UNIT 3: Sensation and Perception
Learning Targets
22-1 Discuss the characteristics of the energy that we see as visible light, and describe the structures in the eye that help focus that energy.
22-2 Describe how the rods and cones process information, and explain the path information travels from the eye to the brain.
22-3 Discuss how we perceive color in the world around us.
22-4 Describe the location and function of feature detectors.
22-5 Explain how the brain uses parallel processing to construct visual perceptions.
What light energy is �visible to humans?
The part of the spectrum visible to humans is actually quite small.
We can see light waves with a frequency of a little less than 400nm and a little more than 700nm.
What are characteristics of �light waves?
frequency (wavelength)
amplitude (height)
What information do light waves �give us?
Wavelength: what hue (or color) am I seeing?
Amplitude: how bright is the color I am seeing?
1. What Would You Answer?
Your best friend decides to paint her room an extremely bright electric blue. Which of the following best fits the physical properties of the color’s light waves?
B. short wavelength; large amplitude
C. short wavelength; small amplitude
D. long wavelength; large amplitude
What structures of the eye help �focus the energy?
What is the cornea?
The cornea is the eye’s clear, protective outer layer covering the pupil and iris.
Light enters the eye first through the cornea.
What is the pupil?
The pupil is a small adjustable opening in the center of the eye through which light passes.
What is the iris?
The iris is a ring of muscle tissue that
forms the colored portion of the
eye around the pupil and controls
the size of the pupil opening by expanding and contracting over the pupil.
What is the lens?
The lens is the transparent structure
behind the pupil that changes shape
to help focus images on the retina.
How does the lens change shape?
To focus the rays, the lens changes its curvature and thickness in a process called accommodation.
If the lens focuses the image on a point in front of the
retina, you see near objects clearly but not distant objects. This nearsightedness—myopia—
can be remedied with glasses, contact lenses, or surgery.
Hyperopia- farsightedness – is a result of the lens focusing light past the retina.
What is the retina?
The retina is the light-sensitive inner
surface of the eye, containing
the receptor rods and cones plus
layers of neurons that begin the
processing of visual information.
Can you name the structures of the eye?
Try to name the first five structures you have learned in the order which light passes through them.
Where is the retina located?
The retina is along the back of the eye and contains the sense receptor cells (rods and cones) that will receive the incoming light waves.
What happens in the retina?
Light waves are transduced into neural impulses by the rods and cones, then passed to the bipolar cells and the ganglion cells.
What are rods?
The rods are retinal photoreceptors that detect black, white, and gray, and are sensitive to movement.
Rods are necessary
for peripheral and twilight vision, when cones don’t respond.
What are some characteristics of rods?
Rods are located along the retina’s outer periphery.
Rods remain sensitive in dim light, and they enable
black-and-white vision.
Rods have no hotline to the brain…they share connections to a single bipolar cell sending a combined message to the brain.
Rods are sensitive to faint light and peripheral motion.
What are cones?
Cones are retinal photoreceptors that are
concentrated near the center of the retina and function in daylight or in well-lit conditions.
Cones detect fine detail and create color sensations.
What are some characteristics of cones?
Cones cluster in and around the fovea.
In dim light, cones become unresponsive and we are unable to see color.
Many cones have their own hotline to the brain: One
cone transmits its message to a single bipolar cell, which relays the message to the visual cortex (where a large area receives input from the fovea).
How many dots do you see at once?
Look at or near any of the twelve black dots and you can see them, but not in your peripheral vision.
What is the fovea?
The fovea is the central focal point in
the retina, around which the eye’s
cones cluster.
This is the area of greatest visual acuity… or sharpness of focus.
What is the �optic nerve?
The optic nerve is comprised of the axons of the ganglion cells.
It leaves through the back of the eye and carries the neural impulses from the eye to the brain.
What is the �blind spot?
The optic disk is the point at which the
optic nerve leaves the eye, creating
a “blind” spot because no receptor
cells (rods or cones) are located there.
Can you find the blind spot of your eye?
Close your left eye, look at the spot, and move your face away until one of the cars disappears. Repeat with your right eye closed. Did the other car disappear? Can you explain why?
2. What Would You Answer?
If you scratch your eye, which structure are you most likely to damage?
B. iris
C. cornea
D. lens
What happens to the neural impulse after it exits the eye?
The optic nerve carries the impulse to the thalamus and on to the visual cortex of the occipital lobes.
Can you put it all together now?
Use these two images to guide you as you correctly label the structures through which light passes.
Can you put it all together now? Cont.
Can you finish tracing the path of the neural impulse once it leaves the eye?
AP® Exam Tip 1
There’s a lot of vocabulary here.
