Perceptual constancy refers to a person or animal's ability to see different sizes, shapes or brightness without having to re-evaluate or re-interpret the properties of the image or object. For example, even though buildings may be different sizes, perceptions maintain constant regardless of the distance.
Perceptual constancy affects sizes, shapes and brightness within sight. Size constancy allows individuals to perceive a person or object as the same size even though distance may make them appear smaller or larger. Senses are also affected by perceptual constancy as the volume may fade, yet the sound is still perceived as loud when it is soft. With perceptual constancy, distance does not always affect what a person is sensing.
Shapes are also affected by perceptual constancy as an individual typically associates an object as a certain shape although it can transform when the angle is changed. For example, an object that is in the form of a circle may, in reality, look more like an ellipse from a distance, however, perceptual constancy allows an individual to still perceive the shape as a circle from a distance or different angle.
Perceptual constancy also refers to a person's ability to recognize and maintain sight of colors, regardless of how it looks under a different level of light or at a different angle. Even though a blue shirt may look black in darker levels of light, perceptual constancy allows the individual to still perceive the shirt as a blue color.