 Psychophysics
 Thresholds (include JND)
 Attention and discrimination
 Inattentional blindness
 Change blindness
 Pop-out phenomenon
 Stroop Effect
Sensation & Perception
How do we construct our representations of the
external world?
To represent the world, we must detect physical
energy (stimulus) from the environment and convert it
into neural signals, a process called sensation.
When we select, organize, and interpret our sensations,
the process is called perception.
• Studies the links between physical stimuli in
the world and the psychological experience of
those stimuli
• Fechner, Wundt, Titchener, Weber
• Among the earliest research to be conducted
in the field of Psychology
Bottom-up Processing (sensation)
Analysis of the stimulus begins with the sense receptors
and works up to the level of the brain and mind.
Letter “A” is sensed as a black blotch decomposed into
features by the brain and perceived as an “A” by our mind .
Top-Down Processing (perception)
Information processing guided by higher-level
mental processes as we construct perceptions
drawing on our experience and expectations.
Making Sense of Complexity
Our sensory and perceptual processes work
together to help us sort out complex images.
“The Forest Has Eyes,” Bev Doolittle
Exploring the Senses
What stimuli cross our threshold for conscious
Could we be influenced by stimuli too weak
(subliminal) to be perceived?
Why are we unaware of unchanging stimuli, like a
band-aid on our skin or the feeling from our
Absolute Threshold: Minimum stimulation needed to
detect a particular stimulus 50% of the time.
For example, young children generally have a lower
absolute threshold for sounds since the ability to detect
sounds at the lowest and highest ranges tends to
decrease with age.
Subliminal Threshold
When stimuli are below one’s absolute threshold for
conscious awareness.
Detect it less than 50% of the time
Difference Threshold
Difference Threshold: Minimum difference between
two stimuli required for detection 50% of the time,
also called just noticeable difference (JND).
For example, if you were asked to hold two objects of
different weights, the just noticeable difference
would be the minimum weight difference between
the two that you could sense half of the time.
Weber’s Law explains the JND
Two stimuli must differ by a constant minimum
proportion (rather than a constant amount), to be
perceived as different. Weber fraction: k = dI/I.
Constant (k)
Signal Detection Theory
• Predicts when we will detect weak signals
• Ask why people respond differently to the
same stimuli??
• Why does the same person’s response vary as
the circumstance changes
• Sensitivity and responsiveness increases with
emotional state
• Example: Hearing your baby cry…
Sensory Adaptation
Diminished sensitivity as a consequence of constant
stimulation. Sometimes referred to as habituation
Put a band aid on your arm and after a while
you don’t sense it.
Selective Attention
Perceptions about objects change from moment to
moment. Different forms of Necker cube become
available to our perception, however, one can pay
attention only to one aspect of the object.
Necker Cube
Selective Attention
• Discrimination
– we have the ability to filter out stimuli rather
than process every single stimuli that is
bombarding our sensory receptors, will be helpful
in conditioning (learning by association)
• Cocktail party effect
– the ability to focus one's listening attention on a
single talker among a mixture of conversations
and background noises, ignoring other
Inattentional Blindness
Inattentional blindness refers to inability to see a an
object or a person amidst an engrossing scene.
Keep your eye on the ball and count how many times
the team with the white shirts passes it…
Change Blindness
Change blindness is a form of inattentional blindness,
where two-thirds of direction giving individuals failed
to notice a change in the individual who was asking
for directions.
Pop-out phenomenon
• A powerful and distinct stimulus demands our
• We don’t choose to see them, can’t ignore it
• A type of automatic processing
Automatic processing
Controlled processing
Stroop Effect
• Our brain can process information faster
when it is presented in the way we expect it
• When too many areas of our brain are active,
we have a pause in our processing
• Try
Name the color of the font
AP stuff
• Stimulus attention
– Selective attention (cock-tail party)
– Stimulus discrimination
– Habituation
• Thresholds
– Absolute (detectable greater than 50% of time)
– Subliminal (detectable less than 50% of time)
– Just noticeable difference (Weber’s Law)
• It’s a proportion of the original stimulus
Types of Transduction
Light and Sound Characteristics
Parts of the eye
The process of vision
Cells within the retina
Shape Detectors and Feature Detectors
Theories of vision
In sensation, transformation of stimulus energy into
neural impulses.
