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Sensation and Perception

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Miss Schwinge

on 11 October 2016

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Transcript of Sensation and Perception

Sensation and Perception
Making Sense Of The World
In our everyday experiences,
sensation and perception
tend to
blend
together in a continuous process. However, we tend to start with the
sensory receptors
and work up to higher levels of processing.
Smell and Taste
Touch and Pain
Touch is
essential to our development
, which is evident in premature babies who gain weight faster and go home sooner if they are stimulated by hand massage.
Hearing
Vision
For humans,
vision
is the major sense since
more of our brain cortex is devoted to vision than to any other sense.
But our senses also interpret what our senses detect. We
construct perceptions
drawing both on sensations coming bottom-up to the brain and on our own
beliefs, cognitions, experiences and expectations
, which is known as "
top down
" processing.
Some of this may be conscious, but some may also be unconscious. If you are
expecting
to come across a certain pattern, then you are focusing your attention on
looking for evidence consistent with that pattern
, and not just automatically processing whatever is in view.
Through
selective attention
, our conscious awareness focuses on only a very
limited
aspect of all that you experiences (our five senses take in
11,000,000 bits of information per second
, but we only
consciously
process around
40
of them).
At the level of conscious awareness, we are "blind" to all but a
tiny sliver
of the immense array of visual stimuli constantly before us. This is known as "
inattentional blindness
." There is also a similar
blindness to change
referred to as "
change blindness
."

Sensory inputs
get registered onto a sensory memory, and then are processed at higher and higher levels until a match is finally found with something in long-term memory. This
entry level analysis
is known as "
bottom up
" processing.
Absolute thresholds
refer to the
minimum stimulus needed to detect a particular light, sound, pressure, taste, or odor 50%
of the time.
Detecting a
weak stimulus
, or signal, depends
not only on the signal's strength
(like the hearing test), but also on
our psychological state
(our experience, expectations, motivation and alertness). For example, being
primed
for the sound test instead of being placed in a room with the sound playing without your knowledge.
Signal detection theory predicts when we will detect weak signals. There is
no single absolute threshold
, it also depends on the person and situation.
Different people have different absolute thresholds
for each of their senses because some people are much more sensitive than others. But even though our absolute thresholds may differ, we all need them
low enough
to allow us detect important sights, sounds, textures, tastes and smells.
Some examples of
generalized thresholds
:
Vision:
a flame from a single candle 30 miles away
Hearing:
ticking of a watch 20 feet away
Taste:
one teaspoon of sugar in two gallons of water
Smell:
one drop of perfume in a small house
Touch:
the wing of a bee brushing your cheek
The
difference threshold
(also called the
just noticeable difference
) is the
minimum difference a person can detect between any two stimuli at a time
This
detectable difference increases with the size of the stimulus
(adding 1oz to a 10oz weight will be noticeable, but adding 1oz to a 100oz weight will most likely not be).
Weber's Law
states that in order to be perceived as different, two stimuli must differ by a
constant percentage
(rather than a constant amount).
On the other hand,
sensory adaptation is our diminished sensitivity to an unchanging stimulus

