceptual distortions of tactile space have been documented in healthy adults. In isolated focal dystonia impaired spatial somatosensory processing is suggested to be a central pathophysiological finding, but the structure of tactile space for different body parts has not been previously explored., Objectives: The objective of this study was to assess tactile space organization with a novel behavioral paradigm of tactile distance perception in patients with isolated focal dystonia and controls., Methods: Three groups of isolated focal dystonia patients (cervical dystonia, blepharospasm/Meige syndrome, focal hand dystonia) and controls estimated perceived distances between 2 touches across 8 orientations on the back of both hands and the forehead., Results: Stimulus size judgments differed significantly across orientations in all groups replicating distortions of tactile space known for healthy individuals. There were no differences between groups in the behavioral parameters we assessed on the hands and forehead., Conclusions: Tactile space organization is comparable between patients with isolated focal dystonia and healthy controls in dystonic and unaffected body parts. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society., (© 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.)

The distances between pairs of tactile stimuli oriented across the width of the hand dorsum are perceived as about 40% larger than equivalent distances oriented along the hand length. Clear anisotropies of varying magnitudes have been found on different sites on the limbs and less consistently on other parts of the body, with anisotropies on the center of the forehead, but not on the belly. Reported anisotropies on the center of the forehead, however, might reflect an artefact of categorical perception from the face midline, which might be comparable to the expansion of tactile distance perception observed for stimuli presented across joint boundaries. To test whether tactile anisotropy is indeed a general characteristic of the tactile representation of the face, we assessed the perceived distance between pairs of touches on the cheeks and three locations on the forehead: left, right, and center. Consistent with previous results, a clear anisotropy was apparent on the center of the forehead. Importantly, similar anisotropies were also evident on the left and right sides of the forehead and both cheeks. These results provide evidence that anisotropy of perceived tactile distance is not a specific feature of tactile organization at the limbs but it also exists for the face, and further suggest that the spatial distortions found for tactile distances that extend across multiple body parts are not present for stimuli that extend across the body midline.

Recent studies have demonstrated that mental representations of the hand dorsum are distorted even for healthy participants. Perceptual hand maps estimated by pointing to specific landmarks (e.g., knuckles and tips of fingers) is stretched and shrunk along the medio-lateral and the proximo-distal axes, respectively. Similarly, tactile distance perception between two touches is longer along the medio-lateral axis than the proximo-distal axis. The congruency of the two types of distortions suggests that common perceptual and neural representations may be involved in these processes. Prolonged stimulation by two simultaneous touches having a particular distance can bias subsequent perception of tactile distances (e.g., adaptation to a long distance induces shorter stimuli to be perceived even shorter). This tactile distance adaptation aftereffect has been suggested to occur based on the modulations of perceptual and neural responses at low somatosensory processing stages. The current study investigated whether tactile distance adaptation aftereffects affect also the pattern of distortions on the perceptual hand maps. Participants localized locations on the hand dorsum cued by tactile stimulations (Experiment 1) or visually presented landmarks on a hand silhouette (Experiment 2). Each trial was preceded by adaptation to either a small (2 cm) or large (4 cm) tactile distance. We found clear tactile distance aftereffects. However, no changes were observed for the distorted pattern of the perceptual hand maps following adaptation to a tactile distance. Our results showed that internal body representations involved in perceptual distortions may be distinct between tactile distance perception and the perceptual hand maps underlying position sense., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Categories provide a fundamental source of information used to structure our perception of the world. For example, when people reproduce the remembered location of a dot in a circle, they implicitly impose vertical and horizontal axes onto the circle, and responses are biased towards the center of each of the resulting quadrants. Such results reveal the existence of spatial prototypes, which function as Bayesian priors and which are integrated with actual memory traces. Spatial prototypes have been extensively investigated and described in previous studies, but it remains unclear what type of information is used to create spatial categories. We developed a new approach that allowed to 'image' patterns of spatial bias in detail, and map the internal representational structure of objects and space. Previous studies, using circular shapes suggested that boundaries are established based on a viewer-based frame of reference, therefore using cues extrinsic to the object. Given that a circle has radial symmetry, the axes imposed cannot come from the shape itself. Here we investigated if the same applies for shapes with clearly-defined symmetry axes and thus intrinsic frames of reference. Using rotated shapes (squares and rectangles), where extrinsic and intrinsic cues are dissociated, we observed flexible usage of multiple reference frames. Furthermore, in certain contexts, participants relied mostly on cues intrinsic to the shape itself. These results show that humans divide visual space as a function of multiple reference frames, in a flexible, and context dependent manner., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Recent studies have reported that adaptation to extreme body types produces aftereffects on judgments of body normality and attractiveness, and also judgments of the size and shape of the viewer's own body. This latter effect suggests that adaptation could constitute an experimental model of media influences on body image. Alternatively, adaptation could affect perception of test stimuli, which should produce the same aftereffects for judgments about participant's own body or someone else's body. Here, we investigated whether adaptation similarly affects judgments about one's body and other bodies. We were interested in participants' own body image judgments, i.e., we wanted to measure the mental representations to which the test stimuli were compared and not the perception of test stimuli per se . Participants were adapted to pictures of thin or fat bodies and then rated whether bodies were fatter or thinner than either: their own body, an average body (Experiment 1), or the body of another person (Experiments 2 and 3). By keeping the visual stimuli constant but changing the task/type of judgment, i.e., the internal criterion participants are asked to judge the bodies against, we investigated how adaptation affects different stored representations of bodies, specifically own body image vs. representations of others. After adaptation, a classic aftereffect was found, with judgments biased away from the adapting stimulus. Critically, aftereffects were nearly identical for judgments of one's own body and for other people's bodies. These results suggest that adaptation affects body representations in a generic way and may not be specific to the own body image., (Copyright © 2019 Ambroziak, Azañón and Longo.)

