synesthesia

A condition where real information from one sense is joined with false perceptions from other senses. People with this condition can "see" sound, or "smell" colors, etc. The experience varies from person to person. One synesthetic may have a solid color overlaying their vision, corresponding to pitch and volume; another may see different colors for different letters (K is always red, C is always blue for example). Synesthesia is often experienced when taking high doses of LSD; the likelihood of this effect appears to directly correlate to dosage.