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?

Question

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

Answer 1

The effect is caused by parallax. This happens because both eyes are each seeing a finger overlapping the background. The left eye is seeing your left finger, and your right eye is seeing your right finger. Your brain doesn’t receive any “background” information for that part of the scene, only “finger” information, so it merges the two “finger” parts into the floating hot dog illusion.