Marina Sangkavichai
Perceiving the World
 Sensory systems
 What are our senses?
 How do we make meaningful interpretations from
what our senses take in?
Senses
 Seeing
 Smell
 Hearing
 Taste
 Touch
 We have an amazing ability to distinguish different
sensations. For example, a touch sensation does
not “feel” the same as a “hearing” sensation.
Sensation and Perception
 Sensation: process that occurs when special receptors
in the sense organs are activated, allowing various
forms of outside stimuli to become neural signals in
the brain.
 Perception: the method in which the sensations
experienced at any given moment are interpreted and
organized in some meaningful fashion.
Perception
Sensory Coding
 Our senses “boil down” floods of information into
a stream of useful data.
 After our senses analyze information, our senses
use sensory “coding.”
 Sensory coding: important features of the world
are converted into neural messages understood by
the brain. Also known as “ transduction.”
 Exercise: Put pressure on your eyes, hold for a few
seconds. The pressure you put on your eyes is
“encoded” into visual features…not pressure. This
is because the retina encodes visual information.
Senses
 The minimum stimulation necessary to detect a
particular stimulus ( light, sound, pressure, taste,
odor ) is called its absolute threshold.
 Example: we can feel a bee falling on our cheek, or
smell a drop of perfume in a small apartment
 How loud does someone have to call out your
name before you can hear it.
Absolute Thresholds
 We don't notice radio waves, x-rays, or the microscopic
parasites crawling on our skin. We don't sense all the odors
around us or taste every individual spice in our gourmet
dinner. We only sense those things we are able too since we
don't have the sense of smell like a bloodhound or the
sense of sight like a hawk; our thresholds are different from
these animals and often even from each other.
Bacteria On Our Skin
Signal Detection
Theory
This refers to our
attempt to focus on
one particular
stimulus and ignore
the flood of
information entering
our senses.
For example,
focusing on a friends
conversation at a
party while trying to
ignore the
surrounding noises.
Absolute Threshold
What is the dimmest light this lifeguard could
perceive in the darkness?
Absolute threshold measures have been established
by sensory psychology.
Just as a threshold of a doorway is the dividing point
between being outside or inside a room, the
absolute threshold of a sense marks the difference
between not being able to perceive a stimulus and
being just barely able to perceive it.
Absolute Thresholds
 Absolute thresholds define the sensory worlds of
humans and animals.
 Humans can hear sounds down to 20
 Hertz ( vibrations ) per second and up to 20,000
hertz.
 This is a practical range because if your ears could
sense tones below 20 hertz, you would hear the
movements of your muscles!
Absolute Thresholds
 Dogs, bats, and cats, and other animals can hear
sounds well above 20,000 hertz.
 Dog whistles ( 40,000 to 50,000) can be heard by dogs
but not by humans.
 For humans this sound is beyond our awareness.
Absolute Thresholds
 The minimum amount of sensory stimulation that can be detected 50% of the
time
Sensory Adaptation
 Tendency of sensory receptor cells to become less
responsive to a stimulus that is unchanging.
 Receptors are no longer sending signals to the brain
 Clothes would drive us crazy, ticking of the clock, and
odors from our home would not go away.
Perceptual
Constancies
The perceived size of
an object remains
the same, even
though the size of its
image on the retina
changes is called
SIZE CONSTANCY.
For example: hold
your left hand up to
your nose, and right
hand at arms length.
Has your right hand
suddenly grown
smaller? No
The Amazing Eye
 Light is one form of electromagnetic waves which
travel around us.
 The transparent covering on the front surface of the
eyeball that bends light rays inward toward the pupil is
called the CORNEA.
The EYE
 The cornea bends light inward and usher it into
the pupil which is the small dark opening in the
color of the iris. ( the pupil is a hole in your eye ).
The iris controls the contraction of this pupil. It is
an involuntary reflex.
 In very bright light, it can contract to the size of a
head pin.
 In dim light, ( dark) it dilates ( that is WIDENS) to
the size of a pencil eraser. Why do you think this is
so?
