Joe Banks is an installation artist and researcher, and author of the book “Rorschach Audio – Art & Illusion for Sound” –

Part 1 of “The Analysis of Beauty” & Blind-Spots – Evolution & Neuroscience can be found here


A common-sense understanding of perception might suggest that objects exist in our visual world, light bounces off them, enters our eyes, and we simply see those objects – almost always accurately – without much mental effort being involved. So if, on the basis of the illusions produced by watching “The Analysis of Beauty” art exhibit (referred to in the first part of this article), it seems counterintuitive to suggest that what we see is partly made up of mental guesswork, there’s an even more striking demonstration that proves the point well. Simply draw two dots, about 5mm wide and 10cm apart on a card, then move the card backwards and forwards in front of your eyes. Cover your right eye with your right hand, and, holding the card with your left hand, focus your left eye on the right dot, but remain aware of the left dot as it appears in your peripheral vision. Keeping the left eye still focussed on the right point, move the card to and fro, adjusting the viewing distance until the left dot… disappears.

The portion of the retina that folds back into the rear of the eye (to transmit information to the brain along the optic nerve) is insensitive to light, and the disappearance you’ve just experienced takes place at the distance which causes the image of the dot to fall onto that blind-spot. The fact that blind-spots can be used to make images (and indeed whole objects) disappear is intriguing and entertaining enough in itself, but what’s most revealing about this phenomenon is something that’s often neglected. It’s easy to forget that blind-spots are always there, and since the mind “copies and pastes” imagery from around blind-spots, to prevent our vision being impaired by visual holes, what blind-spots ultimately show us is that the apparently seamless visual field that we experience as visual reality is in some respects itself a carefully constructed optical illusion. In fact the mind’s ability to “fill-in the blanks” isn’t limited to the blind-spot, as similar mental guesswork is also used to compensate for visual gaps produced by the network of blood-vessels that criss-cross the retina.

So (referring back to the first part of this article) William Hogarth not only asserted that the mind inverts upside-down images and combines stereoscopic visual sense-data into this single visual field, Hogarth also asserted that “the eye may be subdued and forced into forming and disposing of objects… by the prejudgment of the mind”; and, while this assertion may also come across as somewhat counterintuitive, it’s surprisingly easy to prove. In fact the mind analyses visual sense-data, detects information, assigns meanings to objects, and classifies objects in relation to their practical importance in the day-to-day business of performing tasks like walking up and down stairs without tripping and injuring ourselves, etc.

It may seem strange to assert that the mind can edit whole objects out of visual perception, since common-sense suggests that we just see what’s there in front of us, and our vision is usually accurate. In fact however the mind edits our visual field continually. We’ve all had experiences of tearing the house apart searching for lost wallets and keys, and, while these do sometimes show-up down the back of the sofa, in many cases they were on the table all the time, but, for neurological rather than optical reasons, our brains failed to see them. Likewise, rather than being obscure, the ultimate proof of this theory always was hiding in plain sight, literally in front of us all our lives – when we stroll in the park we enjoy a smooth and apparently uninterrupted visual field, as soon as we think about our nose however, that object, which was previously invisible, suddenly reappears.

The writer Aldous Huxley is primarily known as the author of “The Doors of Perception”, what’s less well-known is that Huxley’s partial blindness led to a fascination with opthalmology. In his book “The Art of Seeing” Huxley states that “sensing is not the same as perceiving” and that “the eyes and nervous system do the sensing, the mind does the perceiving”. Huxley describes how “by inhibiting the activity of the interpreting mind”, it’s possible to “catch a hint of the raw sensum, as it presents itself to the eyes of the newborn child”. He recalled how “while coming out of an anaesthetic… awareness began with pure visual sensations”. These sensations “were not objects existing ‘out there’ in the familiar, three-dimensional world”, but were “just coloured patches, existing in and for themselves, unrelated not only to the external world, but also to myself – for the knowledge of self was still wholly lacking, and these meaningless and unattached sense impressions were not mine, they simply were.”

So, the ultimate value of psychology of illusion lies not in the fact that intriguing and sometimes beautiful illusions can be made to appear from the pages of psychology textbooks and from strange images in videos, etc. The way illusions are presented in newspaper and magazine articles, books and on-line science features, often encourages us to think of illusions and disappearing spots etc, as being little more than amusing novelties and sources of occasional perceptual mistakes. It is however far more fruitful to be aware of the fact that the guesses which the mind projects out into our environment are usually right, and that they do in fact usually provide accurate descriptions of our external world. It is also helpful to understand that illusions arise as by-products of critically important perceptual faculties, faculties which serve real practical purposes, which emerged as products of evolutionary biology. With that in mind it follows that “the great and necessary purpose” that William Hogarth alluded to 260 years ago is of course human survival; and the fact that many (even non-mammalian) species compensate for visual blind-spots suggests that such mental faculties precede humans in the history of evolution.

The writer J.G. Ballard put it very beautifully – “The central nervous system is nature’s Sistine Chapel, but we have to bear in mind that the world our senses present to us… is a ramshackle construct which our brains have devised to let us get on with the job of maintaining ourselves and reproducing our species. What we see is a highly conventionalised picture, a simple tourist guide to a very strange city. We need to dismantle this ramshackle construct in order to grasp what’s really going on.”

Article copyright © Joe Banks May 2016


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