Perera, Andrea Treshi-Marie

278 Pages·2017·1.98 MB·English

by  Christine Middleton

THE MECHANISMS UNDERLYING ALTERED SOMATOPERCEPTION
AND SOMATOSENSATION IN HEALTHY AND SUBCLINICAL
POPULATIONS

Andrea Treshi-marie Perera

Thesis submitted to the University of Nottingham
for the degree of Doctor of Philosophy

July 2016
ABSTRACT
Manipulating somatic representations has been found to alter somatic experiences;
however, the precise mechanisms underlying these altered somatic experiences are as yet
unclear. This thesis primarily investigated the mechanisms underlying altered somatic
experiences following illusions that manipulated perception of the body representation.
The current thesis also addressed individual differences in somatic perception across
individuals with propensities towards various clinical conditions, including amplified
somatosensory sensitivity and medically unexplained symptoms (MUS).
The pilot investigation in Chapter 3 provided evidence for susceptibility and
ownership towards somatic illusions generated using the MIRAGE mediated-reality
system, thus validating manipulations induced using this system. In Chapter 4, longer and
shorter body representations were judged as veridical (or normal) following stretched and
shrunken illusions respectively, while in contrast to early studies ownership was not lost
as a result of the illusory manipulations. An association between self-reported somatic
sensitivity and illusion strength was also observed for females, with females reporting
increased somatic sensitivity being more susceptible to the illusion.
Chapter 5 demonstrated that illusory alterations of body shape and size improved
perception of near threshold tactile stimuli. However, changes in tactile perception were
driven by differing mechanisms when body size at the site of stimulation was altered,
whilst similar mechanisms drove this change when body size away from the site of
stimulation was altered. Interestingly, a detached condition (in which the finger-tip and
stump were disconnected) resulted in a significant reduction in overall positive reports of
feeling tactile stimuli. Finally, overall false-touch reports and reduced sensitivity (i.e., the
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inability to discern between touch present and absent trials) were found to be
characteristic of those with propensities towards MUS.
Chapter 6 demonstrated that a purely visual illusion, in the absence of any real
somatic input, did not interfere with external tactile perception or lead to different
response patterns between individuals with increased or decreased tendencies towards
MUS.
The thesis provides evidence for the dynamic and bidirectional flexibility of the
body representation by providing direct evidence for the immediate updating of the body
representation following size-altering illusory manipulations. These illusions also altered
external somatic sensations via different underlying mechanisms and reflected individual
differences in response patterns between healthy and sub-clinical populations, thus
suggesting that susceptibility to such illusions may be clinically relevant, and useful in
identifying the nature various psychological pathologies.

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ACKNOWLEDGEMENTS
I am extremely grateful to my supervisors, Dr Kirsten McKenzie and Dr Roger
Newport for their support and guidance throughout my PhD. They are fabulous, sharp
and insightful! And have helped me to express my ideas more clearly. Thank you for the
encouragement especially at the latter stages of the thesis and for giving me the
confidence boost (I needed) to explore my research interests and preventing me from
feeling lost during the process.
A big big thank you to Dr Julien Mayor, who gave me great advice and was
helpful in many ways during the final year of my PhD. Dr Jess Price has the BEST laugh
and was always there to listen and cheer me up whenever I needed it – thank you.
I would also like to thank both Dr Sheppard and Prof Ehrsson for taking the time
to read this thesis.
Thank you to my fellow PhD folks at BB47 who were always entertaining and
reduced the stress. In particular, I would like to thank Jiin, Cheng, Azlina and Ai-Suan
for their friendship that helped make Malaysia a home away from home. I could also not
thank Vrush enough for being patient and training me with the MIRAGE and SSDT when
I first joined – awkward hug! To all my participants, who were patient and gave me their
time (and manged to keep awake) during my super-long experiments – thank you!
On a personal note, I would like to thank my family and friends back in Sri Lanka
for their love and support. Finally, thank you Alberto for just being amazing and keeping
me sane when it all felt a bit overwhelming.
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TABLE OF CONTENTS
Abstract ................................................................................................................................ I
Acknowledgements ........................................................................................................... III
List of figures ................................................................................................................... XII
List of tables ..................................................................................................................... XV
List of abbreviations ...................................................................................................... XVI

CHAPTER 1 General introduction (I) ............................................................................ 1
1.1 Self-awareness .......................................................................................................... 2
1.1.1 Disorders of body ownership and embodiment ...................................... 4
1.2 Investigating ownership and embodiment under laboratory settings ..................... 12
1.2.1 Somatic illusions ................................................................................... 13
1.2.2 Rubber hand illusion ............................................................................. 14
1.3 Modifying perceived shape and size of body representation and
somatic perception ................................................................................................ 19
1.3.1 Inconsistencies in previous research ..................................................... 22
1.4 MIRAGE….. .......................................................................................................... 24
1.4.1 Studies that used the MIRAGE mediated reality device....................... 25
1.5 Summary: Misperceptions, somatic illusions and the MIRAGE system ............... 31

CHAPTER 2 General introduction (II) ........................................................................ 33
2.1 Cross-modal integration ......................................................................................... 33
2.2 Visuotactile interactions ......................................................................................... 37
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2.2.2 Manipulating perceived body size and tactile perception ..................... 39
2.2.3 Summary of vision and manipulated body representations on
somatosensation .................................................................................... 40
2.3 The Somatic Signal Detection Task (SSDT; Lloyd et al., 2008) ........................... 41
2.3.1 Studies using the SSDT ........................................................................ 42
2.4 False-alarms on the SSDT as a laboratory analogue of unexplained physical
symptoms .............................................................................................................. 47
2.5 Clinical models of MUS ......................................................................................... 49
2.5.1 The dissociation model ......................................................................... 50
2.5.2 The conversion model ........................................................................... 51
2.5.3 Somatisation and cognitive behavioural models ................................... 52
2.5.4 Perceptual processing models ............................................................... 56
2.5.5 An integrative conceptual model .......................................................... 58
2.6 Individual differences in somatic misperceptions .................................................. 59
2.7 Aims and objectives of the current Thesis ............................................................. 63

