Basic Principles of Sensation and
Perception
Sensation vs. Perception
• Basketball Study:
http://www.youtube.com/watch?v=vJG698U2
Mvo
• Inattentional Blindness = inability to see
an object or a person in our midst.
Intuitively, we think that as long as our eyes
are open, we are seeing. Research beginning
with Ulrich Neisser’s “basketball study,” has
clearly indicated that visual perception is not
like a videotape.
Sensation vs. Perception
Sensation /Bottom-Up Processing
• The stimulation of sensory
receptors (cilia in ears,
rods/cones in vision, taste
buds) by the properties of
the stimulus (sound waves,
light energy, chemicals) and
the transmission of sensory
information into the central
nervous system
Perception/Top-Down Processing
• The process by which the
brain organizes and
interprets the data received
from the senses, enabling us
to recognize meaningful
objects and events.
• Interpreting what we sense
based on prior knowledge or
context
Psychophysics = study of the relationship between
physical characteristics of stimuli and our psychological
experience of them (light  brightness, sound  volume,
pressure  weight, taste  sweetness)
Sensation vs. Perception
Bottom-Up Processing
Analysis of the stimulus begins with the
sense receptors and works up to the
level of the brain and mind.
Picture is really black and white
blotches broken down into features by
the brain
Top-Down Processing
Information processing guided by
higher-level mental processes as we
construct perceptions, drawing on
our experience and expectations.
Based on expectations, context or “love
of dogs”, we make meaning out of
the black and white blotches and
perceive a dog.
What is this picture?
4
Sensation vs. Perception
Bottom-Up Processing
Analysis of the stimulus begins with the sense receptors and works up to the level of
the brain and mind.
Letter “A” is really a black blotch broken down into features by the brain that we
perceive as an “A.”
Top-Down Processing
Information processing guided by higher-level mental processes as we
construct perceptions, drawing on our experience and expectations.
THE CHT
5
Sensation/Perception
• Transduction: sensory receptors (eyes, ears, nose, skin,
tongue) convert the stimulus into neural impulses which
are sent to the brain
• EX: Receptor cells in the inner ear convert sound
waves/vibrations into electrochemical signals. These
signals are carried by neurons to the brain
Process of Sensation and Perception
1. Any change in energy in environment creates stimuli
(light waves, sound vibrations, pressure)…
2. which activates receptor cells of sense organs (eye,
ear) to trigger electrical signals or impulses…
3. which are transformed by the brain into…
4. sensations or meaningless bits of sensory
information…
5. to which experience automatically adds meanings,
feelings, and memories…
6. which result in meaningful patterns or images known
as perceptions.
Sensation & Perception Don’t “Just Happen”
Sensation
 Light bounces off Lemon
 Light forms image of Lemon
on retina (upside down)
 Image generates electrical
signals in receptors
 Signals travel along nerve
fibers to the brain...
Perception
Signals are processed and you “perceive” Lemon
Detection
Absolute
Threshold
Intensity
No
No
No
Yes
Yes
Observer’s Response
Detected
Tell when you (the observer) detect the light (50% of the time).
9
Absolute Thresholds
100
Percentage
of correct
detections 75
50
Subliminal
stimuli
25
0
Low
Absolute
threshold
Medium
Intensity of stimulus
Sensing the World: Basic Principles
• Absolute Threshold = the lowest amount of stimulus needed to notice
it 50% of the time.
– Measure absolute threshold by recording the stimulation needed
for us to pinpoint its appearance 50% of the time
– As stimulus intensity increases, subjects’ probability of responding
to stimuli gradually increases
– There is no single stimulus intensity at which the subject jumps
from no detection to completely accurate detection  not really
“absolute” or constant. Threshold varies within a person over
time – due to changing psychological states, hormone levels,
sensory adaptation, etc
– EX: You turn down the radio to a point where you only hear the
faint sound half the time. Then that loudness (decibel) is your
absolute threshold for sound.
