The term synesthesia comes from the Greek: syn = together and aisthesis = sensation. Synesthesia is a special ability in which sensory impressions mix. This means that when a sensory organ is aroused, it is accompanied not only by sensory sensations but also by sensory organs of another type: For example, music acquires forms and structures that change with the melody and timbre in front of the inner eye.
With all your senses
Such connections are possible between all five senses. Most common, however, is the "colored hearing". Here, sounds, music or speech are experienced simultaneously with colors. Synesthesia is much more common in women than in men (8: 1 ratio) and in many families much more often than in others. Scientists suspect that there is a genetic modification of the X chromosome in synesthetes. The concrete proof is still pending. The frequency in the population is about 1: 1000.
To explain how it can come to mixed sensory perceptions, there are many theories. For example, that synesthesia occurs through a so-called "cross talk" between otherwise separate nerve tracts. That is, on the way from the sensory organs to the processing centers in the brain, the signals come into contact with each other.
Types of synesthesia
Researchers distinguish "genuine" synesthesia, which usually begins in early childhood and where a sensory stimulus is tightly coupled with a particular color or shape perception, and acquired synesthesia that occurs in neurological diseases or under drugs such as LSD or mescaline and usually not permanent. A third form is the sense synesthesia: it is not necessarily triggered by a stimulus, the affected persons can induce them arbitrarily.
Finally, there is the "associative pseudo-synesthesia": Here, people in childhood have actively learned to associate letters with colors.