2 Various Types of Synesthesia

According to Peter G. Grossenbacher, three types of synesthesia can generally be distinguished with respect to their origin: 1) For people with genuine synesthesia, there are couplings of inducer and concurrent that are constant over time and were always present. 2) In the case of the acquired form, consistent couplings occur due to a neuropathological state. 3) In drug-induced synesthesia, there are temporary, variable couplings caused by psychoactive substances (such as, e.g., LSD or mescaline). This article will only deal with genuine synesthesia.

In the area of genuine synesthesia, the scientific literature most frequently describes colored hearing, in which spoken words, letters, numbers, voices, or sounds activate visual impressions like colors and/or figures, so-called photisms. During the course of Synaesthesia and Sound, a research and development project by Jamie Ward and Samantha Moore, it was shown that visualizations of synesthetic photisms in combination with sounds were perceived as particularly aesthetic even by non-synesthetes.

The perception of photisms is less frequently triggered by taste, smell, or when a person feels pain. A little-researched phenomenon is so-called emotional synesthesia. This term is used in two respects: It describes a form of synesthesia in which a sensory modality, such as, e.g., the sense of touch, elicits a feeling depending on the stimulus. Vilayanur S. Ramachandran, for example, describes a woman who felt inferior when she touched denim with her hand, while she felt calm and strong when she touched smooth metal. In its other meaning, emotional synesthesia can also describe synesthetic perceptions that are caused by an emotional state (Emrich 2002).

However, there are not only many different forms of synesthesia, there also can be major differences between perceptions by synesthetes within the same form of synesthesia. While, for instance, some grapheme-color synesthetes report they see colors on the letters themselves, or projected around them, others report that the colors cannot really be seen visually, but only in their mind’s eye.