– EX: The level of heat on a car heat warmer to feel it half the time.
– EX: Lemon Lab – the number of lemons it takes to smell the scent
of lemons in a room half the time
Sensing the World: Basic Principles
• Difference Threshold (just noticeable difference
or jnd) = the lowest difference between two
stimuli that person can detect 50% of the time.
• EX: A musician must detect minute discrepancies
in an instrument’s tuning
• EX: A wine taster must detect the slight flavor
difference between two vintage wines
• EX: Parents must detect the sound of their own
child’s voice amid other children’s voices
• EX: Lemon Lab – students must detect the slight
weight, firmness, size, etc between the lemons.
Difference Threshold
Difference Threshold: Minimum difference
between two stimuli required for detection 50%
of the time, also called just noticeable difference
(JND).
Difference
Threshold
No
No
Yes
Observer’s Response
Tell when you (observer) detect a difference in the light. (50% of the time)
Light intensity – the two light bulbs must differ by 8% (Weber’s Law)
13
Sensing the World: Basic Principles
• Weber’s Law = regardless of magnitude, two stimuli must
differ by a constant proportion for the difference to be
noticeable.
• Light intensity – 8%
• Tone frequency - .3%
• Weight – 2%
– EX: Lemon Lab – if you lemon weighs 6 oz then the next
lemon will have to weigh .12 oz heavier or .12 oz lighter in
order to detect the difference between lemon
– JND varies according to the strength or intensity of the
original stimulus. The greater the stimulus the greater the
change necessary to produce JND
• EX: If a farmer grows giant lemons, a greater difference
threshold will be needed to determine a change from a
500 oz lemon, such as a change of 10 oz versus .12 oz
with a 6 oz lemon.
Sensing the World: Basic Principles
• Fechner’s Law – larger and larger increases in stimulus intensity are
required to produce perceptible increments in the magnitude of
sensation. Constant increments in stimulus intensity produce smaller
and smaller increases in perceived magnitude of sensation.
• Scene #1: dark room – add one light bulb – difference in light is
striking
• Scene #2: same room – add a second light bulb – the amount of light
is doubled but the room does not seem twice as bright
• Scene #3: same room – add a third light bulb, it adds just as much
light as the second, but you barely notice the difference
• Three equal increases in stimulus intensity produces
progressively smaller differences in the magnitude of sensation
Sensing the World: Basic Principles
• Sensory Adaptation = lowered sensitivity due to constant
exposure from a stimulus. After constant exposure to a
stimulus, our nerve celss fire less frequently
– EX: 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
– EX: forget your sunglasses are on the top of your head.
– EX: Lemon Lab – students toward the end had a harder time
detecting their lemon
Sensing the World: Basic Principles
• Signal Detection Theory – predicting when we will notice a weak
stimulus (signal). Detecting a weak signal depends on:
1. Signal’s strength
2. Our internal psychological state (experience, motivation, and
fatigue)
 Absolute threshold is not really “absolute”! Absolute Threshold
varies depending on the level and nature of ongoing sensory
stimulation; differs moment to moment and person to person
– EX: exhausted parents of a newborn will notice the faintest
whimper from the cradle, while failing to notice louder,
unimportant sounds.
– EX: On a dark night, on a lonely street, a twig snapping might
trigger a stimulus that wouldn’t fire if it were light and busy.
– EX: Lemon Lab – fatigue, embarrassment, motivation among
students can influence the detection of the lemon
Sensing the World: Basic Principles
• A stimulus is Subliminal if it is below your absolute
threshold, you detect it less than 50% of the time.
