Most infants chose the shallow side. The nearly universal emergence of depth perception at this time suggests that it depends more on brain development than it does on individual learning. It is very likely that at least a basic level of depth perception is innate. A number of depth cues combine to produce our experience of three-dimensional space. Depth cues are features of the environment and messages from the body that supply information about distance and space.
Muscular cues come from within the body.
The lens in each eye must bend or bulge to focus nearby objects. Sensations from muscles attached to the lens are channeled back to the brain. Differences in these sensations help us judge distances within about 4 feet of the eyes. Beyond 4 feet, accommodation has a limited effect on depth perception. Convergence , a second bodily source of information about depth, a binocular cue.