Synesthesia is not one singular condition. The word ‘synesthesia’ pertains to a number of different conditions, as it involves separate areas of a person’s brain. It can range from tasting colors to smelling sounds. Synesthesia can occur between any two senses or perceptual modes. If we only regarded the five basic senses (sight, smell, sound, taste, and touch) and mixed these into pairs, there would already be twenty different types of synesthesia. Considering that these twenty different types only pertain to a pairing of the five basic senses, then theoretically, there are much more possibilities than just these twenty types. Solomon Shereshevsky, a synesthete, reportedly experienced a link between all five of the basic senses.

While there are plenty of logically possible combinations, there are several synesthesia types which occur most commonly.

Grapheme to Color Synesthesia

This is one of the most common types of synesthesia. A person who experiences this may associate/see individual letters or numbers with a specific color. Usually, two people won’t report the same color for letters and numbers. However, studies have shown that many synesthetes will see some letters the same way (for example, ‘A‘ is likely to be red).

Sound to Color Synesthesia

It is said that people who have sound to color synesthesia are able to experience “fireworks” when they hear certain sounds. For example, a barking dog may trigger a visualization of colors that take shape and dance around the room, only fading when the sound that triggered them ceases to resonate. For certain people, the stimuli are limited, and only a few types of sounds will trigger a reaction. However, other people report that a multitude of sounds trigger a reaction.

Number Form Synesthesia

A number form is defined to be a mental map which consists of numbers. When a person with number form synesthesia thinks about numbers, a number map is involuntarily visualized. It is sometimes suggested that the number forms are a product of “cross-activation” between regions in the parietal lobe which is involved in numerical and spatial cognition.

Personification

This type is known as ordinal-linguistic personification, or OLP. A person who has this will associate ordered sequences with various personalities. Ordered sequences may include numbers, letters, months and so on. For example, a person with OLP may look at the letter ‘A’ and think in his mind that ‘A’ is a rude letter. Personally, I think it’s rather amusingly self-deprecating – but that’s just me. Check out Seattle graphic designer, Jesse Jaren’s unique portrayal of ordinal-linguistic synesthesia (shown in the graphic below) in this entertaining and informative blog post.  You’ll agree, it’s pretty awesome.

In addition to thinking that certain ordinal sequences have a personality, a synesthete may also imbue a personality within an object. While occurrences have been reported early on, this is a type of synesthesia which has only gained attention from researchers in recent years.

Lexical to Gustatory Synesthesia

Lexical to gustatory synesthesia is one of the rare synesthesia types. Synesthetes who have this kind of synesthesia are able to evoke different kinds of tastes when they hear certain words or phonemes. According to research, associations between the words and what a synesthete is able taste are constrained by tastes he or she has experienced early in life.