100
Percentage
of correct
detections
75
50
Subliminal
stimuli
25
0
Low
Absolute
threshold
Intensity of stimulus
Medium
Not always about
unconscious processing,
just means below
absolute threshold
(consciously detect a
weak stimulus some of
the time)
Vision
Visual Processing: SENSATION->light waves cornea pupil
(iris) lens retina (rods and cones – Begin Color trichromatic
theory bipolar ganglion – 1st stage of Color opponent process)
optic nerve (blind spot) thalamus occipital lobe (visual cortex – end
of Color opponent process ) feature detectors abstraction (cells in
parietal and temporal lobe combine info from feature detectors)
PERCEPTION
Acuity = sharpness of vision
- Nearsightedness = nearby objects seen more clearly; lens
focuses image of distant objects in front of retina
- Farsightedness = faraway objects seen more clearly; lens
focuses near objects behind retina
 Farsighted
Vision
Nearsighted
Vision
Normal
Vision
Nearly a million messages can be sent by the optic nerve at once, through nearly 1
million ganglion fibers.
One cone often synapses onto one bipolar and ganglion cell, while the axons of many
rods have to share one bipolar and ganglion cell  allows cones to be more senstivie
to detail.
Union of Opposites: Rods and cones are responsible for
transduction - the transformation of stimulus energy
(sights, sounds, smells) into neural impulses.
Blind Spot: Point where the optic nerve leaves the eye because
there are no receptor cells located there.
Blind Spot Activity – Cover one eye and hold up a
finger at arm’s length. Have them focus straight
ahead and move the finger about two palm widths
25
to the side until it disappears.
Hermann Grid
Hermann Grid
4 bright patches in the inhibitory
surround  inhibits cell, less neural
activity so seems less bright
Look directly at intersection,
the OFF and ON regions are so
small that both fit within the
width of a strip. Thus, all the
cells around the region of
fixation give the same response,
whether in the intersection or
not
2 bright patches in the inhibitory
surround  less inhibition so more neural
activity
Motion Aftereffects
• Waterfall Illusion:
http://www.michaelbach.de/o
t/mot_adapt/index.html
– Fixing gaze  sensory
adaptation (over-stimulate cells
that detect outward movement)
– Shift gaze  when the
outward-movement detectors
stop firing, there is a tendency
for inward-movement detectors
to start firing for a few seconds
*Motion Blindness:
• http://www.michaelbach.de/o
t/mot-mib/index.html
(-)
(+)
(-)
Activated by
outwardmovement
Activated by
inward-movement
 Parallel Processing
 simultaneous
processing of several
aspects of a problem
simultaneously
 the brain divides a
visual scene into
subdivisions such as
color, depth, form,
movement, etc.
 Feature Detectors
 nerve cells in the visual
cortex respond to
specific features
 shape
 angle
 movement
Visual Information Processing
Retinal Processing
Rods & Cones Bipolar Cells Ganglion Cells
Feature Detection
Detector cells respond to elementary features
Abstraction
High-level cells respond to combined info
from feature-detector cells
Recognition
Brain matches the constructed image with stored images
From Sensation to Recognition
33
Color Vision
Do objects possess color?
Is a lemon “yellow”?
NO!
Light has no color – brain
constructs color from the
variations in light waves
reflected from objects
Is a chili pepper “red”?
Two basic types of color mixing: Psychophysics!
1. subtractive color mixture - combining different color paints
Different pigments subtract different wavelengths: red subtracts all
but red, blue all but blue, green subtracts blue and red, etc…
2. additive color mixture - combining different color lights.
By combining lights of different wavelengths we can create the
perception of new colors. Examples: red + green = yellow; red +
blue = purple; green + blue = cyan; red + blue + green = white
http://www.michaelbach.de/ot/col_mix/index.html
• Hue (color) = dimension of color determined by the wavelength of
light (the distance from the peak of one wave to the peak of the next
wave). Visible light has wavelengths from about 400nm to 700nm
• Intensity (brightness) = amount of energy in a wave determined by
the amplitude.
• Saturation = richness or purity of light determined by the
smoothness or complexity of the waves
Most humans can distinguish 7
million different color shades
Wavelength (hue) - different wavelengths of light result
in different colors.
