Download The Visual System PPT

The Visual System
A.P. Psychology
Ms. Sullivan
Light
For People to see there
must be light
Light - a form of
electromagnetic radiation
that travels as a wave
Varies in amplitude,
wavelength, and purity
Light
Amplitude: height; affects
perception of brightness
Wavelength: (distance
between peaks) affects
perception of color
Purity: (how varied the mix is)
affects perception of saturation,
or richness of colors
The Eye
Eye serves 2 main purposes
1. Channel light to the
neural tissue that receives
it
2. House the neural tissue
The Eye
The Eye
Cornea: Light enters
here; like a transparent
window
Lens: the transparent
eye structure that
focuses the light rays
falling on the retina
The Eye
Nearsightedness: close
objects cannot be seen
clearly but distant objects
appear blurry
Because the focus of light
from distant objects falls
short of the retina
Eyeball is too long
The Eye
Farsightedness: distant
objects are seen clearly but
close objects appear blurry
Focus of light from close
objects fall behind the retina
Eyeball is too short
The Eye
Pupil: the opening in the
center of the iris that helps
regulate the amount of light
passing into the rear chamber of
the eye
Retina:is the neural tissue
lining the inside back surface of
the eye; it absorbs light,
processes images, and sends
visual information to the brain
The Eye
Rods: specialized visual
receptors that play a key role in
night vision and peripheral
vision
Cones: specialized visual
receptors that play a key role in
daylight vision and color vision
Pathways to Brain
Optic Chiasm: the point at
which the optic nerves from the
inside half of each eye cross
over and then project to the
opposite half of the brain
Color
 Lights people see are
mixtures of various
wavelengths
 Perceived Color is
primarily a function
of the dominant
wavelength in these
mixtures
Color
Long wavelengths = Red
Short wavelengths= Violet
Color is a psychological
interpretation, it is not a
physical property of light
Color Mixing
Humans can perceive about
a million different colors
Most of the diverse colors
are the result of mixing a
few basic colors
There are two kinds of color
mixing
Color Mixing
Subtractive Color
Mixing - works by
removing some
wavelengths of
light, leaving less
light than was
originally there
Additive Color
Mixing - works
by superimposing
lights, putting
more light in the
mixture than
exists in any one
light by itself
Theories of Color Vision
1. Trichromatic Theory - the
human eye has three types of
receptors with differing
sensitivities to different light
wavelengths
Red, green, blue
Eye does its own color mixing
of these 3 colors
Additive mixture of red, green
and blue fool you into seeing
all the colors of a natural scene
Theories of Color Vision
Color Blindness - tied to
Trichromatic Theory - variety of
deficiencies in distinguishing
between colors
Occurs more frequently in men
Blindness does not mean all colors,
most deal with only two color
channels (dichromats)
Theories of Color Vision
Opponent Process Theory -
color perception depends on
receptors that make antagonistic
responses to three pairs of colors
Complementary Colors - pairs
of colors that produce gray tones
when mixed together
Afterimage - a visual image that
persists after a stimulus is
removed; the color of the
afterimage will be the compliment
of the color you originally stared at
The basic assumption of Opponent-Process Theory is that colors come in pairs. The
"achromatic system" of black-white (brightness) and the "chromatic system" of red-green
and blue-yellow. The achromatic system sees brightness contrast while the chromatic
system sees color contrast. The picture above shows how the three classes of
photoreceptor map on to the opponent process pairs.
Yellow
If you ask people to describe
colors but restrict them to using
three names, they run into
difficulty
Would you describe “Yellow” as
“reddish green”?
Add Yellow to the 3 basic colors
and people are more
comfortable