Sensory adaptation of smell is easy to notice, but what about
vision
?
We perceive the world not exactly as it is, but as it is useful for us to perceive it
. To free up our attention, we adapt to what is constant, and detect only change.
Like touch, our sense of
taste
involves several basic sensations. We originally thought there were only four tastes (
sweet, sour, salty, and bitter
), but research has shown that there is a fifth taste:
umami (savory)
Survival Functions of Basic Tastes:
-
Sweet
= energy source
-
Salty
= sodium essential to physiological processes
-
Sour
= potentially toxic acid
-
Bitter
= potential poisons
-
Umami
= proteins to grow and repair tissues
Taste is a chemical sense
. Inside each little bump on the top and sides of your tongue (called
papillae
) are 200 or more taste bud, each containing a
pore
that catches food chemicals.
Into each taste bud pore,
50 to 100
taste receptor cells project antennalike hairs that sense food molecules.
Certain hairs respond more strongly to the five tastes, and people differ in their ability to taste food.
Taste receptors reproduce themselves
every week or two
, however as you age the number of taste buds
decreases
(as does taste sensitivity).
The more
densely packed
your taste buds, the
more chemicals are absorbed
, and the more
intensely
the food is tasted.
Sensory Interaction
Taste also illustrates the phenomenon of
sensory interaction
. When you plug your nose it prevents you from accurately tasting flavors. This is because
other senses often influence each other.
In the case of food, smell plus taste equals flavor.
The senses are
not
separate channels. Our brain
blends
seeing, hearing, tasting, and smelling to help us interpret the world. But sometimes our brain blends them to the point where they become
joined
together.
This joining of senses is known as
synesthesia
. Synesthesia comes from the Greek words "syn" (together) and "aisthēsis" (sensation), and is where
one sort of sensation
(like hearing sound)
produces another
(such as seeing color).
Thus, hearing music or seeing a certain color may activate color-sensitive cortex regions and trigger a sensation of color.
Taste
Smell
Our sense of
smell
also depends on
chemicals emitted by substances
. Molecules of substances rise into the air, and some are drawn into our nose and into the mucous membrane at the top of each nostril. They are then
absorbed
by receptor cells located there, which directly relays to our
olfactory bulb
and sends the information to our
brain.
What's special about our sense of smell is that the nerve fibers from our olfactory bulb connect to the brain at the amygdala and then to the hippocampus (which make up the
limbic system
and are responsible for
emotional impulses and memory
).
All of our other senses must go through the thalamus
first before being sent to the appropriate cortices;
smell is the only sense with a direct connection.
This may explain why smell is such a powerful trigger for memories.
Audition
, our sense of
hearing
, is highly adaptive. We can hear a
wide range of sounds
, but we hear sounds with
frequencies in a range
corresponding to that of the
human voice
the best.
The
strength
, or
amplitude
, of sound waves determines their
loudness
. Waves also
vary in length
, and therefore in
frequency
. Their frequency then determines the
pitch
(highness/lowness) we experience.
Long waves have low frequency and low pitch. Short waves have high frequency and high pitch.
We measure sound in
decibels,
and the
absolute threshold for hearing is 0 decibels
(a normal conversation is around 60 decibels and is around 10,000 times more intense than a 20 decibel whisper, while a passing subway train is 10 billion times more intense)
In order to hear we must somehow
convert
these sound waves into
neural activity
, which requires an intricate mechanical chain reaction.
We start with sound waves being collected in our
outer ear
, or
pinna
. The waves then travel down the
ear canal
(also known as the
auditory canal
), until they reach the
eardrum
(a tight membrane that vibrates with the waves).
The middle ear then transmits the
eardrum's vibrations
through a piston made of
three tiny bones
(the hammer, anvil, and stirrup) to the
cochlea
; a snail shaped tube in the inner ear
The incoming vibrations cause the cochlea's membrane (the
oval window
) to
vibrate
, which
moves the fluid
that fills the tube. This causes
ripples
which
bend the hair cells
lining the surface.
This
hair movement
triggers
impulses
in the adjacent nerve cells, whose axons converge to form the
auditory nerve
, which sends neural messages via the
thalamus
to the
temporal lobe's auditory cortex.
Loudness is interpreted by the brain from the number of activated hair cells
, and even if a hair cell loses sensitivity to soft sounds. it may still respond to loud sounds.
Hermann von Helmholtz's
place theory
states that we hear different pitches because
different sound waves trigger activity

