Cultural Synesthesia

"Synesthesia" is a term broadly applied to connections between sensory pathways in people who have it (who are typically called “synesthetes”).

So synesthetes might taste sounds, associate specific numbers with colors (9 is blue, 4 is yellow, etc), or feel like days of the week or certain years are located in different spacial locations (Tuesdays are close while Wednesdays are far, or maybe 1982 is located at a higher elevation than 1995).

There's an ongoing debate about what causes synesthesia, and one dominant explanatory paradigm—which was originally posited back in the early 19th century—is that there's some kind of overlap or cross-wiring between brain regions that causes the firing of, for instance, a smell-related neuron to trigger (or partially trigger) neurological mechanisms related to sight, sound perception, or taste.

This theory would seem to be backed by the hereditary nature of synesthesia—about half of confirmed synesthetes have first-degree relatives who are also synesthetes—but that theory hasn't been confirmed, and it doesn't tell us anything about why people who perceive in this entangled way perceive the specific things they do.