Roger Newport

Fake hands in action: embodiment and control of supernumerary limbs

Demonstrations that the brain can incorporate a fake limb into our bodily representations when stroked in synchrony with our unseen real hand [(the rubber hand illusion (RHI)] are now commonplace. Such demonstrations highlight the dynamic flexibility of the perceptual body image, but evidence for comparable RHI-sensitive changes in the body schema used for action is less common. Recent evidence from the RHI supports a distinction between bodily representations for perception (body image) and for action (body schema) (Kammers et al. in Neuropsychologia 44:2430–2436, 2006). The current study challenges and extends these findings by demonstrating that active synchronous stroking of a brush not only elicits perceptual embodiment of a fake limb (body image) but also affects subsequent reaching error (body schema). Participants were presented with two moving fake left hands. When only one was synchronous during active touch, ownership was claimed for the synchronous hand only and the accuracy of reaching was consistent with control of the synchronous hand. When both fake hands were synchronous, ownership was claimed over both, but only one was controlled. Thus, it would appear that fake limbs can be incorporated into the body schema as well as the body image, but while multiple limbs can be incorporated into the body image, the body schema can accommodate only one.

A Kinematic Analysis of Goal-directed Prehension Movements Executed under Binocular, Monocular, and Memory-guided Viewing Conditions

Vision is critical for the efficient execution of prehension movements, providing information about: The location of a target object with respect to the viewer; its spatial relationship to other objects; as well as intrinsic properties of the object such as its size and orientation. This paper reports three experiments which examined the role played by binocular vision in the execution of prehension movements. Specifically, transport and grasp kinematics were examined for prehension movements executed under binocular, monocular, and no vision (memory-guided and open-loop) viewing conditions. The results demonstrated an overall advantage for reaches executed under binocular vision; movement duration and the length of the deceleration phase were longer, and movement velocity reduced, when movements were executed with monocular vision. Furthermore, the results indicated that binocular vision is particularly important during “selective” reaching, that is reaching for target objects which are accompanied by fl...

Where the eye looks, the hand follows; limb-dependent magnetic misreaching in optic ataxia.

The posterior parietal cortex (PPC) is thought to play an important role in the sensorimotor transformations associated with reaching movements. In humans, damage to the PPC, particularly bilateral lesions, leads to impairments of visually guided reaching movements (optic ataxia). Recent accounts of optic ataxia based upon electrophysiological recordings in monkeys have proposed that this disorder arises because of a breakdown in the tuning fields of parietal neurons responsible for integrating spatially congruent retinal, eye, and hand position signals to produce coordinated eye and hand movements . We present neurological evidence that forces a reconceptualization of this view. We report a detailed case study of a patient with a limb-dependent form of optic ataxia who can accurately reach with either hand to objects that he can foveate (thereby demonstrating coordinated eye-hand movements) but who cannot effectively decouple reach direction from gaze direction for movements executed using his right arm. The demonstration that our patients misreaching is confined to movements executed using his right limb, and only for movements that are directed to nonfoveal targets, rules out explanations based upon simple perceptual or motor deficits but indicates an impairment in the ability to dissociate the eye and limb visuomotor systems when appropriate.

Noninformative Vision Improves Haptic Spatial Perception

Previous studies have attempted to map somatosensory space via haptic matching tasks and have shown that individuals make large and systematic matching errors, the magnitude and angular direction of which vary systematically through the workspace. Based upon such demonstrations, it has been suggested that haptic space is non-Euclidian. This conclusion assumes that spatial perception is modality specific, and it largely ignores the fact that tactile matching tasks involve active, exploratory arm movements. Here we demonstrate that, when individuals match two bar stimuli (i.e., make them parallel) in circumstances favoring extrinsic (visual) coordinates, providing noninformative visual information significantly increases the accuracy of haptic perception. In contrast, when individuals match the same bar stimuli in circumstances favoring the coding of movements in intrinsic (limb-based) coordinates, providing identical noninformative visual information either has no effect or leads to the decreased accuracy of haptic perception. These results are consistent with optimal integration models of sensory integration in which the weighting given to visual and somatosensory signals depends upon the precision of the visual and somatosensory information and provide important evidence for the task-dependent integration of visual and somatosensory signals during the construction of a representation of peripersonal space.

