sensory adaptation

Sensory adaptation is the way your senses quietly turn down the volume on anything that stays the same. When a stimulus — a smell, a sound, the press of your clothes against your skin — holds steady and unchanging for a while, the detector cells that first noticed it (called receptors) gradually fire fewer and fewer signals, until you barely notice it at all. Think of walking into a bakery: the warm bread smell is overwhelming at first, but a few minutes later it has faded into the background, even though the air is just as full of it. The smell did not weaken; your response to it did.

This happens because nervous systems care far more about change than about steadiness. A constant, unchanging signal carries almost no new information, so it would be wasteful to keep shouting it to the brain — so the receptors and their pathways dial themselves down, freeing up attention for whatever shifts next. The shrinking of the response over time is the adaptation. It is also why you stop feeling your wristwatch, your glasses, or a steady background hum, yet snap to attention the instant any of them change — the watch slipping, the hum stopping. Your senses are built to flag the new, not to dwell on the familiar.