Everyone's brain focuses on images received by the eye. Normally all of our attention is given to the object at which we are directly looking. With practice it is possible to concentrate on images that are coming in from the corner of ones eyes. To develop this skill try walking along a road gazing at a distant object straight ahead. Then without moving your eyes from that object try to concentrate on images coming in from your peripheral vision. I was very surprised to discover what you can learn from objects that your not actually looking at. It's amazing how your mind tunes out the object at which your eyes are directed and tunes into details from objects elsewhere.
This is one technique that can be used to see ghosts.
This is one technique that can be used to see ghosts.