Violet
Indigo
400 nm
Short wavelengths
Blue
Green
Yellow
Orange
Red
700 nm
Long wavelengths
Intensity (brightness) - Blue color with varying levels of
intensity. As intensity increases or decreases, blue color
looks more “washed out” or “darkened.”
37
Color Perception pg 418
• Humans are able to discriminate 7 million different
hues.
• Colors convey important information:
– Ripeness of food
– Danger signals
• Trichromatic theory (1st stage, occurring at the level
of cones)
– Eye contains 3 different color sensitive elements
• Blue, green or red elements
• Trichromatic theory accounts for color mixing of lights.
• Opponent-Process theory (2nd stage, occurring
further on in the visual system
– Visual system is organized into red-green, blue-yellow and
black-white units.
• Theory can account for negative color afterimages.
Trichromatic Theory of Color Vision
Human eye has 3 types of cone
receptors sensitive to different
wavelengths of light.
Short
Helmholtz 1852
Medium
Long
People see colors because the
eye does its own “color mixing”
by varying ratio of cone
neural activity
Theories of Color Vision: Trichromatic Theory
Wavelength Input
Cone
“Blue”
“Green”
“Red”
Signal to Brain
Blue
Equal
Parts
Red and
Green =
Yellow
Theories of Color Vision: Trichromatic Theory
•
Trichromatic Theory can explain some aspects
of colorblindness:
– most of us are trichromats
– someone missing one of the three cone
types is a dichromat
• dichromats have only two primaries:
any color they can see can be
matched with differing proportions of
the two wavelengths to which they
are sensitive
• most common is deuteranopia (~3%
of men, <1% of women) - missing
“green” cones
• cannot see color difference between
reds and greens - but they can see
luminance difference
– someone missing two is a monochromat
– someone missing all cone types is called a
rod monochromat (very poor vision!)
People who suffer red-green
blindness have trouble
perceiving the number within
the design
Some Views With and
Without Color Vision
44
Link Jay and Maureen Neitz Color Vision Page
Theories of Color Vision: Opponent-Process Theory
Theories of Color Vision: Opponent-Process Theory
Double Opponent Cells in V1
G+R-
Y+B-
R + G-
B+Y-
R + G-
B+Y-
G+R-
Y+B-
Red/Green
Blue/Yellow
Opponent Process- Afterimage Effect
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.
Explaining Complementary Afterimages
• white normally stimulates the red and green
cells equally
• exposure to green fatigues the green cell
while the red cell rests
• exposure to white NOW causes red
receptor to respond but green receptor is
“tired”
• we see red instead of white
Opponent Process – Afterimage Effect
 Color Constancy
 Perceiving familiar
objects as having
consistent color, even
if changing
illumination alters the
wavelengths reflected
by the object
 Visual Pathway
Review Activity
“If a tree falls…”
If a tree falls in the
forest and there is nobody
around to hear it…
Does it make a noise?
NO…Sound (like color) is all in your head!
What is Sound? Compression & expansion (rarefaction) of
air molecules.
Pitch – high or lowness of sound
• The greater the number of cycles per second, the higher the pitch.
Longer the wave = lower the pitch / Shorter the wave = higher the
pitch
• Frequency – number of cycles per second as expressed in the unit Hertz.
• Hertz – A unit expressing the frequency of sound waves. One Hertz, or
1Hz, equals one cycle per second.
• Human hearing  detect sounds ranging in frequency from
20Hz – 20,000Hz
Pitch and Age
Presbycusis: Older people tend to hear low frequencies
well but suffer hearing loss for high frequencies
https://www.youtube.com/watch?v=VxcbppCX6Rk
Loudness
• The higher the amplitude of a wave, the louder the sound.
• Amplitude – strength or height of wave.
• Decibel – A unit expressing the loudness of a sound,
abbreviated dB.
• Perceived loudness doubles about every 10 decibels.
The absolute threshold for hearing is arbitrarily
defined as 0 decibels.
