Sensation and Perception
Chapter 6
Sensation
Detection of physical energy from the
environment which we encode as neural
signals
Perception
Organize and interpret our sensations
Bottom- up processing
Beginning level of sensory analysis.
Bottom up processing- is sensory analysis
that begins at the entry level, with
information flowing from the sensory
analysis that begins at the entry level with
information flowing from the sensory
receptors to the brain
Top-down processing
The information processing guided by
higher-level mental processes, as when
someone constructs perceptions drawing
on our experience and expectations.
Prosopagnosia
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Faceblindness
the inability to recognize and connect the
outside the world. Complete sensation was
present but perception was incomplete. It
is the lack of top-down processing
Psychophysics
The study of relationships between the
physical characteristics of stimuli, such as
their intensity, and our psychological
experience of them.
Thresholds
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Absolute threshold is the minimum
stimulation needed to detect a particular
stimulus 50 percent of the time
A hearing specialist would expose an
individual to varying sounds in order to
figure out their absolute threshold
Thresholds
Signal detection theory is the theory which
predicts how and when we detect the
presence of a faint stimulus amidst
background stimulation. Assuming that
there is no single absolute threshold and
the detection depends partly on a person’s
experience, expectations, motivation and
level of fatigue.
A person’s heightened attention decreases
after 30 minutes.
Sensory Adaptation of the eye. Notice that
the images
disappear and reappear as the eye moves.
Thresholds
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More false alarms are detected in heightened
responsiveness
A stimulus is Subliminal if it is below your
absolute threshold, you detect it less than 50%
of the time. For instance, a microscopic cell is
subliminal to you because you cannot see it with
your naked eye.
Subliminal advertisements (Drink Coke,
eat popcorn etc.), does have an affect on you
but do not persuade you.
The final statement of subliminal messages
could be that much of our information
processing occurs automatically, out of sight, off
the radar screen of our conscious mind.
Thresholds
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The Difference Threshold (just noticeable difference
or ”jnd”) is the lowest difference you can detect between
the two stimuli 50% of the time.
For example, let's say I asked you to put your hand out
and in it I placed a pile of sand. Then, I add tiny amounts
of sand to your hand and ask you to tell me when you
notice any change in the overall weight. As soon as you
can detect any change in the weight, that difference
between the weight of the sand before I added that last
bit of sand and the amount of sand after I added it, is the
difference threshold. .
Priming is an acuteness to stimuli because of exposure
to a certain event or experience.
For example, an individual who has just purchased a new
car may now start to notice with more frequency other
people driving her same make and model. This person
has been primed to recognize more readily a car like hers
because of the experience she has driving and owning
one.
Thresholds
Weber’s Law states that two stimuli must
differ in percentages or ratios, not amount, for
a person to detect it (“jnd”).
Example: if a waiter holding tray containing four
glasses were just able to detect the added
weight of one glass, he would just be able to
feel the added weight from two more glasses if
the tray already held eight glasses. The amount
of detectable added weight would always be in
the same proportion, in this case ¼. .
Sensory Adaptation
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Sensory Adaptationlowered sensitivity due to constant
exposure from stimulus. For example,
when you go into someone’s house you
notice an odor…but this only lasts for
a little while because sensory adaptation
allows you to focus your attention
on changing environment.
Sensory Adaptation
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If a constant image was maintained on the eye’s
inner surface, the person will first see the
complete image, then their sensory receptors
will begin to fatigue and the image will start to
vanish. The image will reappear and then
disappear. This experiment reveals that
perceptions are organized by the meanings that
the mind imposes.
This adaptation allows the person to focus on
informative changes, leaving out uninformative
constant stimulations.
Vision
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Transduction refers to Sensory energy being
convert (transformed) into Neural energy/impulses.
Light is composed of electromagnetic waves with
Wavelengths (distance from one peak to another peak
on a wave) and Amplitudes (height of the wave)
Wavelength determines hue and pitch determines
the frequency in sound.
Amplitude determines intensity and loudness in
sound.
External Light entering the eye first travels through
the Cornea (protective layer)
Pupil (an adjustable opening) is
controlled by Iris (muscle around the pupil)
Lens (an oval transparency) that changes
shape to focus light by a process
called accommodation.
Spectrum of
electromagnetic
energy -this
spectrum ranges
from gamma rays as
short as the
diameter of an atom
to radio waves over
a mile long. The
narrow band of
wavelengths visible
to the human eye
extends form the
shorter waves of the
blue violet light to
the longer waves of
the red light
Retina
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light is then focused onto the back of the
eye called Retina (multi-neuron surface).