The EYE
 Your pupil responds to emotions as well as light!
 When a person looks at someone or something
highly desirable, the pupils dilate ( widen ) as if to
take in more of the pleasing view!
 It also dilates ( widens ) when a person is
frightened, telling a lie, or sexually aroused.
 Pupil size is also related to mental effort, the more
intense the mental activitiy, the larger the pupil
becomes.
Wide Pupils More Attractive
Hess Studies
In one of the studies they
conducted, they showed men
two sets of photographs of
women. In one set, the pupils of
each woman had been enlarged.
In the other set of photos, the
pupils of each woman had been
reduced. Results showed that
the men preferred the photos of
the women with the enlarged
pupil, even though the men
could not explain why those
were their favorites. When the
test was performed on a group of
women, the results were the
same.
The EYE
 The lens is just behind the iris and the pupil. This
changes shape as it focuses on the retina.
 The retina is at the back of the eye. Images are
projected from the lens.
Depth Perception
 Depth Perception: is the ability to see three
dimensional space and to accurately judge distances.
You wouldn’t be able to drive a car or ride a bicycle,
play catch, etc.
 The world would look like a flat surface!
 Images cast on the retina do not contain depth. They
are flat, just like a photograph. So how do we perceive
depth????
Binocular Depth Cues
 Binocular depth cues are depth cues that depend on
two eyes working together.
 Close one eye and see how your visual world changes!
Binocular Depth Cues
 Each eye is about 2 ½ inches apart, just enough to give
each eye a slightly different view of the objects focused
on, and consequently a slightly different retinal image.
 These slightly different views are called binocular
disparity.
Class Exercise
 Hold a pencil/pen at arms length straight in front
of you. Then close your right eye and focus on the
pencil, then left, than right.
 The pencil will appear to be moving side by side.
This is BINOCULAR DISPARITY.
 Two different images on the retina which allow you
to perceive depth. Helps us see things in 3D. Each
eye gets a different view of the world, this provides
you with depth perception.
A Hole In Your Hand
 Instructions: Roll a piece of paper into a tube. Close
your left eye. Hold tube to your right eye like a
telescope. Place left hand halfway down tube. Now
open left eye.
 You will see a “hole” in your hand. Your brain blends
these two images automatically.
The Visual Cliff Experiment
 Researchers Eleanor Gibson and Richard Walk wanted
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to test depth perception in children
Built a special table that had a big drop on one side.
They called it the “visual cliff.”
Different size of the pattern was a clue for depth.
Whole table was then covered by a clear glass top, so
that a baby could safely be placed on or crawl across
the “deep” side. ( video )
Youtube.com Visual Cliff ( 1950s)
Joseph Campos-Visual Cliff
Visual Cliff Results
 Infants tested in this study ranged from 6 months to 14
months old.
 81 percent refused to crawl over the deep side.
 They interpreted this as a very early sign of depth
perception.
