Chromesthesia

Chromesthesia or sound-to-color synesthesia is a type of synesthesia in which heard sounds automatically and involuntarily evoke an experience of color. For the purpose of disambiguation, this article will refer to this chromesthesia in inducer-concurrent terms used to describe other forms of synesthesia. With sounds inducing color concurrents, chromesthesia is more accurately termed sound-color synesthesia. 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 that would be triggered in the average person. That is, the synesthetic color experience supplements, but does not obscure real, modality-specific perceptions. As with other variations of synesthesia, individuals with sound-color synesthesia perceive the synesthetic experience spontaneously, and without effort, and in a way that the individual learns to accept as normal within their realm of experience.

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, all studies to date have reported that synesthetes and non-synesthetes alike match high pitched sounds to lighter or brighter colors and low pitched sounds to darker colors, indicating that there may be some common mechanism that underlies the associations present 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 variants 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 as being in the external space are often called projectors, and those that perceive the color in the mind's eye are often called associators, but these terms can be very misleading in terms of understanding the true nature of the experience. For most synesthetes, the condition is not wholly sensory/perceptual.

For some individuals, the synesthesia is only triggered by speech sounds, while others' synesthesia can be triggered by all known auditory stimuli. In a study investigating variability within categories of synesthesia, 40% of subjects with synesthesia for spoken words reported that voice pitch, accent, and prosody influenced the synesthetic concurrent, 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 voluntarially 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.

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