State of the art - Synaesthesia

What colour is the letter A? What does the number 1 taste of? Does listening to music, speaking or eating food produce colours, shapes or textures? For most people, questions such as these will either yield a look of bewilderment or an emphatic ‘No!’ However, when I have posed this question to our intake of psychology undergraduates at University College London, as many as 1 per cent are certain that they experience something like this. These students may well have synaesthesia.