Which of the following is NOT a monocular cue for depth perception?

Retinal disparity is a binocular cue for depth perception, which means it relies on the two separate images that each eye sends to the brain. The slight difference between these two images allows our brains to perceive depth. In contrast, the other choices—texture gradient, relative size, and interposition—are all monocular cues. These cues can be utilized with just one eye and allow us to perceive depth through various visual information provided by the environment.

For instance, texture gradient refers to the change in the texture of surfaces that appears more coarse and defined when close and becomes smoother as distance increases. Relative size involves the perception that smaller objects are further away compared to larger objects, and interposition occurs when one object overlaps another, indicating which object is closer based on the visual occlusion. Thus, retinal disparity is distinctive in that it requires binocular vision, while the other options can be perceived with one eye.