Johannes Kepler revealed that the retinas
did receive upside- down images.
Researchers later revealed that the retina
does not read the image as a whole,
receptor cells convert light energy into
neural impulses and these impulses then
are sent to the brain, it is then that the
image is constructed and perceived.
Retina
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Acuity is how sharp and clear a vision is
There are three basic types of Acuity :
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normal
nearsightedness (only see near things clearly)
farsightedness (only see far things clearly)
The Retina has 2 types of receptor cells :
Rods and Cones. Cells connecting these
detectors form the Optic Nerve that
sends the impulses to brain.
Receptor cells are the specialized cells that
respond to a particular type of energy.
Rods are receptor cells in the retina responsible
for night vision and perception of darkness.
Retina
Everyone has a Blind Spot, a small region
in the visual field where nothing could be
seen. This is because there are no
receptor cells where the optic nerve leaves
the eye in the retina. Normally, we don’t
witness this effect because we have two
eyes that compensate for each other’s
blind spot, and the fact that our eyes are
constantly moving.
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Retina
Fovea is the region in the retina where light is
centrally focused. The fovea has no rods, only
cones.
When light energy strikes the rods and cones,
neural signals are generated. These signals
activate the bipolar cells. The bipolar cells then
activate the ganglion cells. They then form the
optic nerve.
Cones allow detail an color
Cones allow one to perceive color. In the dark,
the cone is ineffective. The rods are not
affected by the dim light and many rods will
focus their energy into one bipolar cell.
Visual Information Processing
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The retina is brain tissue that floats to the eye
during early fetal development
There are three levels in which visual
information is received.
First, the retina processes information before
sending it via the thalamus to the brain’s cortex.
The retina also analyzes the sensory information
Information from the retina is received and
transmitted ganglion cells.
Pressure can trigger the retina
Visual Information Processing
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Nobel prize winners Hubel and Wiesel
discovered Feature Detectors in the brain
cortex that are sensitive to
specific features in what we see ,like
shape, color, depth, movement, and form.
Perret identified nerve cells that specialize
in responding to a specific gaze, head
angle, posture.
Parallel Processing
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Our brain Processes lots of
information simultaneously.
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For example, looking at an orange, the brain
processes the orange color, the round shape,
and the bumpy texture all at the same time.
People who cannot consciously perceive
can still remarkably locate objects but are
consciously unaware of how they
knew. Such a phenomenon
is called Blind Sight
Parallel Processing
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The processing of many aspects of a
problem simultaneously, the ban natural
mode of information processing for many
functions, including vision. Contrast with
eh step by step (serial) processing of most
computers and of conscious problem
solving.
Ex. Blindsightness
Color Vision
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Young and von Helmholtz revealed that color
can be created by combining the light
waves of blue, red and green colors. They
inferred that the eye must have three types of
color receptors.
Color processing is described in 2 stages :
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1) Young-Helmholtz trichromatic (three-color)
theory – Light is detected by 3 types of cones
each specifically sensitive to Red, Blue, or Green.
Combinations of them produce intermediate colors
(yellow, cyan, purple)
2) Opponent-Process theory – Color is then
processed by their opponent colors (red-green, blueyellow, black-white). Some cells are excited by
blue and inhibited by yellow, vice versa. Thus, you
cannot see a bluish-yellow.
Hearing
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Hearing is highly adaptable
Hearing Frequency (Pitch) is the number
of waves traveling through a point in one
second, relates to how fast a wave travels.
Audition, or hearing, requires sounds
waves converted into
neural impulses, and this is
done in the ear.
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Hearing
Sound travels through the 3
sections of the ear to the brain :
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Outer ear : Auditory Canal
Middle ear: Ear drum (tight membrane) .
Concentrates the vibrations of the eardrum to the
hammer, anvil, and stirrup to the cochlea’s oval
window
Inner ear : contains the Cochlea (coiled, fluidfilled tube) that contains the Basilar Membrane,
which is lined with hair cells that vibrates to excite
nerve fibers. The fibers form the Auditory Canal
connecting to the brain.
Loudness is determined by number of activated hair
cells.
Harder to hear sounds are amplified more than
How do we perceive Pitch?
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Place theory says that we hear different
pitches because specific “places” in the cochlea
are stimulated.
Frequency theory says that we hear different
pitches because the speed of neural impulses
traveling to the brain matches the speed of the
sound waves (“frequency”). Does not explain
how we hear low-pitched sounds, it can explain
our sensation of high pitched sounds.