Perceived limb position is known to rely on sensory signals and motor commands. Another potential source of input is a standard representation of body posture, which may bias perceived limb position toward more stereotyped positions. Recent results show that tactile stimuli are processed more efficiently when delivered to a thumb in a relatively low position or an index finger in a relatively high position. This observation suggests that we may have a standard posture of the body that promotes a more efficient interaction with the environment. In this study, we mapped the standard posture of the entire hand by characterizing the spatial associations of all 5 digits. Moreover, we show that the effect is not an artifact of intermanual integration. Results showed that the thumb is associated with low positions, while the other fingers are associated with upper locations. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

New research demonstrates systematic errors of tactile localisation, involving confusions of body parts and body sides. Such errors do not follow the organisation of topographic maps in somatosensory cortex, suggesting that tactile localisation involves coding of abstract features of limbs., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The processing of touch depends of multiple factors, such as the properties of the skin and type of receptors stimulated, as well as features related to the actual configuration and shape of the body itself. A large body of research has focused on the effect that the nature of the stimuli has on tactile processing. Less research, however, has focused on features beyond the nature of the touch. In this review, we focus on some features related to the body that have been investigated for less time and in a more fragmented way. These include the symmetrical quality of the two sides of the body, the postural configuration of the body, as well as the size and shape of different body parts. We will describe what we consider three key aspects: (1) how and at which stages tactile information is integrated between different parts and sides of the body; (2) how tactile signals are integrated with online and stored postural configurations of the body, regarded as priors; (3) and how tactile signals are integrated with representations of body size and shape. Here, we describe how these different body dimensions affect integration of tactile information as well as guide motor behavior by integrating them in a single model of tactile processing. We review a wide range of neuropsychological, neuroimaging, and neurophysiological data and suggest a revised model of tactile integration on the basis of the one proposed previously by Longo et al.

