Search

Bodily illusions have been used to investigate one's sense of self and body ownership. This study explored the effect of the height of the first-person perspective (1PP) on out-of-body experience (OBE) illusion in which participants see their backs through a head-mounted display, receive visuotactile stimulation, and gradually feel as if they are sitting behind themselves, experiencing a sensation similar to an OBE. We hypothesized that increasing or decreasing the height of the 1PP would induce the OBE illusion at all heights and that participants' perceived own heights would adjust according to the 1PP height. We also predicted that the size and distance of external objects would vary according to the perceived height of one's own body. The results revealed that the OBE illusion occurred at all 1PP heights and was stronger when the 1PP height was lower or higher than usual. Meanwhile, the participants' perceived own heights, the sizes and distances of external objects did not change. These results suggest that manipulating the 1PP may affect the magnitude of the OBE illusion, but not the perception of the dimensions of the self or external objects. The height of 1PP may be one of the important factors in the bodily illusion. [ABSTRACT FROM AUTHOR]

Introduction: We report a very unique clinical presentation of a patient who complained, after a left parietal brain damage, about feeling tactile stimulations on his right upper limb without being able to localize them. Methods: Using a single case study approach, we report three experiments relying on several custom-made tasks to explore the different levels of somatosensory information processing, ranging from somato-sensation to somato-representation. Results: Our results showed a preserved ability to localize tactile stimuli applied on the right upper limb when using pointing responses while the ability to localize was less efficient when having to name the stimulated part (akin Numbsense). When the stimuli were applied on more distal locations (i.e., on the hand and on fingers), the number of correct responses decreased significantly independently of the modality of response. Finally, when visually presented with a stimulus delivered on the hand of an examiner in synchrony with the stimulation on the hidden hand of the patient, responses were largely influenced by the visual information available. Altogether, the convergence of these different customized tasks revealed an absence of autotopagnosia for motor responses for the right upper limb, associated with altered abilities to discriminate stimulus applied on distal and restricted/closer zones in the hand. Discussion: The somato-representation of our patient seemed to significantly rely on visual information, leading to striking deficits to localize tactile stimuli when vision and somesthesic afferences are discordant. This case report offers a clinical illustration of pathological imbalance between vision and somesthesia. Implications of these troubles in somato-representation on higher cognitive level processes are discussed. [ABSTRACT FROM AUTHOR]

IntroductionWe report a very unique clinical presentation of a patient who complained, after a left parietal brain damage, about feeling tactile stimulations on his right upper limb without being able to localize them.MethodsUsing a single case study approach, we report three experiments relying on several custom-made tasks to explore the different levels of somatosensory information processing, ranging from somato-sensation to somato-representation.ResultsOur results showed a preserved ability to localize tactile stimuli applied on the right upper limb when using pointing responses while the ability to localize was less efficient when having to name the stimulated part (akin Numbsense). When the stimuli were applied on more distal locations (i.e., on the hand and on fingers), the number of correct responses decreased significantly independently of the modality of response. Finally, when visually presented with a stimulus delivered on the hand of an examiner in synchrony with the stimulation on the hidden hand of the patient, responses were largely influenced by the visual information available. Altogether, the convergence of these different customized tasks revealed an absence of autotopagnosia for motor responses for the right upper limb, associated with altered abilities to discriminate stimulus applied on distal and restricted/closer zones in the hand.DiscussionThe somato-representation of our patient seemed to significantly rely on visual information, leading to striking deficits to localize tactile stimuli when vision and somesthesic afferences are discordant. This case report offers a clinical illustration of pathological imbalance between vision and somesthesia. Implications of these troubles in somato-representation on higher cognitive level processes are discussed.

