However, when it is present, depth is almost always perceived. Much of the apparent depth of a good movie comes from the relative motion of objects captured by the camera. People who can only see with one eye depend heavily on motion parallax. Often, they make frequent head movements to exaggerate parallax and improve depth perception. Pictorial depth cues are not entirely universal .
Some cultures use only selected pictorial cues to represent depth.
For example, researcher William Hudson tested members of remote tribes who do not use relative size to show depth in drawings. These people perceive simplified drawings as two-dimensional designs. They do not assume, as we do, that a larger image means that an object is closer. Like the bodily depth cues, we constantly use the pictorial cues to gauge depth and judge distances. Cues of both types also combine to produce an intriguing illusion.