The stage at which processing of tactile distance occurs is still debated. We addressed this issue by implementing an adaptation-aftereffect paradigm with passive touch. We demonstrated the presence of a strong aftereffect, induced by the simultaneous presentation of pairs of tactile stimuli. After adaptation to two different distances, one on each hand, participants systematically perceived a subsequent stimulus delivered to the hand adapted to the smaller distance as being larger. We further investigated the nature of the aftereffects, demonstrating that they are orientation- and skin-region-specific, occur even when just one hand is adapted, do not transfer either contralaterally or across the palm and dorsum, and are defined in a skin-centered, rather than an external, reference frame. These characteristics of tactile distance aftereffects are similar to those of low-level visual aftereffects, supporting the idea that distance perception arises at early stages of tactile processing., Competing Interests: The authors declare no conflict of interest.

Body image distortions are common in healthy individuals and a central aspect of serious clinical conditions, such as eating disorders. This commentary explores the potential implications of body image and its distortions for the insurance hypothesis. In particular, we speculate that body image may be an intervening variable mediating the relationship between perceived food scarcity and eating behavior.

To perceive the location of touch in space, we integrate information about skin-location with information about the location of that body part in space. Most research investigating this process of tactile spatial remapping has used the so-called crossed-hands deficit, in which the ability to judge the temporal order of touches on the two hands is impaired when the arms are crossed. This posture induces a conflict between skin-based and tactile external spatial representations, specifically in the left-right dimension. Thus, it is unknown whether touch is affected by posture when spatial relations other than the right-left dimension are available. Here, we tested the extent to which the crossed-hands deficit is a measure of tactile remapping, reflecting tactile encoding in three-dimensional space. Participants judged the temporal order of tactile stimuli presented to crossed and uncrossed hands. The arms were placed at different elevations (up-down dimension; Experiments 1 and 2), or at different distances from the body in the depth plane (close-far dimension; Experiment 3). The crossed-hands deficit was reduced when other sources of spatial information, orthogonal to the left-right dimension (i.e., close-far, up-down), were available. Nonetheless, the deficit persisted in all conditions, even when processing of non-conflicting information in the close-far or up-down dimensions was enough to solve the task. Together, these results demonstrate that the processing underlying the crossed-hands deficit is related to the encoding of tactile localization in three-dimensional space, rather than related uniquely to the cost of processing information in the right-left dimension. Furthermore, the persistence of the crossing effect provides evidence for automatic integration of all available information during the encoding of tactile information., (Copyright © 2016 Elsevier B.V. All rights reserved.)

When locating touch, we remap its location from skin-based to external coordinates as a function of body posture. While remapping is thought to occur whenever there is tactile input, research has focused on a special case, the crossed-hands deficit, where tactile localization is impaired when the limbs are crossed compared with uncrossed. To date, these studies have always stimulated portions of the limbs that are crossed, such as a finger of each hand. It is therefore unknown whether the deficit induced by arm crossing is specific to the crossed portion of the limb or affects the limb as a whole. In Experiments 1 and 2, we stimulated the shoulders and elbows and found that tactile localization, measured with temporal order judgments, was unaffected by crossing the forearms. In Experiment 3, a crossed-limbs deficit was observed for touches on a single skin location when that location was distal-but not proximal-to the crossing point of the arms. In Experiment 4, we found a similar crossed-limbs deficit irrespective of how far distally to the crossing point touch was applied. Together, these results demonstrate that crossing the limbs affects tactile perception only distal to the point of crossing. The process of remapping tactile events does not take into account the end-point location of the limb, but an extremely precise metric description of the touch relative to the configuration of both arms. (PsycINFO Database Record, ((c) 2016 APA, all rights reserved).)

