Further to my earlier post about the number-colour test, I have found some clarification in the most recent issue of New Scientist (19 May 07) which I purchased yesterday.
The test (or one very similar, it doesn’t specify) was carried out by a leading synaesthesia researcher called Vilayanur Ramachandran, and he found that there were two different types of grapheme-colour synaesthetes: those who actually see the colours on the page and those who see the colours in their mind’s eye. I am of the latter group (the ones who can’t pick the 2s from the 5s) which according to this article means that the concept of the letter, not just the sensory data, causes the synaesthetic response.
That sounds about right to me. It fits with my previous thoughts that the colour responses stem from learnt associations or connections in the brain.
