Vision Part 2
Theories on processing colors
Objectives: The Student Will
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Compare and contrast color theories (VENN)
Explain the Gestalt Theory
List your Depth and Distance “cues”
What is visual consistency?
chapter 6
Sensation and perception
How do we see color?
• Trichromatic theory- theory of color
perception Red, green, blue.
• Pattern firing of 3 color receptors
• Processes initial stages in the cone cells
• Happens in retina, combination theory
• cones in retina absent or malfunction= color
blind
OTOH
• Opponent-process theory- Explains some
color blindness and Negative Afterimages
• Electromagnetic Energy= short wavelengths
• Happens in ganglion cells, thalamus, visual
cortex
• Opponent process cells; cancel colors out
chapter 6
Trichromatic theory
Young (1802) and
von Helmholtz (1852)
both proposed that
the eye detects 3
primary colors
Red, blue, and green
All other colors
derived by
combination
chapter 6
Opponent-process theory
A competing theory of color vision,
which assumes that the visual system
treats pairs of colors as opposing or
antagonistic
Opponent-process cells are inhibited
by a color, and have a burst of activity
when it is removed.
chapter 6
Form perception
Gestalt principles describe the brain’s
organization of sensory building blocks into
meaningful units and patterns.
Gestalt Theory
• Perceptual tricks: Blinking lights on Marquee
• Gestalt Theory= Patterns in the brain
• Gestalt means perceptual pattern or
configuration in German.
• Raw material of stimulation is sum of sensory
parts
• EQUATION
chapter 6
Gestalt principles
Proximity
Things close to one another are grouped together
Closure
The brain tends to fill in gaps to perceive complete forms
2 principals
• Proximity- Group things that are near each
other
• F.E. 3 groups of red dots not 12 individual dots
or Blue vertical columns not horizontal rows
• Closure: Makes you see incomplete figures as
wholes by supplying the missing elements.
• None of pictures complete
chapter 6
Gestalt principles
Similarity
Things that are alike are perceived together
Continuity
Seeing continuity in lines that could be interpreted as either
continuous or abruptly shifting in direction.
2 more Gestalt principals
• Similarity- Group together things that have a
similar look.
• circles form X; See Horizontal stars because
outlined or red
• Continuity- we prefer smoothly connected
and continuous figures to disjointed ones
chapter 6
Your turn
Which Gestalt
principle is illustrated
by the fact that we
see columns of dots
rather than rows in
this diagram?
1.
2.
3.
4.
Similarity
Proximity
Closure
Continuity
chapter 6
Your turn
Which Gestalt
principle is illustrated
by the fact that we
see columns of dots
rather than rows in
this diagram?
1.
2.
3.
4.
Similarity
Proximity
Closure
Continuity
Depth and Distance Perception
• Binocular convergence(need both eyes): How
the lines of vision from each eye converge at
different angles on objects at different distances
• Put finger 6 in from face, move finger 1 foot back.
Feel anything?
• Binocular disparity: Different perspectives in
each eye= different in retina either side
• Finger 12 in. from face, alternate eyes
• Gives us depth information
chapter 6
Depth and distance
perception
Binocular cues: visual cues that require
the use of both eyes
Convergence
Turning inward of the eyes, which occurs when they focus
on a nearby object
Retinal disparity
The slight difference in lateral separation between two
objects as seen by the right and left eyes
Monocular Cues= 1 eye only
• Relative size: objects in mirror closer than appear
• Light and shadow: Bright=Closer; Dim=farther
away
• USED BY ARTISTS
• Relative motion: Watch poles from car window,
closer object the faster it seems to move
• Interposition: Book obscures the background,
stop sign in front if a car... Perceived as closer
• Atmospheric perspective: haze or fog makes
buildings look farther away
chapter 6
Depth and distance
perception
Monocular cues: visual cues that can be
used by one eye
chapter 6
Visual constancies
The accurate perception of objects as
stable or unchanged despite changes
in the sensory patterns they produce
Shape constancy
Location constancy
Size constancy
Brightness constancy
Color constancy
But apple red in kitchen and outside?
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Part sensory adaptation
Adapt to bluish outside (short wave)
Indoors long wave length
Brain takes into account all wavelengths in
visual field
Visual illusions
• Lines same length- Branches are perspective
cues that suggest depth
• A. 1889, German sociologist
• B. one is like a near end of a building, other
like far corner of room
• Because if same size on retinal image, farther
one away, farther one is larger one
• Misinterprets information.
chapter 6
The Müller-Lyer illusion
chapter 6
Fooling the eye
The cats in (a) are the same size.
The diagonal lines in (b) are parallel.
You can create a “floating fingertip frankfurter” by
holding hands as shown, 5–10 inches in front of face.
Summary
• Color theories
• Gestalt
• Visual consistencies