Answer: According to several self reports, the most common form of synesthesia is grapheme-color synesthesia, meaning that a person sees a color associated with specific numbers or letters.
Synesthesia is the condition where associated person perceives the activation of one sense modality when another sense is activated. Among people with synesthesia, there are a wide range of senses that can abnormally activated, and almost any of the senses may become active. Even though synesthesia is considered abnormal, it is non clinical and does not present any risks to a person. In most people with synesthesia, they find it to be pleasurable. People who experience these sensations are called synesthetes. It is estimated that about 1-3% of people have some sort of synesthesia.
The senses may be crossed in a person with synesthesia. The most common form, according to a study on synesthetes, is a grapheme-color synesthesia. In this combination, a person may see a color when a particular letter is shown to them. The color they perceive is internally consistent, meaning that if if a person sees green when they see the letter “A,” they will always see green when the letter “A” appears. However, this does not consistently apply across different people with synesthesia; another person with grapheme-color synesthesia might see the color orange with the letter “A”. Associated with this is a number-color synesthesia, where a person sees a color with certain numbers. Together, grapheme-color synesthesia and number-color synesthesia make up about 65% of synesthetes.
The next most common form of synesthesia is sound-color. For these people, when they perceive certain sounds, they may see colors associated with that sound stimulus. These people report being able to detect the character of the color after hearing a certain sound. According to one study, this sound-color synesthesia occurs in about 15% of synesthetes.