Psychology of visual perception
COMMUNICATION DESIGN,
ANIMATED IMAGE
2014/2015
EXTENDED SUMMARY
Lesson #9: Nov. 24th 2014
Lecture plan:
VISUAL ILLUSIONS
– General aspects
– Geometrical & angular illusions
– Size & distance illusions
– Direction & position illusions
Extended lesson summary:
VISUAL ILLUSIONS
GENERAL ASPECTS
NATURE OF VISUAL ILLUSIONS
 Richard GREGORY: - it is astonishingly difficult to define "illusion" în a
satisfactory way;
 Cognitive impenetrability - the illusory effect persists even after we check
the illusory nature of perception.
 General characteristics of visual illusions:
– The distortion is stimulated by near comparative elements (context), which
suggests the existence of a relationship;
– There is always an "inducing element" that causes the misinterpretation
and a "test element" that is the subject of it.
In the picture above the inducing elements are the grey circles and the test
elements are the brown circles.
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PSYCHOLOGY OF VISUAL PERCEPTION
2014/2015
WHY STUDY THE ILLUSIONS?
 Practical reasons: Many important decisions in our lives are taken
based on visual information.
 Scientific reasons: allows us to clarify some aspects of our visual
system.
GEOMETRICAL & ANGULAR ILLUSIONS
ILLUSIONS OF SIZE/DISTANCE
 The Müller-Lyer Illusion
This is one of the best known illusions.
In the picture above segment B looks longer than segment A although they are
exactly the same size.
In this variation of the ML illusion the distance from the tip pf the arrow on the left
to the vertical yellow line is exactly the same than the distance from the vertical
yellow line to tip of the arrow on the right, although it looks shorter. You can check
with a ruller.
– Explanations for the Müller-Lyer Illusion
Explanation based on depth perception;
our brain makes assumptions about the relative depths of each of the rows
based on pictorial monocular cues.
We live in a world of square
rooms where corners with the
shape of figure A above, are
generally closer to us, than
corners with the shape of
figure B. If distant corners
have the same length as near
corner, our brain
overcompensates and makes
us see distant corners bigger.
This is the most accepted
explanation.
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Explanation based on the movement of the eyeball:
This explanation assumes our eyeball moves when seeing the figures, so as
it has to move more to see fig. A than to see fig. B, our brain interprets this
as A being longer.
Theory of limited visual acuity;
We have a good accuracy in the center of the retina, decreasing drastically
in the periphery, which causes the images appear blurry; in a blurry picture
the various elements that compose it seem closer to each other than they
actually are
Theory of the disparity between the limits;
The illusion is created because people do a perceptual measurement of
figures from the limits of the arrowheads.
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SIZE & DISTANCE ILLUSIONS
WUNDT INVERTED T ILLUSION
The vertical line appears longer than the horizontal line,
although they are the same size.
 Explanation for the illusion of Wundt
– Classical Explanations are based on the eye-movement easier and faster
horizontally;
PONZO ILLUSION
In the figures bellow the horizontal lines are exactly the same length although the
upper line looks longer.
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In the figure bellow the vertical thick black line on the right looks longer than the
vertical line on the left.

Explanation of the Ponzo illusion
– There may be two possible explanations:
1. Illusory effect seems to be related to the relativism among the filled and
empty spaces.
Line B fills more space so it looks longer.
2. Illusory effect is related to perception of distance.
Due to the perspective effect from the lateral oblique lines line B is
perceived as being more distant. If is more distant and has the same
retinal length our brain assumes it must be longer.
THE MOON ILLUSION
 The full moon, when it's just a little above the horizon, it seems
much larger than when it is high in the sky.
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
2014/2015
Explanation theories:
– Apparent distance theory: - the Moon looks bigger because it seems
more distant than when it is at the zenith. There is a strong association
between the indicators of distance and the Moon illusion.
– Size: contrast theory-the Moon looks bigger because when appears on
the horizon the subtended angle in the retina is larger than the surrounding
elements, in contrast with what happens when is at the zenith.
DIRECTION & POSITION ILLUSIONS
THE ZÖLLNER ILLUSION
Although the vertical lines are perfectly parallel they look slightly oblique.
This is a variant of the Zöllner Illusion.
The inducing elements are the small oblique line elements.
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THE POGGENDORFF ILLUSION
THE FRASER SPIRAL
 In the next figures we see spiraling curve lines, but in reality they are
circular lines.

The visual elements (directional units) fool the directional visual
system analyzers.
Triangular shapes work as directional units (arrow points).
Faro, 11/19/2014
Professor in charge of CU:
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