From Tom Clarke
Could the phenomenon of autostereography (“How to play tricks with dots”, 9 October 1993 and Letters, 24/31 December) explain the appearance of “visions” both paranormal and religious?
First, the human brain can create imagery out of commonly occurring shapes. Clouds can appear as faces, embers in the fire can suggest dragons, rocks in caverns may be named after a resemblance to some object or figure. The Rorschach inkblot test relies on such subjective visual interpretation. Significantly, the texture of the image is unimportant, but the suggested appearance is easily shared with fellow onlookers.
Secondly, the “wallpaper effect”, discovered by the Scottish physicist David Brewster, originally described the experience of stereopsis in relation to a commonly occurring visual experience of the time (Victorian wallpaper patterning). The unexpected (and therefore notable) feature here was the appearance of three-dimensionality in an otherwise flat uniform pattern. As above, the texture is of the image is unimportant, but unlike the above, the 3-dimensionality cannot be shared without detailed explanation and practice. This, of course, is the basis for the current craze for autostereograms.
Thirdly, once an autostereographic image is acquired by an observer, it can be held over a significant distance even if the observer moves away from the generating pattern. I have found that an image generated on an A4 sheet can be clearly held up to approximately 5 metres distance, with an optimal image at around 2 metres.
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So how could autostereognosis explain a “vision”? For the sake of example, imagine a young girl standing in front of a stone wall, daydreaming (and with her visual axes therefore parallel). Fortuitously, the angle of the sunlight on the regular pattern of the wall creates an autostereographic image. As all those familiar with the phenomenon will know, this is striking, real (no doubt the more so if it appears completely unexpectedly), and can be held by the observer.
That the image is not a detailed representation of the Virgin Mary (for instance) does not matter; the “reality” of it is subjectively interpreted as such. Furthermore, the experience could not be shared even with close bystanders, who would be scanning in vain with focussed eyes.
Finally the image would be lost and most likely unrecreatable even by the observer. Such a chance effect could also be invoked to explain paranormal apparitions such as “ghosts”, usually (always?) unrecordable by photographic means.
