“Synesthesia is a rare neurological condition where someone’s senses become entangled. What’s it like to see sound and taste color?” – YT
“Synesthesia is both involuntary but elicited (Cytowic, 1996) and irrepressible.
“That means, the synesthete does not have to trigger the second sensory experience consciously; it happens on its own as a response to a stimuli, i.e. it is also elicited.
“This also means that the synesthete cannot control when the synesthesia happens or to what stimulus in a certain sensory modality (touch, taste, etc) the synesthete will respond.
“Synesthesia is also very stable. The associations between letters and colors in color-graphemic synesthesia, for example, are formed very early and do not change over time.”
Read more at The Synesthesia Project