Loudness of Sound
Richard Kaylin/ Stone/ Getty Images
120dB
58
70dB
Highest Frequency? Loudest? Highest
Amplitude? Highest Pitch?
A.
B.
C.
The Ear
Outer Ear - acts as a funnel to direct sound waves towards inner structures
Middle Ear - consists of three small bones (or ossicles) that amplify the
sound
Inner Ear - contains the structures that actually transduce sound into neural
61
response
Outer Ear
Pinna - collect and direct “sound” into auditory canal
Auditory Canal (ear canal) - amplify and funnel “sound to
tympanic membrane
Tympanic Membrane – collect “sound” and vibrate ossicles
Middle Ear
Malleus (Hammer) - vibrate & move the Incus
Incus (Anvil) - vibrate & move the Stapes
Stapes (Stirrup) - vibrate against Oval Window of
Cochlea
Inner Ear
Cochlea - filled with fluid & contains
receptors for hearing (Hair Cells)
Basilar Membrane – divides length
of cochlea and holds the hair cells
*Semicircular Canals=Vestibular Senses (Balance and Equlibrium)
Closer Look at the Cochlea
-The structures of the ear transform changes in air pressure
(sound waves) into vibrations of the Basilar Membrane.
-As the Basilar Membrane vibrates it causes the hairs in the
Hair Cells to bend.
-The bending of the hairs leads to a change in the electrical
potential within the cell
Perceiving Pitch (Class Demo)
Place Theory (Traveling Wave Theory)
= pitch determined by point of maximal vibration on basilar membrane.
Different pitches activate different places of the cochlea’s basilar membrane.
Only applicable to high pitched sounds – over 5000 Hz
(low pitched sounds do not localize as well)
Frequency Theory
= frequency of a tone (or pitch) matches the rate
at which the hair cells fire or the rate of nerve
impulses
traveling up the auditory nerves (i.e., 1KHz tone
cause
hair cells to fire 1k times/sec)
Only applicable to sounds under 1000 Hz
(individual neurons cannot fire faster than 1000
times/sec)
Therefore Volley Theory (1000-5000Hz)
= receptors in the ear fire in sequence. Several
neurons together, firing in sequence, can send a
more rapid series of impulses to the brain than one.
Localization of Sounds
Sound Shadows (Class demos) Clack & Tube
We locate a sound by sensing differences in the speed and
intensity with which it reaches our ears.
The head acts as a “shadow” or partial sound barrier. A sound that
comes from directly ahead will be harder to locate than a sound
that comes from off to one side.
Because we have two ears,
sounds that reach one ear faster
than the other ear cause us to
localize the sound.
Time differences as small as
1/100,000 of a second can cause
us to localize sound.
67
Hearing Loss
Conduction Deafness
•
•
•
•
Caused by the failure of the three tiny bones inside the middle ear to pass along sound
waves to the inner ear or the failure of the eardrum to vibrate in response to sound
waves
Possible cause is a build-up of fluid
Hearing aids - amplifies sound (many people lose sensitivity to soft sounds but not
loud sounds – unfortunately, some hearing aids amplify all sounds)
Normal hearing may return.
Sensory-Neural Deafness
• Damage to the inner
ear. Most often caused
by loss of hair cells
that will not
regenerate.
• Damage to the
auditory nerve.
• Cochlear implants can
help patients with this
form of deafness.
Tinitus:
http://www.youtube.com/watch?v
=OE5fIoveLoM
Stimulation Deafness
• Exposure to very loud
sounds
• Prolonged exposure to
85 dB can cause
stimulation loss.
• Tinnitus - ringing
sound can mean hair
cells have been
damaged
Touch
Touch
Sensory receptors located around the roots of hair cells fire when surface of
skin is touched (mechanical and thermal energy).
The sense of touch is a mix of four distinct skin senses—pressure, warmth, cold,
and pain.