Eye contact enhances mimicry of intransitive hand movements

When two people meet in a bar, a subtle interplay of social behaviours, including eye contact and unconscious mimicry of actions play an important role in how much the individuals like each other by the end of the evening. However, it is not known how these different social signals interact. Here, we adopt a rapid mimicry paradigm, to test if eye contact can modulate mimicry on a second by second time scale. Our results show that direct eye contact rapidly and specifically enhances mimicry of hand actions. These findings have implications for understanding the role of eye contact as a controlling signal in human non-verbal social behaviour.

Prisms and neglect: What have we learned?

Since Rossetti et al. (1998) reported that prism adaptation (PA) can lead to a substantial reduction of neglect symptoms PA has become a hot topic in neglect-research. More than 280 articles have been published in this area. Not all of those studies investigated the therapeutic potential of this technique, many studies examined the responsiveness to PA as a way to subdivide neglect into separate subsyndromes, other studies focussed on the process of PA itself in an effort to illuminate its underlying neurobiological mechanisms. In this article we will review research in all of these three areas to determine whether and to what extent research on PA in neglect patients has fulfilled its promise as a new way to improve the treatment of neglect, enhance our understanding of this complex syndrome and provide new insights into the neurobiology of sensorimotor learning.

Posterior parietal cortex and the dissociable components of prism adaptation

Recent evidence has implicated posterior parietal cortex (PPC) in adaptation to optical displacing prisms. It has been suggested that PPC contributes to the strategic component of prism adaptation necessary for perceptual realignment (true adaptation). It has also been suggested, however, that the part of PPC responsible for corrections to ongoing movements (a putative strategic component) may not be necessary for successful adaptation. A patient presenting with bilateral posterior parietal damage (patient JJ) was tested with both hands on two versions of a prism adaptation task--one using prism goggles and one using a virtual prism arrangement. JJ displayed independent deficits: his right hand failed to show strategic control, yet adapted fully to the prisms whereas his left hand showed evidence of strategic control without subsequent adaptation. The data indicates that the ability to implement control strategies may not be necessary for successful adaptation to prisms. A proposed model for the role of posterior parietal cortex in prism adaptation is also presented.

Links between vision and somatosensation: Vision can improve the felt position of the unseen hand

During reaching movements, sensory signals must be transformed into appropriate motor commands. Anatomical, electrophysiological, and neuropsychological evidence suggest that there is no single, supramodal map of space that is used to guide reaching. Instead, movements appear to be planned and controlled within multiple coordinate systems, each one attached to a different body part. Recent neuropsychological investigations demonstrating that somatosensory impairments can be ameliorated by visual cues, and visual impairments by proprioceptive cues, have been interpreted as evidence that arm-centered representations may exist in humans. A critical difference between the findings obtained in the monkey and in humans, however, is that in the latter case, vision of the limb appears be critical for visual somatosensory binding. Here, we report a case study of a patient (C.T.) recovering from unilateral somatosensory impairment, including tactile extinction, who executed reaches toward visually defined or proprioceptively defined locations. We demonstrate that when the target location of a reach was defined proprioceptively, by passively positioning our patients impaired hand beneath the table surface, vision of the workspace immediately adjacent to the unseen hand dramatically increased the endpoint accuracy of her reaching movements, even though such cues could not possibly signal the position of the target directly.

There may be more to reaching than meets the eye: re-thinking optic ataxia.

Optic ataxia (OA) is generally thought of as a disorder of visually guided reaching movements that cannot be explained by any simple deficit in visual or motor processing. In this paper we offer a new perspective on optic ataxia; we argue that the popular characterisation of this disorder is misleading and is unrepresentative of the pattern of reaching errors typically observed in OA patients. We begin our paper by reviewing recent neurophysiological, neuropsychological, and functional brain imaging studies that have led to the proposal that the medial parietal cortex in the vicinity of the parietal-occipital junction (POJ) - the key anatomical site associated with OA - represents reaching movements in eye-centred coordinates, and that this ability is impaired in optic ataxia. Our perspective stresses the importance of the POJ and superior parietal regions of the human PPC for representing reaching movements in both extrinsic (eye-centred) and intrinsic (postural) coordinates, and proposes that it is the ability to simultaneously represent multiple spatial locations that must be directly compared with one another that is impaired in non-foveal OA patients. In support of this idea we review recent fMRI and behavioural studies conducted by our group that have investigated the anatomical correlates of posturally guided movements, and the movements guided by postural cues in patients presenting with optic ataxia.

