Perceptual constancy is our tendency to perceive objects as unchanging in the face of changes in sensory stimulation. Once we have formed a stable perception of an object, we can recognize it from almost any angle. Thus, size, shape, brightness, and color constancies help us understand and relate to the world better. Memory and experience play an important part in perceptual constancy, compensating for confusing stimuli.

In addition to past experience and learning, several personal factors color our perception. For example, our familiarity with a symbol or object affects our expectation of how the object should look, even if we observe subtle changes in its appearance. Our perceptions are also influenced by our individual ways of dealing with the environment and by our cultural background, values, motivation, personality, and cognitive style.

We can perceive distance and depth through monocular cues, from one eye, or binocular cues, which depend on the interaction of both eyes.

Superposition is a monocular distance cue in which one object, by partly blocking a second, appears closer. Linear perspective is another monocular cue to distance and depth based on the fact that two parallel lines seem to come together at the horizon. Other monocular cues include aerial perspective, elevation, texture gradient, shadowing, and motion parallax.

With binocular cues, the stereoscopic vision derived from combining the two retinal images makes perceptions of depth and distance clearer. Retinal disparity accounts for the different images each eye receives. Convergence is another binocular cue. Humans, apes, and some predatory animals with the ability to use binocular cues have a distinct advantage over animals whose vision is limited to monocular cues.

Sounds, too, add to our sense of space. Monaural cues, such as loudness and distance, require only one ear. On the other hand, binaural cues, such as discrepancies in the arrival time of sound waves and their volume, help us to locate the source of a sound. Binaural cues depend on the collaboration of both ears.

Perception of movement is a complicated process involving both the visual messages from the retina and messages from the muscles around the eyes as they shift to follow a moving object. At times our perceptual processes trick us into believing that an object is moving when, in fact, it is stationary. Thus, there is a difference between real movement and apparent movement.

Autokinetic illusion, the perceived motion created by a single stationary object, stroboscopic motion, resulting from the flashing of a series of still pictures in rapid succession, and the phi phenomenon, which occurs when lights flashed in sequence are perceived as moving, are all examples of apparent movement.

Visual illusions occur when we use a variety of sensory cues to create perceptual experiences that do not actually exist.

More easily understood are physical illusions, an example of which is the bent appearance of a stick when placed in water. Perceptual illusions depend primarily on our own perceptual processes and occur because the stimulus contains misleading cues.