psychology of visual perception
COMMUNICATION DESIGN,
ANIMATED IMAGE
2014/2015
Lesson #6: Nov. 03rd 2014
Lecture plan:
CONTENTS OF VISUAL PERCEPTION
FORM PERCEPTION
DEPTH PERCEPTION
Extended lesson summary:
CONTENTS OF VISUAL PERCEPTION
FORM PERCEPTION
• Form perception is mainly related to identification of objects (What is it) and how we
see objects – this topic has been studied under the topic of Gestalt Psychology. Gestalt
Psychology explains how we see forms.
DEPTH PERCEPTION
Note: You can complement this brief notes with reference material from the internet. There is
plenty and reliable material. You can find it searching with the keywords: “depth
perception” “visual perception + depth cues” etc..
Once you get the feeling of the concepts you can also try to find materials on your own
language.
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Definition: set of mechanisms in the human visual system from which it is possible
to determine the relative positions of two objects in three-dimensional space;
The basic problem of depth perception: - how do we create 3D vision? -There
are no receptors for the distance. Depth is evaluated from a set of data (cues) of
various types.
Depth cues:
o Physiological cues:
Accommodation:
• Oculomotor cue: - Kinesthetic sensations resulting from
contraction and relaxation of the ciliary muscles are sent to the
visual cortex where they are used to construct the notion of
distance; It is a relatively weak evidence; It is most effective in
nearby objects (< 2 m.).
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Convergence:
• Oculomotor cue: - Information on the depth from the
convergence of both axes of the eyeballs;
The information about the convergence angle is conveyed to the
brain through the activity of the muscles that control eye
movements; Especially effective at distances up to 3 m. Explains
how we see stereograms:
You can read more about stereograms in the internet.
How to see a stereogram.
Try if can see the 3d image in the picture in the next page.
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This is the 3D picture hidden in the picture.
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Wall paper stereograma
Psychological cues
Binocular cues
• Binocular disparity. Practical exercise: Put a finger in front of
your nose and close alternatively one eye or the other. You will
see your finger kind of jumping to one and the other side.
o
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Anaglyphic image
Monocular cues of depth
• Interposition: - When an object stands or cover partially our
vision of another subject, we perceive the object which is
covered as being farther than the subject that is fully visible;
Probably one of the most important monocular clues.
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Aerial Perspective: Due to light scattering by the
atmosphere, objects that are a great distance away have lower
luminance contrast and lower color saturation. Due to this,
images seem hazy the farther they are away from a person's
point of view. In computer graphics, this is often called
"distance fog." The foreground has high contrast; the
background has low contrast. Objects differing only in their
contrast with a background appear to be at different depths.
The color of distant objects are also shifted toward the blue end
of the spectrum (e.g., distant mountains). Some painters,
notably Cézanne, employ "warm" pigments (red, yellow and
orange) to bring features forward towards the viewer, and
"cool" ones (blue, violet, and blue-green) to indicate the part of
a form that curves away from the picture plane.
Note how the mountains in the distance look blue and the distant grass has a bluish tone.
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Texture Gradient: - The closer we are to an object the more
detail we can see of its surface texture. So objects with smooth
textures are usually interpreted being farther away. This is
especially true if the surface texture spans all the distance from
near to far.
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Discontinuities in texture gradients provide information
about spatial relations among the various surfaces with
texture.
Liner perspective: - The property of parallel lines converging
in the distance, at infinity, allows us to reconstruct the relative
distance of two parts of an object, or of landscape features. An
example would be standing on a straight road, looking down
the road, and noticing the road narrows as it goes off in the
distance.
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Relative elevation: - When an object is visible relative to the
horizon, we tend to perceive objects which are closer to the
horizon as being farther away from us, and objects which are
farther from the horizon as being closer to us
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Relative size: - If two objects are known to be the same size
(e.g., two trees) but their absolute size is unknown, relative size
cues can provide information about the relative depth of the
two objects. If one subtends a larger visual angle on the retina
than the other, the object which subtends the larger visual
angle appears closer.
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Lighting and shading: - The way that light falls on an object
and reflects off its surfaces, and the shadows that are cast by
objects provide an effective cue for the brain to determine the
shape of objects and their position in space.
shade: - distribution of luminous intensity on the
surface of the object-less luminous objects seem
farther/objects more bright seem closer to the observer;
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There is an exception about shading and depth perception, which is the perception of
human faces. We always have the same depth perception regardless the shading,
because our visual system that noses are always convex and noses are always
projected outwards.
shadow: - projection of blocking light by the subject on
adjacent surfaces
Notice how changing the shadow we change the
perception of the distance of balls from the chessboard.
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See how the lady speaker seems to float because we interpret the shadow
of an unseen flag as a the shadow of the rug where the lady stands.
Motion parallax: - When an observer moves, the apparent
relative motion of several stationary objects against a
background gives hints about their relative distance. If
information about the direction and velocity of movement is
known, motion parallax can provide absolute depth
information. Our brain uses this information to give us the
notion od distance. This effect can be seen clearly when driving
in a car. Nearby things pass quickly, while far off objects appear
stationary. Some animals that lack binocular vision due to their
eyes having little common field-of-view employ motion parallax
more explicitly than humans for depth cueing (e.g., some types
of birds, which bob their heads to achieve motion parallax, and
squirrels, which move in lines orthogonal to an object of
interest to do the same).
You can see a video example at:
https://www.youtube.com/watch?v=uBDcCtwKYMQ
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Familiarity: - Since the visual angle of an object projected
onto the retina decreases with distance, this information can be
combined with previous knowledge of the object's size to
determine the absolute depth of the object. For example, people
are generally familiar with the size of an average automobile.
This prior knowledge can be combined with information about
the angle it subtends on the retina to determine the absolute
depth of an automobile in a scene.
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We perceive the hand in the picture on the left to be closer to us, because it is
bigger.
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Depth cues in art (painting)
Gustave Caillebote, Paris street: A rainy day
In the painting above the artist explores almost all the depth cues to give a 3D impression
to the scene. Can you spot the cues?
Faro, 30/10/2014
Professor in charge of CU:
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