Xaver Fuchs

An augmented reality home-training system based on the mirror training and imagery approach

Mirror training and movement imagery have been demonstrated to be effective in treating several clinical conditions, such as phantom limb pain, stroke-induced hemiparesis, and complex regional pain syndrome. This article presents an augmented reality home-training system based on the mirror and imagery treatment approaches for hand training. A head-mounted display equipped with cameras captures one hand held in front of the body, mirrors this hand, and displays it in real time in a set of four different training tasks: (1) flexing fingers in a predefined sequence, (2) moving the hand into a posture fitting into a silhouette template, (3) driving a “Snake” video game with the index finger, and (4) grasping and moving a virtual ball. The system records task performance and transfers these data to a central server via the Internet, allowing monitoring of training progress. We evaluated the system by having 7 healthy participants train with it over the course of ten sessions of 15-min duration. No technical problems emerged during this time. Performance indicators showed that the system achieves a good balance between relatively easy and more challenging tasks and that participants improved significantly over the training sessions. This suggests that the system is well suited to maintain motivation in patients, especially when it is used for a prolonged period of time.

The Importance of Synchrony and Temporal Order of Visual and Tactile Input for Illusory Limb Ownership Experiences – An fMRI Study Applying Virtual Reality

In the so-called rubber hand illusion, synchronous visuotactile stimulation of a visible rubber hand together with ones own hidden hand elicits ownership experiences for the artificial limb. Recently, advanced virtual reality setups were developed to induce a virtual hand illusion (VHI). Here, we present functional imaging data from a sample of 25 healthy participants using a new device to induce the VHI in the environment of a magnetic resonance imaging (MRI) system. In order to evaluate the neuronal robustness of the illusion, we varied the degree of synchrony between visual and tactile events in five steps: in two conditions, the tactile stimulation was applied prior to visual stimulation (asynchrony of −300 ms or −600 ms), whereas in another two conditions, the tactile stimulation was applied after visual stimulation (asynchrony of +300 ms or +600 ms). In the fifth condition, tactile and visual stimulation was applied synchronously. On a subjective level, the VHI was successfully induced by synchronous visuotactile stimulation. Asynchronies between visual and tactile input of ±300 ms did not significantly diminish the vividness of illusion, whereas asynchronies of ±600 ms did. The temporal order of visual and tactile stimulation had no effect on VHI vividness. Conjunction analyses of functional MRI data across all conditions revealed significant activation in bilateral ventral premotor cortex (PMv). Further characteristic activation patterns included bilateral activity in the motion-sensitive medial superior temporal area as well as in the bilateral Rolandic operculum, suggesting their involvement in the processing of bodily awareness through the integration of visual and tactile events. A comparison of the VHI-inducing conditions with asynchronous control conditions of ±600 ms yielded significant PMv activity only contralateral to the stimulation site. These results underline the temporal limits of the induction of limb ownership related to multisensory body-related input.

Challenging the assumptions for thermal sensation scales

ABSTRACT Scales are widely used to assess the personal experience of thermal conditions in built environments. Most commonly, thermal sensation is assessed, mainly to determine whether a particular thermal condition is comfortable for individuals. A seven-point thermal sensation scale has been used extensively, which is suitable for describing a one-dimensional relationship between physical parameters of indoor environments and subjective thermal sensation. However, human thermal comfort is not merely a physiological but also a psychological phenomenon. Thus, it should be investigated how scales for its assessment could benefit from a multidimensional conceptualization. The common assumptions related to the usage of thermal sensation scales are challenged, empirically supported by two analyses. These analyses show that the relationship between temperature and subjective thermal sensation is non-linear and depends on the type of scale used. Moreover, the results signify that most people do not perceive the categories of the thermal sensation scale as equidistant and that the range of sensations regarded as ‘comfortable’ varies largely. Therefore, challenges known from experimental psychology (describing the complex relationships between physical parameters, subjective perceptions and measurement-related issues) need to be addressed by the field of thermal comfort and new approaches developed.

