What is synesthesia ?
Etimology : "syn" is the Anciant Greek for "together" and "aisthesis" for "sensation"
This means that one sensory or the perception of words and numbers is automaticly and involuntary linked to another sensory. People under this condition are called synesthetes.
Synesthesia is a very infrequent condition, it has been estimated that synesthetes represent only a part between 1/20 and 1/2 000 of individuals, this lack of precision comes from the fact that it is difficult to diagnose it for many reasons. One is that most of the time people are not conscious that what they experience is unusal or even have a name.
There is different kind of synesthesia, the most common is Grapheme ---> Color synesthesia wich is a perception of color or numbers with an inherent color.
For exemple when a synesthete reads a newspaper he will be conscious that the numbers and the letters are written in black but he will automaticly see colors added to the real colors. For each letter or each number there is a specific and precise color and it never changes over time but it changes from a synesthete to another. In rare cases graphemes can also have different texture and size.
Then you have almost every sensory combinations such as Sound ---> Color, Smell ---> Taste, Pain ---> Color, ect...
Another form of synesthesia is number-form synesthesia wich is when a synesthete associates a location to numbers, like the example below.
The last form identified is personification synesthesia, this is when numbers, letters, days or month and any ordered sequences possesses a personality and gender. For example one synesthete reports that :
"February is an introverted female, while F is a dodgy geezer male . Similarly, May is soft-spoken and girly while M is an old lady who natters a lot, and while August is a boy among girls, A is a mother type female."