Transcript Unit Four

Sensation and Perception
What is Sensation?
 A “sensation” occurs when something
around you changes…So what does that
mean?
 Any aspect of or change in the
environment to which an organism
responds is called a stimulus.
 Example: a light switch being turned on
fills a room with light.
What is Sensation?
 A stimulus can be measured
in a variety of ways including
it’s size, duration, intensity, or
wavelength.
 A Sensation occurs anytime a
stimulus activates one of your
receptors.
 The sense organs then detect
any change in energy, such
as light, heat, sound, and
physical pressure.
What is a Perception?
 A sensation may be combined with other
sensations and your past experience to
yield a perception.
 A perception is the organization of sensory
information into meaningful experiences.
 What are the relationships between
sensation and perception?
Psychophysics
 Psychophysics: The study of the
relationships between sensory
experiences and the physical stimuli that
cause them!
 Ok, so that explains how sensation and
perception are related…but how are they
different?
Fraser’s Spiral
 Fraser’s spiral
illustrates the
difference between
sensation and
perception. Our
perception of this figure
is that of a spiral, but it
is actually an illusion. If
you want, trace a circle
carefully…You will
always come back to
the beginning!
Absolute Threshold
 In order to determine how we judge
sensation and perception, we must first
figure out the weakest amount of a stimuli
that is required to produce a sensation. In
other words, we must find the absolute
threshold.
 The Absolute Threshold is: the level of
stimulus that produces a positive response
of detection 50% of the time!
The Absolute Thresholds for the “5” senses
in humans are the following:
 1. Vision: Seeing a candle flame 30 miles away
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on a clear night.
2. Hearing: Hearing a watch ticking 20 feet
away.
3. Taste: Tasting 1 teaspoon of sugar dissolved
into 2 gallons of water.
4. Smell: Smelling one drop of perfume in a 3
room house.
5. Touch: Feeling a bee’s wing falling a
distance of one centimeter onto your cheek.
Sensory Differences and Ratios
 Another type of threshold is the Difference
Threshold.
 The Difference Threshold refers to the minimum
amount of difference a person can detect
between 2 stimuli.
 Example: A light dial is turned until you can see
the light. That is the Absolute threshold. The
light dial is then turned until you can say “yes,
the light is brighter,” that is the difference
threshold.
Weber’s Law
 “The larger or stronger the
stimulus, the larger the change
required for a person to notice
that anything has happened to
it.”
 Weber’s law: The principle that
for any change in a stimulus to
be detected, a constant
proportion of that stimulus must
be added or subtracted.
Reactions to Stimuli
Sensory Adaptation
 Psychologists have found that your senses are
the most responsive to increases and
decreases, and to new events rather than to
ongoing, unchanging stimulation.
 We are able to respond to the changes in our
environment because our senses have the
ability to adapt, or adjust themselves, to a
constant level of stimulation.
 Once your senses get used to a new level of a
stimulation, they respond only to deviations from
it!
Examples of Adaptation
 1. Your eyes eventually adjust to a
darkened movie theatre. At first you see
blackness, but eventually, you can see
what is going on around you.
 2. When you first jump into a pool that
“feels cold” your body reacts to the
stimulus. Eventually, your body adapts to
the sensation and you become
“comfortable.”
 3. When you first walk into a sports locker
room, the smell is almost nausiating. After
a while, your senses adjust and you can
hardly tell.
Adapting to the Darkness
What do you see…Or don’t you?
Signal Detection Theory
 There is no sharp boundary
between the stimuli you can
perceive and the stimuli you
cannot perceive.
 The signal-detection theory
studies the relations between
motivation, sensitivity, and
decision making in the
presence of a stimulus.
 Definition: The study of
people’s tendencies to make
correct judgments in detecting
the presence of stimuli.
The Stroop Effect
Try to name the colors as
fast as you can. Not that
hard right? How fast are
you?
The Stroop Effect
-Now, try to name
the colors of the
words you see
here as fast as
you can!
-Not so easy is it?
-How you like
them apples?
-Why was it more
difficult to name
these colors?
Vision!
 Vision is the most studied of all of the senses!
 How does vision occur?
 1. Light enters through the pupil: The opening in the
iris that regulates the amount of light entering the eye.
 2. Light then reaches the lens: A flexible, elastic,
transparent, structure in the eye that changes its shape
to focus light on the retina.
 3. Light then hits the retina: The innermost coating of
the back of the eye, containing the light-sensitive
receptor cells. Photo receptors = rods & cones.
 4. This light energy is then turned into “neuronal
impulses,” which are sent down the optic nerve: The
nerve that carries impulses from the retina to the brain.
The Human Eye
Color Deficiency
 When some or all of a person’s
cones (light receptors) do not
function properly, he or she is said
to be color-deficient.
