archimedes laboratory
What is an Optical Illusion?
deco 2
arrow back Back | Home arrow home


“Things are not what they seem;
nor are they otherwise”
- excerpt from Lankavatara Sutra

figure-ground illusionThe puzzle of seeing (II)
by G. Sarcone
and Marie-Jo Waeber

  Sure, we have five main senses – sight, hearing, taste, touch and smell – but about 75 per cent of the information humans receive about our environment comes from our sight, making it the most ‘important’ of the five senses. The vision depends, obviously, on the EYES to see (with optic receptors called rods and cones) and on the BRAIN to make sense of what we see. The optic nerve at the back of the eye connects to the central nervous system in the brain. The brain receives electrical impulses (stimuli) from our eyes which are interpreted as SIGHT, but the brain adds two extra ingredients to the received image: memory and interpretation (in short, perception). Sometimes the brain is deceived by information received from the eyes. Visual illusions are caused when differences occur between our perceptions or expectations and the image seen by the eye. Actually, there are particular illusions which deceive the human visual system into perceiving something that is not present, or incorrectly perceiving what is present. Optical illusions can be roughly categorized as physical illusions, physiological illusions and cognitive illusions.
  Physical illusions are phenomenal illusions which occur before light enters the eye, such as a mirage, a rainbow... Physiological illusions are the effects on the eyes or brain of prolonged stimulation of a specific type: brightness, tilt, color, movement... Visual cognitive illusions interact with different levels of perceptual processing, and inbuilt assumptions or ‘knowledge’ become misdirected. When we experience a visual cognitive illusion, the perceptual error remains compelling even when we are fully aware of its nature. In this case, awareness of the perceptual error by itself does not produce a more accurate perception. These kinds of illusions are, hence, exceedingly difficult to overcome! Cognitive illusions are commonly divided into ambiguous illusions, distorting illusions and paradoxical illusions.

  Therefore, if visual illusions have existed since the dawn of mankind, what is the oldest optical illusion created by man? Perhaps it was performed by the first prehistoric woman to put on make-up... But – joking aside – it can easily be reasoned that the concept of optical illusion is as old as man himself.   Notwithstanding the lack of any written trace, the first human beings would certainly have noticed optical phenomena such as mirages, the size of the Moon at its zenith, sticks or poles which appear to be broken in two when half-immersed in water, a negative image after having looked at the sun… One of the first optical illusions (or ambiguous images) knowingly created by man is from 2,500 years ago; in some coins from the island of Lesbos, Greece, you can see the profiles of two animals facing each other, apparently herbivores such as calves or goats, which, however, form a third animal – a ferocious animal (maybe a wolf) – when seen from the front.

  So, in this website section various classic and new optical illusions are depicted to cover all the above categories: ambiguous and completion figures, impossible figures, hidden objects, illusions involving colors, geometric illusions, illusory moving patterns, verbal illusions and visual paradoxes. All these illusions were designed by the authors with the aim of allowing the visitor to:
• discover how we perceive things,
• test and enhance the power of observation and critical thinking skills,
• improve mental flexibility,
• have fun being deceived by puzzling visual challenges.

        arrow What is "seeing" exactly?

Creative Commons License
'What is an optical illusion' by G. Sarcone is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.


arrow back Back | Home arrow home


About Us | Sponsorship | Press-clippings | ©opyrights | Link2us | Sitemap

© Archimedes' Lab | Privacy & Terms | The web's best resource for puzzling and mental activities