Uploaded August 2026 | Updated September 2026, 2 weeks ago
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Tim demonstrates a number of his 'Hollow Face' items, and the amazing illusion they produce.
The Hollow Face 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 the late Professor Richard Gregory calls the ‘top-down knowledge for vision.’
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Some while ago, Tim demonstrated a little paper dragon that you could cut out and make your own little 'hollow face illusion'. You can find that video here - youtube.com/watch?v=_Q_kSrOVdHw - and in the text below the video there is a link to a free PDF file that you can print out as an A4 print, and make your own little dragon.
Sign up for the free Grand Illusions newsletter, at conta.cc/3dplns1
______________________________________________________________________
Tim demonstrates a number of his 'Hollow Face' items, and the amazing illusion they produce.
The Hollow Face 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 the late Professor Richard Gregory calls the ‘top-down knowledge for vision.’
__________________________
Some while ago, Tim demonstrated a little paper dragon that you could cut out and make your own little 'hollow face illusion'. You can find that video here - youtube.com/watch?v=_Q_kSrOVdHw - and in the text below the video there is a link to a free PDF file that you can print out as an A4 print, and make your own little dragon.
