Abe cut a large circle out of a piece of heavy cardboard. He was going to use it to demonstrate something he had been studying to his eight-year-old sister. He held the circle up so it was directly facing her and asked her what she saw. Her answer was a circle. He then held a towel up in front of the cardboard and rotated it quite a lot. He then lowered the towel and asked her what she saw. She answered that it looks like an oval now but it is still a circle. What was Abe demonstrating?

binocular cues

perceptual constancy

monocular cues