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

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2.4 General Discussion
Chapter 2
Taken together, these measures detail the prevalence and characteristics of
mirror-touch synaesthesia. In relation to prevalence, the findings suggest that:
• mirror-touch synaesthesia is one of the more common forms of
synaesthesia
• there are two sub-types (specular and anatomical) depending on the
visuo-tactile spatial transformation used
• the specular (mirror-reflected) sub-type is the more common
• the effects are quite specific to observed touch to a human body.
In many respects, mirror-touch synaesthesia shares common ground with other
types of synaesthesia; for instance, with regards to phenomenology, automaticity,
consistency (of the spatial mapping), reliability over time, and possibly with regards
to associated traits (e.g. attributing personalities and genders to graphemes).
However, when one turns to consider its neural basis the similarities are less apparent.
A current area of debate in the synaesthesia literature is whether synaesthetic
experience is due to cross-activation between brain regions or cortical disinhibition
(Bargary and Mitchell, 2008; Cohen Kadosh, Henik, Catena, Walsh, and Fuetnes,
2009; Cohen Kadosh and Walsh, 2008; Grossenbacher and Lovelace, 2001; Hubbard
and Ramachandran, 2005; Rouw and Scholte, 2007). Thus far, accounts of
synaesthesia in terms of cross-activation have mainly focussed on grapheme-colour
synaesthesia and highlight the role of adjacency between visual grapheme and colour
processing areas in the fusiform gyrus (Ramachandran and Hubbard, 2001). It is
possible that adjacency is one of several biasing principles that influence which forms
of synaesthesia will, and will not, be found. Another biasing principle may be the
‘normal’ architecture for multi-sensory interactions. As noted before, there is now