Our visual awareness of the world around us likely differs a lot from person to person. I’m colour blind in reds and greesn but manage to get by without too much alarm or concern. Imaging studies on the human brain have revealed that the part important for initial higher order processing of visual information, an area termed V1 at the back of the brain (occipital lobe to be all technical) varies is size a lot between people. Does that mean we all see the world in slightly different ways? Possibly, but then we are often constrained by conventions – like my colour blindness and traffic lights. I was taught that the top light is red and to me the top light ‘looks’ red!
Supernatural phenomena (like ghosts) are part of the fabric of our consciousness – the stories our parents tell us when we are children and so on. Such beliefs are encoded within our brains and should you for example dress up in a sheet with 2 eyes holes cut out and rattle some chains most people in the UK will recognize you as a ‘ghost’. Is it possible that visual stimuli can trigger such thoughts – yes. Are they really there? Impossible to say but it all comes back to how the nerve cells in our brain constantly sample our environment around us and work together to help us understand those signals, ghosts or not!