Gestalt Theories of Perception
Gestalt
 A German word that refers to the whole form, pattern, or configuration
a person perceives
 Figure-ground
When viewing the world, some object (the figure) often seems to
stand out from the background (the ground)
Figure-Ground Images
Figure Ground Images
Gestalt Principles of Grouping
Perceptual Constancies
Allows perceived objects to maintain stable properties (size,
shape, brightness) despite differences in distance, viewing
angle, and lighting:
 Size constancy – as objects move away they seem to
maintain same size
 Brightness constancy – objects seem to maintain a
constant level of brightness regardless of differences in
lighting conditions
 Shape constancy – objects are perceived as having an
unchanging shape regardless of viewing angle changes
that alter the retinal image
Perception of Images
Perception Exercise
Cultural Influence on Emotional
Perceptions
 Two studies tested the hypothesis that in judging people’s emotions
from their facial expressions, Japanese, more than Westerners,
incorporate information from the social context. In Study 1,
participants viewed cartoons depicting a happy, sad, angry, or neutral
person surrounded by other people expressing the same emotion as the
central person or a different one. The surrounding people’s emotions
influenced Japanese but not Westerners’ perceptions of the central
person. These differences reflect differences in attention, as indicated
by eye-tracking data (Study 2): Japanese looked at the surrounding
people more than did Westerners. Previous findings on East–West
differences in contextual sensitivity generalize to social contexts,
suggesting that Westerners see emotions as individual feelings,
whereas Japanese see them as inseparable from the feelings of
the group. (…)
Influences on Perception
Attention
 Process of sorting through sensations and selecting some for further
processing
 Some sensations are automatic requiring minimal mental effort
 Inattentional blindness
 Changes in objects not receiving direct attention are not noticed
 Cocktail party phenomenon
 When you hear your name, focus follows due to assumption that other
meaningful information will follow
 Focus
 Information that receives focus is remembered while other stimulation
received at same time is lost
 Hearing words spoken into both ears at same time; only words that
receive focus of attention are recalled
 (Invisible video)
Piano Stairs in Sweden
 A Volkswagen initiative called The
Fun Theory is setting out to prove
that people’s behavior can be
changed for the better by making
mundane activities fun. In a recent
experiment, they set up musical
piano steps on the staircase of a
Stockholm, Sweden subway station
to see if more people would be more
willing to choose the healthier
option and take the stairs instead of
the escalator. That day, 66
percent more people took the
stairs than usual, proving that
fun is the best way to get
people to change their ways.
© E.R. Degginger/Animals Animals
What do you see?
Can you find the human face here?
Optical Illusion
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Curved lines or straight lines

Which one of the surrounded
circles is bigger?
What do you see?

How many prongs are there?

There’s a baby in this picture
Animals on hands!
Guido Danieli Animal on Hands
Impossible Scenes
Psychology Question
 Please define the terms sensation and perception.
 If a tree makes a sound in the forest, does it still make
a sound? What are your thoughts?
Supermarket Psychology
 Consumers buying more than what they need
 Slow music
 Red and yellow are NOTICEABLE
 Green evokes feelings of health
 Blue means reliable and trusting
 Visual merchandising is key
 Fresh flowers in the front to appeal to your sense of
smell! Oh, earthly joy!
 Cereal and coffee usually in the middle aisles!
Hearing
 How do humans hear?
 By picking up sound waves in the air.
 Sound waves are invisible ripples of high and low air
pressure created by objects that vibrate or shake
rapidly to and fro.
 You can “feel” sound waves if you’ve ever put your hand
on a loud, booming speaker.
Sounds Waves
 A little science!
 Sound waves have amplitude ( which is the height of
each wave and frequency which is the number of
waves per second).
 Low pitch sounds have low frequency, and low
amplitude
 High pitch sounds high amplitude and high frequency.
Illustration.
How we hear!
 The ear converts this type of energy-in this
case the energy of sound waves, into tiny
electrical nerve signals.
 Sound waves are transmitted into the cochlea, a
snail shaped tube in the ear. There are tiny hairs in
this cochlea that are stimulated. These vibrations
are then transmitted to the brain as sound.
 Exposure to loud noises can damage the ear so be
careful….jack hammers, airports, etc.
Smell
 Airborne molecules must reach receptors in the
back of the nose in order to smell.
 Sniffing swirls the air up into these receptors.
 Messages from these receptors are sent to the brain
temporal lobe and to parts of the limbic system.
 That’s why certain smells conjure up memories!
 Smell is important because it signals us to dangers
in our environment such as smelling something
burning, poisonous gases, etc.
Taste
 Your tongue is covered with small bumps called
the papillae. Each papillae has 100-200 taste buds (
sensory receptors of taste!)
 Basic taste sensations are sweet, salt, sour, bitter,
 Smell and taste work together ( colds don’t help!)
 Taste adds to our enjoyment of food.
 Taste signals travel slowly to the brain ( it may take
a few seconds to realize what the taste is ).
 End of lecture