TOUCHANDACTION · Touch and action in spatial perception

Touch and action in spatial perception

To respond to a touch, it is often necessary to localize it in space, and not just on the skin. The computation of this external spatial location involves the integration of somatosensation with visual and proprioceptive information about current body posture. Failures in the encoding of this external mapping would prevent us from retrieving the correct location of tactile events, impairing normal interactions with the environment. It would be like feeling the tickle of an insect on the skin, without knowing where to reach out to swat it away. The aim of the current project is to elucidate the mechanisms whereby self-generated movements and preceding tactile information is used by the remapping system to improve tactile localization. A summary of this process is found in a review that we have recently published (Heed & Azanon, 2014; http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3925972/). We used temporal order judgements as an entirely implicit measure of tactile spatial perception in several studies. In these experiments participants were asked to judge the order of two touches applied in quick succession, one to each hand, by moving the hand that was stimulated first. By changing the posture of participants‘ hands, from crossed to uncrossed and vice versa, we directly assessed the localization of touch in external space. Following every posture change, participants received several of these bi-manual touches. We tested how the localization of a touch varied as a function of the number of preceding touches in the same posture, following a self-generated movement. In several experiments, the degree to which touches were attended was also manipulated. Specifically, preceding touches could be task-relevant or -irrelevant. This allowed us to gain deeper understanding of the degree of automaticity of this process. Our results yield several entirely new pieces of knowledge about how the brain processes stimuli on the skin after movement. First, the process that combines touch and proprioception improves over time by cumulating information from previous tactile experience, as tactile spatial localization improved with each successive touch in a new posture; Second, this improvement is extremely fast: a single temporal order judgement was sufficient to improve localization of the next touch. Third, the effect neither required performance feedback, nor even attention to preceding touches, strongly suggesting that this improvement in tactile spatial localization is automatic. Fourth, the improvement required tactile stimulation and did not occur merely as a function of time following movement. From these results, we concluded that tactile remapping is a pre-attentive, yet flexible sensory process that develops with tactile experience. In most previous studies, the coordinate transformations between different reference frames are simply assumed as ‘givens’, and are then just implemented in a feedforward manner. Surprisingly, almost no previous studies have tested how a new transformation mapping is initiated, and what information is used to refine it. Our results provide the first experimental insight into both these questions. Our results reveal an experience-dependent flexibility of the tactile remapping system, demonstrating its repeated updating and rapid stabilisation with each body movement. This offers a new view of the transformation between spatial reference frames. That is, the brain progressively builds spatial transformation functions on the basis of previous sensory experience: our experiments show that this process is happening touch-by-touch. These novel findings are now under revision in a peer-reviewed scientific journal (Azanon, Stenner, Cardini & Haggard, submitted). In a second study of the project we have found that the mental representation of the hand changes depending on the posture. Specifically, a hand that has crossed the midline is perceived as being smaller (Azanon, Haggard & Longon, in preparation). This fits well with several recent finding that perception of pain on a hand is reduced when that hand has crossed the midline. In addition, we have also found that tactile location is estimated by integrating postural information about the stimulated body part, and is independent of the configuration of all connected portions of the limbs (Azañón, Radulova, Haggard & Longo, submitted). The Marie Curie grant has also promoted the development of several links between European institutions allowing the generation of several projects which are still ongoing: 1) Prof Longo at Birkbeck University, involved in the above-mentioned studies; 2) Dr Heed and Prof Roder at the University of Hamburg, Germany, with the aim to uncover a network of neural areas involved in tactile remapping. 3) Prof Dolan and Dr Stenner (The Wellcome Trust Center for Neuroimaging, UCL) in a project related to the perception of touch during self-generated movement; 4) Dr Bremner (Goldsmiths University, University of London) in a project related to the development of tactile remapping in children. The project has also allowed transfer of basic research knowledge to the industry sector. We are currently studying the neural mechanisms underlying transient-force tactile and proprioceptive stimuli during movement using a device for blind individuals. This project started at the Nippon Telegraph and Telephone Corporation (NTT) in Japan, with the generation of the new device, and now continues at University College London. So far, we have characterized electrophysiological correlates of this new form of tactile stimulation. Overall, the project has allowed a better understanding of the remapping systemn in relation to the experience of action and touch. Because tactile remapping is widely regarded as a protoype of (spatial) transformation in sensory processing, these results contribute to an understanding of fundamental principles of brain function. Moreover, the outputs of this research are of great interest in the area of robotics, aiming at improving systems of tactile feedback in robotic surgery and human controlled manipulators like exoskeletons. Finally, the project has allowed the fellow to acquire competencies that contribute substantially to her prospects of reaching a position of professional maturity. The fellow has expanded her current expertise on tactile remapping and gained inter-disciplinary methodological expertise. She has had the opportunity to benefit from interaction and collaboration with other researchers across the EU and in Japan, which has allowed the establishment of long-lasting research links. During the course of the training period she has acquired new technical and statistical abilities, and expertise in new experimental approaches and methods. She has enhanced her leadership qualities by mentoring students. Finally, the fellow has had also the opportunity to improve scientific communication skills, her CV and develop dissemination activities.

Data: CORDIS, © European Union