Synesthesia is loosely defined as a merging of the senses, the notion that one sensation can trigger a separate perception. This is most commonly manifested as individuals who perceive color with letters or numbers (known as grapheme-color synesthesia), however other variants include experiencing taste with words, texture with taste, or color with music. It is important to note that the secondary, or concurrent, sensation does not replace the primary, or inducer, perception, but is instead experienced in addition to it. There are currently 61 known variants of synesthesia, spanning the perceptual spectrum of color, taste, sound, touch, and even higher level cognitive conceptions, such as language. At first glance, these phenomena seem quite unique and binary (after all, you either taste rectangle or you don't), and the prevalence of synesthesia was originally thought to be roughly 1 in 1000. However, new research on sensory integration has revealed that varieties of synesthesia may be much more common than originally thought, and that there may be a sliding scale in the amount of sensory cross-talk among individuals.