Can vision of the body ameliorate impaired somatosensory function (original) (raw)
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Persistence of visual–tactile enhancement in humans
Neuroscience Letters, 2004
We report two experiments in which non-informative vision of the finger enhanced tactile acuity on the fingertip. The right index finger was passively lifted to contact a grating. Twelve participants judged orientations of tactile gratings while viewing either the fingertip, or a neutral object presented via a mirror at the fingertip's location. In Expt. 1, tactile orientation discrimination for near-threshold gratings was improved when viewing the fingertip, compared to viewing the neutral object. Experiment 2 examined the temporal persistence of this effect, and found significant visual-tactile enhancement when a dark interval of up to 10 s intervened between viewing the finger and tactile stimulation. These results suggest that viewing the body modulates the neural circuitry of primary somatosensory cortex, outlasting visual inputs.
Experimental Brain Research, 2020
Vision of the body has been reported to improve tactile acuity even when vision is not informative about the actual tactile stimulation. However, it is currently unclear whether this effect is limited to body parts such as hand, forearm or foot that can be normally viewed, or it also generalizes to body locations, such as the shoulder, that are rarely before our own eyes. In this study, subjects consecutively performed a detection threshold task and a numerosity judgment task of tactile stimuli on the shoulder. Meanwhile, they watched either a real-time video showing their shoulder or simply a fixation cross as control condition. We show that non-informative vision improves tactile numerosity judgment which might involve tactile acuity, but not tactile sensitivity. Furthermore, the improvement in tactile accuracy modulated by vision seems to be due to an enhanced ability in discriminating the number of adjacent active electrodes. These results are consistent with the view that bimod...
Tactile Acuity is Enhanced in Blindness
2003
Functional imaging studies in blind subjects have shown tactile activation of cortical areas that normally subserve vision, but whether blind people have enhanced tactile acuity has long been controversial. We compared the passive tactile acuity of blind and sighted subjects on a fully automated grating orientation task and used multivariate Bayesian data analysis to determine predictors of acuity. Acuity was significantly superior in blind subjects, independently of the degree of childhood vision, light perception level, or Braille reading. Acuity was strongly dependent on the force of contact between the stimulus surface and the skin, declined with subject age, and was better in women than in men. Despite large intragroup variability, the difference between blind and sighted subjects was highly significant: the average blind subject had the acuity of an average sighted subject of the same gender but 23 years younger. The results suggest that crossmodal plasticity may underlie tactile acuity enhancement in blindness.
Tactile spatial acuity enhancement in blindness: evidence for experience-dependent mechanisms
The Journal of neuroscience, 2011
Tactile spatial acuity is enhanced in blindness, according to several studies, but the cause of this enhancement has been controversial. Two competing hypotheses are the tactile experience hypothesis (reliance on the sense of touch drives tactile-acuity enhancement) and the visual deprivation hypothesis (the absence of vision itself drives tactile-acuity enhancement). Here, we performed experiments to distinguish between these two hypotheses. We used force-controlled grating orientation tasks to compare the passive (finger stationary) tactile spatial acuity of 28 profoundly blind and 55 normally sighted humans on the index, middle, and ring fingers of each hand, and on the lips. The tactile experience hypothesis predicted that blind participants would outperform the sighted on the fingers, and that Braille reading would correlate with tactile acuity. The visual deprivation hypothesis predicted that blind participants would outperform the sighted on fingers and lips. Consistent with the tactile experience hypothesis, the blind significantly outperformed the sighted on all fingers, but not on the lips. Additionally, among blind participants, proficient Braille readers on their preferred reading index finger outperformed nonreaders. Finally, proficient Braille readers performed better with their preferred reading index finger than with the opposite index finger, and their acuity on the preferred reading finger correlated with their weekly reading time. These results clearly implicate reliance on the sense of touch as the trigger for tactile spatial acuity enhancement in the blind, and suggest the action of underlying experience-dependent neural mechanisms such as somatosensory and/or cross-modal cortical plasticity.