Phototransduction: Conversion of light energy into
neural impulses that brain can understand
(the rods and cones in the retina)
Auditory/Acoustic transduction: Conversion of
sound waves into neural impulses (the cilia in the
Light Characteristics
1. Wavelength (hue/color)
2. Intensity (brightness)
3. Saturation (purity)
Wavelength (Hue)
Hue (color):
dimension of color
determined by
wavelength of
Wavelength the
distance from the
peak of one wave
to the peak of the
Intensity (Brightness)
Amount of
energy in a
determined by
related to
The Eye
Parts of the eye
Cornea: Transparent tissue where light enters the
Iris: Muscle that expands and contracts to change
the size of opening (pupil) for light.
Lens: Focuses the light rays on the retina.
Retina: Contains sensory receptors that process
visual information and send it to the brain.
The Lens
Lens: Transparent
structure behind pupil
that changes shape to
focus images on the retina.
Accommodation: The
process by which the eye’s
lens changes shape to help
focus near or far objects
on the retina.
The Lens
Nearsightedness: A
condition in which
nearby objects are seen
more clearly than distant
Farsightedness: A
condition in which
faraway objects are seen
more clearly than near
Retina: The lightsensitive inner
surface of the eye,
receptor rods and
cones plus layers of
other neurons
(bipolar, ganglion
cells) that process
visual information.
Bipolar & Ganglion Cells
Bipolar cells receive
messages from the
photoreceptor cells
(rods and cones) and
transmit those messages to
ganglion cells which have
long axons that are
intertwined and
form the optic nerve.
Optic Nerve, Blind Spot & Fovea
Optic nerve: Carries neural impulses from the eye to the brain.
Blind Spot: Point where optic nerve leaves the eye, because
there are no receptor cells located here, it creates a blind spot.
Fovea: Central point in the retina, around which the eye’s
cones cluster.
Test your Blind Spot
Use your textbook. Close your left eye, and with the
right eye fixate on the black dot. Move the page
towards and away from your eye. At some point the
car on the right will disappear due to blind spot.
Or, take a piece of paper, roll it up, look through it
with one eye and bring your opposite hand next to
the paper. There should be a hole in your hand!!!!
(thanks Emilie B.)
E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969
Why don’t they see which color it is?
Feature Detection
Nerve cells in the visual cortex respond to specific
features, like edges, angle, and movement.
Feature detectors allow us to see the lines, motion,
curves of this power point slide
What happens when you overwhelm these
feature detectors?
Watch the center of the spiral…
Shape Detection
Ishai, Ungerleider, Martin and Haxby/ NIMH
Specific combinations of temporal lobe activity occur
as people look at shoes, faces, chairs and houses.
Perception in Brain
Our perceptions are a combination of sensory
(bottom-up) and cognitive (top-down) processes.
Visual Information Processing
Processing of several aspects of the stimulus
simultaneously is called parallel processing. The brain
divides a visual scene into subdivisions such as color,
depth, form and movement etc.
Watch the car video closely and note the different forms of
processing that are occurring simultaneously…
2 Theories of Color Vision
Trichromatic theory: Based on behavioral
experiments, Young-Helmholtz suggested that
retina contains three receptors sensitive to red, blue
and green colors.
Color Blindness
Genetic disorder in which people are blind to green or
red colors supports Trichromatic theory.
Opponent Process Theory
• As our receptor cells sense colors in our
environment, the cones are also firing the
opponent (opposite) color
BlackWhite RedGreen BlueYellow
Gaze at the middle of the flag for about 30
Afterimage Effect
Dark adaptation
• The process by which the rods and cones
adjust to changes in levels of light
• Rods are more sensitive to light and so take
longer to fully adapt to the change in light
• The fovea is blind to dim light (due to its
cone-only array) and the rods are more
• Insufficient adaptation to dark environment,
called “night blindness”.
