WordNet (r) 3.0 (2006):

visualization
    n 1: a mental image that is similar to a visual perception [syn:
         visual image, visualization, visualisation]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "visualization":
   Vorstellung, concept, conception, conceptualization, eidetic image,
   envisaging, envisioning, image, imagery, imagery study, imaging,
   imagism, imagistic poetry, lifelike image, mental image,
   mental picture, mental representation, objectification, picture,
   picturing, poetic imagery, vision, visual image, word-painting