The researchers behind the experiment were studying a memory phenomenon called perceptual filtering, which is the reason that we can recognize something perfectly well without remembering any picky details. Brains don’t waste energy on non-essentials: for the most part we remember just enough—yup, looks like a penny—to comfortably get by. We filter out the rest, which means that we don’t pay any attention to it. In other words, nobody really knows what a penny looks like.