Analgesic effects of multisensory illusions in osteoarthritis

Sir, There is increasing evidence that drug-free illusion therapies can be beneficial for the amelioration of chronic pain, particularly so for conditions in which some of the pain is thought to have a cortical origin. For example, mirror therapy and size reduction illusions can reduce pain in complex regional pain syndrome type 1 (CRPS1) patients, the majority of whom have disturbed body representations with some reporting their hand as larger than in reality [1] and others describing parts of their hand as foreshortened [2]. If cortical misrepresentation of body parts contributes to pain, then manipulating the appearance of those body parts might be a useful tool in the reduction of pain. This letter describes an exploratory experiment using unique visuo-proprioceptive illusions that manipulated the perceived size of painful and non-painful parts of the hand in an attempt to modulate pain experienced in OA. Illusions were applied using a MIRAGE system [3] that presents real-time video capture of the actual hand from the same position and perspective as if viewing the real hand directly (Fig. 1a). Visual manipulations can be applied to the image such that they appear to happen to the real hand. The experimental manipulations were stretching (Fig. 1b) and shrinking (Fig. 1c): gently pulling or pushing on part of the hand while simultaneously elongating or shortening the image gives a strong illusion that the hand is being stretched or shortened (see supplementary material for video). Control illusions included stretching and shrinking a non-painful part of the hand and visually enlarging/reducing the entire hand. Fig. 1 (a) A healthy participant having her finger stretched using MIRAGE; examples of arthritic hands after being stretched (b) and shrunk (c) and (d) the percentage pain reduction after manipulation for painful and non-painful body parts. A direct comparison ... A total of 20 OA sufferers [2 males; mean (s.d.) age: 70.5 (6.5) years] with clinically diagnosed arthritic pain in the hands and/or fingers for >12 months were tested. Participants gave written consent in accordance with the Declaration of Helsinki. The study met with ethical approval from the University of Nottingham School of Psychology Ethics Committee (code: 20072010). None of the participants were pain free on the day of testing and none had used pain medication other than paracetamol. Participants verbally reported their pain levels on a 21-point numerical rating scale (NRS) with 0 indicating no pain at all and 20 indicating the most unbearable pain imaginable. The scores were adjusted relative to a baseline condition of gently pulling or pushing the hand without visual manipulation. NRS ratings of pain for the painful part of the hand were taken before and after stretching or shrinking the painful and non-painful parts of the hand as well as before and after enlarging or reducing the entire hand. Overall, illusory manipulation was extremely beneficial, on average halving the reported pain in 85% of participants. Some reported greater reduction in pain for stretching, some for shrinking and some for both. Crucially, pain reduction was only observed when the painful part of the hand was manipulated and not when manipulating the non-painful part (Fig. 1d) or when enlarging or reducing the whole hand (although the latter was only tested in a minority of participants). For those in whom stretching was beneficial, the mean reduction in pain was ∼50% (pre = 6.42 on the NRS; post = 3.33), while beneficial shrinking produced a ∼45% reduction (pre = 5.83; post = 3.15). Remarkably, illusory stretching or shrinking of the painful body part temporarily eliminated all pain in one-third of all participants and in 41% of those for whom the illusion was effective. Although not formally assessed, many participants spontaneously reported an increased range of movement following manipulation and most reported pain reduction before active movement was permitted. Many participants gave spontaneous verbal reports such as: ‘I can feel my whole body relaxing.’; ‘My pain has completely gone.’; and ‘I wasn’t able to move like that before.’ This experiment demonstrates a strong analgesic effect of multisensory illusions for OA, which (though not tested directly) is consistent with the idea that some of the pain experienced in arthritic conditions may result from dysfunctional representations of the body [4]. Furthermore, the methods described may provide a mechanism for promoting therapeutic exercise normally prevented by painful movement. The effects of mini-magnification appear to be specific to the part of the body in which the pain is experienced and do not require active movement of the hand. Intriguingly, both shrinking and stretching were found to be beneficial in different, and sometimes the same, participants. This may be due to two distinct processes: the matching of cortical representations and the reduction of apparent swelling, which may vary between participants according to different physical and cortical representations. Although the current experiment describes striking analgesic effects, it does not completely rule out placebo effects and more comprehensive experimental research is necessary to investigate the underlying mechanisms and validate the beneficial effects. In particular, the effects of having attention drawn to the painful part of the hand while being manipulated must be adequately controlled for. However, these initial results suggest that multisensory illusions are a useful avenue of research for the treatment of pain in OA. Disclosure statement: The authors have declared no conflicts of interest.