“Synaesthesia: From Greek syn (together) and aisthesis (perception). Meaning “joined perception.” Synesthesia is a condition in which one sense (for example, hearing) is
simultaneously perceived as if by one or more additional senses (such as sight). Another form of synesthesia joins objects such as letters, shapes, numbers or people’s names with a sensory perception such as smell, color or flavor. It can affect all of the senses.
Four percent of the population, when seeing number five, also see color red. Or hear a C-sharp when seeing blue. Or even associate orange with Tuesdays. This neurologically-based condition is called synesthesia in which people involuntarily link one sensory perception
to another. “ Darya L. Zabelina Ph.D, Psychology Today (n.d)

But the associations are fixed for any one person. And are automatic. Helps memory. But can it limit imagination and creativity through limiting flexibility of possible associations.

Synaesthetic associations vary between people. This variability offers interesting possibilities for widening human experience.