1) Beholder 2) Observer 3) Perceiver 4) Visualiser 1) Visualiser 
[advertising] A Visualizer or visualiser is a largely redundant name for a Storyboard artist or Concept Artist and is a mainly freelance occupation found in Advertising agencies to assist Art directors in drawing scamps and storyboards to a standard that they themselves could not manage for presentation to clients. Their work is used most o...
• (n.) One who visualizes or is proficient in visualization; • (n.) one whose mental imagery is prevailingly visualization.
Vis'u·al·iz`er noun One who visualizes or is proficient in visualization; esp. (Physiol.) , one whose mental imagery is prevailingly visualization. 
[n] - one whose prevailing mental imagery is visual
visualiser noun one whose prevailing mental imagery is visual