Final answer:
The illusion of depth in devices like stereoscopes and 3-D movies is created by retinal disparity, a binocular cue based on the differences between the images each eye perceives.
Step-by-step explanation:
The illusion of depth created by stereoscopes, viewmasters, and 3-D movies, which project a separate image to each eye, is created by the cue of retinal disparity. This is a form of binocular cue that exploits the slight difference in the visual information reaching each eye due to their horizontal separation (interocular distance). This creates a perception of depth as our brain fuses these two images into a single three-dimensional scene.
Other depth cues mentioned such as convergence, linear perspective, and interposition serve different functions in depth perception. Convergence is related to the muscular movement of our eyes when they turn inwards to focus on an object that's close, while linear perspective and interposition are monocular cues that can also contribute to the perception of depth but are primarily used in two-dimensional representations of space such as in drawings or paintings.