Transcript Sensation and Perception

Sensation and Perception
Sensation: your window to the world
Perception: interpreting what comes in
your window.
Bottom Up and Top Down Processing!
Sensory Adaptation
• Decreased
responsiveness to
stimuli due to constant
stimulation.
• Not hearing the fan in
the room.
• Smell of perfume
diminishes
• Walk into a restaurant
Do you feel your underwear all day?
Cocktail-party phenomenon
• The cocktail party effect
describes the ability to
focus one's listening
attention on a single talker
among a mixture of
conversations and
background noises, ignoring
other conversations.
• Form of selective attention.
Transduction
• Transforming signals
into neural impulses.
• senses thalamus ,
 other brain parts.
Sensation- Thresholds
• Absolute Threshold
– minimum stimulation needed to detect a particular
stimulus
– defined as the stimulus needed for detection 50% of the
time
• Difference Threshold or just noticeable difference (JND)
– minimum difference between two stimuli that a subject
can detect 50% of the time
– increases with magnitude, need more difference with
more weight (Weber’s Law)
• Signal Detection Theory
– No single absolute due to outside factors
– Sentry during war, new mommy, average homebody
Sensation- Thresholds
• Signal Detection Theory
– predicts how and when we detect the presence of a
faint stimulus (signal) amid background stimulation
(noise)
– assumes that there is no single absolute threshold
– detection depends partly on person’s
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experience
expectations
motivation
level of fatigue
Sensation- Thresholds
• Signal Detection Theory
– Assumes TWO things going on:
– 1. sensitivity to stimulus (physical)
– 2. response bias – also called decision criterion
(psychological)
– Can measure & plot these in a Receiver Operating
Characteristic curve (ROC curve)
Sensation- Thresholds
• Weber’s Law- to perceive a difference
between two stimuli, they must differ by a
constant proportion
• a constant for each sense:
– light intensity- 8%, weight- 2%
– tone frequency- 0.3%
– Just noticable difference has a proportion to be
met in order to sense difference
Weber’s Law
• Classic and still identified today but it did not
account for extreme values….175 watt and a
200 watt…
• Ability to recognize difference diminishes….so
in 1860s
Sensation- Thresholds
• Fechner’s Law- “upgrade” of Weber’s law
– includes increase of jnd with extreme
measures/magnitude
– Adding the relationship of the perceived
magnitude to physical intensity of a stimuli
• Same basic idea:
– ½ pound book in 2lb vs. 60lb backpack
– 1 voice in chorus of 10 versus 2 in 20
Sensation- Thresholds
• Steven’s Power Law - upgrade to Fechner
(Fechner’s law didn’t work for pain*, other stimuli)
– Strength of a sensation related to the intensity
of the stimuli raised to some power
– So pain like electric shock you will sense a a
small change at higher intensities than at the
lower intensities when more may be needed to
recognize difference
Stevens
Fechner
Vision
• Our most dominating
sense.
• Visual Capture
• What we see
surpasses what we
feel, taste, smell,
or hear….most seen
in experiments with
hearing
Phase One: Gathering Light
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The height of a wave gives us it’s intensity (brightness).
The length of the wave gives us it’s hue (color).
ROY G BIV – color schemas
The longer the wave the more red.
The shorter the wavelength the more violet.
Phase Two: Getting the light in
the eye
Phase Three: Transduction
Transduction Continued
• Order is Rods/Cones to
Bipolar to Ganglion to
Optic Nerve.
• Sends info to thalamusarea called lateral
geniculate nucleus
(LGN).
• Then sent to cerebral
cortexes.
• Where the optic nerves
cross is called the optic
chiasm.
Pathways from the Eyes to the
Visual Cortex
Phase Four: In the Brain
We have specific cells that see
the lines, motion, curves and
other features of this turkey.
These cells are called feature
detectors.
• Goes to the Visual
Cortex located in
the Occipital Lobe
of the Cerebral
Cortex.
• Feature Detectors.