 There are many different types of
color deficiency. Most people see
at least some form of color, but
some see none.
 Red – Green, Shades of gray,
complete color loss.
Visual Definitions You Should Know…But We Will
Not Go Into Detail On Them!
 Binocular Fusion: The process of
combining the images received from the
two eyes into a single, fused image.
 Retinal Disparity: The differences
between the images stimulating each eye.
 Pencil or pen test!
The “Changing Flag” Test
 See Page 218 in your Textbook!
 Read and follow the directions for figure
8.8!
 What happened?
Hearing
 Hearing depends on vibrations in the air
called sound waves.
 Sound waves from the air pass through
various bones until they reach the inner
ear, which contains tiny hair like cells that
move back and forth.
 These hair cells change sound vibrations
into neuronal signals that travel through
the auditory nerve to the brain.
Deafness
 There are 2 types of deafness:
 1. Conduction Deafness: occurs when anything
hinders physical motion through the outer or middle
ear or when the bones of the middle ear become rigid
and cannot carry sounds inward. (Can be helped with
a conventional hearing aid.)
 2. Sensorineural Deafness: Occurs from damage to
the Cochlea, the hair cells, or the auditory neurons.
(Complete Sensorineural deafness cannot be helped
by a hearing aid.)
Diagram of the Ear!
A few Definitions:
 Auditory Nerve: The nerve that carries impulses
from the inner ear to the brain, resulting in the
perception of sound.
 Vestibular System: Three semicircular canals
that provide the sense of balance, located in the
inner ear and connected to the brain by a nerve.
 Olfactory nerve: The nerve that carries smell
impulses from the nose to the brain.
 Kinesthesis: The sense of movement and body
position.
Perception
Perception
 How do you perceive
yourself? Those around you?
Cars on the road? Noises?
Buildings?
 We do not merely have
sensory experiences, we
perceive objects! The brain
recieves information from the
senses and organizes and
interprets it into meaningful
experiences – unconsciously!
 This process is called
perception!
Perception
 Through the process of perception, the brain is
always trying to comprehend the confusion of
stimuli that bombard the senses.
 The brain makes sense of the world by creating
whole structures out of bits and pieces of
information in the environment!
 This process is called Gestalt!
 Gestalt: The experience that comes from
organizing bits and pieces of information into
meaningful wholes.
Figure-Ground Perception
 The division of experience into
figure and ground.
 Figure-ground perception is
the ability to discriminate
properly between a figure and
its background.
 It is easy to distinguish
between 3 dimensional
objects, but what about 2
dimensional ones?
Let’s try this one!
Perceptual Inference
 Often we have perceptions that
are not based entirely on current
sensory information.
 For instance, when you hear
barking as you approach your
house, you assume its your dog –
not a cat or a rhinoceros or even
another dog!
 When you are driving up a steep
hill and cannot see the road over
the hill, you assume that the road
continues even though you cannot
see it!
 This Phenomenon is called
Perceptual Inference: In other
words, filling the gaps in what you
actually know.
Subliminal Messages
 Subliminal messages are brief auditory or visual
messages that are presented below the absolute
threshold.
 They are presented below the “absolute
threshold” so that there is less than a 50 percent
chance they that they will be perceived.
 Subliminal messages are not as common as you
might think.
 In fact, the vast majority of what you have
probably heard is not true.
Depth Perception
 In order to create a sense of “depth perception,”
people use many monocular depth cues to
perceive distance and depth.
 Monocular depth cues are cues that can be
used with a single eye.
 One of these very important cues is called
motion parallax.
 Motion Parallax: the apparent movement of
stationary objects relative to one another that
occurs when the observed changes position!
A Little bit of Depth Perception
What is Constancy?
 Constancy is the tendency to perceive
certain objects in the same way regardless
of changing angle, distance, or lighting.
 For example, a friend walking towards you
from a long distance away does not
appear to turn into a “giant” regardless of
the fact that the images in your eyes are
becoming larger and larger as your friend
approaches.
Illusions
 What are illusions?
 Illusions: perceptions that misrepresent
physical stimuli.
 Illusions can be very useful in teaching us
how our sensation and perceptual rules
work.
 Illusions are created when our perceptual
keys such as size, space, and depth cues
are changed!
A very Strange Room!
Extrasensory Perception!
Extrasensory Perception or “ESP”:
An ability to gain information by some means
other than the ordinary senses.
There are 4 different types of “ESP”:
1. Clairvoyance – is perceiving objects or
information without sensory input.
2. Telepathy – involves the reading of someone
else’s mind or transferring one’s own
thoughts.
3. Psychokinesis – involves moving objects
through a purely mental effort.
4. Precognition – is the ability to foretell future
events.
ESP is a very highly
contested topic! Why is
this?
More Illusions!
Count the white and black dots!