A conceptual model of tactile processing across body features of size, shape, side, and spatial location

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: (a) how and at which stages tactile information is integrated between different parts and sides of the body; (b) how tactile signals are integrated with online and stored postural configurations of the body, regarded as priors; (c) 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 behaviour 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 and colleagues (2010)

Spatial remapping of Tactile Events: Assessing the effects of frequent posture changes

During the apparently mindless act of localizing a tactile sensation our brain must realign its initial spatial representation on the skin (somatotopicaly arranged) according to current body posture (arising from proprioception, vision and even audition). 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 behavioural 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

Using time to investigate space: a review of tactile temporal order judgments as a window onto spatial processing in touch

Heed T, Azañón E. Using time to investigate space: a review of tactile temporal order judgments as a window onto spatial processing in touch. Frontiers in Psychology. 2014;5:76

Spatial Distortion in Perception and Cognition

Prof Matthew Longo gave his inaugural lecture about “Spatial Distortions in Perception and Cognition” on June 4th. He has been a lecturer in the Department of Psychological Sciences at Birkbeck, University of London, since 2010, and has recently been appointed Professor of Cognitive Neuroscience in the same Department.This post was contributed by Elena Azañón and Luigi Tamè, postdoctoral fellows in Birkbeck’s BodyLab

Dynamic tuning of tactile localization to body posture

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

A three-dimensional spatial characterization of the crossed-hands deficit

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 continuous 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 (near-far dimension; Experiment 3). The crossed-hands deficit was reduced when other sources of spatial information, orthogonal to the left-right dimension, were available. Nonetheless, the deficit persisted in all conditions, even when processing of non-conflicting information 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, regardless of whether or not it is conflicting

Eating and body image: does food insecurity make us feel thinner?

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 relation between perceived food scarcity and eating behavior

Intact Organization of Tactile Space Perception in Isolated Focal Dystonia

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

Anisotropies of tactile distance perception on the face

Data of the two experiments presented in the paper: Anisotropies of tactile distance perception on the face. Authors: Elena Azañón Elena Amoruso Elena Calzolari Michael Ben Yehuda Patrick Haggard Matthew R. Long