Neural Mechanisms
It has been suggested that number-forms are a result of "cross-activation" between regions of the parietal lobe that are involved in numerical cognition and angular gyrus for spatial cognition (Ramachandran & Hubbard 2001; Hubbard et al. 2005). Since the areas that process numerical and spatial representations are close to each other, this may contribute to the increased cross-activation. Compared to non-synesthetes, synesthetes display larger P3b amplitudes for month cues, but similar N1 and P3b responses for arrow (<- or ->) and word (left or right) cues. (Teuscher et al. 2010).
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