Synesthetic percepts are durable and discrete. The associations for an individual Synesthete are stable over their lifetime. If a sound is blue, it will always be blue. Synesthetic experience is memorable. Many synesthetes exhibit hypermnesis.
Synesthesia is emotional in nature.
A synesthetic experience is accompanied by a sense of noetic certitude. Non Uniformity in Synesthetic Perception. In addition to these characteristics it should be added that there is no uniformity amongst the experience of synesthetes. Each individual experiencing synesthesia experiences it in a unique form. Some of these patterns, such as the correpondance between pitch and visual brightness, have been documented repeatedly since they were first described in the experiments of Bleuler and Lehmann in 1881.