Interposition is a monocular depth cue where one object partially blocks another, leading to the perception that the blocked object is farther away.
In more detail, interposition (also known as occlusion) leverages the visual principle that objects closer to us tend to obstruct our view of objects behind them. This obstruction acts as a visual signal, informing our brains about the relative distances of the objects involved. The object that is being blocked is interpreted as being further away, while the object that is doing the blocking is perceived as closer.
How Interposition Works:
- Partial Obstruction: The key element is the partial blockage of one object by another.
- Distance Inference: The brain interprets the blocking object as being in front, and therefore closer.
- Monocular Cue: Interposition is a monocular cue because it can be perceived with just one eye. This distinguishes it from binocular cues like stereopsis, which require input from both eyes.
Examples of Interposition:
- Forest: In a forest, trees that partially obscure other trees appear closer to the observer.
- Overlapping Shapes: In a drawing, if a circle overlaps a square, the circle will appear to be in front of the square.
- Crowded Room: In a crowded room, people standing in front of others will appear closer.
Importance of Interposition:
Interposition is a valuable depth cue, especially in situations where other cues might be ambiguous or unavailable. It allows us to quickly and easily perceive the relative positions of objects in our environment, contributing to our overall spatial awareness. Along with other monocular cues like relative size, texture gradient, and linear perspective, interposition helps us create a three-dimensional representation of the world around us from a two-dimensional image on our retinas.