Viewing the body modulates tactile receptive fields
Experimental Brain Research, 2007
Tactile discrimination performance depends on the receptive field (RF) size of somatosensory cortical (SI) neurons. Psychophysical masking effects can reveal the RF of an idealized ''virtual'' somatosensory neuron. Previous studies show that top-down factors strongly affect tactile discrimination performance. Here, we show that noninformative vision of the touched body part influences tactile discrimination by modulating tactile RFs. Ten subjects performed spatial discrimination between touch locations on the forearm. Performance was improved when subjects saw their forearm compared to viewing a neutral object in the same location. The extent of visual information was relevant, since restricted view of the forearm did not have this enhancing effect. Vibrotactile maskers were placed symmetrically on either side of the tactile target locations, at two different distances. Overall, masking significantly impaired discrimination performance, but the spatial gradient of masking depended on what subjects viewed. Viewing the body reduced the effect of distant maskers, but enhanced the effect of close maskers, as compared to viewing a neutral object. We propose that viewing the body improves functional touch by sharpening tactile RFs in an early somatosensory map. Top-down modulation of lateral inhibition could underlie these effects.
Touch to See: Neuropsychological Evidence of a Sensory Mirror System for Touch
Cerebral Cortex, 2011
The observation of touch can be grounded in the activation of brain areas underpinning direct tactile experience, namely the somatosensory cortices. What is the behavioral impact of such a mirror sensory activity on visual perception? To address this issue, we investigated the causal interplay between observed and felt touch in right brain-damaged patients, as a function of their underlying damaged visual and/or tactile modalities. Patients and healthy controls underwent a detection task, comprising visual stimuli depicting touches or without a tactile component. Touch and Notouch stimuli were presented in egocentric or allocentric perspectives. Seeing touches, regardless of the viewing perspective, differently affects visual perception depending on which sensory modality is damaged: In patients with a selective visual deficit, but without any tactile defect, the sight of touch improves the visual impairment; this effect is associated with a lesion to the supramarginal gyrus. In patients with a tactile deficit, but intact visual perception, the sight of touch disrupts visual processing, inducing a visual extinction-like phenomenon. This disruptive effect is associated with the damage of the postcentral gyrus. Hence, a damage to the somatosensory system can lead to a dysfunctional visual processing, and an intact somatosensory processing can aid visual perception.
Noninformative vision improves the spatial resolution of touch in humans
Current Biology, 2001
Research on sensory perception now often tal setup , and Figure 2 outlines the experimental conditions in which the view given to the participants was considers more than one sense at a time. This varied. Figure 3 shows typical data from two blocks of approach reflects real-world situations, such as trials showing how 2PDT estimates were arrived at. The when a visible object touches us. Indeed, vision results (Figure 4a,b) clearly show that tactile resolution and touch show great interdependence: the sight of was better when visibility of the arm was allowed coma body part can reduce tactile target detection pared to when the arm was in complete darkness. For times [1], visual and tactile attentional systems are those participants who performed binocularly, the mean spatially linked [2], and the texture of surfaces that tactile two-point discrimination threshold was signifiare actively touched with the fingertips is perceived cantly lower (mean ϭ 35 mm) when the arm could be seen using both vision and touch [3]. However, these than when the arm was in complete darkness (mean ϭ 42 previous findings might be mediated by spatial mm; t 8 ϭ 2.1, p ϭ 0.03). This central finding was replicated attention [1, 2] or by improved guidance of in a separate group of participants who performed all four movement [3] via visually enhanced body position conditions monocularly. Visibility of the arm once more sense [4-6]. Here, we investigate the direct effects provided lower thresholds (mean ϭ 27 mm) than when of viewing the body on passive touch. We measured the arm was in darkness (mean ϭ 31 mm; t 9 ϭ 2.9, p ϭ tactile two-point discrimination thresholds [7] on 0.009). This benefit could not be attributed to trivial visithe forearm while manipulating the visibility of the bility of the tactile stimulation, since the arm could not arm but holding gaze direction constant. The be seen during the moment of tactile stimulation. Indeed, spatial resolution of touch was better when the arm a control study revealed that the available visual informawas visible than when it was not. Tactile tion alone (replayed later from a video, without tactile performance was further improved when the view of stimulation) led to only chance performance on judgethe arm was magnified. In contrast, performance ments of the number of tactile stimuli. Moreover, gaze was not improved by viewing a neutral object at the direction was constant across all conditions. Therefore, arm's location, ruling out improved spatial the effects of gaze direction, which are known to affect orienting as a possible account. Controls confirmed tactile performance [8], cannot explain our results. that no information about the tactile stimulation was provided by visibility of the arm. This visual Importantly, visibility of the arm also gave rise to better enhancement of touch may point to online performance than did visibility of the neutral object (mean ϭ reorganization of tactile receptive fields. 30 mm; t 9 ϭ 1.9, p ϭ 0.04; Figure 4d). Also, visibility of
