This is the phenomenon I've noticed when drawing. I'm describing it it's not known. I sometimes practise blind drawing, and drawing from memory, in the street. A lot of the streets and pavements are surfaced with asphalt, which has a grainy surface. When drawing from memory, I try to remember the subject in detail before looking at the paper. Sometimes, I find myself doing so with sufficient intensity that I'm not really aware of my surroundings. Then I'll suddenly "come to", and find myself looking at a pattern in the asphalt which looks similar to what I was thinking about. It feels bizarre, as though I've created the pattern by force of intense concentration. But presumably what's happened is that I've unconsciously directed my gaze towards some region of the asphalt that looks similar to what I was thinking of, and I've only then become aware of it.
Perhaps this is related to pareidolia. The difference is that the images I see depend on what I've just been visualising.