This article originally appeared in The Skeptic, Volume 7, Issue 3, from 1993.
The course tutor was demonstrating a particular method of hypnosis at the front of the class. The room was very brightly lit by a low winter sun. Behind the tutor and his subject was a light cream-coloured wall. The session lasted about half an hour with the subject being brought slowly back to reality at the end. Then followed an unexpected discussion.
A woman sitting by me opened the discussion by saying to the tutor, “has anyone told you that you have a spirit guide?”. “You’re the third person who has told me that”, the tutor replied.
“It’s a man with a beard and he is older than you. He is standing behind you now. And Elizabeth has one as well” (Elizabeth was the subject) “and there has been energy flowing between the two of you all through the session, coloured energy. Surely you can all see this?” she said, appealing to the rest of us.
Those who spoke up, including me, confessed that we had not seen this psychic phenomenon or at least had not been aware of seeing it, and after a little bit of gentle skeptical humour the conversation returned to the hypnosis session we had just witnessed.
The woman was very, very convinced about what she was seeing, so I decided to take her seriously and I looked at the two sitting at the front and at the wall behind them. And lo and behold, I, too, saw the spirit guides and the energy passing between the tutor and Elizabeth. The spirit guide that stood behind the tutor did indeed have a beard but then so did the tutor. The spirit guide was also the same shape as the tutor and even had the shape of a piece of chair at one side just like the chair the tutor was sitting on.
My eyes quickly passed to Elizabeth and it required only a few seconds of staring at her to be able to see her spirit guide on the wall above. When I stared at one of them for any length of time and moved my eyes to the other, a wave of light moved between them.
The woman and I were, of course, seeing ‘after-images‘, a well known phenomenon described in most books about vision and even in general physiology textbooks. I demonstrated it to her at the end of the class by standing at the front with my arms outstretched sideways. I asked her to stare at me for a few seconds and then to stare at the wall. It soon became quite clear to her that she was seeing an after-image of me.
I have never come across such perfect conditions for after-images. The sun was lighting up the pale cream wall behind the tutor and Elizabeth and they therefore presented relatively dark images against this wall. A few seconds of looking at a person was all that was necessary to produce long-lasting after-images.
The effect is caused by light/dark adaption of the light sensitive cells in the retina. The brightness of the wall was causing a high rate of breakdown of pigments in the cells in the outer area of the retina, while the pigment in the cells of the central area (focused on the tutor) were increasing their pigment and hence their sensitivity. Movement of the eye to look at the wall behind exposed all the cells of the retina to the bright wall. The cells which were focused on the tutor were more sensitive and fired at a higher rate, causing a glare effect which was seen as a bright image in the shape of the tutor. Colour can also be involved, with the images being either the same colour as the object or a complementary colour or in fact passing through a sequence of colours, all depending on the specific conditions.
Could it be that the belief in ghosts and spirits has stemmed from peoples’ experiences in certain lighting conditions that have been conducive to after-images? The explanation may be too simplistic. I find it amazing that the person involved did not realise that what she was seeing was in her eyes since the image moved with her eyes.
