Transcript Sensation and Perception - Options

Sensation and Perception
What are Sensation and
Perception?
• Sensation is the
information we receive
from our five senses (sight,
taste, touch, smell, and
hearing)
– The information goes to the
CNS, where the brain
interprets it
• Perception is our
interpretation of that
information and how we
react to it
– We perceive information
based on learning, past
experiences, and attitudes
Absolute Thresholds
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An absolute threshold is the weakest amount of a stimulus that can
be sensed
Scientists have determined absolute thresholds for all five senses
for the average person, but they vary by individual
Absolute thresholds for humans are different than those for animals
(a dog’s hearing threshold is very different from ours
Difference Thresholds
• A difference threshold
is the minimum
amount of difference
we can detect
between two stimuli
– Think of hearing the
notes of different keys
on a piano
– These differ from
person to person as
well
Signal Detection Theory
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Many internal and external forces affect our ability to detect sensory
information
SDT is the method of taking into account the strength of a stimulus
but also environmental influences and an individual’s physical state
and attitudes
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It is much harder to detect the sound of someone’s voice in a quiet room
than it is in a noisy one
The buzzing of fluorescent lights may be more distracting when you are
stressed or have a headache
People tend to focus more on what they personally find important
and ignore what they find unimportant
Sensory Adaptation
• The process by which
we become more
sensitive to weak stimuli
and less sensitive to
unchanging stimuli
• When you enter a very
dark room, your eyes
adapt to the new space
and begin to detect weak
sources of light
• If you live in the city,
your ears adapt to the
constant sound of traffic
in the background and
detect other noise
sources
Vision
Light
• Light is electromagnetic
energy measured in
wavelengths
• Not all light is visible to
humans
• Visible light can be
filtered into a variety of
colors – each color has a
different wavelength
• Blue and violet have the
shortest wavelengths, red
has the longest
The Eye
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Works similar to a
camera
Light enters the eye
through the pupil
The lens adjusts to the
distance of objects by
changing its thickness
The image then is
projected onto the retina
– it acts like film in a
camera
Neurons on the retina,
called photoreceptors,
react to the light and
send the image to the
occipital lobe of the brain
Rods, Cones, and the Blind Spot
• Rods and cones are types
photoreceptors that cover the
retina
• Rods – only sensitive to
brightness of light, allow us to
see in black and white
• Cones detect colors within the
light
• The blind spot is the area of
the eye that connects to the
optic nerve – it does not have
rods or cones and does not
capture a light image at all
Color and Vision
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People with normal vision can
see any color in the visible
light spectrum, but not all
animals can
Cones in the eye are sensitive
to certain colors – either blue,
green, or red
When more than one type of
cone is stimulated, we can
perceive other colors like
yellow, orange, and purple
TVs and computer screens use
only blue, green, and red
pixels to create color images
Color Blindness
• People may be partially
color blind if they cannot
see all of the colors in the
color spectrum
• This occurs when cones
malfunction or when
people are born without a
certain type of cone
• Total color blindness
occurs when people
cannot see any colors,
only black and white –
this is a really rare
condition
Hearing
Sound and Pitch
• Sound is caused by
vibrations that travel
through the air in waves
• How fast they complete a
cycle determines their
pitch
• Shorter waves produce a
higher pitch
• Longer waves produce a
lower pitch
• A violin produces a higher
pitch than a cello, which
has longer strings and
makes longer sound
waves
Loudness
• Loudness is measured by the
height of sound waves – this is
known as amplitude and is
measured decibels
• The absolute threshold of sound
for humans (0 decibels) is the
sound of a ticking watch 20 feet
from the ear in a quiet room
The Ear
• Shaped to capture sounds,
vibrate with them, and transmit
the sound to the brain
• The eardrum is the thin
membrane gateway between
the outer and inner ear
• As sound hits the eardrum, it
vibrates and transmits the
sound to three small bones
• These bones vibrate the
cochlea, a small bony tube
filled with fluid and neurons
that react to movement and
send messages to the auditory
nerve
• The auditory nerve sends
messages to the temporal lobe
Deafness
• Conductive deafness –
caused by damage to the
middle ear, which amplifies
sounds – can be treated
with a hearing aid that
amplifies noises
• Sensorineural deafness –
caused by damage to the
inner ear or destruction of
neurons in the cochlea,
usually from prolonged
exposure to loud noises –
can be treated (sometimes)
with cochlear implants
Smell, Taste, and Touch
Smell
• Smell is linked with taste –