It does explain our sensation of low-pitched
sounds
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How do we locate sounds?
We can tell which direction a sound is coming from
because if it is closer to our right ear, the right ear
will receive the sound slightly faster than left ear and
the brain calculates this difference. If the sound is
directly behind or in front, where the distance
between two ears is the same, then it is difficult to
differentiate.
Sound waves strike one ear sooner and more
intensely than the other.
The ear uses parallel processing to analyze the
differences in the sounds received by the two ears,
and then finds the source.
Hearing loss and Deaf
Culture
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Conduction Deafness – loss of hearing
due to damage of eardrum, and/or the
tiny bones in middle ear. (Could be fixed
by hearing aid)
Sensorneural hearing loss- damage to
the cochlea’s receptors. Destroys the
receptors
Shark and bird hair cells are able to
regenerate.
Cochlear Implants
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Cochlear Implants are the only way to restore
hearing for people with nerve deafness
These implants are wired to many sites on the
auditory nerve, which allows them to transmit
electrical impulses to the brain
Most effective when the child is very young
Deaf people argue against the implants since
they do not view deafness as a disability, they
also believe that the brain’s plasticity allows a
greater strength in another area.
Touch
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Touch is composed of 4 senses : Warmth,
Pain, Cold, and Pressure
Only pressure has specific receptors
Pressure and Cold = wet
Cold and warm = hot
Pressure and Pain = tickling itch
Pain
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Phantom Limb Sensations occur when
pain is felt in a nonexistent limb. Even
though the leg is not present, the receptor
neurons previously connected to them are
still there. And they will fire, resulting in
pain sensations.
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Pain
The Gate-Control Theory
states that the spinal cord has “gates” that opens/closes
to transmit pain impulses.
Small fibers open Gate = pain.
Large fibers close Gate = no pain
Pain is merely a physical and
psychological interpretation. Distraction methods, where
attention is focused elsewhere, can ease the felt pain.
Acupuncture (may affect gate-control),
electrical stimulation, exercise can also relieve pain.
The Biopschosocial perspective reveals that a person’s
experience of pain is influenced by biological influences,
past experiences and social cultural influences.
Taste
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Taste is a Chemical Sense composed of 5 basics :
Sweet, Sour, Salty, Bitter and Umami ( meaty taste)
Taste receptors (taste buds) regenerate every 1 or 2
weeks, but age, smoking, and alcohol will lower taste
bud number and sensitivity.
Sensory Interaction is when one sense affects
another sense, thus interacting. Smell and taste seem to
interact.
Taste buds on top and sides of the tongue and in the
back and on the roof of the mouth contain taste receptor
cells.
The taster receptor cells send information to an area of
the temporal lobe
Smell
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Smell or Olfaction is also a Chemical
Sense that directly transmits information
from nose to the temporal lobe.
The only sense that doesn’t first
relay impulses to the Thalamus.
The sense of smell- if you are to smell a flower, airborne molecules of its fragrance
must reach receptors at the top of your nose. Sniffing swirls air up the receptors
enhancing the aroma. The receptor cells send messages to the brain’s olfactory bulb,
and then onward to the temporal lobe’s primary smell cortex and to the parts of the
limbic system involved in memory and emotion
The olfactory braininformation from the
taste buds (yellow
arrow) travels to an
area of the temporal
lobe not far from
where the brain
receives olfactory
information, which
interacts with taste.
The Brain’s circuitry
of smell (red arrow)
also connects with
areas involved in
memory storage,
which helps explain
why smell can trigger
a memory explosion.
Body Position and
Movement
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Kinesthesis (using sensors in muscles,
tendons, and joints)
Vastibular sense (using fluids
in semicircular canal, cochlea, and
vestibular sacs in inner ear)
Both sense our position, movement,
and balance.
Perceptual Organization
 Gestalt-
“form’ or “whole’,
tendency to organize
cluster of sensations into
meaningful form
 Ex. Necker Cube
Perceptual Organization
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Form Perception
Figure ground- relationship continually
reverses, but always we organize the
stimulus into a figure seen against a
ground.
Following example:
Perceptual Organization
Grouping
1.
Proximity- grouping together visual and
auditory events that are near each other.
2.
Similarity- thinking that similar objects
belong together.
3.
Continuity-grouping stimuli into
continuous patterns
4.
Connectedness-because they are uniform
and linked
5.
Closure- fill in gaps to create a complete
whole object.
Depth Perception
Ability to see objects in three
dimensions although the images
that strike the retina are two
dimensional: allows us to judge
distance.
 EX. Visual cliff- the perception of
depth by infants.
