The Hollow Face Illusion
This is a very powerful optical illusion. Place the mask upright, ideally with some back illumination – you can either stand the mask on a window ledge, or place a small light behind it. View the mask from the concave side, in other words with the mask pointing away from you. Even though you are viewing a face that is concave, the face will appear convex. As you move from left to right, the whole face will appear to swivel and follow you. It also works if you move up and down. In fact, keen observers will spot that the face does not just follow you, it actually moves more than you would expect. So that when you look straight on at the face, it seems to be looking directly at you; move to your right, and the face appears to turn so much that you start to see the face partly in profile.
How Does It Work?
This illusion gives us some insight into the way the brain works, during the process of ‘seeing’. Vision is not just a passive process; the brain does an enormous amount of processing of the patterns of light and shade that fall on the retina, and what we ‘see’ has already been analysed, in a process that we are not conscious of. There are monocular cues of shade and shadows that should tell the brain that the face is concave. In addition there is considerable unambiguous information from the two eyes signalling stereoscopically that the object is hollow. Despite this, the brain’s bias of seeing faces as convex is so strong it counters the conflicting information, and we see the face as convex. When we move, the brain receives visual information that is not consistent with the face being convex. However so strong is the inclination of the brain to see faces as convex that it comes to an alternative (and wrong) conclusion that the face is moving. This phenomenon is evidence for what Professor Richard Gregory calls the ‘top-down knowledge for vision.’
The mask is made from a very strong plastic, known as opal styrene. All plastics will degrade over time, especially if exposed to strong sunlight. In order to at least slow down this process, the masks are made from a plastic that has had an UV inhibitor added to it.
The mask is 43cm high and 31cm wide. The very bottom of the sheet has been bent through 90 degrees, so the mask will stand up by itself.
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For UK deliveries, we use DHL Parcel (UK) and EVRI.
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If the item is faulty, please let us know, and we will ship a replacement or refund your money, as you wish.
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