Recently, Vanden Bulcke, Crombez, Durnez, and Van Damme (2015) investigated whether the attentional prioritization of a specific location due to the anticipation of pain is modality specific or multisensory. They used a temporal order judgment task in which participants judged the order of either two tactile or two visual stimuli, one presented on each hand. Additionally, participants either expected the occurrence of a painful stimulus on one hand or the absence of any pain. Results showed that participants' judgments were biased to the advantage of the stimuli, tactile or visual, presented at the location where pain was expected. The authors concluded that the anticipation of pain leads to a multisensory prioritization of information presented at the threatened spatial location. Here, we would like to question their conclusion in terms of a genuine attentional modulation of multisensory nature, based on methodological and theoretical grounds., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Localizing touch in space is essential for goal-directed action. Because body posture changes, the brain must transform tactile coordinates from an initial skin-based representation to external space by integrating information about current posture. This process, referred to as tactile remapping, generally results in accurate localization, but accuracy drops when skin-based and external spatial representations of touch are conflicting, e.g., after crossing the limbs. Importantly, frequent experience of such postures can improve localization. This suggests that remapping may not only integrate current sensory input but also prior experience. Here, we demonstrate that this can result in rapid changes in localization performance over the course of few trials. We obtained an implicit measure of tactile localization by studying the perceived temporal order of two touches, one on each hand. Crucially, we varied the number of consecutive trials during which participants held their arms crossed or uncrossed. As expected, accuracy dropped immediately after the arms had been crossed. Importantly, this was followed by a progressive recovery if posture was maintained, despite the absence of performance feedback. Strikingly, a significant improvement was already evident in the localization of the second pair of touches. This rapid improvement required preceding touch in the same posture and did not occur merely as a function of time. Moreover, even touches that were not task relevant led to improved localization of subsequent touch. Our findings show that touches are mapped from skin to external space as a function of recent tactile experience., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

To respond to a touch, it is often necessary to localize it in space, and not just on the skin. The computation of this external spatial location involves the integration of somatosensation with visual and proprioceptive information about current body posture. In the past years, the study of touch localization has received substantial attention and has become a central topic in the research field of multisensory integration. In this review, we will explore important findings from this research, zooming in on one specific experimental paradigm, the temporal order judgment (TOJ) task, which has proven particularly fruitful for the investigation of tactile spatial processing. In a typical TOJ task participants perform non-speeded judgments about the order of two tactile stimuli presented in rapid succession to different skin sites. This task could be solved without relying on external spatial coordinates. However, postural manipulations affect TOJ performance, indicating that external coordinates are in fact computed automatically. We show that this makes the TOJ task a reliable indicator of spatial remapping, and provide an overview over the versatile analysis options for TOJ. We introduce current theories of TOJ and touch localization, and then relate TOJ to behavioral and electrophysiological evidence from other paradigms, probing the benefit of TOJ for the study of spatial processing as well as related topics such as multisensory plasticity, body processing, and pain.

Orienting our gaze or attention to the location of tactile events in the skin feels natural and effortless. However, this process requires combining somatosensory and proprioceptive information in a non-trivial, time consuming, fashion. Here we address the time course of tactile remapping, from somatotopically-based representations, to a spatiotopic reference frame. We compared electrical responses at the scalp evoked by touch at one finger as participants held their arms straight or else, crossed about the body midline. This postural manipulation creates a conflict between frames of reference, which can be used to reveal the consequences of spatial remapping. Behavioural performance was gauged online for crossed and uncrossed postures using bimanual temporal order judgment (TOJ) trials occurring occasionally during the recording session. The first electrophysiological signs of tactile remapping were observed around 70 ms after the tactile event, overlapping in time with the somatosensory component N80. This electrophysiological effect was strongly lateralized to the left scalp and independent of the hand being stimulated. Moreover, participants who manifested a stronger behavioural conflict between frames of reference in the TOJ task displayed a larger electrophysiological effect. Based on these findings, and the known properties of the somatosensory network, we argue that remapping of tactile space depends on fast feedback projections from association areas of the parietal cortex, and encompasses a left-lateralized fronto-parietal network supporting the selection of guided actions., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Localizing tactile events in external space is required for essential functions such as orienting, haptic exploration, and goal-directed action in peripersonal space. In order to map somatosensory input into a spatiotopic representation, information about skin location must be integrated with proprioceptive information about body posture. We investigated the neural bases of this tactile remapping mechanism in humans by disrupting neural activity in the putative human homolog of the monkey ventral intraparietal area (hVIP), within the right posterior parietal cortex (rPPC), which is thought to house external spatial representations. Participants judged the elevation of touches on their (unseen) forearm relative to touches on their face. Arm posture was passively changed along the vertical axis, so that elevation judgments required the use of an external reference frame. Single-pulse transcranial magnetic stimulation (TMS) over the rPPC significantly impaired performance compared to a control site (vertex). Crucially, proprioceptive judgments of arm elevation or tactile localization on the skin remained unaffected by rPPC TMS. This selective disruption of tactile remapping suggests a distinct computational process dissociable from pure proprioceptive and somatosensory localization. Furthermore, this finding highlights the causal role of human PPC, putatively VIP, in remapping touch into external space., (2010 Elsevier Ltd. All rights reserved.)