The neural representation of multisensory space near the body is modulated by the active use of long tools in non-human primates. Here, we investigated whether the electrophysiological correlates of visuo-tactile integration in near and far space were modulated by active tool use in healthy humans. Participants responded to a tactile target delivered to one hand while an irrelevant visual stimulus was presented ipsilaterally in near or far space. This crossmodal task was performed after the use of either short or long tools. Crucially, the P100 components elicited by visuo-tactile stimuli was enhanced on far as compared to near space trials after the use of long tools, while no such difference was present after short tool use. Thus, we found increased neural responses in brain areas encoding tactile stimuli to the body when visual stimuli were presented close to the tip of the tool after long tool use. This increased visuo-tactile integration on far space trials following the use of long tools might indicate a transient remapping of multisensory space. We speculate that performing voluntary actions with long tools strengthens the representation of sensory information arising within portions of space (i.e. the hand and the tip of the tool) that are most functionally relevant to one's behavioural goals. [ABSTRACT FROM AUTHOR]

Abstract The peripersonal space (PPS) is the space surrounding our body, represented in a multisensory fashion by integrating stimuli of different modalities. Recently, it has been demonstrated that PPS is emotionally connoted, being sensitive to the different affective valence of the stimuli located inside it. However, how visuo-tactile interactions can be spatially shaped by intrinsic or acquired valence of stimuli is not clear. To investigate this, we conducted three experiments in which participants performed a visuo-tactile interaction task, while the intrinsic valence (Exp. 1 and 2) or the learned valence (Exp. 3) of visual stimuli was manipulated. Participants were asked to respond as fast as possible to a tactile stimulus that was delivered while a visual stimulus was approaching (Exp.1 and 3) or receding (Exp.2) from the hand. Touch was synchronized with different distances of the visual stimulus from the hand. We found that both the expectancy of stimulus and the distance of the visual one from the hand impact RTs to tactile targets. Crucially, we found that spatial modulation was also influenced by stimulus valence, but only for the approaching and not the receding stimuli. At far distances, neutral stimuli yielded overall slower RTs than intrinsically positive or negative stimuli (Experiment 1), while no modulation was exerted by the level of conditioning (Experiment 3). At near distances, response to touches accompanied by looming neutral stimuli became as fast as that occurring with positive and negative ones. Stimulus valence did not interact with the expectancy of a tactile stimulus (Experiment 2). Overall, these findings support the vision that visuo-tactile interactions can be dynamically modulated by the valence of looming visual stimuli when these are located at longer distances from the body. When closer to it, all stimuli acquire saliency, regardless of their intrinsic or acquired valence, due to their proximity, and then relevance, to the body. Overall, a view of PPS as a gradient modulating visuo-tactile integration, also based on stimulus valence, is discussed. Highlights • We examined the impact of intrinsic and acquired valence of stimuli in peripersonal space (PPS). • Transitions in PPS are gradual without an abrupt limit. • Close to the body: positive, negative and neutral stimuli are equivalent. • Far from the body: positive and negative stimuli induce faster responses than neutral one. • Visuo-tactile interactions can be dynamically shaped by stimulus valence. [ABSTRACT FROM AUTHOR]

Neurophysiological investigations in non-human primates have shown that bi- and tri-modal fronto-parietal neurons exist that respond to touch on the body and visual (and/or auditory) stimuli near the body. The receptive fields of these neurons extend into space around the body, producing a zone wherein multisensory information is readily integrated. This space around the body, known as peripersonal space (PPS), has also been investigated behaviourally in humans. Some studies have focused on how far into depth the spatial boundaries of PPS extend. Most of these investigations have focused on the upper body (e.g., hands, face, trunk), while little is known about the size of PPS for the lower body (i.e. legs and feet). Thus, the aim of the current study was to delineate a PPS boundary around the lower limbs in healthy participants using a multisensory interaction task. Participants made speeded responses to the presence of vibrations applied to the toes while a task-irrelevant visual stimulus approached towards (Experiment 1) or receded from (Experiment 2) the feet. Participants responded significantly faster to tactile stimuli when the visual stimulus was within approximately 73 cm from the feet, but only when it approached (and not receded from) the legs. This is the first study, to our knowledge, to outline the size of PPS for the lower limbs. These findings could provide insight into the mechanisms underlying multisensory integration in the lower limbs, and add to the current body of knowledge on PPS representations. [ABSTRACT FROM AUTHOR]

