Sensation &
Perception
Psychology 201
Sensation &
Perception
Sensation is the detection and encoding of
the changes in physical energy (e.g., light
waves, sound waves, pressure, kinetic
energy, etc.) caused by environmental or
internal events.
Sensation &
Perception
Our sense receptors, located in the sense
organs (eyes, ears, tongue, nose, and skin)
convert the physical energy into brain energy
(i.e., electrochemical energy) in a process
called transduction.
Sensation &
Perception
But
sensations alone do not tell us much
about the world until we perceive them.
Sensations are just meaningless energy (e.g.
light waves and sound waves) until we
organize them into meaningful information
(sights and sounds).
Sensation &
Perception
Sensation &
Perception
Sensation &
Perception
If a tree falls in the forest and no one is
around, does it make a sound?
Why?
Senses
How many senses are there?
What are they?
Sensation &
Perception
1. sight
2. sound
3. taste
4. smell
5. touch
More senses
6. heat
7. cold
8. pressure
9. pain (Would any of you like to live a life without any pain?)
10. itching
11. balance
12. nausea
13. proprioception
14. pheromones
15. thirst
16. hunger
17. chemical pain (red hot peppers)
18. infrared (snakes)
19. electrical (sharks and platypuses)
20. sonar (bats)
21. magnetic north (birds and moles)
Reality
What is reality?
What is real?
Do we accurately perceive our world?
Demonstration #1
Demonstration #2
Reality
Do we accurately perceive the
world?
Our brains alter incoming
signals
Our senses are amazingly
sensitive.
It is commonly cited that a normal individual can:
1. see a candle, on a clear, and dark night from a distance of
30 miles
2. hear a watch ticking in a perfectly quiet room from 20
feet (if they don’t have tinnitus)
3. taste a teaspoon of sugar diluted in two gallons of water
4. smell a single drop of perfume diffused throughout a three
bedroom apartment
5. fell the wing of a bee fall on their skin from a height of 1
centimeter
Light is Color
Objects absorb and reflect
light
How many colors can we
perceive?




We can discriminate among 200 steps in the
visible spectrum.
We can distinguish among 500 levels of
brightness.
We can discriminate among 20 levels of
saturation (i.e., how little white light is
reflected)
200 X 500 X 20 = 2 million colors!
Color is determined by the
property of the object
Maple leaf before (a) and after
(b) it changes color in the fall
Why do things look different in
artificial light?
Light energy is transduced
into neuronal energy
Transduction takes place in
the retina.
120 Million Rods and 5 Million
Cones per Eye
A Comparison of Rods and Cones
Rods
Achromatic
Low Light
Less Acuity
High Convergence
Peripheral Vision
Longer Dark Adaptation
120 Million per Retina
Shaped like a Rod
Cones
Chromatic
More Light
More Acuity
Less Convergence
Central Vision
Quicker Dark Adaptation
5 Million per Retina
Shaped like a Cone
Nocturnal vision is, in part, achieved
by higher concentrations of rods.
Light is color and light affects
the brain and mind.


Light causes melatonin secretion to stop and
thereby regulates our circadian rhythms.
Newly discovered photosensitive ganglion
cell affects melatonin secretion.
Newly discovered intrinsically
photosensitive ganglion cell
http://www.brown.edu/Adminis
tration/News_Bureau/200102/01-080.html
Light is color and light affects
the brain and mind.



Light affects mood (e.g., seasonal affective
disorder).
Disruptions of light cause jet-lag and have
been associated with cognitive impairment.
The characteristics of light and the
architecture of our brain cause us to perceive
color.
Neural Processing
Colorful illusions in your mind

You will see a green, black, and yellow flag.
Stare at the circle in the middle for 30
seconds. Then, when the screen changes,
blink once or twice and enjoy your color
illusion.
Theories of Color Vision

Opponent-Process Theory suggests that
color perception depends on receptors that
make antagonistic responses to three pairs of
colors.

After-images
Theories of Color Vision

Trichromatic Theory suggests that humans have three types
of receptors with differing sensitivities to different
wavelengths.

You can make any color by mixing red, green, and blue light
Theories of Color Vision

Trichromatic Theory suggests that humans have three types
of receptors with differing sensitivities to different
wavelengths.

