Synesthesia (also spelled synaesthesia or synaesthesia) is a neurological phenomenon in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway. People who report a lifelong history of such experiences are known as synesthetes.
In one common form of synesthesia, known as grapheme-color synesthesia or color-graphemic synesthesia, letters or numbers are perceived as inherently colored. In spatial-sequence, or number form synesthesia, numbers, months of the year, and/or days of the week elicit precise locations in space (for example, 1980 may be “farther away” than 1990), or may appear as a three-dimensional map (clockwise or counterclockwise). Synesthetic associations can occur in any combination and any number of senses or cognitive pathways.
Little is known about how synesthesia develops. It has been suggested that synesthesia develops during childhood when children are intensively engaged with abstract concepts for the first time. This hypothesis – referred to as semantic vacuum hypothesis – explains why the most common forms of synesthesia are grapheme-color, spatial sequence and number form. These are usually the first abstract concepts that educational systems require children to learn.
Only a fraction of types of synesthesia have been evaluated by scientific research. Awareness of synesthetic perceptions varies from person to person.
Difficulties have been recognized in adequately defining synesthesia. Many different phenomena have been included in the term synesthesia (“union of the senses”), and in many cases the terminology seems to be inaccurate. A more accurate term may be ideasthesia.
Test post. Borrowed from Wikipedia