at different places
along the cochlea's
basilar membrane.
Therefore, the
brain determines a sound's pitch
by recognizing the
specific place on the membrane
that is generating the neural signal.
High frequencies
produce large vibrations
near the beginning
of the cochlea's membrane,
low frequencies at the end.
On the other hand,
frequency theory
suggests that the
brain reads pitch
by
monitoring the frequency
of neural impulses traveling up the auditory nerve. The whole basilar membrane
vibrates with the incoming sound wave
, which triggers neural impulses to the brain at the
same rate
as the sound wave.
Snap test time!
Problems with the mechanical system
that conducts sound waves to the cochlea cause
conductional hearing loss
(for instance, if the tiny bones of the middle ear lose their ability to vibrate, the ear's ability to conduct vibrations diminishes )
On the other hand,
damage to the cochlea's hair cell receptors
or their associated nerves can cause the more common
sensorineural hearing loss
(or nerve deafness)
For now, the only way to restore hearing for people with nerve damage is a
cochlear implant.
This electronic device
translates sounds into electrical signals that, wired into the cochlea's nerves, convey some information about sound
to the brain.
Scientifically speaking, what strikes our eyes is
not color but pulses of electromagnetic energy
that our visual spectrum perceives as color (and we only see a sliver of the spectrum)
Light's
wavelength
(the distance from one wave peak to the next) determines its
hue
(the color we experience)
The
intensity
, or amount of energy in light waves (determined by a wave's amplitude. or height), influences
brightness.
Light enters the eye through the
cornea
, which protects the eye and bends light to provide focus.
The light then passes through the
pupil
, a small adjustable opening surrounded by the
iris
; a colored muscle that adjusts light intake.
The
iris dilates and constricts in response to light intensity
, and even to inner emotions (like desire).
Lights Test!
Behind the pupil is a
lens
that focuses incoming light rays into an image on the
retina
; a multilayered tissue on the eyeball's sensitive inner surface. The lens focuses the rays by changing its curvature.
The retina doesn't "see" a whole image, instead its millions of
receptor cells
convert particles of light energy into neural impulses, and forward those to the brain.
The brain is what reassembles the impulses into images.
How The Eye Works
Once we've made it into the retina, we would find inside its buried receptor cells, the
rods and cones
of the eye. The
rods
are more numerous, some 120 million, and are
more sensitive
to light than the cones (which means they are responsible for
vision at low light levels
). However, they do
not
let us see color.
The receptor cells are where
light energy triggers chemical changes, which sparks neural signals, which then travels to the optic nerve
where it sends the information to your
brain
. This
translation of incoming stimuli
into neural signals is known as
transduction.

Cones
, on the other hand, number 6 to 7 million and provide the eye's
color sensitivity
and they are much more concentrated in the
fovea
(the retina's area of central focus)
However, where the optic nerve
leaves
the eye there are
no receptor cells,
which creates a
blind spot
.
The same
sensitivity
that enables retina cells to fire message can lead them to
misfire
as well.
Eye Rub Test!
Why did you see light to the left? Well, your retinal cells are
so responsive
that even
pressure
triggers them. But your brain
interprets their firing as light
, and more specifically, light to the
left
(the normal direction of the light that activates the right side of the retina)
The retina's
feature detector cells
respond to a scene's
specific features
(edges, lines, angles, and movements)
Damage
to these areas can
prevent
your ability to recognize particular forms and objects.
The way we are are able process and categorize so many things at once is due to
parallel processing
. Our brain divides a visual scene into
many subdimensions
(color, movement, form, depth) and works on each aspect
simultaneously
to allow for a complete whole.
Color Vision
When we see the color red,
we are actually seeing everything BUT red because it rejects (reflects) the long wavelength of red
. Besides, light waves are not really colored, which means the object does not really have color.
For most people, our
absolute threshold for color is so low that
we can discriminate some
7 million
different
color variations.
However, around
1 person in every 50
(usually male) has
color deficient vision
; more commonly known as
colorblindness
.
The Young-Helmholtz
trichromatic theory
states that we have
three types of cones
in the retina: cones that detect the different colors
blue, red, and green
(the primary colors of light). These cones are
activated in different combinations to produce all the colors of the visible spectrum.
But this theory doesn't solve all pats of the color vision mystery; that's where Hering's
opponent-process theory
comes in.
The theory states that the sensory receptors arranged in the retina come in
pairs: red/green, yellow/blue, black/white.
Negative afterimages are caused when the eye's photoreceptors, primarily cone cells, adapt from the over stimulation and
lose sensitivity which causes us to see their opposite
when the color is removed.
Touch also lets us tell the
difference
between
pressure, warmth, cold, and pain.
Fun facts:
- Stroking adjacent pressure spots creates a tickle.
- Repeated gentle stroking of a pain spot creates an itching sensation
- Touching adjacent cold and pressure spots triggers a sense of wetness (cold, dry metal)
- Stimulating nearby cold and warm spots produces the sensation of hot
An example of
top-down influence

