invisible before. Every relevant line, shadow and patch of snow was visible from the beginning. What changed was the organization of those features. Initially, the visual system grouped them primarily as elements of a winter landscape. Later, some of the same features were grouped as components of a human face. Hidden-image puzzles take advantage of precisely this possibility: one arrangement can support more than one meaningful interpretation.
The effect also demonstrates why context is so powerful in perception. When an image is introduced as a winter forest containing a deer,
