Synaesthesia occurs from early in life and is known to have a genetic component [4]

1. Synaesthesia (Candidate: 123456) Definitions and Characteristics What Causes It? • Unusual sensory experiences triggered by a stimulus • that does not normally elicit that response • Examples: experiencing letters and numbers as • coloured (top left), visualising sequences spatially (top • right), tasting words, seeing music and so on • Colour experiences from verbal stimuli (words, letters, • numbers) are the most common form = 4 to 5% of • population [1] • Synaesthesia occurs from early in life and is known to have a genetic component [4] • Environment has some role too - e.g. letters and numbers are culturally acquired • One suggestion is that synaesthesia is associated with greater localised connectivity in the brain, and studies of white matter tracts supports this idea [5] • The anatomical proximity of regions in the brain sensitive to colour and those recognising letters may result in these areas becoming connected together [6] • Synaesthesia may also be acquired in adults after • sensory loss (e.g. Blindness) but has somewhat • different characteristics The human colour area (red) and grapheme area (green) lie adjacent [6] • Different synaesthetes experience different colours • but their own colours tend to be stable over time [2] • The experiences are reported to occur automatically: • synaesthetes cannot switch it on or off Is it Real? • The automaticity of synaesthesia is demonstrated • using Stroop-like interference tasks [2]. E.g. if a • synaesthete experiences A=red then he/she will be • slower to name the true text colour for A relative to A What are the Consequences of it? • Ramachandran and Hubbard [6] argue that it is linked • to creative and artistic tendencies • People with synaesthesia appear to have better • memory for words and colours, and better colour • perception abilities [7] Congruent Colour Naming Time (ms) Incongruent • fMRI studies show that the brains’ of synaesthetes • respond differently when presented with stimuli that • induce synaesthesia • In this study, ‘coloured speech’ synaesthetes listened to • words in a scanner. This was compared with tones (not • triggering colours), and the same conditions in controls • [3] References [1] Simner, J., et al. (2006). Perception, 35, 1024-1033 [2] Mattingley, J. B., et al. (2001). Nature, 410, 580-582. [3] Nunn, J. A. et al. (2002). Nature Neuroscience, 5, 371-375 [4] Asher, J. E., et al. (2009). American Journal of Human Genetics, 84, 279-285. [5] Rouw, R., & Scholte, H. S. (2007). Nature Neuroscience, 10, 792-797. [6] Ramachandran, V. S., & Hubbard, E. M. (2001). Journal of Consciousness Studies, 8, 3-34. [7] Yaro, C., & Ward, J. (2007). Quarterly Journal of Experimental Psychology, 60, 682-696. The human colour area (V4) responds when synaesthetes listen to speech [3]