Mirror-touch synaesthesia: the role of shared ... - UCL Discovery

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ABSTRACT
Synaesthesia is a condition in which one property of a stimulus results in conscious
experiences of an additional attribute. In mirror-touch synaesthesia, the synaesthete
experiences a tactile sensation on their own body simply when observing touch to
another person. This thesis investigates the prevalence, neurocognitive mechanisms,
and consequences of mirror-touch synaesthesia. Firstly, the prevalence and
neurocognitive mechanisms of synaesthesia were assessed. This revealed that mirror-
touch synaesthesia has a prevalence rate of 1.6%, a finding which places mirror-touch
synaesthesia as one of the most common variants of synaesthesia. It also indicated a
number of characteristics of the condition, which led to the generation of a
neurocognitive model of mirror-touch synaesthesia. An investigation into the
perceptual consequences of synaesthesia revealed that the presence of synaesthesia is
linked with heightened sensory perception - mirror-touch synaesthetes showed
heightened tactile perception and grapheme-colour synaesthetes showed heightened
colour perception. Given that mirror-touch synaesthesia has been shown to be linked
to heightened sensorimotor simulation mechanisms, the impact of facilitated
sensorimotor activity on social cognition was then examined. This revealed that
mirror-touch synaesthetes show heightened emotional sensitivity compared with
control participants. To compliment this, two transcranial magnetic stimulation
(TMS) studies were then conducted to assess the impact of suppressing sensorimotor
activity on the expression recognition abilities of healthy adults. Consistent with the
findings of superior emotion sensitivity in mirror-touch synaesthesia (where there is
facilitated sensorimotor activity), suppressing sensorimotor resources resulted in
impaired expression recognition across modalities. The findings of the thesis are
discussed in relation to neurocognitive models of synaesthesia and of social cognition.