Chromesthesia

Chromesthesia or sound-to-color synesthesia is a type of synesthesia in which sound involuntarily evokes an experience of color, shape, and movement. Individuals with sound-color synesthesia are consciously aware of their synesthetic color associations/perceptions in daily life. Synesthetes that perceive color while listening to music experience the colors in addition to the normal auditory sensations. The synesthetic color experience supplements, but does not obscure real, modality-specific perceptions. As with other forms of synesthesia, individuals with sound-color synesthesia perceive it spontaneously, without effort, and as their normal realm of experience. Chromesthesia can be induced by different auditory experiences, such as music, phonemes, speech, and/or everyday sounds.

The color associations, that is, which color is associated to which sound, tone, pitch, or timbre is highly idiosyncratic, but in most cases, consistent over time. Individuals with synesthesia have unique color pairings. However, studies to date have reported that synesthetes and non-synesthetes alike associate high pitched sounds with lighter or brighter colors and low pitched sounds with darker colors, indicating that a common mechanism may underlie those associations in normal adult brains. There are forms of pseudo-chromesthesia that may be explained by associations synesthetes have made and forgotten from childhood.

As with other types of synesthesia, sound-color synesthesia can be divided into groups based on the way the colors are experienced. Those that 'see' or perceive the color in external space are called projectors, and those that perceive the color in the mind's eye are often called associators, but these terms can be misleading to understanding the nature of the experience. For most synesthetes, the condition is not wholly sensory/perceptual.

For some individuals, chromesthesia is only triggered by speech sounds, while others' chromesthesia can be triggered by any auditory stimuli. In a study investigating variability within categories of synesthesia, 40% of subjects with chromesthesia for spoken words reported that voice pitch, accent, and prosody influenced the synesthetic color, whereas few subjects reported that volume or speed of talking had any influence. Within these subjects, many reported that the speaker's emotional inflection could influence the synesthetic color, but only two reported that their own mood had such influence. Of participants categorized as having synesthesia for music in this study, 75% reported concurrents exclusively when listening to notes being played. When asked whether the experience of the concurrent could be voluntarily controlled, only 33% of participants indicated an ability to smother, ignore, or willfully evoke their concurrents without great effort. Attention to the inducing stimulus was reported as influential in 59% of participants. Other contributing factors included concentration level, fatigue, sleep habits, fever, emotions, and substances, such as caffeine or alcohol.

Sound-color synesthesia is far more common than color-sound synesthesia, although there are reported cases where sounds and colors activate bidirectionally. One individual sees colors when she hears sounds and also hears sounds when she sees colors. This type of synesthesia interferes greatly with daily life. This individual's associations were highly consistent over time, but the associations were not necessarily the same in either direction. Another individual who had absolute pitch, as well as Chromesthesia, claimed that her absolute pitch was less stable than her Chromesthesia.

There may be an effect of semantic mediation in some individuals with sound-color synesthesia. One subject self-triggered notes on a synthesizer and noted the color associations. When the synthesizer was transposed without her knowledge, she reported identical color associations to the notes that she believed she was hearing, rather than the absolute pitch of the tones.

The terms synesthesia and chromesthesia have developed and evolved considerably throughout history. The first documented synesthete was Georg Tobias Ludwig Sachs in 1812. Although he did not give a specific name to his experience, in a medical dissertation regarding his albinism (written in Latin), he mentioned obscure ideas and described how colored ideas appeared to him. Even earlier than Sachs, however, Johann Gottfried Herder discussed similar ideas in his Treatise on the Origin of Language in 1772. He talked about how people, "through a sudden onset immediately associate with this sound that color".

The first concrete term associated with chromesthesia was given by Charles-Auguste-Édouard Cornaz in an eye disease dissertation in 1848. Color blindness was a common condition known as chromatodysopsia and, since Cornaz saw chromesthesia as the opposite, he named it hyperchromatopsia or perception of too many colors.