Modulation of somatosensory perception and multisensory integration as a function of habitual patterns of action

Dempsey-Jones, Harriet (2016). Modulation of somatosensory perception and multisensory integration as a function of habitual patterns of action PhD Thesis, School of Psychology, The University of Queensland. doi:10.14264/uql.2016.343

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Author Dempsey-Jones, Harriet
Thesis Title Modulation of somatosensory perception and multisensory integration as a function of habitual patterns of action
School, Centre or Institute School of Psychology
Institution The University of Queensland
DOI 10.14264/uql.2016.343
Publication date 2016-06-20
Thesis type PhD Thesis
Supervisor Ada Kritikos
Virginia Slaughter
Tamar Makin
Total pages 238
Total colour pages 15
Total black and white pages 223
Language eng
Subjects 1109 Neurosciences
1701 Psychology
Formatted 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 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 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.
Keyword Tactile perceptual learning
Rubber hand illusion
Proprioceptive drift
Optimal integration theory
Multisensory integration

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Created: Thu, 16 Jun 2016, 05:13:33 EST by Harriet Dempsey-jones on behalf of Learning and Research Services (UQ Library)