Make sure you understand the location and
function of each part of the eye.
To learn how all the parts fit together, it may help to make rough sketches and then compare your sketches with Figures 22.3 and 22.4 in your textbook.
You’ll be better off making several quick, rough sketches
than one time-consuming, nicely drawn one.
How do we see color?
“ Only mind has sight and hearing;
all things else are deaf and blind.”
Epicharmus, Fragments, 550 B.C.E.
We say that a tomato is red…but is it?
Is red housed in the tomato or in our mind?
If no one sees the tomato, is it still red?
What is the Young-Helmholtz �trichromatic (three-color) theory?
The theory
that the retina contains three
different types of color receptors (cones)—
one most sensitive to red, one
to green, one to blue—which,
when stimulated in combination,
can produce the perception of any color.
What about people who cannot see color?
The photo on the left shows how people with red-green deficiency perceived a 2015 Buffalo Bills versus
New York Jets football game.
“Everyone looks like they’re on the same team,”
said one color-blind fan.
The photo on the right shows how the game looked
for those with normal color vision.
What are some characteristics of �color blindness?
About one person in 50 is color blind.
Males are more affected since the defect is
genetically sex-linked.
Most people are not actually blind to all colors. They simply lack functioning red- or green-sensitive cones, or sometimes both.
Vision is monochromatic (one color) or dichromatic
(two-color) and seems ‘normal’ to them.
AP® Exam Tip 2
There is typically a question about color blindness on
the AP ® Exam.
It is important to remember that color blindness is most prevalent in males and that the red-green cone deficiency is the most common form of color blindness.
What is the Hering opponent-process theory?
The theory that cone photoreceptors are paired together (red-green, blue-yellow, white-black)
to enable color vision.
Activation of one color of the pair inhibits
activation of the other.
For example, some cells are stimulated by green and inhibited by red; others are stimulated by
red and inhibited by green.
The opponent-process theory.
Stare at the center of the flag for a minute.
Then go to the next slide.
The opponent-process theory, cont.
Stare at the black dot above.
What do you see?
So what happened?
Did you see a red, white and blue
British Union Jack?
Here’s the answer for why the green became red:
So… how does color processing occur?
1
The retina’s red, green, and blue cones respond in varying degrees to different color
stimuli, as the Young-Helmholtz trichromatic theory suggested.
2
The cones responses are then processed by opponent-process cells, as Hering’s
opponent-process theory proposed.
What are feature detectors and �where are they located?
Feature detectors are nerve cells located in the visual cortex of the occipital lobe that respond to a scene’s edges, lines, angles and movements.
But what do feature detectors do?
Feature detectors receive information from individual ganglion cells in the retina and
pass it to other cortical areas, where
supercell clusters respond to more complex patterns.
How do feature detectors �operate in real life?
In a 2011 World Cup match, USA’s Abby Wambach instantly
processed visual information about
the positions and movements of
Brazil’s defenders and goalkeeper and managed to get the ball around them all and into the net.
What is parallel processing?
Parallel processing is thinking about many aspects of a problem simultaneously.
This is the brain’s natural mode of information processing for many functions, including vision.
How does parallel processing operate?
The brain delegates the work of processing motion, form, depth, and color to different areas.
After taking a scene apart, the brain integrates these subdimensions into the perceived image.
How do we recognize faces using parallel processing?
To recognize a face, your brain integrates information projected by your retinas to several
visual cortex areas and compares it with stored information, thus enabling your fusiform
face area to recognize the face: Grandmother!
Some supercells—actually nicknamed
grandmother cells—do appear to respond very
selectively to 1 or 2 faces in 100.
(Bowers, 2009; Quiroga et al., 2013)
3. What Would You Answer?
Which perceptual process explains why you can see varied aspects of your favorite singer’s face and instantly recognize him or her?
B. accommodation
C. psychokinesis
D. blindsight
So in the end…. how do we “see”?
As you read these words, the letters reflect light rays onto your retina, which triggers a process that sends formless nerve impulses to several areas of your brain, which integrate the information and decode its meaning. The
amazing result: we have transferred information across time and space, from our minds to your mind.
That all of this happens instantly, effortlessly, and continuously is indeed awesome.
Learning Target 22-1 Review
Discuss the characteristics of the energy
that we see as visible light, and describe the structures in the eye that help focus that energy.
Learning Target 22-2 Review
Describe how the rods and cones process
information, and explain the path information
travels from the eye to the brain.
Learning Target 22-3 Review
Discuss how we perceive color
in the world around us.
Learning Target 22-4 Review
Describe the location and function
of feature detectors.
Learning Target 22-5 Review
Explain how the brain uses parallel
processing to construct visual perceptions.