Multisensory integration of visuo-tactile information presented on the body or a dummy body has a strong impact on body image. Previous researches show that alteration of body image induced by visuo-tactile integration is closely related to the activation of the parietal cortex, a sensory association area. The expression of brain-derived neurotrophic factor (BDNF) in the parietal area of macaque monkeys is thought to modulate the activation of the parietal cortex and alter the extension of body image during tool-use learning. However, the relationship between parietal cortex activation related to body image alterations and BDNF levels in humans remains unclear. We investigated the relationship between human serum BDNF levels and electroencephalography responses during a visuo-tactile integration task involving a rubber hand. We found cortical oscillatory components in the high frequency (gamma) band in the left parietal cortex. Moreover, the power values of these oscillations were positively correlated (p < 0.05) with serum BDNF levels. Our results suggest that serum BDNF could play a role in modulating the cortical activity in response to visuo-tactile integration processes related to body image alteration in humans. [ABSTRACT FROM AUTHOR]

• Relationship between the multisensory representation of peri -personal Space (PPS) and individual Empathy levels. • Higher Empathic Concern individuals have reduced visuo-tactile interactions within PPS. • They also show less segregation between PPS and extra-personal space (EPS). • These PPS features may facilitate the representation of others in a more extended interaction space. To investigate whether individual differences in Empathy predict the characteristics of Peripersonal Space (PPS) representations, we asked participants to complete the IRI questionnaire and a visuo-tactile crossmodal congruency task (CCT) as an index of PPS. In the CCT, they responded to the elevation of a tactile target while ignoring a visual distractor presented at the same (i.e. congruent) or different (i.e. incongruent) elevation. The target-distractor distance was also manipulated in depth, with visual distractors randomly presented at near, middle or far locations (0 cm, 25 cm or 50 cm). The near and middle crossmodal congruency effects (CCE) were inversely related to participants' scores on the Empathic Concern sub-scale (EC). Furthermore, the slope of participants' CCE across locations was related to EC scores, with flatter slopes for higher EC individuals. Thus, higher EC individuals showed reduced visuo-tactile integration responses within PPS and a reduced differentiation between PPS and extra-personal space (EPS). [ABSTRACT FROM AUTHOR]

Abstract: Humans rely on the integration of information from multiple sensory modalities to interact successfully with their environment. In the present series of studies, we investigated how the visuomotor system integrates congruent and incongruent visual and tactile sensory inputs for goal-directed action comprehension and execution. Specifically, we investigated whether orienting of attention towards vision, touch, or both vision and touch enhances the impact of one modality over another. In Experiment 1 participants were presented with visual (on a computer monitor) and/or tactile (in unseen left hand) sensory inputs of an action, and made button-press responses to categorise it as ‘wide’ or ‘narrow’. Responses were significantly faster when attending to vision compared with touch, and faster in fully congruent compared with grasp congruent and incongruent conditions. Thus, both vision and touch are significant in action comprehension, but visual inputs are in general more influential than tactile inputs. Moreover, responses to wide grasp actions were significantly faster than to narrow-grasp actions. In the same task was performed but the participants made reach-to-grasp movements, recorded with ProReflex motion capture system. Although actions to wide objects produced wider peak grasp overall than to a narrow object, in contrast to action comprehension, there was no systematic effect of attended modality or tactile input in action execution. We speculate that action comprehension and execution utilize visual and tactile inputs differentially. [Copyright &y& Elsevier]

