Hole in the Plate

In this exhibit, a metal plate has two pipes projecting out. Another small metal plate has been placed a little distance away from the right pipe.

Look through both pipes with both eyes open. While you see the distant scene clearly through the left eye, you right eye sees a non-existent hole in the small plate! One eye registers the hole in the tube on the same part of the retina as the other eye registers the small plate. The brain superposes the two views. This is because our brain has evolved to superpose the views seen by the two eyes that results in perceiving depth or distance of an object.

The model here has a metal plate cut in the shape of a human face. There are two pipes projecting out of this metal plate where one can position their eyes. One of the pipes is a longer one and the other is a very short one. There is another rectangular metal plate attached to the outer surface of the longer pipe at a little distance behind the face shaped plate.

Position your eyes in front of the projections with both the eyes being opened. You will see a hole through the rectangular metal plate which is not seen when viewed only through the left eye.

How is this hole which is really not made on the plate appears to be made when viewed through pipe ?

This is an optical illusion. Now let us see how our eyes fall into this illusion.

When we view any object with a single eye, closing the eyes one after the other we can notice that our view of the object slightly gets shifted. That is , we have two images of the object one from each eye. But, when we look at the same object with both eyes being open, we see a single view.

This is because we aim both eyes at the object so that its image falls on the same central part of both retinas. Our brain interprets these two images of the object as coming from the same object located in a unique place. This is the way in which our eyes & brain work together which enables us to see objects and judge distances.

In the model here, we are giving our brain two different images. The left eye is seeing the rectangular metal plate and the right eye is seeing some objects viewed through the tube.

Since one eye registered the hole in the tube on the same part of one retina as the other eye registered the plate on the other retina our brain superposed these two image and we end up seeing a non existant hole in the plate.