PPT for Absent Students
Vision
Day 4 Bell Ringer
Identify the sequence of events for a picture to be
taken.
Goals for Today
• Explain how the human eye is similar to a
camera
• Explain the human blind spot
• Describe visual sensation and perception
– Absolute thresholds
– Signal Detection Theory
– Light description and categorization
Label the Eye
• On the blank EYE diagram in your guided
notes:
– Read the definitions for the EYE and using the
definitions as context CLUES, LABEL the diagram
as best you can.
• Below the diagram
– Identify the sequence of events in order for a
vision to be perceived?
How do the eyes work anyway?
• Camera vs Human Eye
Vision
Process of Seeing
•
•
•
•
Light enters our eye through the CORNEA
Light passes through the PUPIL
The LENS focuses the light onto the RETINA
Light energy is converted into neural energy–
light TRANSDUCTION
Oh no! I’m blind!!!
• Cover your left eye and look at the star shape
with your right eye.
• Move the paper closer to your face.
• At some point, you will notice that the circular
dot on the right will disappear.
• Looking at your eye diagram, explain why the
DOT disappeared.
Retina
Retina: sensory tissue
that lines that back of
the eye. It contains
millions of
photoreceptors (rods
and cones) that
convert light rays into
electrical impulses
that are sent to the
brain through the
optic NERVE.
Rods
Cones
Retina’s Reaction to Light- Receptors
 Rods
 Help with peripheral vision
 detect black, white and gray
 Good at twilight or low light
 Cones
 near center of retina
 fine detail and color vision
 Better in daylight or well-lit conditions
Photoreceptors
Blue
Cones
Green
Cones
Red
Cones
When more than
one type of cone is
stimulated we
perceive other
colors such as
yellow or purple.
Short
wave
Medium
wave
Long
wave
Do you know?
• What is the afterimage color of blood?
• Why are hospital gowns the color they are?
Visual Information Processing
Optic nerves connect to the thalamus in the middle
of the brain, and the thalamus connects to the
visual cortex.
The light we see
• Light is electromagnetic energy that travels in
wave (same as sound)
– Cosmic rays wavelengths are a fraction of an inch
long, sound waves can be miles long, and visible
light waves are in-between.
Light Characteristics
1. Wavelength/frequency
(hue/color)
2. Intensity/amplitude
(brightness)
Wavelength (Hue)
Hue (color) is the
dimension of
color determined
by the wavelength
of the light.
Wavelength is the
distance from the
peak of one wave
to the peak of the
next.
The spectrum of
electromagnetic
energy
Wavelength (Hue)
Violet
Indigo
400 nm
Short wavelengths
Blue
Green
Yellow
Orange
Red
700 nm
Long wavelengths
Different wavelengths of light result
in different colors.
Cop lights
• Why do cops have their lights designed the
way they are?
• Is there a better choice of colors or display?
Intensity (Brightness)
Intensity
Amount of
energy in a
wave
determined by
the amplitude.
It is related to
perceived
brightness.
Intensity (Brightness)
Blue color with varying levels of intensity.
As intensity increases or decreases, blue color
looks more “washed out” or “darkened.”
DON’T SAY IT! Write it down!
Is there a number? If you see one,
what number is it?
Define color-deficient vision
• If you’re color blind you most likely have a
problem with what type of photoreceptor?
• Dichromatic vision- 2 cones working and 1
cone does not work properly.
– Red-green color deficiency is due to lack of red or
green cones.
– Seeing the world in blues, yellows and gray.
– Could you drive?... Should you drive?
What is an Absolute Threshold?
Another view of thresholds: Signal
Detection Theory
• Can you hear the announcements in the
morning?
Assumes there is no absolute threshold
and that detection depends partly on a
person’s experience, expectations,
motivation, and alertness.
• This is similar to what?
Signal Detection
• Predicts when we will detect weak signals
• Hearing-test tone
• People’s ability to catch a faint signal diminishes
after 30 minutes
– TSA screening
• When looking into a crowd and trying to identify
someone, do you misidentify more people with
or without knowing the shirt color?
Signal Detection Theory (SDT)
Predicts how and when we detect the presence
of a faint stimulus (signal) amid background
noise (other stimulation). SDT assumes that
there is no single absolute threshold and
detection depends on:
Carol Lee/ Tony Stone Images
Person’s
experience
Expectations
Motivation
Level of fatigue
SDT Matrix
The observer decides whether she hears the tone
or not, based on the signal being present or not.
This translates into four outcomes.
Decision
Yes
No
Present
Hit
Miss
Absent
False
Alarm
Correct
Rejection
Signal
??????
• How do night time road construction teams
set you up for better signal detection of
workers in the area??
Questions
• What is an astigmatism?
• What is the biological problem for blind people?
– Multiple reasons mostly stemming from problems with the optic
nerve.
• What does Lasik eye surgery do?
– What do you think they correct?
• Why do our eyes dilate more or less on drugs?
– Certain drugs affect the neurotransmitters in our eyes that tell
us to dilate our pupils.
• What do 3D glasses do?
– They let you see 2 movies for the price of one!
• What about drunk goggles?
– What do you think???