Final answer:
Depth perception is the brain's ability to perceive objects that are smaller on our retina as farther away, which is due to the phenomenon of retinal disparity caused by the different angles each eye views the world from.
Step-by-step explanation:
The phenomenon where the brain perceives a person as merely farther away despite them being smaller on our retina is known as depth perception. This is possible because of retinal disparity, which arises from the fact that our eyes are offset from each other by approximately 6 to 6.5 cm, allowing each eye to see the world from a slightly different angle. When the brain combines these two slightly different images, it can determine how far away objects are, creating a 3D effect from the 2D images on our retinas.
To understand this concept, one can perform a simple experiment. By holding up a finger close to your face and alternating the viewing eye, you'll notice your finger appears to move more when it's closer to your face than when it is held at arm's length, which demonstrates retinal disparity. This difference in the image's position on each retina is used by the brain to gauge distance, allowing it to compensate for the smaller size an object appears to have when it is farther away.