Synesthesia

SYNESTHESIA (synaesthesia), the appearance, upon stimulation of a specific sense organ, of not only sensations specific to that organ, but also accompanying "sensations" characteristic of another sensory domain. Synesthesia apparently can arise between all possible types of sensations, but cases predominate where light phenomena, so-called photisms or synopsias, are added to sensations arising in the usual way in one sensory domain or another. If auditory sensations are accompanied by photisms—a combination that is most frequently encountered and best studied—then one speaks of phonopsias or "colored hearing" (audition colorée). Significantly less frequently observed are phonisms, sound phenomena accompanying primarily visual sensations. A propensity for synesthesia is an individual characteristic of certain persons, which does not relate to pathology. It is believed that synesthesia occurs in approximately 12% of all people ("colored hearing" in 4%). An examination of the blind revealed 30 people with colored hearing out of 150 examined. Colored hearing most often manifests in that, upon hearing vowel sounds, impressions of specific colors arise, with the quality of the sounds having greater significance than the pitch of their tone. Very often, photisms arise when hearing singing or the playing of musical instruments: here, the light phenomena depend sometimes on the character of the instrument, sometimes on the note, sometimes on the properties of the melody, or even on the individual characteristics of a specific composer. Wegofer, who, like Bleuler, made observations on himself, reports that the structure of a musical passage (rhythm, harmony, and melody) causes in him visual images of a specific geometric structure that are regularly associated with it. Often, synopsias are also caused by the timbre of the human voice. Among other synopsias, colored gustatory and olfactory sensations are frequent, and tactile ones are somewhat rarer. In a significant number of cases, photisms possess properties that do not allow them to be identified with ordinary visual sensations: they are usually devoid of corporeality, rather transparent and superficial, most of all resembling the colored shades of a clear sky or the colors of a rainbow, and cases are known where their analysis reveals contradictions with the laws of color perception. They are projected not into the field of vision, but in space associated with the region of the primary sensation, i.e., in relation to colored hearing, where the corresponding auditory perceptions are localized. Taking into account, however, that synesthesia always arises as a response to peripheral stimulation of specific sense organs and has the character of a directly evoked, rather than reproduced, impression, Bleuler considers them "secondary" sensations. One should not confuse synesthesia in the proper sense with corresponding reproduced images arising, for example, when recalling impressions usually accompanied by synesthesia, or upon seeing letters representing sounds that cause synopsias, etc. The physiological basis of synesthesia has not been clarified. In the opinion of some, synesthesia arises under the influence of emotional associations: the secondary sensation has for the given person the same emotional coloring as the primary one, and therefore always arises together with the latter. Bleuler, however, proceeding from observations on himself, asserts that secondary sensations of a completely different emotional shade than the primary ones that evoke them are not rare. He himself defends the idea that brain processes evoked by the stimulation of a specific sense organ, in a significant number of cases, condition sensations not only of one specific character; accompanying secondary sensations, however, are for the most part very weak and are suppressed, whereas in cases where differentiation has remained insufficient, synesthesia is formed. Bleuler, in this regard, has in mind not irradiation from one brain center to another, but a primary process of brain excitation corresponding to the given stimulation.