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

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Chapter 1
word/grapheme-colour synaesthesia triggered by speech (Paulesu et al., 1995); fMRI
studies of grapheme-colour (Aleman, Rutten, Sitskoorn, Dautzenberg, and Ramsey,
2001; Hubbard, Arman, Ramachandran, and Boynton, 2005; Weiss, Zilles, and Fink,
2005; Sperling, Prvulovic, Linden, Singer, and Stirn, 2006; Rich et al., 2006), mirror-
touch (Blakemore, Bristow, Bird, Frith, and Ward, 2005), word-colour (Aleman et al.,
2001; Nunn et al., 2002; Gray, Parslow, Brammer, Chopping, Vythelingum, and
ffytche, 2006), digit-colour (Elias et al., 2003), people-colour (Weiss, Shah, Toni,
Zilles, and Fink, 2001), time-colour (Steven, Hansen, and Blakemore, 2006), time-
space (Steven et al., 2006), sound-vision (Stewart, Mulvenna, Griffiths, and Ward, in
prep), and bidirectional synaesthesia (Cohen Kadosh, Cohen Kadosh, and Henik,
2007). In addition, there have been two diffusion tensor imaging studies (DTI) of
grapheme-colour synaesthesia (Rouw and Scholte, 2007; Jäncke, Beeli, Eulig, and
Hänggi, 2009).
While there is some inconsistency between studies, the majority point to
synaesthetic experience being correlated with activations in brain regions involved in
normal perceptual experience. For example, studies investigating synaesthesia
involving colour tend to report activation of colour area V4 / V8 for synaesthesia
inducing stimuli (e.g. Hubbard et al., 2005; Nunn et al., 2002; Sperling et al., 2006),
although not always (i.e. Paulesu et al., 1995; Weiss et al., 2005; Figure 1.1). The
reasons behind this inconsistency remain unclear, although they may be related to
differences in task demands, statistical power, or qualitative differences between
synaesthetic subjects (Hubbard et al., 2005). Moreover, by correlating performance
on different synaesthetic psychophysical paradigms with fMRI activations, Hubbard
and colleagues (2005) show that synaesthetes who show larger effects on