A one is green, an A is violet, a red apple is C major and a Riesling wine tastes blue. Sounds absurd, but there are these people who perceive and feel the world this way because they experience external stimuli not only through a sensory perception. They see letters and/or numbers in colour although they are in front of them in black and white, sounds of a music have different colours and shapes, they can taste words and colours and shapes or letters and numbers trigger feelings in them. Seasons, months and days of the week can also evoke different colours and emotions in them. Synaesthetes are "normal" people with an additional talent for processing sensory stimuli, perception and thinking.
Neuroscientists have found that synaesthetes have an increased functional coupling between brain regions that make simultaneous sensory perceptions possible. Stimulation of one sense - such as hearing - triggers an additional sense perception - such as seeing colours or geometric figures. These perceptual phenomena are not pathological. They are a special ability called synaesthesia. Synaesthesia means a blending of the senses, a simultaneous sensory perception that occurs involuntarily. This ability of double perception has been known for a long time, but it has only been properly taken up and researched since imaging techniques have made it possible to follow the processes in the brain. Researchers have discovered that synaesthetes have an increased functional coupling between brain regions that make simultaneous sensory perceptions possible. In the 1990s, the frequency of synaesthetes was assumed to be 0.1 percent of the total population, but more recent studies indicate a much higher percentage of about four percent. That would be 3.2 million people in Germany. This fact and also the increasingly better examination possibilities might be responsible for the fact that the interest in the scientific research of synaesthesia has noticeably grown internationally. By researching synaesthesia, neuroscientists hope to learn more about the organisation and function of the brain and thus gain new insights into the functioning of human consciousness.