Only pressure has identifiable receptors. All other skin sensations are
variations of pressure, warmth, cold and pain.
Two pathways: #1 – signals from thermal receptors + pain signals; #2 – signals
from tactile stimulation (pressure)
Hot = warm ( firing)
+cold ( firing)
Wet = pressure + cold
Tickling itch = pressure
+ pain
74
Sensory Homunculus
Homunculus - Latin for
"little human“; any
representation of a human
being.
The Motor Cortex is the
area at the rear of the
frontal lobes that
control voluntary
movements. The
Sensory Cortex
(parietal cortex)
receives information
from skin surface and
sense organs.
Sensory Homunculus
• Two-Point Threshold – to assess sensitivity to
pressure - the least distance by which two rods
touching the skin must be separated before the
subject will report that there are two rods, not one,
on 50% of occasions
• Most sensitive – fingertips, lips, noses and cheeks
1. nerve endings are more densely packed in the
fingertips and face than in other locations
2. a greater amount of sensory cortex is devoted to the
perception of sensations in the fingertips and face
Gate-Control Theory
Spinal cord contains neurological “gates” that
either block pain or allow it to be sensed.
•
•
•
•
Small fibers (pain + temp) = open gate =
pain. When tissue is injured, the small fibers
activate and open the neural gate
– Slow pathway – lags a second or two
behind the fast system; longer lasting,
aching pain
– Fast pathway – registers pain and relays
it to the cortex in a fraction of a second
Large fibers (tactile – pressure or
vibration) = close gate = no pain.
– Stimulate (massage, rub, acupuncture)
gate closing activity to treat pain.
– Also closed by signals from the brain –
attention and expectations
Endorphins can also close gate
Brain (attention and expectations) also 77
close
gate
Biopsychosocial Influences
78
Phantom Limbs
• How do you Amputate a • Phantom Limbs = involves
Phantom Limb?
feeling pain in a limb after it has
• http://www.npr.org/templ
been amputated
ates/story/story.php?stor • The awareness we have our
yId=101788221
physical self is constructed by
the brain. How our body feels
depends on the maps of the
body that are held within our
brain and emerges as a
conscious output. People with
pathological pain have distorted
maps of the body
Body Integrity Identity Disorder
• BIID = relentless desire
to amputate healthy
limbs.
• Lobby for surgery as a
safe and legal option to
remove body part
• Medical Mysteries
Clip
• Determined to
Amputate: One
Man's Struggle With
Body Integrity
Identity Disorder
• http://www.foxnews.c
om/story/0,2933,5208
11,00.html
Taste
Traditionally, taste sensations consisted of sweet,
salty, sour, and bitter tastes. Recently, receptors for
a fifth taste have been discovered called “Umami”.
Sweet
Bitter
Sour
Salty
Umami
(Savory/Meaty)
http://www.npr.org/templates/story/story.php?storyId=1813416
Study: Tastes Form in Infancy
81
Smell
Like taste, smell is a chemical sense. Odorants
enter the nasal cavity to stimulate 5 million
receptors to sense smell. Unlike taste, there are
many different forms of smell.
82
Smell and Memories
The brain region for
smell (in red) is closely
connected with the
brain regions involved
with memory (limbic
system). That is why
strong memories are
made through the sense
of smell.
83
Sensory Interaction
When one sense affects another sense, sensory
interaction takes place. So, the taste of strawberry
interacts with its smell and its texture on the
tongue to produce flavor.
FLAVOR DEPENDS ON…
•Temperature
•Odor
•Texture
•Taste
(I T.O.T.T. you about flavor)
84
KINESTHESIS – The sense that informs us about the positions and motion of
parts of our bodies
VESTIBULAR SENSE – The sense of equilibrium that informs us about the
positions of our bodies and our heads relative to gravity; sense of balance
Read “The Remarkable Case of Ian Waterman” on page 31
Visual Capture
• When vision competes with our other
senses, vision usually wins – a
phenomena called visual capture.