Frames of Reference for Mapping Tactile Stimuli in Brain-Damaged Patients
Journal of Cognitive Neuroscience, 1999
n Twelve normal controls, twelve left-brain-damaged patients, and thirty-six right-brain-damaged patients with or w ithout tactile extinction or tactile neglect were asked to report light touches delivered to the left or the right hand or simultaneously to both hands. The hands could be in anatomic position or one hand could cross over the other. M oreover, the two hands could be in the left or the right hemispace or across the corporeal midline. Controls and nontactile-extinction groups performed better w hen the hands were in anatomical than in crossed position. By contrast, patients with tactile extinction detected contralesional stimuli w ith higher accuracy in crossed than in anatomical position. This result suggests that, in these patients, impairments in detecting contralesional stimuli can be due not only to sensory but also to spatial factors contingent upon the position of the hands. There was no interaction between the effect of crossing the hands and the hemispace w here the crossing took place. This suggests that coding the position of a hand as left or right does not necessarily occur in relation to the bodily midline, but it may arise from the computation of the position of the other hand. n
Short-Term Visual Deprivation Does Not Enhance Passive Tactile Spatial Acuity
PloS one, 2011
An important unresolved question in sensory neuroscience is whether, and if so with what time course, tactile perception is enhanced by visual deprivation. In three experiments involving 158 normally sighted human participants, we assessed whether tactile spatial acuity improves with short-term visual deprivation over periods ranging from under 10 to over 110 minutes. We used an automated, precisely controlled two-interval forced-choice grating orientation task to assess each participant's ability to discern the orientation of square-wave gratings pressed against the stationary index finger pad of the dominant hand. A two-down one-up staircase (Experiment 1) or a Bayesian adaptive procedure (Experiments 2 and 3) was used to determine the groove width of the grating whose orientation each participant could reliably discriminate. The experiments consistently showed that tactile grating orientation discrimination does not improve with short-term visual deprivation. In fact, we found that tactile performance degraded slightly but significantly upon a brief period of visual deprivation (Experiment 1) and did not improve over periods of up to 110 minutes of deprivation (Experiments 2 and 3). The results additionally showed that grating orientation discrimination tends to improve upon repeated testing, and confirmed that women significantly outperform men on the grating orientation task. We conclude that, contrary to two recent reports but consistent with an earlier literature, passive tactile spatial acuity is not enhanced by short-term visual deprivation. Our findings have important theoretical and practical implications. On the theoretical side, the findings set limits on the time course over which neural mechanisms such as crossmodal plasticity may operate to drive sensory changes; on the practical side, the findings suggest that researchers who compare tactile acuity of blind and sighted participants should not blindfold the sighted participants.
Experimental Brain Research, 2008
Growing evidence suggests that blind subjects outperform the sighted on certain tactile discrimination tasks depending on cutaneous inputs. The purpose of this study was to compare the performance of blind (n = 14) and sighted (n = 15) subjects in a haptic angle discrimination task, depending on both cutaneous and proprioceptive feedback. Subjects actively scanned their right index finger over pairs of two-dimensional (2-D) angles (standard 90 degrees ; comparison 91-103 degrees ), identifying the larger one. Two exploratory strategies were tested: arm straight or arm flexed at the elbow so that joint movement was, respectively, mainly proximal (shoulder) or distal (wrist, finger). The mean discrimination thresholds for the sighted subjects (vision occluded) were similar for both exploratory strategies (5.7 and 5.8 degrees , respectively). Exploratory strategy likewise did not modify threshold in the blind subjects (proximal 4.3 degrees ; distal 4.9 degrees ), but thresholds were on average lower than for the sighted subjects. A between-group comparison indicated that blind subjects had significantly lower thresholds than did the sighted subjects, but only for the proximal condition. The superior performance of the blind subjects likely represents heightened sensitivity to haptic inputs in response to visual deprivation, which, in these subjects, occurred prior to 14 years of age.