Final answer:
Perceptual constancy is the actual size, shape, orientation, & brightness of an object are perceived as remaining relatively constant even when there are extreme changes in the image it casts on the retina.
Step-by-step explanation:
Perceptual constancy allows for the perception of objects as stable in size, shape, orientation, and brightness, even under varying conditions. It includes color constancy, which maintains the perceived color of objects. This perceptual stability is due to the brain's processing, even leading to perceptual illusions where the brain corrects for environmental changes.
This is a fundamental feature of human visual perception, ensuring that the objects in our environment appear consistent despite various viewing conditions such as changes in illumination, distance, or angle. For example, the apparent size of an object perceived by the eye depends on the angle the object subtends from the eye, causing objects to appear larger or smaller on the retina based on their distance, but our perception compensates for this.
Another aspect of perceptual constancy is color constancy, where our visual system maintains the perceived color of objects under varying lighting conditions. This demonstrates that the eye-brain system is capable of complex processing to maintain a stable and consistent view of the world, despite the fact that the information reaching our eyes can change dramatically. Perceptual illusions further illustrate how our brain adjusts perception to maintain this stability, as in the example of an illusion where two squares are perceived differently in color due to a shadow, despite being the same color.