when your ability to smell is
impaired, your ability to taste
decreases
• Molecules in odors travel into
the nose and contact receptor
neurons high in the nose
• These neurons send
messages to the olfactory
nerve
• Our sense of smell is highly
adaptable and we can quickly
lose our awareness of certain
smells
Taste
• Our sense of taste is
connected to smell,
texture, and temperature
• Apples and onions taste
very similar, but their
odors create very
different flavors
• We can distinguish four
main taste qualities –
sweet, sour, bitter, and
salty
• Receptor neurons on the
tongue detect various
qualities and send
information to the brain
• We regularly kill taste
receptors, but they grow
back within a week – the
taste system is the most
resilient of our senses
Skin Senses
• Our skin can detect pain,
pressure, and
temperature – some
receptors detect just one
type of stimulus while
others may detect all
three
• Many receptors are
located at the roots of our
body hair
• They are not evenly
distributed – parts of the
body have many more
receptors than others
Temperature and Pain Receptors
• Temperature receptors are just
below the skin, some detect
warmth while others detect
cold
• Our sense of temperature is
adaptable, we acclimate to
warmer or cooler settings
pretty quickly
• Pain receptors motivate the
body to try and stop the painful
stimulus
• Sometimes we can overload
the brain’s messages to ease
pain – rubbing an injury can
distract the brain from pain
signals
Body Senses
• Vestibular Sense – our
sense of balance – tells
us when we are upright
and whether we are
falling or changing speed
– Allows us to know that we
are standing up or moving
in an elevator when our
eyes are closed
• Kinesthesis – the sense
that informs people about
the position and motion of
their bodies
– Allows us to touch our nose
with our eyes closed
Perception
How Do We Organize Sensory
Information?
• Our brain learns to use a
variety of methods to sort
and make sense out of
sensory information
• Closure
• Figure-ground perception
• Proximity
• Similarity
• Continuity
• Common fate
Closure
• The tendency to
perceive or complete a
whole figure even when
there are gaps in what
your senses tell you
• You try to fit the pieces
you have into a familiar
pattern to create a
whole image
Figure-Ground Perception
• The perception of figures
against a background
• our perception can
change depending on
what we interpret as a
background and what we
view as a figure
• We use this method of
perception every day
Proximity
• Grouping objects
because of its
nearness to other
objects
• there is no reason
to group the objects
other than the fact it
is located next to
other objects
Similarity
• The process of
grouping similar
objects together
• People often perceive
of similar objects as
being a part of the
same group, even if
they could be
grouped differently
Continuity
• People prefer to see smooth, continuous
patters rather than disrupted ones
Common Fate
• People or objects that
move together or
perform the same
action must have the
same purpose
• A group of people
running in the same
direction must all be
running to the same
place – they have a
common fate
Perception of Movement
• We perceive movement
when we see an object
move in relation to
other objects
• We look for stable
objects to use as
markers for movement
(buildings, trees, the
sidewalk)
Stroboscopic Motion
• An illusion of movement
• Created by showing a
rapid series of images or
objects that are not
moving, but each image
is just slightly different
than the previous one (flip
books)
• Movies work in a similar
way
Depth
Perception
People use two main cues to
gauge distances
Monocular cues – need only one
eye to be perceived
Perspective, clearness,
overlapping, shadowing are used
to determine which objects are
closer and which are farther away
Binocular cues – need two eyes
to be perceived
Retinal disparity – each retina
captures different images of an
object (finger test)
Convergence – our eyes try to
maintain a single image of an
object and turn inward, or
converge, as the object gets
closer
Constancies
• Everybody
creates
constancies in
their minds
• They are based
on size, color,
brightness and
shape
Size Constancy
• We perceive of an object to
be one size no matter how
far away it is and even
though is creates a differentsized image on the retina
• We base size constancy on
past experiences
• We know that a dog standing
20 feet away is the same
size as if it was right next to
us, even though our eye
senses a smaller image
Color Constancy
• We know that certain
objects do not change
colors even though
we may not be able to
see the colors
• I know my house is
the same color in the
nighttime that it is
during the day even
though I cannot see
its color without light
Brightness Constancy
• We perceive
of an object
as being
equally bright
even when
the intensity
of light
around it
changes
Shape Constancy
• We know that an object does not change shape
even though it may look different from various
angles
• We know that a door is rectangular even though
it may look like a trapezoid from some angles
Visual Illusions
• Sometimes our
constancies cause us
to interpret information
incorrectly
• The visual cues we
use fool our brains
into perceiving objects
as having a different
size, shape, or color
than they actually do