Abstract: Investigations in macaques and humans have shown that the anterior intraparietal sulcus (IPS) has an important function in the integration of information from tactile and visual object manipulation. The goal of this study was to investigate the special functional role of the anterior IPS in visuo–tactile matching in humans. We used the “virtual-lesion” technique of repetitive transcranial magnetic stimulation (rTMS) to test the functional relevance of anterior IPS for visuo–tactile crossmodal matching. Two crossmodal (visual encoding and tactile recognition and vice versa) and two unimodal delayed matching-to-sample tests with geometrical patterns were performed by 12 healthy subjects. We determined error rates before and after focal low-frequency rTMS applied over the left anterior IPS, right anterior IPS and vertex. During the manipulation of objects with the right hand, rTMS over the left anterior IPS induced a significant deterioration for visual encoding and tactile recognition, but not for tactile encoding and visual recognition. For the visual and tactile unimodal conditions, no significant alterations in task performance were found. rTMS application over right IPS when manipulating objects with the left hand did not affect crossmodal task performance. In conclusion, we have demonstrated an essential functional role of the left anterior IPS for visuo–tactile matching when manipulating objects with the right hand. However, we found no clear evidence for left IPS involvement in tactile encoding and visual recognition. The differential effect of rTMS on tactile and visual encoding and recognition are not consistently explained by previous concepts of visuo–tactile integration. [Copyright &y& Elsevier]

The development and expression of many higher-level cognitive functions, such as imitation, spatial perception and tool-use, relies on a multi-modal representation of the body known as the body schema. Although many studies support the hypothesis that the body schema is adaptive and alterable throughout ontogenetic development, the mechanisms underlying its plasticity have yet to be clarified. Here, we argue that the temporal integration of multisensory information is a plausible candidate mechanism to explain how manipulated objects (e.g., tools) can become incorporated into the body schema. To demonstrate the validity of our idea, we introduce a model of body schema adaptation instantiated in a small-sized, table-top, tool-using humanoid. The robot's task is to learn to reach for and touch a visually salient distant object, first with its 'bare' hand and then — using the acquired know-how — with a reach-extending tool (a stick). Our experimental results show that in order to successfully causally relate and integrate vision, touch and proprioception, and to learn to use the tool, timing is of crucial relevance. On a more general note, this study also suggests that synthetic modeling might not only be a valid avenue towards getting a better grasp on results provided by neuropsychology and neurophysiology, but also a powerful approach for building advanced tool-using robots. [ABSTRACT FROM AUTHOR]

Adaptation experiments in shape tracing were conducted to investigate finger and eye movements in various conditions of visual and tactile information. Maximum velocity, mean velocity, maximum acceleration and reacceleration point were calculated from finger movements. Number of eye fixations and lead time of eye fixation to finger position were calculated from eye movements. The results showed that for the finger movement the values of the indices studied were higher in the combined visual and tactile condition than in the visual only condition. The number of eye fixations decreased when subjects repeated the tracing and was more marked in the combined visual and tactile condition than in the visual only condition. The results suggest that finger movements become faster and use of vision is reduced when both visual and tactile information are given. [ABSTRACT FROM PUBLISHER]

Peripersonal Space (PPS) is the multisensory space immediately surrounding our body. Visual and tactile stimuli here are promptly processed, since their interaction gradually strengthens as the distance between visual stimulus and the body decreases. Recently, a modified version of the Temporal Order Judgment (TOJ) task was proposed to assess PPS based on the spatial congruence between somatosensory and visual stimuli. Here, we used this paradigm to explore how a temporary vs a permanent state of anxiety can alter PPS. Indeed, previous research showed that PPS boundaries are not fixed, but they can be enlarged by contingent factors (i.e. emotional features). Participants performed the TOJ paradigm twice, just before and after completing an anxiety-inducing task (experimental breathing condition) or a neutral one (control breathing condition), while their trait and state anxiety levels were repeatedly measured. We found that the pattern of visuo-tactile integration in PPS changes in the very opposite way following the two breathing tasks for participants with high levels of temporary anxiety, by strengthening and weakening its power after the experimental and control conditions, respectively. On the contrary, both the breathing tasks are capable of reducing the cross-modal interplay as compared to baseline for high trait-anxious participants, who show an overall stronger visuo-tactile integration inside the PPS than low trait anxious individuals. These results are discussed in the light of the double dissociation between orienting and alerting attentional network over-functioning, reported in state anxiety participants, and impoverished prefrontal attentional control shown by trait anxiety individuals. [ABSTRACT FROM AUTHOR]

An abstract of the article "Interregional Long-Range and Short-Range Synchrony: A Basis for Complex Sensorimotor Processing," by Friedhelm C. Hummel and Christian Gerloff is presented.