The image is ambiguous—the corner indicated by the black region may be an inside corner or an outside corner. At first you are likely to perceive it one way or the other, though with some effort you can change your perception to the alternate interpretation. Once your mind has fixed on an understanding, however, it may be difficult to see the other perspective. (This turns out to be true of intellectual perspectives as well.) Your brain’s interpretation of the image actually influences your experience of it.
