Final answer:
Perceptual constancy refers to the ability to maintain a stable perception of an object despite variations in sensory input. An example of perceptual constancy is when a glass of milk still appears white in dim light.
Step-by-step explanation:
Perceptual constancy refers to the ability of our perception system to maintain a stable perception of an object despite variations in sensory input. In this case, the example of perceptual constancy is when a glass of milk still seems white in dim light. Our color vision system, through a process called color constancy, can accurately perceive the true color of an object under different lighting conditions by comparing it with its surroundings. So, even in dim light, our perception system allows us to see the glass of milk as white.