Wifeshui’s sisters visited us at the weekend, and we got into an interesting conversation about ghosts. Her family hail from Cornwall, where piskies (pixies) hide behind every stone, the Spiritualist Church is alive and well and every cave, well or cottage comes with a spooky story attached. As a result, she’s about the only one amongst them who doesn’t give credence to tales of the supernatural, so the battle-lines were pretty clearly delineated. I won’t go into the details of our debate, but I was struck by one of my sisters-in-law’s statements regarding what she would consider “evidence”:

“I’ve never seen a ghost, but if I saw something I thought was a ghost, then I’d believe in them.”

A purer example of confirmation bias would be hard to find. No matter that there is no evidence for the continued existence of consciousness after death, no known method by which a ghost could manifest itself and no reliable findings in the field of paranormal research – if something might be a ghost, then it must be a ghost, end of story.

Our senses are not to be trusted. Many other bloggers have commented on the issue of pareidolia, whereby the brain finds structured images in random patterns. We see things which aren’t there, we miss things that are (Dr Simons famous “Gorilla Experiment” is a good example), our hearing range is limited, our sense of smell laughably poor. Here’s a well-known and straightforward demonstration of why you can’t always trust your senses:

The three horizontal lines appear, to the human eye, to be of different lengths. Try as you might, it’s almost impossible to draw any other conclusion from the visual data. If you get hold of a ruler, however, and hold it up to the screen, you’ll see that all three lines are, in fact, the same length. Scientific testing demonstrates the truth, even when sensory information tells a different story.

Personally experienced sensory data always needs to be carefully examined before it can be accepted as evidence at the best of times, and when it seems to contradict known science… well, let’s just say if I saw something I thought was a ghost, I’d be taking a long, hard look at what else it could have been before jumping to the conclusion that the spirit world indisputably exists.