When you let two fingers touch in front of your eye and but focus on the background, why does it look like they are merging or ‘building a bridge between each other’ before they physically touch?
In: Physics
It has to do with the way the eyes work together. When looking far away (at the background), the eyes move apart so they’re both pointing toward the same thing. When you look close up, the eyes normally move in toward your nose so they’re both pointing at the same point close up. (Imagine drawing a line from each eye to a point up close and to a point far away,. The lines going to the far away point will be farther from your nose, whereas the lines going to the closer point will be closer to your nose).
When you focus on the background, your eyes see your fingers as double (try this with one finger instead of two) you’ll see two fingers. The reason is that your eyes are turned out (away from your nose) to look at the same spot in the distance but your up-close finger ends up double because both eyes are not pointed toward it so each eye perceives the finger to be in a different spot. With both fingers up, you get a double image of both fingers (ie 4 fingers – two real a s two double images). The double image of one finger overlaps the opposite real finger and you get a finger bridge.
If you try the same thing you describe but with one eye closed, you’ll see blurry fingers but you won’t see a finger bridge because you’re not getting double finger images.
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