We appear to have three types of cones
Theories of Color Vision

Opponent Process Theory

Trichromatic Theory

Which theory is correct?
Genetics affect color perception
and color deficiency (not color
blindness)



Color deficiency affects either blue/yellow or
red/green perception.
Color deficiency is much more common in
men, especially men with European ancestry
(8%) (men with Asian ancestry 5%, men with
African ancestry 3%).
Monochromatism or true colorblindness
occurs in 1 out every 100,000 people.
Ishihara Test
Ishihara Test
“Color blindness…”

Why is the term color blindness a poor term?
Color Perception varies among
Animals



Insects and ultraviolet
Snakes and infrared
Nocturnal animals have more rods
Color Perception varies among
Species



Bees can detect three colors: ultraviolet, blue, and
yellow, but not red.
The ability to see red is rare for insects.
The butterfly is an exception; they can perceive the
widest range of visual wavelengths (310 nm to 700 nm)
From: http://landsat.gsfc.nasa.gov/education/compositor/
http://www.robijns.nl/prod-info/julbo_zonnebrillen.php
Color Perception Varies
among Humans

Newborns do not possess cones and
therefore can’t perceive color or detail.
The lack of cones also affects
visual acuity
Color Perception Disorders




Color deficiency (retinal)
Color blindness (cortical)
Synesthesia
Brain Damage
Cortical Color Blindness or
Cerebral Achromatopsia


Mr. I was in an automobile accident and
experienced brain damage. He wrote Dr.
Oliver Sacks and said “My brown dog is dark
gray. Tomato soup is black. Color TV is a
hodge-podge…”
Mr. I had been a successful painter.
Cerebral Achromatopsia
Cerebral Achromatopsia
Cerebral Achromatopsia
Cerebral Achromatopsia
More Brain Damage
Visual Motion Blindness or
Akinetopsia

From: http://www.undergrad.ahs.uwaterloo.ca/~tbolton/Dorsal%20Disorders.htm
Questions



What color is the sound of a fog-horn?
What color is the sound an old-fashioned bicycle
horn makes?
What color is a siren?
Synesthesia




Some people see sounds, feel sights, taste words,
or see emotions.
Synesthesia is experienced when stimulating one
sensory modality leads to a perceptual experience in
another.
Color-word synesthesia may be most common and
vowel sounds may be most common triggering
stimuli (e.g., a = blue or red; e = yellow or white; o =
yellow, red, white, or black; u = blue or black).
http://web.mit.edu/synesthesia/www/karen.html
Synesthesia
Pitch (Hz)

30
Loudness (dB)
100
Visual Experience
a strip 12-15 cm. in length and the color of old,
tarnished silver

50
100

100
86

250(alto sax =196)
64
a brown strip against a dark background with redtongue-like edges
a strip with a reddish-orange hue in the center and it
gradually faded towards the edges until it ended in
pink
a velvet cord with fiber jutting out on all sides

500 (violin=440)
100
a streak of lighting splitting the heavens in two

500
74
dense orange color that which made him feel as
though a needle had been thrust into his spin

2000
113
"It looks something like fireworks tinged with a pinkred hue. The strip of color feels rough and
unpleasant and has an ugly taste- -rather like a briny
pickle…you could hurt your hand on this
one”
Does color exist in the external
world or only in our minds?



What makes a tomato red?
Why do long wavelengths (usually) look red?
Support for color existing in our minds:





Animals’ color perception
Color deficiency or blindness
Cortical color blindness
Synesthesia
Illusions
Copyright © 2002 Wadsworth Group. Wadsworth is an imprint of the
Wadsworth Group, a division of Thomson Learning
Page 104 (26)
Some major subdivisions of the Human cerebral cortex
Monocular versus
binocular depth cues
How do we know how far away
an object is by simply looking at
it?
Overview of Questions

How can we see far into the distance based on
the flat image of the retina?

Why do we see depth better with two eyes than
with one eye?

Why don’t people appear to shrink in size when
they walk away?
Binocular Depth Cues

Oculomotor - cues based on sensing the position
of the eyes and muscle tension

Convergence - inward movement of the eyes
when we focus on nearby objects

Accommodation - change in the shape of the
lens when we focus on objects at different
distances
Figure 8.2 (a) Convergence of the eyes occurs when a person looks at something that is very close. (b) The eyes
look straight ahead when the person observes something that is far away.
Monocular Depth Cues

Monocular - cues that come from one eye

Pictorial cues - sources of depth information
that come from 2-D images, such as pictures

Interposition - when one object partially
covers another

Relative height - objects that are higher in
the field of vision are more distant
Monocular Depth Cues

Relative size - when objects are equal size, the
closer one will take up more of your visual field

