Chapter 6
Section 2: Vision
What we See
• Stimulus is light
–Visible light comes from sun, stars,
light bulbs, & is reflected off objects
–Travels in the form of waves &
these waves affect 3 psychological
aspects of our visual world
What We See
• Hue: The dimension of visual
experience specified by color names
& related to the wavelength of light.
• Saturation: Vividness or purity of color
–The dimension of visual experience
related to the complexity of light
waves.
• Brightness: Lightness & luminance
–Intensity corresponds to the amplitude
of the wave
• More light an object reflects, the
brighter it appears
–The dimension of visual experience
related to the amount of light emitted
from or reflected by an object.
Structures of the Human Eye
• Lens subtly changes shape to focus
light from objects that are close or far
away
• The amount of light that gets into the
eye is controlled by muscles in the iris
• Visual receptors are located in the
back of the eye (retina)
• Rods: Visual receptors that respond
to dim light.
• Cones: Visual receptors involved in
color vision.
• Dark Adaptation: The process by
which visual receptors become
maximally sensitive to light.
• Where the optic nerve leaves the eye,
there are no rods or cones, creating a
blind spot
–Unaware of it because
• Image projected on the spot is
hitting a different “nonblind” spot in
the other eye
• Our eyes move so fast we can pick
up the complete image
• Our brain fills in the gap
• Activity page 185
• It’s the brain’s job to take
fragmentary information about
lines, angles, shapes, motions,
brightness, texture, & patterns to
figure out that a chair is a chair
How we see Colors
• Trichromatic Theory
–The eye detects 3 primary colors
• Red, blue, & green
–All other colors can be derived by
combining these three
Opponent-Process Theory
• Assumes that the visual system treats
pairs of colors as opposing or
antagonistic.
• Opponent-Process cells are inhibited
by a color, & have a burst of activity
when it is removed.
• Example page 186
Constructing the Visual World
• Form Perception
–To make
sense of the
world, we
must know
where one
things ends &
another begins
Gestalt Principles
• Means “form” or “configuration”
• “The whole is more important than the
sum of its parts”
• People always organize the visual field
into figure & ground
–Figure stands out from the rest of the
environment
–Lower part of a scene tends to be seen
as figure, upper part as background
• Gestalt principles describe the brain’s
organization of sensory building
blocks into meaningful units and
patterns.
–Proximity- things that are near each
other, tend to be grouped together
–Closure- brain tends to fill in the
gaps in order to perceive complete
forms
–Similarity- things that are alike in
some way tend to be perceived as
belonging together
–Continuity- lines & patterns tend to
be perceived as continuing in time &
space
• Quiz
• LIVE!Psych
Depth and Distance Perception
• Binocular Cues: Visual cues to depth or
distance that require the use of both
eyes.
–Convergence: Turning inward of the
eyes, which occurs when they focus on
a nearby object
–Helps us establish distance up to 50 ft
–Retinal Disparity: The slight
difference in lateral separation
between two objects as seen by the
left eye and the right eye.
• Monocular Cues: Visual cues to depth
or distance that can be used by one
eye alone.
–Linear perspective page 190 & 191
Visual Constancies: When Seeing
is Believing
• Perceptual constancy- ability to
perceive objects as stable or
unchanging even though the sensory
patterns they produce are constantly
shifting
–Shape constancy
–Location constancy
–Size constancy
–Brightness constancy
–Color constancy
Visual Illusions: When Seeing is
Misleading
• Illusions are valuable in
understanding perception
because they are systematic
errors.
–Illusions provide hints about
perceptual strategies
• In the Muller-Lyer illusion (above)
we tend to perceive the line on
the right as slightly longer than
the one on the left.
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, 510” in front of face.