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Binocular Cues
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The use of two eyes to perceive objects
and do tasks
Retinal Disparity- computing distance
between two images, a binocular cue.
Monocular Cues
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Depth cues such as interposition and
linear perspective available to either eye
alone.
Distances: Ex. St. Louis Gateway Arch
Monocular Cues
Light and Shadow Effect:
Nearby objects reflect
more light to our eyes.
Thus, given two identical
objects, the dimmer one
seems farther away.
Shading too, produces a
sense of depth
consistent with our
assumption that light
comes from above.
Invert the illustration
below and the bottom
row will become a hill.
Monocular Cues
Relative motion- as we move,
objects that are actually
stable may appear to move.
If while riding on a bus in
front of the fixation point
appear to move back ward.
The farther those object
beyond the fixation point
appear to move with you
objects you fix your gaze on
some object, say a house, the
objects beyond the fixation
point appear to move with
you; objects in front of the
fixation point appear to move
backward. The farther those
objects are from the fixation
point , the faster they seem
to move.
Monocular Cues
Interposition-if
one object
partially blocks
our view of
another, we
perceive it as
closer. The depth
cues provided by
interposition
make this an
impossible scene
Monocular Cues
Linear perspectiveparallel lines such
as railroad tracks,
appear to converge
with distance. The
more they
converge, the
greater their
perceived distance.
Monocular Cues
Relative height- we
perceive objects higher
in our field of vision as
farther away. Because
we perceive the lower
part of a figure ground
illustration as closer, we
perceive it as a figure.
Invert the illustration
above and the black
become ground like a
night sky.
Motion Perception
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Stroboscopic Movement- continuous
movement in a rapid series of slightly
varying images.
Phi Phenomenon -when two adjacent
stationary lights blink on and off in quick
succession, we perceive a single light
moving back and forth between them
Perceptual Constancy
Recognize objects without
being deceived by changes in
their shape, size, brightness,
or color.
Perceptual Constancy
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Shape and Size
Constancies- do the
tops of these tables
have different
dimensions? They
appear to. But, it or
not, they are
identical. With both
tables, we adjust our
perceptions relative to
our viewing angle.
Shape consistancy- a door casts an increasingly
trapezoidal image on our retinas as it opens,
yet we still perceive it as rectangular.
Size Constancy
Color constancy
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Refers to the importance of surrounding
background effects on perceived
color. Color constancy states that colors
don’t look different even in different
illumination (i sunlight or dark room), even
if the light and wavelengths change.
Lightness Constancy
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We perceive an object as having a
constant lightness while its illumination
varies.
Relative Luminance- amount of light an
object reflects relative to its surroundings.
Perceptual Interpretation
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The effect of
experience on our
ability to perceive the
world
Restored vision to
people who had none
had different
interpretations of
faces.
Sensory deprivation
experiments in
animals and humans
show that the critical
period can effect
visual experience.
Perceptual Adaptation
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Changed visual input makes the world
seem normal again. The ability to adjust
to an critically displaced or even inverted
visual field.
Example: inverted goggles
Perceptual Set
Believing is seeing; what do you perceive in these photos?
A) is this Nessie, the Loch Ness Monster, or a log?
B) Are these flying saucers or clouds?
We often perceive what we expect to see.
Perceptual set- a mental predisposition to perceive
one thing And not the other.
Example: if you see a saxophonist or a woman’s face will likely
depend on which of the other two drawings was viewed first. In
each of those images, the meaning is clear, and it will establish
perceptual expectations.
Perceptual Set
Recognizing faces- when briefly flashed a caricature of
Arnold Schwarzenegger was more accurately recognized
than Schwarzenegger himself. Ditto for other familiar male faces.
Context Effects
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A given stimulus may trigger radically
different perceptions, partly because of
our differing set, but also because of the
immediate context.
Ex:
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“eel is on the wagon”
“eel is on the orange”
Context Effect
The “little guy” shown
here is actually a 6’9”
former Hope College
he seemed like a
short player when
matched in a semi
pro-game against the
worlds tallest
basketball player 7’9”
Sun Ming Ming from
China.
Perception and the Human Factor
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Human factors psychologists- work with
designs that attempt to help the human
element of perception and inclinations.
ATM’s
TiVo
Apple/ipod/iphone
Extrasensory Perception (ESP)
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Perception without sensory input
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Telepathy- mind to mind communication
Clairvoyance-perceiving remote events
Precognition-perceiving future events
Parapsychology-study of paranormal
phenomena, including ESP and
Psychokinesis (mind over matter- moving
things)