Final answer:
The phenomenon of seeing a friend appear small like a doll from a distance, yet knowing they haven't actually shrunk, is explained by perceptual constancy, a psychological concept allowing consistent perception despite changes.
Step-by-step explanation:
When you see a friend down the street and they appear to be the size of a doll, yet you know they haven't shrunk, this perception is due to perceptual constancy. Perceptual constancy allows us to perceive objects as being a constant size, shape, and color, regardless of changes in perspective, distance, and lighting. The apparent size of an object perceived by the eye depends on the angle it subtends from the eye. As an object moves further away, like your friend down the street, it subtends a smaller angle and projects a smaller image onto the retina, but your brain corrects for this to maintain the object's perceived constant size. This phenomenon is a foundational concept in understanding how our perceptions are a result of both the physical stimuli we receive and the mental interpretations our brains perform based on past experiences and context.