on touch sensation:
Important
sensors
in your joints, tendons, bones, ears, and skin enable your
kinesthesis
(your sense of the position and movement of your body parts)
A companion
vestibular sense
(the sense of a body's movement and position, including the sense of balance), monitors your head's movement and position through a sense of
equilibrium
in your inner ear.
Twirl Test!
The reason you still feel a bit dizzy after spinning is because your inner ears and kinesthetic receptors
did not immediately return to their normal state.
Even though we don't always appreciate it,
pain is our body's way of telling you that something has gone wrong
.
...However, as we
age
our sense of balance
decreases
.
Pain
Our pain experiences
vary widely
, depending on our
physiology, experiences and attention
, as well as our surrounding culture. This means
our feelings of pain combine both bottom-up sensations and top-down processes.
Gate control theory explains that some pain messages have higher priority than others.
When a higher priority message is sent, the gate swings open for it and then swings shut for a low priority message (which means we won't feel it).
However, since
we feel, see, hear, taste, and smell with our brain,
there are times when we sense things that
aren't there
. An example of this would be
phantom limb sensation
, in which an amputee may feel pain or movement in
nonexistent
limbs due to the brain
misinterpreting
the spontaneous central nervous system activity that occurs in the
absence of normal sensory input
.
This is the same reason
placebos
work; they dampen the brain's attention and response to painful experiences.
Perceptual Organization
Now that we've gone over the processes by which we see, hear, touch, taste, and smell, it's time to figure out
how we organize and interpret all of those sensations
so they become
meaningful perceptions.
The word "
gestalt
" refers to an
organized whole
. Gestalt psychologists emphasize our
tendency to integrate pieces of information into meaningful wholes
.
Figure-ground refers to the organization of the visual field
into objects (the figures) that stand out from their surroundings (the ground)
Such reversible figure-ground illustrations demonstrate that
the same stimulus can trigger more than one perception
In order to keep the world we see
organized and manageable
, we like to
group
stimuli together. There are 5 main grouping rules:
We see these 6 lines as 3 groups of 2
We see the triangles and circles as vertical columns instead of horizontal rows of dissimilar shapes
We see two smooth, continuous pattern rather than alternating semi circles
We see each set of two dots and the line between them as a single unit
We fill in gaps to create a complete, whole object
From the two-dimensional images falling on our retinas we somehow organize three-dimensional perceptions.
Depth perception, seeing objects in three dimensions
, enables us to estimate their distance from us.
Connection between binocular cues and retinal disparity:
Finger Sausage Test!
Binocular
cues require the use of both eyes, while
monocular
cues are available to each eye separately. Monocular cues also
influence our everyday perceptions.
Horizontal-vertical illusion
is when we perceive vertical dimensions as longer than identical horizontal dimensions.
Our brain constructs our perceptions
Despite the fact that this apple is purple, we are still aware that it is an apple (even though there is no such thing as a purple apple). This is an example of
perceptual constancy
.
Even though the two monsters
cast the same retinal images
, the l
inear perspective
tells our brain that the monster in pursuit is
farther away
(this is why we perceive it as
larger
)
Relative luminance
is the amount of light an object reflects relative to its surroundings.
Our experience of color depends on more than just the
wavelength information
received by the cones in our retina; it also depends on the
surrounding context
. When we
removed the cue-producing surroundings
we saw that the squares were the same color.
Perceptual adaptation
refers to our ability to
adjust
to an artificially displaced or even inverted visual field
Perception Test!
So what determines our
perceptual set
? We form
schemas
(concepts) through
experiences
that organize and interpret unfamiliar information. Like pain,
perception is a biopsychosocial phenomenon
.
Extrasensory Perception (ESP)
Claims of
paranormal phenomena
("psi") include astrological predictions, psychic healing, communication with the dead, and out-of-body experiences.
There are three main types of
ESP
:
-
Telepathy
(mind to mind communication)
-
Clairvoyance
(perceiving remote events)
-
Precognition
(perceiving future events)
"A person who talks a lot is sometimes right"
-- Spanish Proverb
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