Modulation of somatosensory perception and multisensory integration as a function of habitual patterns of action Harriet Dempsey-Jones Bachelor of Psychological Science (Hons) A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in 2015 School of Psychology 1 Abstract Somatosensation refers to an integrated percept consisting of information from the skin and muscles, e.g., touch and proprioception. Together these disparate inputs provide information about the state of the body, with respect to itself and the external world. Due to the partially unconscious nature of the somatic senses and the complexity of this distributed system, much remains unknown about its supportive neurocognitive mechanisms. In the current thesis I aimed explore the modulation of somatosensory perception and integration as a function of habitual patterns of action. That is, how patterns of sensory input resulting from activity can shape the organisation of the somatosensory system and multisensory integration processes. Distinct experimental paradigms and somatosensory sub-modalities were explored, to provide converging evidence for this investigation. The first series of experiments looked at how habitual tactile stimulation might affect the representation of touch in the somatosensory system. Touch perception of the fingers can be improved by tactile stimulation (i.e. tactile perceptual learning). Learning transfers from trained to untrained fingers in a pattern reflecting the underlying relationships between fingers in the somatosensory system. I predicted repetitive patterns of touch resulting from daily use between fingers should affect this representation and, therefore, be reflected in learning transfer. A trained group underwent seven sessions of testing and training over four days. This was compared with an untrained control group. A divergence was identified in the transfer of learning from a trained middle finger to two fingers that are physically and cortically adjacent to the trained finger. I suggest this divergence may have resulted from documented differences in cooperative finger use with the middle finger. These results demonstrate how repetitive patterns of action are a potential organising force in the human somatosensory system. In a second line of research, I expanded my investigation into multisensory contributions to somatosensory perception. I used a modification of the classic rubber hand illusion (RHI) to investigate the integration of proprioceptive and visual hand position information. In this paradigm, an illusory spatial disparity is created between visual and proprioceptive hand position, and the strength of multisensory integration is measured by the shift of felt position towards the seen position (proprioceptive 2 drift). Here I was interested in how habitual patterns of action can shape multisensory integration within peripersonal space. I predicted a difference in the integration of visual and proprioceptive hand information within the habitual action space of the arm, versus beyond the action space of the arm. Unlike previous studies I fixed the relative distance between the real and false hand, while varying the absolute position of the two hands in space. By doing so I was able to look at the effect of proximity to the action space alone without the confounding influence of the relative distance between sensory inputs (also known to affect integration). In Experiment One, I demonstrated a spatial modulation of drift across the workspace of the left hand – where visuo-proprioceptive integration was greatest in the habitual action space of the hand. In a follow up experiment, I compared this effect for the left and right hands to reveal these integration differences are indeed due to the hand position, and not a simple processing bias within the left or right hemispace. Overall, my results suggest that multisensory integration is anchored to action space, rather than to the hand itself. In a final experiment I investigate the multicomponent model of self-representation. I ask whether self-localisation (i.e. the sense of where your body is located in space) is a related, but dissociated phenomenon to subjective self-representation (i.e. embodiment and ownership). I predicted that these phenomena are distinct processes, supported by different mechanisms of multisensory integration. To test this prediction I tested the RHI under a condition that was expected to alter self-localisation (measured using ‘drift’) but not subjective self-representation (measured using a questionnaire). In this condition, I placed the participant’s hand within the habitual action space of the arm and shifted felt position laterally out from this location, towards extracorporeal space (RHI Out Condition). I compared this with a control condition that was not expected to modulate either drift or subjective questionnaire outcomes (RHI In Condition). It was predicted that drift would be greater in the Out condition as compared to In, but that there would be no significant difference in subjective questionnaire reports. This dissociation should be possible because, we suggest, subjective illusion is based on a different mechanism of multisensory integration that is unrelated to functional interaction with space. It would, therefore, be unaffected by proximity of the hand to action space. Results revealed drift was indeed greater in the Out condition compared to In, but subjective illusion was not different between conditions. My results support the dissociation of subjective and 3 drift related outcomes of the RHI. I discuss the related, but distinct multisensory mechanisms supporting these two outcomes and their likely neural locus. In conclusion, the results of the current thesis revealed that there is significant evidence that patterns of habitual action affect somatosensory perception and integration processes. Specifically, functional interaction with the world shapes somatosensory processing through schedules of sensory input. Manipulation of somatosensory perception is a useful tool for studying the neurocognitive mechanisms supporting such processes. 4 Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis. Harriet Dempsey-Jones September 2015 5 Publications during candidature Journal articles Dempsey-Jones, H., & Kritikos, A. (2014). Higher-order cognitive factors affect subjective but not proprioceptive aspects of self-representation in the rubber hand illusion. Consciousness and Cognition, 26, 74-89. Dempsey-Jones, H., Harrar., V., Oliver, J., Johnansen-Berg, H., Spence, C. & Makin, T. (2015). Transfer of tactile perceptual learning reflects neighborhood use relationships. J Neurophysiol, jn 00181 02015. doi: 10.1152/jn.00181.2015. 6 Conference Abstracts Dempsey-Jones, H. & Kritikos, A. (2011). Like the back of my hand: Greater shifts in self-location away from the body than towards the body in The Rubber Hand Illusion. Poster presented at the 2nd Australian Cognitive Neuroscience Conference. Dempsey-Jones, H. & Kritikos, A. (2012). Proprioceptive drift towards the body is associated with changes in self-ownership and embodiment in the Rubber Hand Illusion (RHI) – but drift away from the body is not. Poster presented at the 39th Experimental Psychology Conference. Dempsey-Jones, H. & Kritikos, A. (2012). Handedness and proprioceptive position estimation: Are left handed people more accurate in self-representation and is this representation resistant to manipulation by the Rubber Hand Illusion? Front. Hum. Neurosci. Conference Abstract: ACNS-2012 Australasian Cognitive Neuroscience Conference. doi: 10.3389/conf.fnhum.2012.208.00138. Dempsey-Jones, H. & Kritikos, A. (2013). Handedness and the weighting of visual- proprioceptive information in position estimation: the effect of illusory visual position information. Journal of Vision, 13(9), 877. doi: 10.1167/13.9.877. 7 Dempsey-Jones, H. & Kritikos, (2013) A. Visual biases override proprioceptive biases in the estimation of limb position following a visual