Transcript Sensation and Perception

Sensation and
Perception
• Sensation – the process of detecting physical
energy and transforming it into neural signals
– This transformation process is called transduction
• Perception – selecting, organizing, and interpreting
sensations
• Do we see the world as it actually is?
– Nope.
• The world we see is a construct of our minds. There is
no color. There is no sound.
• Bottom up processing – Sensation to perception.
Body to brain.
• What is the smallest amount of something
you can sense?
• Absolute threshold – the minimum amount
of stimulation you can detect 50% of the
time
• Try it..
• Some common absolute thresholds include:
• Why “50% of the time?”
• Signal Detection Theory – our ability to sense
things is influenced by our:
– Experience – some people are trained to
detect specific things (police officers)
– Expectations – you may/may not be
ready (clowns)
– Motivation – you may/may not care
– Level of fatigue/alertness – you might be
tired
Subliminal messages
• Can we be influenced by things below our
absolute threshold?
• Can we be manipulated through subliminal
messages?
• Yes and no
• They may have a brief effect
– Priming
• Studies have shown that subliminal
messages do not produce a lasting
outcome
A_ _OM_BI_E
• How much does a stimulus have to change
before we notice a difference?
• For example, how bright does a light need
to be before we can tell it is brighter? How
much does a sound need to change before
we can tell it is louder?
• Difference Threshold/Just Noticeable
Difference (JND)- minimum difference
between two stimuli required for detection
50% of the time
• A quick experiment..
• Weber’s Law – to be perceived as different,
two stimuli must differ by a constant
minimum percentage
• In other words, it’s not the amount of stimuli
that matters, it’s the percentage; it’s the
ratio of the second stimulus to the first
• Light intensity – 8%
• Weight – 2%
• Tone frequency - .3%
Other examples
• Suit and sweater, which first?
• New cars
Sensory Adaptation
• Diminished sensitivity as a result of constant
stimulation
• Do you notice the chair pressing against
your legs?
• If you put a band aide on, very soon you
won’t notice it
• So then if you stare at something, shouldn’t it
disappear as the sense receptors in your eye
become used to it?
Yes
It should..
It would..
But…
Your eyes are always moving, even when
you stare
• Try this…
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Phototransduction
• Conversion of light energy into neural
signals the brain can understand
Light and color
• Light can behave as a wave or a particle
• Wavelength – the distance from the peak of one
wave to the peak of the next
• Hue (color) – dimension
determined by the wavelength of
light
Wavelength (Hue)
Violet
Indigo
400 nm
Short wavelengths
Blue
Green
Yellow
Orange
Red
700 nm
Long wavelengths
Different wavelengths of light result
in different colors.
• Intensity – amount of energy in a wave,
determined by amplitude (i.e. how “bright”
a light is)
Intensity (Brightness)
Blue color with varying levels of intensity.
As intensity increases or decreases, blue color
looks more “washed out” or “darkened.”
The spectrum of
electromagnetic
energy
Parts of the Eye
Cornea – outer covering
Pupil – adjustable opening in center of eye
Iris – muscle that controls the pupil
Lens- transparent structure behind the iris
that changes shape to focus images
• Retina – inner surface of the eye. Contains
receptor rods and cones, and a bunch of
other neurons (bi-polor, ganglion cells)
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 Rods
 peripheral retina
 detect black, white and gray
 twilight or low light
 Cones
 near center of retina
 fine detail and color vision
 daylight or well-lit conditions
Rods
Cones
• Nearsightedness – nearby objects are seen
more clearly
• Farsightedness – faraway objects are seen
more clearly
• Optic nerve- carries neural impulses
from the eye to the brain
• Fovea- central point in the retina,
where the eye’s cones cluster
• Blind spot
• See if you can find your blind spot..
Processing visual
information
Feature Detection
• Parallel processing – processing
several aspects of a problem
simultaneously
• Blindsight – seeing without seeing.
Huh?
Color Vision
• Trichromatic theory (Young-Helmholtz) – since any
color can be created by combinations of red, blue,
and green, the eye must have three types of
receptors for these three colors
• Subtractive- subtracts wavelengths from the
reflected light
• Additive
Color blindness
• 8% of males show a color
weakness, but only .05% of
females
• Who’s better at discriminating
color?
• Why?
Opponent-Processing
theory
• Yellow is a mixture of red and green
light, but people blind to red and
green can often see yellow. How is this
possible?
• Afterimages
After Images
• Stare at the eye of the red parrot while you slowly count to 20, then
immediately look at one spot in the empty birdcage. The faint, ghostly
image of a blue-green bird should appear in the cage.
Opponent Colors
Gaze at the middle of the flag for about 30
Seconds. When it disappears, stare at the dot and report
whether or not you see Britain's flag.
Complementary
Afterimages
• In the nervous system, color processing
cells are grouped together like this:
• Red-green
• Blue-yellow
• Black-white
• When you stare at one color, you
exhaust that receptor, so when you
look at a white page, you see the
opponent color
Opponent Process Theory
Hering proposed that we process four primary
colors combined in pairs of red-green, blueyellow, and black-white.
Cones
Retinal
Ganglion
Cells
Color Constancy
• Color is relative
• The color you see depends on the context
Hearing (audition)
What causes sound?
• Molecules bump into each other at different rates,
causing small changes in air pressure. Your brain
converts these changes to neural impulses that
interprets as sound
• Sound energy is measured in decibels
• Absolute threshold for hearing is 0 decibels, a loud
thunder crack is 120
120dB
Parts of the ear
• Sound travels through your outer ear and causes
your eardrum to vibrate
• these vibrations are then transferred to the middle
ear where they cause three bones – called the
hammer, the anvil, and the stirrup – to vibrate
• The vibrations cause the fluid in the cochlea to
ripple
• These ripples bend tiny hair cells
• The hair cells send neural messages to the brain
• = hearing
• Loudness is determined by the number of activated
hair cells
• Pitch
• Place theory
• Frequency theory
How does the brain locate
sounds?
Hearing loss
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Conduction hearing loss
Nerve hearing loss
Cochlear implants
Sensory compensation
• Sensory interaction
Touch
• Mixture of pressure, warmth, cold, and pain
• Only pressure has specific nerve receptors
• Touch localization
Pain
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A product of the body and the brain
Gate control theory
Sensitivity to pain
People who feel no pain
Pain control
Taste
• Chemical sense
• Taste buds
o Regeneration
• Super tasters
Taste
Traditionally, taste sensations consisted of sweet,
salty, sour, and bitter tastes. Recently, receptors
for a fifth taste have been discovered called
“Umami”.
Sweet
Sour
Salty
Bitter
Umami
(Fresh
Chicken)
Taste
• Your sensitivity to taste will decline if you:
o Smoke heavily
o Consume large amounts of alcohol
o Grow older
Taste
• Culture and taste preferences:
Smell
• Peaks in early adulthood and then declines (like the
other senses)
• Chemical sense (receptor cells in nasal cavity)
• Not filtered by thalamus
• Smell and memories
• Who has the best
sense of smell?
• Subliminal smells
• T-Shirt experiments
Number
of correct
answers
Women and young adults
have best sense of smell
4
Women
3
Men
2
0
10-19
20-29
30-39
40-49
50-59
60-69
Age Group
70-79
80-89 90-99
Body Position
• Kinesthesis
• Vestibular sense