Summary

People with synesthesia have unusual sensory experiences whereby one stimulus elicits another: Words may evoke tastes, numbers evoke colors, and so on. The eliciting stimulus is called the inducer, whereas the synesthetic experience, which is normally percept-like in quality, is referred to as the concurrent. Synesthetic experiences use some of the same neural substrates as “real” perception. The associations are influenced by cross-modal correspondences between the senses (e.g., high pitch being bright or light) and regularities in one’s own environment. Synesthesia comes in many varieties, but these likely stem from a common cause (because different varieties tend to co-occur together). This is normally explained in terms of an atypical neurodevelopmental cascade from genetic differences that affect brain development and give rise to an atypical profile of behaviors (of which synesthesia is one). People with synesthesia not only have unusual sensory experiences—this being the trait that defines them—but also present with a distinctive cognitive profile (affecting memory, imagery, perception) that has impacts on their life choices (e.g., occupation) and may predispose selectively toward certain clinical vulnerabilities.