Synesthesia is described as a blending of the modes in the cerebral cortex. The result of this is a complex situation where an individial may experience a visual and olfactory conection (commonly described as seeing smells), auditory and visual connections (tones induce colours) and even auditory taste connections, which results in the tasting of tones. There are many theories to explain why this occurs that branch into all psychological schools of thought. These are covered in thorough detail in the paper.