• Parallel Processing
Retina’s Reaction to Light
• Receptive fields – regions in which receptors
respond to light
• Lateral inhibition – receptor (or neuron) making
it’s neighbors less sensitive
– Helps in things like edge detection
Visual Information
Processing
• Feature Detectors
• neurons in the visual
cortex respond to
specific features
– shape
– angle
– movement
Cell’s
responses
Stimulus
Visual Information Processing
• Parallel Processing
– simultaneous processing of several
dimensions through multiple pathways
– color
– motion
– form
– depth
Visual Information Processing
Abstraction:
Brain’s higher-level cells
respond to combined
information from
feature-detector cells
Feature detection:
Brain’s detector cells
respond to elementary
features-bars, edges, or
gradients of light
Retinal processing:
Receptor rods and
conesbipolar cells
 ganglion cells
Recognition:
Brain matches the
constructed image with
stored images
Scene
Visual Information Processing
• Neural pathways (multiple!)
– Optic nerve through optic chiasm (crossover),
becomes the optic “tract” then…
– Primary visual cortex (striate cortex) then splits
into…
– The “what” path (thru temporal lobes)
– The “where” path (up into parietal lobes)
Color Vision
Two Major Theories
Trichromatic Theory:
Young–Helmholtz theory
Three types of cones:
• Red
• Blue
• Green
• These three types of cones
can make millions of
combinations of colors.
Visual Information Processing – Color
vision
• But Tri-chromatic didn’t explain afterimages or color-blindness!
So…
• Opponent Process Theory
– Black-white receptors (for brightness & saturation)
– Red-green receptors (for hue)
– Blue-yellow receptors (for hue)
Opponent Process- Afterimage
Effect
Color-Deficient Vision
• People who suffer redgreen blindness have
trouble perceiving the
number within the
design
Opponent-Process theory
The sensory receptors
come in pairs.
• Red/Green
• Yellow/Blue
• Black/White
• If one color is
stimulated, the
other is inhibited.
Visual Information Processing
Opponent-Process Theory- opposing retinal processes
enable color vision
“ON”
“OFF”
red
green
green red
blue
yellow
yellow
blue
black white
white black
Afterimages
Visual Information Processing – Color
vision
• So who’s right???
– Turns out they’re both right:
– Tri-chromatic theory works in the retina
– Opponent process works in the higher visual processing
parts of the brain
– Together they explain what we know about color vision
quite well.
Hearing
Our auditory sense
We hear sound WAVES
• The height of the wave gives us the amplitude of the
sound.
• The frequency of the wave gives us the pitch if the sound.
The Ear
Transduction in the ear
• Sound waves hit the eardrum
then anvil then hammer then
stirrup then oval window.
• Everything is just vibrating.
• Then the cochlea vibrates.
• The cochlea is lined with mucus
called basilar membrane.
• In basilar membrane there are
hair cells.
• When hair cells vibrate they
turn vibrations into neural
impulses which are called organ
of Corti.
• Sent then to thalamus up
auditory nerve.
It is all about the vibrations!!!
Pitch Theories
Place Theory and Frequency Theory
Place Theory
• Different hairs
vibrate in the
cochlea when they
different pitches.
• So some hairs
vibrate when they
hear high and other
vibrate when they
hear low pitches.
Frequency Theory
• All the hairs vibrate
but at different
speeds.
Deafness
Conduction Deafness
• Something goes wrong
with the sound and the
vibration on the way to
the cochlea.
• You can replace the
bones or get a hearing
aid to help.
Nerve (sensorineural)
Deafness
• The hair cells in the cochlea
get damaged.
• Loud noises can cause this
type of deafness.
• NO WAY to replace the hairs.
• Cochlea implant is possible.
Touch
• Receptors located in
our skin.
• Gate Control Theory
of Pain
Taste
• We have bumps on
our tongue called
papillae.
• Taste buds are
located on the
papillae (they are
actually all over the
mouth).
• Sweet, salty, sour
and bitter.
Vestibular Sense
• Tells us where our
body is oriented in
space.
• Our sense of
balance.
• Located in our
semicircular canals
in our ears.
Kinesthetic Sense
• Tells us where our
body parts are.
• Receptors located in
our muscles and
joints.
Without the kinesthetic sense
you could touch the button to
make copies of your buttocks.