Color Constancy
Color of an object remains the same under different
illuminations. However, when context changes color
of an object may look different.
R. Beau Lotto at University College, London
AP stuff…
• Cornea-pupil-lens-retina-photoreceptorsbipolar-ganglion-optic nerve-visual cortex
• Photo transduction takes place in the rods
(light) and cones (color)
• Fovea is the point of focus (what happens if..)
• Why a blind spot?
• Real image and virtual image (WOW!)
• Remember frequency and amplitude
 Parts of the Ear and the hearing process
 Theories of audition
 Hearing loss
The Stimulus Input: Sound Waves
Sound waves are composed of compression and
rarefaction of air molecules.
Acoustical transduction: Conversion of sound waves
into neural impulses in the cilia (hairs cells) of the inner
Sound Characteristics
1. Frequency (pitch)
2. Intensity (loudness)
3. Quality (timbre)
Frequency (Pitch)
Frequency (pitch):
Dimension of
determined by
wavelength of
Wavelength: The
distance from the
peak of one wave
to the peak of the
Intensity (Loudness)
Intensity (Loudness):
Amount of energy in
a wave determined
by amplitude relates
to perceived
Loudness of Sound
Richard Kaylin/ Stone/ Getty Images
Quality (Timbre)
Quality (Timbre): Characteristics of sound from a
zither and a guitar allows the ear to distinguish
between the two.
The Ear
Guess what, you don’t hear with your
ear. You hear with your …
Outer Ear
Pinna: Collects sounds. Shaped like a funnel
Auditory canal: The auditory canal is a tube that connects
the pinna and the tympanic membrane (eardrum)
-funnels sound toward eardrum, protects eardrum
Middle Ear
Middle Ear: Chamber between eardrum and cochlea
containing three tiny bones (“ossicles”-hammer, anvil,
stirrup) that concentrate the vibrations of the
eardrum on the cochlea’s oval window.
Inner Ear
Inner Ear: Innermost part of the ear, containing the cochlea,
semicircular canals, and vestibular sacs.
Cochlea: Coiled, bony, fluid-filled tube in the inner ear that
transduces sound vibrations to auditory signals.
Process of hearing
• 1. Sound waves enter through the pinna and travel
through the auditory canal
• 2. The sound waves begin to vibrate the tympanic
membrane (eardrum)
• 3. The ossciles of the middle ear (H.A.S.) move and
the stirrup presses on the cochlea’s oval window
• 4. Fluid in the cochlea circulates causes the
movement of the cilia along the basilar membrane
• 5. Neural messages travel along the auditory nerve
toward the temporal lobe
Video segment on hearing
Theories of Audition
Place Theory suggests that sound frequencies stimulate
basilar membrane at specific places resulting in perceived
Some hairs vibrate when the pitch is low and some when it
is high, ----this explains detection of high frequencies
Theories of Audition
Frequency Theory states that the rate of nerve
impulses traveling up the auditory nerve matches the
frequency of a tone, thus enabling us to sense its pitch.
All hairs vibrate but at different speeds
--explains detection of low frequencies
100 Hz
Auditory Nerve
Action Potentials
Localization of Sounds
Because we have two ears sounds that reach one
ear faster than the other makes us localize the
Hearing Loss
Conduction Hearing Loss: Hearing loss caused by
damage to the mechanical system that conducts
sound waves to the cochlea. The waves never reach
the cochlea.
Sensorineural Hearing Loss: Hearing loss caused by
damage to the cochlea’s receptor cells or to the
auditory nerve, also called nerve deafness.
Hearing Deficits
Older people tend to hear low frequencies well but suffer
hearing loss for high frequencies.
AP info…
• Outer ear (pinna) is shaped like a funnel,
auditory canal and ends at tympanic
• Middle (mechanical) ear has ossicles
– Hammer, Anvil, Stirrup (pushes on oval window)
• Inner ear has cochlea, basilar membrane and
cilia (acoustic transduction here)
• Mechanical and Sensory neural hearing loss
• Do you still remember frequency and
Other Senses
Somasthetic sense
Gustatory sense
Olfaction sense
Kinesthetic sense
Vestibular sense
Touch (somasthetic sense)
Bruce Ayers/ Stone/ Getty Images
Sense of touch is a mix of four distinct skin sensespressure, warmth, cold, and pain.
