Q.Explain, with a suitable example, how perceptual constancies help us function efficiently in a constantly changing visual world.

Perceptual constancies let us perceive objects as stable in size, shape, and brightness despite the constantly changing raw sensory information reaching us, which keeps our everyday perception of the world efficient and reliable. …

As we move through our environment, or as the objects around us move or the lighting changes, the raw sensory information any single object sends to our eyes is genuinely never fixed -- its retinal image keeps changing in size as its distance from us changes, in shape as our viewing angle changes, and in reflected brightness as the surrounding illumination changes. Despite this continuous underlying variation, perceptual constancies allow us to go on perceiving that same object as fundamentally stable and unchanged.

Consider a friend walking toward us across a large open ground. As the friend approaches, the retinal image they cast on our eyes grows steadily larger -- yet, because of size constancy, we do not experience our friend as literally 'growing' in size; we continue to perceive them as the same-sized person throughout, simply getting closer. Likewise, as the friend turns to face us from different angles while walking, the shape of the retinal image formed by their outline shifts considerably -- yet, thanks to shape constancy, we do not perceive them as changing shape; we recognise them as the same person regardless of the angle. And whether we meet this friend outdoors in bright sunlight or indoors under dim lighting, the friend's clothing appears to retain roughly the same colour and brightness to us, thanks to brightness constancy, even though the actual quantity of light reflected off the clothing into our eyes is very different in the two settings. …