Subjective constancy or perceptual constancy is the of an object or quality as constant even though our of the object changes. While the physical characteristics of an object may not change, in an attempt to deal with our external world, our perceptual system has mechanisms that adjust to the stimulus.
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.
But lacking perceptual constancy isn't the only way that babies see the world differently. Other research has shown that babies also see colors differently, and seem to have some form of synesthesia.
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.