Children often say it best.

My child said this as he heard me speaking about ADHD.

I asked him what he meant, and he said it’s what a room seems like to him.  I asked him what an empty room seems like, and he described how he will notice the shapes, curves, and corners of the walls; bumps on the ceiling; light seeping under the door; and the texture of the floor, adding that carpet’s like a maze of threads.  He concluded, “Even an empty room is filled with so much.  It’s insane.”