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Synaesthesia: Definitions, Characteristics, and Causes in Human Brain

Synaesthesia is a phenomenon where unusual sensory experiences are triggered by stimuli, like seeing letters as colors or tasting words. It has genetic and environmental factors and may be linked to brain connectivity and creativity. Synaesthetes experience stable, automatic color associations that can enhance memory and perception abilities. Studies show distinct brain responses in synaesthetes compared to controls.

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Synaesthesia: Definitions, Characteristics, and Causes in Human Brain

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  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]

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