This is a wonderful film by Terri Timely which depicts synesthesia. Synesthesia is not easy to define and impossible to pin down, but basically it is when one sensory stimulus triggers a non-traditional neurological response. Popular media often depicts people using hallucinogenic drugs as seeing music dripping like paint -- that is synesthesia.
Example: I smell cinnamon and perceive the scent as a color (brown). I hear a certain musical instrument and feel the smooth texture of velvet. It is a sensuality that crosses the neurological borders which we are taught that the five senses include.
According to Wikipedia, as many as 1 in 23 people may be synesthetes. The most common manifestation, apparently, is assigning color values to individual letters and/or numbers.
I hope you enjoy this amazing video. ~~GH