CHAPTER 3 Examining the degree of subjective susceptibility to multisensory
illusions of body shape and size ............................................................................ 65
3.1 Introduction ............................................................................................................ 65
3.2 Methods .................................................................................................................. 68
3.2.1 Participants ............................................................................................ 68
3.2.2 Apparatus and Material ......................................................................... 68
3.2.2 Procedure .............................................................................................. 71
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3.3 Results .................................................................................................................... 72
3.4 Discussion .............................................................................................................. 77

CHAPTER 4 Altered body representations following a brief exposure to
multisensory distortions of the hand.................................................................... 80
4.1 Introduction ............................................................................................................ 81
4.2 Experiment 1 .......................................................................................................... 85
4.3 Experiment 1 Method ............................................................................................. 86
4.3.1 Participants ............................................................................................ 86
4.3.2Apparatus and Material .......................................................................... 86
4.3.3 Procedure .............................................................................................. 88
4.4 Experiment 1 Results ............................................................................................. 89
4.4.1 Questionnaire responses ........................................................................ 89
4.4.2 Judgments of perceived finger length: online resizing ......................... 92
4.5 Experiment 1 Discussion ........................................................................................ 93
4.6 Experiment 2 .......................................................................................................... 94
4.7 Experiment 2 Method ............................................................................................. 95
4.7.1 Participants ............................................................................................ 95
4.7.2 Apparatus and Material ......................................................................... 96
4.7.3 Procedure .............................................................................................. 97
4.8 Experiment 2 Results ............................................................................................. 99
4.8.1 Questionnaire responses ........................................................................ 99
4.8.2 Judgments of perceived finger length: online resizing ....................... 101
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4.8.3 Judgments of perceived finger length: offline size estimation ........... 102
4.9 Experiment 2 Discussion ....................................................................... 103
4.10 Experiment 3 ...................................................................................................... 104
4.11 Experiment 3 Method ......................................................................................... 106
4.11.1 Participants ........................................................................................ 106
4.11.2 Apparatus and Material ..................................................................... 106
4.11.3 Procedure .......................................................................................... 108
4.12 Experiment 3 Results ......................................................................................... 109
4.12.1 Questionnaire measures .................................................................... 109
4.12.2 Association between SSAS scores and illusion strength and ownership
ratings ................................................................................................. 110
4.13 Experiment 3 Discussion .................................................................................... 111
4.14 General discussion ............................................................................................. 112

CHAPTER 5 Investigating the effects of multisensory distortions of the hand on
near threshold tactile perception ....................................................................... 118
5.1 Introduction .......................................................................................................... 119
5.2 Experiment 1 ........................................................................................................ 122
5.3 Experiment 1 Method ........................................................................................... 123
5.3.1 Participants .......................................................................................... 123
5.3.2 Apparatus and Material ....................................................................... 123
5.3.3 Design and Procedure ......................................................................... 128
5.4 Experiment 1 Results ........................................................................................... 129
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5.4.1 Questionnaire responses ...................................................................... 129
5.4.2 SSDT parameters ................................................................................ 132
5.5 Experiment 1 Discussion ...................................................................................... 135
5.6 Experiment 2 ........................................................................................................ 137
5.7 Experiment 2 Method ........................................................................................... 137
5.7.1 Participants .......................................................................................... 138
5.7.2 Apparatus and material ....................................................................... 138
5.7.3 Design and Procedure ......................................................................... 140
5.8 Experiment 2 Results ........................................................................................... 141
5.8.1 Questionnaire responses ...................................................................... 141
5.8.2 SSDT parameters ................................................................................ 144
5.9 Experiment 2 Discussion ....................................................................... 148
5.10 Experiment 3 ...................................................................................................... 151
5.11 Experiment 3 Method ......................................................................................... 154
5.11.1 Participants ........................................................................................ 154
5.11.2 Apparatus and Material ..................................................................... 154
5.11.3 Design and Procedure ....................................................................... 156
5.12 Experiment 3 Results ......................................................................................... 156
5.12.1 Questionnaire responses .................................................................... 156
5.12.2 SSDT parameters .............................................................................. 159
5.12.3 Correlation between self-reported MUS and SSDT parameters ....... 163
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5.13 Experiment 3 Discussion .................................................................................... 166
5.14 General discussion ............................................................................................. 169

CHAPTER 6 Does visually evoked somatosensation interfere with somatic
sensations? ............................................................................................................ 176
6.1 Introduction .......................................................................................................... 177
6.2 Method ................................................................................................................. 180
6.2.1 Participants .......................................................................................... 180
6.2.2 Apparatus and Material ....................................................................... 181
6.2.3 Design and Procedure ......................................................................... 183
6.3 Results .................................................................................................................. 184
6.3.1Questionnaire responses ....................................................................... 184
6.3.2 SSDT parameters ................................................................................ 186
6.3.3 Tendency of experiencing MUS and changes in somatic perception . 186
6.4 Discussion ............................................................................................................ 187

CHAPTER 7 General discussion ................................................................................. 191
7.1 Background to Thesis ........................................................................................... 191
7.2 Summary of Findings ........................................................................................... 193
7.2.1 Chapter 3: Examining the degree of subjective susceptibility to
multisensory illusions of body shape and size ................................... 193
7.2.2 Chapter 4: Altered body representations following a brief exposure to
multisensory distortions of the hand ................................................... 194
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