To investigate attentional shifting in perihand space, we measured performance on a covert visual orienting task under different hand positions. Participants discriminated visual shapes presented on a screen and responded using footpedals placed under their right foot. With the right hand positioned by the right side of the screen, mean cueing effects were significantly greater for targets presented on the right compared to the left side, at the shortest stimulus onset asynchrony. The right hand still affected attention when the left foot was used to respond and when the right hand was crossed over the midline, indicating that this effect is not restricted to the right hemifield and cannot be accounted for by greater stimulus-response compatibility with the right (responding) foot. These experiments provide preliminary evidence that the presence of the right hand can modulate shifts of visual attention but emphasise the importance of stimulus-response compatibility effects in such investigations., (Copyright 2010 Elsevier Inc. All rights reserved.)

Reacting to a touch on the skin often requires the remapping of the initial somatotopicaly-based representation of the stimulus into an external frame of reference that incorporates information about current body posture. A growing number of studies support the view that tactile encoding in external coordinates occurs automatically. However, it remains unclear whether or not spatial task demands are required to trigger this remapping process, casting some doubt on the automaticity hypothesis. We designed three experiments in which space was progressively removed, and tactile remapping across different body postures was gauged through the modulation of visual performance. We used speeded two-alternative forced-choice colour judgements (i.e., a nonspatial selection feature) about visual targets presented laterally following a spatially noninformative (congruent or incongruent) tactile cue on one hand. In experiment 1, using footpedal responses, visual performance was modulated according to the external location of the tactile cue, regardless of hand posture (either crossed or uncrossed). In experiment 2, using verbal responses, external cueing was also observed (albeit in an attenuated fashion) despite the removal of space from response set. In experiment 3 we removed spatial uncertainty about cue and target locations by presenting tactile cues and visual targets from fixed positions, yet spatial congruency still exerted some modulation on visual performance, again independent of hand posture. These results demonstrate that engaging in spatial tasks is not a prerequisite for triggering tactile remapping, and are thus in agreement with previous accounts suggesting that touch is automatically remapped.

The neural circuits underlying initial sensory processing of somatic information are relatively well understood. In contrast, the processes that go beyond primary somatosensation to create more abstract representations related to the body are less clear. In this review, we focus on two classes of higher-order processing beyond somatosensation. Somatoperception refers to the process of perceiving the body itself, and particularly of ensuring somatic perceptual constancy. We review three key elements of somatoperception: (a) remapping information from the body surface into an egocentric reference frame, (b) exteroceptive perception of objects in the external world through their contact with the body, and (c) interoceptive percepts about the nature and state of the body itself. Somatorepresentation, in contrast, refers to the essentially cognitive process of constructing semantic knowledge and attitudes about the body, including: (d) lexical-semantic knowledge about bodies generally and one's own body specifically, (e) configural knowledge about the structure of bodies, (f) emotions and attitudes directed towards one's own body, and (g) the link between physical body and psychological self. We review a wide range of neuropsychological, neuroimaging and neurophysiological data to explore the dissociation between these different aspects of higher somatosensory function., (2009 Elsevier Ltd. All rights reserved.)

Recent years have seen increasing numbers of transcranial magnetic stimulation (TMS) studies focusing on somatosensory processing. Most have centered on the primary somatosensory functions of tactile detection, localization and discrimination, and have applied TMS to primary somatosensory areas. These studies confirm the basic functions of primary somatosensory areas, and the behavioural and physiological effects of different TMS protocols. Fewer studies, however, have investigated higher somatosensory function. Here, we review the somatosensory TMS literature both in and beyond primary somatosensory areas. We discuss the plausibility of modulating multisensory representations of one's own body via TMS, and highlight the potential for TMS to probe higher cognitive functions through the modulation of unimodal perceptual systems such as touch, vision or proprioception.

