are not what they seem;
nor are they otherwise”
- excerpt from Lankavatara Sutra
puzzle of seeing (II)
and Marie-Jo Waeber
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.
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.
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.
is "seeing" exactly?