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

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Chapter 3
sensory representations. In the case of colour, it has been suggested that linguistic
labels are necessary to categorize colours across a perceptual continuum (Davidoff,
2001) and cross-cultural differences in the number of colour labels has been shown to
influence colour perception and memory (Robertson, Davies, and Davidoff, 2000). It
may be the case that for some colour synaesthetes (i.e. grapheme-colour
synaesthesia), the presence of stable associations with colour increases the number of
colour terms and thereby impacts on the internal structure of colour space (Yaro and
Ward, 2007). In accordance with this, Simner and colleagues (2005) report that
grapheme-colour synaesthetes produce a greater depth of colour descriptions and use
more colour terms than non-synaesthete control participants. It is unclear however,
how this would extend to other variants and concurrent perceptual systems such as
enhanced tactile acuity in mirror-touch synaesthesia.
Additionally, insights into the influence of enriched perceptual experience on
sensory enhancement in the deprived brain would suggest that it is unlikely that extra
synaesthetic percepts are the cause of superior perceptual processing (Pascual-Leone,
Amedi, Fregni, and Merabet, 2005). For example, blind subjects have been shown to
be superior to sighted subjects on the grating orientations test, however this
superiority does not correlate with Braille reading experience or differ between Braille
readers and blind non-readers (Goldreich and Kanics, 2003; Van Boven, Hamilton,
Kauffman, Keenan, and Pascual-Leone, 2000). This indicates that mechanisms of
cross-modal plasticity following visual deprivation (rather than increased tactile
experiences) drives tactile acuity enhancement in the blind (Goldreich and Kanics,
2003). Consistent with this, in sighted-subjects visual deprivation induced by long-
term blindfolding results in temporary enhancements of passive tactile acuity, but
enriched tactile experience on the same finger does not (Kauffman, Théoret, Pascual-