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Sound to color synesthesia, or Chromesthesia, is a specific type of synesthesia in which heard sounds automatically induce an involuntary experience of color. Individuals with sound to 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 to color synesthesia perceive the snyesthetic experience spontaneously, and without effort, and in a way that the individual learns to accept as normal within their realm of normal experience.

Various Forms
The color associations, that is, which color is associated to which sound, tone, pitch, or timbre is highly idiosynchratic, and in most cases, consistent over time. Individuals with synesthesia all have unique color pairings.

As with other variations of synesthesia, sound to 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.

Research
The cross-activation theory of synesthesia was formulated by V.S. Ramachandran and E.M. Hubard, based on converging evidence over studies of the various forms of synesthesia that sensory areas for processing real and synesthetic information tend to be neighboring brain regions. This is most apparent in grapheme-color snyesthesia, because the brain regions for color processing and visual word form processing are adjacent. Individuals with chromesthesia show activation of brain areas involved in visual processing, such as V4, immediately after the auditory perception, indicating an automatic linking of sounds and colors. The reason for this cross-activation is still unclear, but one hypothesis is that the increased connectivity between adjacent brain regions is due to a reduction in the pruning back of neuronal networks during childhood.

The disinhibited feedback model provides an alternative to the cross-activation theory. The disinhibited feedback model rejects the assumption of increased connectivity in synesthetes and proposes that the cross-activation is due to a decrease of inhibition.

The causality of synesthesia is also unclear at this time, although evidence points to a genetic predisposition. Synesthesia is known to run in families, though the condition may present idiosyncratically within a family. Additionally, synesthesia may skip a generation. However, there are cases of monozygotic twins where only one has synesthesia, indicating there may be additional factors involved.

In addition to the high interconnectivity in synesthesia, there is an apparent contribution by the inferior parietal cortex during synesthetic experiences, possibly serving as the mechanism to bind the real and synesthetic perceptions into one experience. Parietal lobe activation is most apparent when the synesthete is directing attentional focus to the synesthetic experience.

Research Complications
What criteria defines an individual as having synesthesia. These are not consistent across all studies.
 * Consistent over time
 * Spatially mapped
 * Neurologically defined

List 2 or 3 different approaches (methods)
 * Subjects match color to a vector in RGB space
 * The goal was to make quantifiable comparisons
 * Not very successful due to idiosyncratic nature
 * However, synesthetic and non synesthetic individuals alike, associated higher pitches to lighter colors, possibly divulging information about the brain's underlying ability to make synesthetic associations.

Experiences
Examples of several individual (and unique) cases of chromesthesia from book.
 * Exclusively sound -> color case
 * 5-fold synesthesia case (including bidirectional sound <-> color)
 * It can be beneficial or overwhelming.

Prevalence?
The prevalence is difficult to determine at this time (reference one or multiple articles to back this up. It's in at least 5 of them.)
 * American Synesthesia Association statistics, Day's efforts to register cases
 * Self-report bias
 * Definitional bias
 * Subjectivity bias

Associated Cognitive Traits
The proportion of synesthetes among artists is around twice as high as in the general population. Synesthetic artists tend to chose an art form where they may benefit from their form of synesthesia. Individuals with chromesthesia are thus more inclined to play a musical instrument.

Absolute Pitch can, but is not always present in chromesthesia. This ability is more heavily dependent on early instruction and explicit naming of pitches than on chromesthesia.

All about Citations
This is the text for my first citation. continue writing article and here is the second citation and I plan to use this one more than once type more article. Finally we cite the "name" article again.