Post-Amputation Pain Is Associated with the Recall of an Impaired Body Representation in Dreams—Results from a Nation-Wide Survey on Limb Amputees

The experience of post-amputation pain such as phantom limb pain (PLP) and residual limb pain (RLP), is a common consequence of limb amputation, and its presence has negative effects on a person’s well-being. The continuity hypothesis of dreams suggests that the presence of such aversive experiences in the waking state should be reflected in dream content, with the recalled body representation reflecting a cognitive proxy of negative impact. In the present study, we epidemiologically assessed the presence of post-amputation pain and other amputation-related information as well as recalled body representation in dreams in a sample of 3,234 unilateral limb amputees. Data on the site and time of amputation, residual limb length, prosthesis use, lifetime prevalence of mental disorders, presence of post-amputation pain, and presence of non-painful phantom phenomena were included in logistic regression analyses using recalled body representation in dreams (impaired, intact, no memory) as dependent variable. The effects of age, sex, and frequency of dream recall were controlled for. About 22% of the subjects indicated that they were not able to remember their body representation in dreams, another 24% of the amputees recalled themselves as always intact, and only a minority of less than 3% recalled themselves as always impaired. Almost 35% of the amputees dreamed of themselves in a mixed fashion. We found that lower-limb amputation as well as the presence of PLP and RLP was positively associated with the recall of an impaired body representation in dreams. The presence of non-painful phantom phenomena, however, had no influence. These results complement previous findings and indicate complex interactions of physical body appearance and mental body representation, probably modulated by distress in the waking state. The findings are discussed against the background of alterations in cognitive processes after amputation and hypotheses suggesting an innate body model.

Perceptual drifts of real and artificial limbs in the rubber hand illusion

In the rubber hand illusion (RHI), transient embodiment of an artificial hand is induced. An often-used indicator for this effect is the “proprioceptive drift”, a localization bias of the real hand towards the artificial hand. This measure suggests that the real hand is attracted by the artificial hand. Principles of multisensory integration, however, rather suggest that conflicting sensory information is combined in a “compromise” fashion and that hands should rather be attracted towards each other. Here, we used a new variant of the RHI paradigm in which participants pointed at the artificial hand. Our results indicate that the perceived positions of the real and artificial hand converge towards each other: in addition to the well-known drift of the real hand towards the artificial hand, we also found an opposite drift of the artificial hand towards the real hand. Our results contradict the notion of perceptual substitution of the real hand by the artificial hand. Rather, they are in line with the view that vision and proprioception are fused into an intermediate percept. This is further evidence that the perception of our body is a flexible multisensory construction that is based on integration principles.

The rubber hand illusion depends on a congruent mapping between real and artificial fingers

The rubber hand illusion (RHI), in which a visible artificial hand is touched (or moves) synchronously with the participants unseen own hand, indicates that body representations can undergo rapid changes. While several constraints for this illusion have been described, some reports highlight a remarkable flexibility of body representations, even contradicting a priori assumptions regarding body appearance and anatomy (e.g., the subjective embodiment of a third arm). Here we examine the impact of congruence between touches at (or movements of) the real and the artificial hand, as well as the role of predictability of touches (or movements). We implemented two versions of the RHI paradigm, based on passive tactile stimulation and active voluntary movements. The results show that (a) predictability does not modulate perceived embodiment, and that (b) congruent mapping between real and artificial fingers is a necessary condition for both the tactile and the motor RHI. Together with previously reported constraints for bodily illusions, these results are reduced to four principles, which determine subjective embodiment: temporal synchrony, congruence of mapping between real and artificial body parts, body unity and body shape.

Do Mirror Glasses Have the Same Effect on Brain Activity as a Mirror Box? Evidence from a Functional Magnetic Resonance Imaging Study with Healthy Subjects

