and y is the "concurrent" or additional experience. For example, perceiving letters and numbers (collectively called graphemes) as colored would be indicated as grapheme-color synesthesia. Similarly, when synesthetes see colors and movement as a result of hearing musical tones, it would be indicated as tone → (color, movement) synesthesia. While nearly every logically possible combination of experiences can occur, several types are more common than others. Grapheme–color synesthesia In one of the most common forms of synesthesia, individual letters of the alphabet and numbers (collectively referred to as "graphemes") are "shaded" or "tinged" with a color. While different individuals usually do not report the same colors for all letters and numbers, studies with large numbers of synesthetes find some commonalities across letters (e.g., A is likely to be red). Some authors had argued that the term synaesthesia may not be correct when applied to the so-called grapheme-colour synesthesia and similar phenomena in which the inducer is conceptual (e.g. a letter or number) rather than sensory (e.g. sound or color). They have postulated that the term ideasthesia is a more accurate description. Chromesthesia Another common form of synesthesia is the association of sounds with colors. For some, everyday sounds can trigger seeing colors. For others, colors are triggered when musical notes or keys are being played. People with synesthesia related to music may also have perfect pitch because their ability to see and hear colors aids them in identifying notes or keys. The colors triggered by certain sounds, and any other synesthetic visual experiences, are referred to as photisms. According to Richard Cytowic, chromesthesia is "something like fireworks": voice, music, and assorted environmental sounds such as clattering dishes or dog barks trigger color and firework shapes that arise, move around, and then fade when the sound ends. Sound often changes the perceived hue, brightness, scintillation, and directional movement. Some individuals see music on a "screen" in front of their faces. For Deni Simon, music produces waving lines "like oscilloscope configurations lines moving in color, often metallic with height, width, and, most importantly, depth. My favorite music has lines that extend horizontally beyond the 'screen' area." Individuals rarely agree on what color a given sound is. Composers Franz Liszt and Nikolai Rimsky-Korsakov famously disagreed on the colors of musical keys. Spatial sequence synesthesia Those with spatial sequence synesthesia (SSS) tend to see ordinal sequences as points in space. People with SSS may