• Receptors are located all over the skin, some
areas more concentrated than others
• The sensory cortex located in the parietal lobe
receives the information (left side of
body=right brain)
• The more sensitive a body part is, the more
surface area is given to it in the cortex
Skin Senses
Only pressure has identifiable receptors, all other skin
sensations are variations of pressures, warmth, cold
and pain.
Burning hot
Cold, warmth and pain
Pain tells the body that something has gone wrong.
Usually pain results from damage to the skin and
other tissues. There is a rare disease in which the person
feels no pain.
Ashley Blocker (right) feels neither pain
nor extreme hot or cold.
Biopsychosocial Influences
Gate-Control Theory
Melzak and Wall (1965, 1983) proposed that our spinal
cord contains neurological “gates” that either block
pain or allow it to be sensed. The release of
endorphins would close the gate.
Gary Comer/
Pain Control
Pain can be controlled by a number of therapies
including, drugs, surgery, acupuncture, exercise,
hypnosis and even thought distraction.
Traditionally taste sensations consisted of sweet, salty,
sour and bitter tastes. Recently receptors for a fifth
taste have been discovered called “Umami”.
Sensory Interaction
When one sense affects another sense sensory
interaction takes place. So the taste of starburst
interacts with its smell and its texture on the tongue to
produce flavor.
Like taste smell is a chemical sense. Odorants enter the
nasal cavity to stimulate 5 millions receptors to sense
smell. Unlike taste there are many different forms of
Age, Gender and Smell
Ability to identify smell peaks during early adulthood
but steadily decline after that. Women are better at
detecting odors than men.
Smell and Memories
Brain region (red) for
smell is closely connected
with brain regions (limbic
system) involved with
memory, that is why
strong memories are
made through the sense
of smell.
Body Position and Movement
The sense of our body parts’ position and movement
is called kinesthesis (joints and muscles).
And the vestibular sense (semicircular canals in inner
ear) monitors the head (and body’s) position.
Neo learning to move his body
Wire walk over Niagara Falls
Kinesthetic Sense
• provides the parietal cortex of the brain with
information on the relative positions of the
parts of the body
• describes how much we know about where
we are in space and where all of our
parts are in relationship to each other
• Our kinesthetic sense helps us move
with greater precision, avoid injuries,
and be fully present in the moment
• Close your eyes and touch the tip of
your nose with the tip of your finger
Vestibular Sense (equilibrium)
• Monitors the position of the head in relation
to the body, the sensations of body rotation
and of gravitation and movement
• Operates based on movement of fluid within
the semi-circular canals of the inner ear
• The vestibular system sends signals primarily
to the neural structures that control eye
movements, and to the muscles that keep a
creature upright
• Abnormalities may cause “vertigo”
Ap stuff…
• Transduction – process by which sensory information
is transformed into neural impulses.
• Adaptation – the decreasing response of a sense
when they are exposed to continuous stimulation.
• Opponent-process theory – The thalamus of the
brain responds to two pairs of colors (red/green and
• Tri-chromatic theory – Cones in the eye pick up
three colors: green, red and blue.
Ap stuff cont…
• Frequency theory – the rate at which nerve
impulses reach the brain determine how low
the pitch of the sound is. Low pitches have
lower frequency. The higher the frequency,
the higher the pitch
• Place theory – The area within the basilar
membrane of the cochlea determines how we
hear high pitch sounds
More AP info…
• Touch- pressure, pain, temperature (not hot)
• Taste and smell are chemical senses and
linked together (flavor), not in the thalamus
• Kinesthetic sense-position of body parts and
movement (in joints and muscles)
• Vestibular sense-whole body position, balance
(in semi-circular canals of the inner ear)
• Optic-sight
• Acoustic-hearing
• Olfactory-smell
• Gustatory-taste
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