Perspective convergence - parallel lines appear
to come together in the distance

Familiar size - distance information based on our
knowledge of object size
Figure 8.3 A scene in Tucson, Arizona containing a number of depth cues: occlusion (the cactus occludes the hill,
which occludes the mountain); perspective convergence (the sides of the road converge in the distance); relative size
(the far motorcycle is smaller than the near one); and relative height (the far motorcycle is higher in the field of view;
the far cloud is lower).
Monocular Depth Cues

Atmospheric perspective - distance objects are
fuzzy and have a blue tint

Texture gradient - equally spaced elements are
more closely packed as distance increases

Shadows - indicate where objects are located
Figure 8.5 A scene along the coast of California that illustrates atmospheric perspective.
Figure 8.6 A texture gradient in Death Valley, California.
Monocular Depth Cues

Motion parallax - close objects in direction of
movement glide rapidly past but objects in the
distance appear to move slowly

Deletion and accretion - objects are covered or
uncovered as we move relative to them

Also called occlusion-in-motion
Binocular Depth Perception

Binocular (or retinal) disparity - difference in
images between the two eyes

Difference can be described by examining
corresponding points on the retina that
connect to same places in the cortex
Figure 8.16 The two images of a stereoscopic photograph. The difference between the two images, such as the
distances between the front cactus and the window in the two views, creates retinal disparity. This creates a
perception of depth when (a) the left image is viewed by the left eye and (b) the right image is viewed by the right
eye.
Binocular Depth Information - continued

Stereopsis - depth information provided by
binocular disparity

Stereoscope uses two pictures from slightly
different viewpoints

3-D movies use the same principle and
viewers wear glasses to see the effect

Random-dot stereogram has two identical
patterns with one shifted to the right
Stereograms

http://www.eyetricks.com/3dstereo.htm
Figure 8.33 Two cylinders resting on a texture gradient. The fact that the bases of both cylinders cover the same
number of units on the gradient indicates that the bases of the two cylinders are the same size.
Size Constancy

Perception of an object’s size remains relatively
constant

This effect remains even if the size of the object
on the retina changes
Demonstration



Look at the red circle on the next slide for 30
seconds.
Then look at a piece of paper and blink a few
times. How many inches across do you
perceive the circle after image to be?
Then look at the wall…
Figure 8.31 The principle behind the observation that the size of an afterimage increases as the afterimage is viewed
against more distant surfaces.
Light directly on each coin. Each coin was the same
distance from the observer. Which did they think was
the farthest away?
I
wondered why the baseball
was getting bigger. Then, it hit
me.
Visual Illusions

Nonveridical perception occurs during visual
illusions

Müller-Lyer illusion:

Straight lines with inward fins appear shorter
than straight lines with outward fins

Lines are actually the same length
Which is larger?

Front Monster or back monster?
Figure 8.34 The Müller-Lyer illusion. Both lines are actually the same length.
Müller-Lyer Illusion

Why does this illusion occur?

Misapplied size-constancy scaling:

Size constancy scaling that works in 3-D
is misapplied for 2-D objects

Observers unconsciously perceive the
fins as belonging to outside and inside
corners

Outside corners would be closer and
inside would be further away
Müller-Lyer Illusion - continued


Since the retinal images are the same, the
lines must be different sizes
Problems with this explanation:

The “dumbbell” version shows the same
perception even though there are no “corners”

The illusion also occurs for some 3-D displays
Figure 8.35 According to Gregory (1973), the Müller-Lyer line on the left corresponds to an outside corner, and the
line on the right to an inside corner. Note that the two vertical lines are the same length (measure them!).
Figure 8.39 The Ponzo (or railroad track) illusion. The two horizontal rectangles are the same length on the page
(measure them), but the far one appears larger.
Fig. 8-40, p. 187
The Ames Room

Two people of equal size appear very different in
size in this room

The room is constructed so that:

Shape looks like normal room when viewed
with one eye

Actual shape has left corner twice as far away
as right corner
Figure 8.41 The Ames room, showing its true shape. The woman on the left is actually almost twice as far away from
the observer as the woman on the right; however, when the room is viewed through the peephole, this difference in
distance is not seen. In order for the room to look normal when viewed through the peephole, it is necessary to
enlarge the left side of the room.
Fig. 8-40, p. 187
The Ames Room - continued


Why does the illusion occur?
One possible explanation:
 Observer thinks the room is normal
 Women would be at same distance
 One has smaller visual angle (R)
 Due to the perceived distance (D) being the
same
 Her perceived size (S) is smaller
The Ames Room - continued

Another possible explanation:

Perception of size depends on relative size

One woman fills the distance between the top
and bottom of the room

Other woman only fills part of the distance

Thus, first woman appears taller
What is the difference between
these two animals?