Since its original proposal, mirror therapy has been established as a successful neurorehabilitative intervention in several neurological disorders to recover motor function or to relieve pain. Mirror therapy seems to operate by reactivating the contralesional representation of the non-mirrored limb in primary motor- and somatosensory cortex. However, mirror boxes have some limitations which prompted the use of additional mirror visual feedback devices. The present study evaluated the utility of mirror glasses compared to a mirror box. We also tested the hypothesis that increased interhemispheric communication between the motor hand areas is the mechanism by which mirror visual feedback recruits the representation of the non-mirrored limb. Therefore, mirror illusion capacity and brain activations were measured in a within-subject design during both mirror visual feedback conditions in counterbalanced order with 20 healthy subjects inside a magnetic resonance imaging scanner. Furthermore, we analyzed task-dependent functional connectivity between motor hand representations using psychophysiological interaction analysis during both mirror tasks. Neither the subjective quality of mirror illusions nor the patterns of functional brain activation differed between the mirror tasks. The sensorimotor representation of the non-mirrored hand was recruited in both mirror tasks. However, a significant increase in interhemispheric connectivity between the hand areas was only observed in the mirror glasses condition, suggesting different mechanisms for the recruitment of the representation of the non-mirrored hand in the two mirror tasks. We conclude that the mirror glasses might be a promising alternative to the mirror box, as they induce similar patterns of brain activation. Moreover, the mirror glasses can be easy applied in therapy and research. We want to emphasize that the neuronal mechanisms for the recruitment of the affected limb representation might differ depending on conceptual differences between MVF devices. However, our findings need to be validated within specific patient groups.

Peripheral origin of phantom limb pain: is it all resolved?

ervasive belief that cortical plasticity causes phantom pain. The lternative explanation of the correlation, that pain-provoking fferent discharge causes the remapping, is rarely mentioned espite solid evidence that this indeed occurs [1,8]. In our view, he cortical theory became dogma not because of compelling evience of causality, and certainly without the RCT evidence that oell et al. demand of the PNS ectopia hypothesis, but rather ecause the neuropsychological community ‘‘likes’’ it. Our study nd recent work by Makin et al. [7] are among the few attempts o critically examine cause versus effect in PLP. Finally, Foell et al. ask whether PLP might reappear despite ilenced peripheral ectopia. Indeed, some central nervous system heories ignore the existence of PNS ectopia altogether, and posit hat amputation eliminates afferent input, triggers increased senory gain in the cortex, and hence generates PLP [6]. Answering oell et al.’s question will require an effective method of permaently suppressing ectopia. We maintained pain relief for 12 days sing drug infusion, and this approach could presumably be xtended indefinitely using an implantable pump system. This hould be tried. Moreover, because low and therefore relatively ontoxic concentrations of membrane stabilizers ought to suffice 3], the time between reservoir refills could be quite long. Although LP is sufficiently common to justify clinical development of this pproach, it might also be applicable to much more prevalent onditions involving DRG ectopia, including postherpetic euralgia, radicular low back pain (sciatica), and some traumatic europathies.

Introducing a Social Beads Task

‘Jumping to conclusions’ is a cognitive bias relevant to delusional ideation that has been reliably replicated with the Beads Task decision-making paradigm. Due to the artificial nature of this classical task, little is known about the generalization of hasty decision-making to more naturalistic, real-life situations. In this study the construction and psychometrical evaluation of an experimental Social Beads Task paradigm are reported. The task involves eighteen neutral, self-relevant and delusion-relevant scenarios in which participants have to decide between alternative explanations by obtaining complex, naturalistic pieces of information. Besides satisfying psychometric properties in the present non-clinical sample (N = 92), the proposed enhancing impact of self-relevant and delusion-relevant scenarios on hasty decision-making was corroborated, F(2, 160) = 25.26, p, < 0.01, partial η2 = 0.24. The Social Beads Task could therefore be a useful tool in delusion research that allows the investigation of cognitive biases in social scenarios.

Illusory Hand Ownership Induced by an MRI Compatible Immersive Virtual Reality Device

In this paper, we introduce a virtual reality based setup for triggering and studying illusory sensations of limb ownership as known from the popular rubber hand illusion. Unlike a similar setup introduced recently, this experiment is triggered by software automatically, which provides for a good synchrony and for high accuracy of visuotactile stimulation. The system is usable inside a magnetic resonance scanner which allows observing cortical activations at the same time. We tested two participants, one highly and the other lowly susceptible to the induction of illusory limb ownership, assessing their subjective experiences as well as their brain activity using functional magnetic resonance imaging. We present preliminary results suggesting that our setup induces illusory ownership experiences for a virtual limb successfully, accompanied by neuronal activation in integrative brain areas.