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OBJECTS AND INSTRUMENTS98 Further Illusions

PSYCHOLOGISTS AND PHYSIOLOGISTS have studied optical architects knew parallel upright lines appeared to bend
illusions for decades in pursuit of what they tell us about the toward each other in the middle, and so calculated
brain. Yet many illusions, including some shown here, are still precisely how much to fatten columns to make them
not agreeably understood. Artists make pictorial illusions appear straight. Michelangelo, among others, perfected
when they paint or draw, and we learn to read the styles of the acceleration of perspective (see pp.116-17) to make
diverse cultures and periods. Today we are bombarded with painted figures look correct when viewed from below. In the
images but rarely have difficulty reading them. 1960's, Op(tical) artists, such as Bridget Riley, made paintings
that depended upon the physical sensation of our brain's
Some artists use known optical illusions to make art; reaction to known optical illusions.
others adjust works to avoid their effects. Ancient Greek

SEEING TWO OPTIONS

Sometimes, when drawing the outline of a three-dimensional form, we will find that
in terms of the direction it faces, it oscillates between t w o possibilities. It is a curious
fact that we can never see both options at once; we can only look from one t o the
o t h e r If an artist is not aware this can happen in their image, their picture could be
ambiguous. A few suggestive marks will tip the decision one way or the other

Closing the surface

W h e n a transparent elliptical object has been
d r a w n , such as t h e dish seen here o n t h e left,
it can oscillate between facing
t o w a r d o r away f r o m us, as
shown on the right. Closing
the surface of the form
seals o u r decision as t o
which way it faces.

Two ways of seeing

T h i s is t h e b o x c r e a t e d in t h e f o u r t h
step o n p.76. It is possible t o r e a d i t
t w o ways: as a t r u n c a t e d rectangular
pyramid seen directly from above; or
as a sloping-sided rectangular tray
(both are illustrated far right)

"The brain is so eager to name a fragment we see that we need
only a suggestion to grasp the whole. Artists can communicate
much in few lines and the viewer will do the rest of the work."