This morning, i again meditated out in the "paradise" parking lot behind the condo where we are staying. My Rhode Island meditation friend, with whom i Skype-meditate every morning at 6 a.m., said that she saw how perception worked this morning. She was looking at the Skype image of the trees in the woods, and she saw a face. A sad face with deep compassionate eyes. A face of benevolence.
People of the Buddha's time believed in tree spirits. Cultures who have had animistic beliefs still have many of those old beliefs. Thai people provide spirit houses for the tree spirits to live in after their tree homes have been cut down.
Our culture doesn't believe in such spirits. Perhaps it's more accurate to say, we don't see such spirits. Our perception has been trained to see trees, so we see trees.
Unless you see something else.