The mindless act of swatting a mosquito on the hand poses a remarkable challenge for the brain. Given that the primary somatosensory cortex maps skin location independently of arm posture [1, 2], the brain must realign tactile coordinates in order to locate the origin of the stimuli in extrapersonal space. Previous studies have highlighted the behavioral relevance of such an external mapping of touch, which results from combining somatosensory input with proprioceptive and visual cues about body posture [3-7]. However, despite the widely held assumption about the existence of this remapping process from somatotopic to external space and various findings indirectly suggesting its consequences [8-11], a demonstration of its changing time course and nature was lacking. We examined the temporal course of this multisensory interaction and its implications for tactile awareness in humans using a crossmodal cueing paradigm [12, 13]. What we show is that before tactile events are referred to external locations [12-15], a fleeting, unconscious image of the tactile sensation abiding to a somatotopic frame of reference rules performance. We propose that this early somatotopic "glimpse" arises from the initial feed-forward sweep of neural activity to the primary somatosensory cortex, whereas the later externally-based, conscious experience reflects the activity of a somatosensory network involving recurrent connections from association areas.

During the apparently mindless act of localizing a tactile sensation, our brain must realign its initial spatial representation (somatotopicaly arranged) according to current body posture (arising from proprioception, vision and even audition).1-3 We have recently illustrated4 the temporal course of this recoding of tactile space from somatotopic to external coordinates using a crossmodal cueing psychophysical paradigm5,6 where behavioral reactions to visual targets are evaluated as a function of the location of irrelevant tactile cues. We found that the tactile events are initially represented in terms of a fleeting, non-conscious but nevertheless behaviorally consequential somatotopic format, which is quickly replaced by the representations referred to external spatial locations that prevail in our everyday experience. In this addendum, we test the intuition that frequent changes in body posture will make it harder to update the spatial remapping system and thus, produce stronger psychophysical correlates of the initial somatotopically-based spatial representations. Contrary to this expectation, however, we found no evidence for a modulation when preventing adaptation to a body posture.

Localizing and reacting to tactile events on our skin requires the coordination between primary somatotopic projections and an external representation of space. Previous research has attributed an important role to early visual experience in shaping up this mapping. Here, we addressed the role played by immediately available visual information about body posture. We asked participants to determine the temporal order of two successive tactile events delivered to the hands while they adopted a crossed or an uncrossed-hands posture. As previously found, hand-crossing led to a dramatic impairment in tactile localization, which is a phenomenon attributed to a mismatch between somatotopic and externally-based frames of reference. In the present study, however, participants watched a pair of rubber hands that were placed either in a crossed or uncrossed posture (congruent or incongruent with the posture of their own hands). The results showed that the crossed-hands deficit can be significantly ameliorated by the sight of uncrossed rubber hands (Experiment 1). Moreover, this visual modulation seemed to depend critically on the degree to which the visual information about the rubber hands can be attributed to one's own actions, in a process revealing short-term adaptation (Experiment 2).

Patients with right hemisphere brain lesions often suffer from deficits in spatial attention that can be manifested in different sensory modalities. It has recently been claimed that a relationship (i.e., association) could exist between symptoms of hemi-inattention in different modalities, based on correlations between the results of visual and auditory clinical tests of neglect or extinction. However, it should be noted that the visual and auditory tasks varied greatly both in response type and level of sensitivity. Here, we have examined cross-modal associations in spatial attention deficits using a temporal order judgment task (TOJ) in which patients were required to identify which of two visual or auditory objects had appeared first. When compared to age and education matched control participants, the patients needed, on average, the contralesional stimulus to lead the ipsilesional stimulus to achieve the point of subjective simultaneity (PSS). No association between the degree of visual and auditory hemi-inattention was observed amongst the patients, suggesting that there is a certain degree of independence between the mechanisms subserving spatial attention across sensory modalities.