The vestibular system is the part of the inner ear that helps us m.docx

The vestibular system is the part of the inner ear that helps us
maintain our balance and sense of head orientation and
movement. It's as old as the cochlea in evolutionary time. The
systems are highly similar. In both, hair cells transduce motion
into nerve
signals, but the vestibular system senses much slower vibrations
of just a few Hz in contrast to the cochlea's 20 to 20,000 Hz.
The cochlea, on the right hand of the picture, gives us our sense
of hearing. The three semicircular canals of the vestibular
apparatus, on the left, are fluid-filled tunnels in the skullbone.
Each semicircular canal contains hair cells in the bulge at its
base, the ampulla. Because the semicircular canals on each side
of the head are oriented roughly at right angles to each other,
they signal head movement no matter how we move.
The utricle and saccule sense static head position. They contain
particles of calcium carbonate that pull on hair cells. The hairs
in the utricle are vertical, while those of the saccule are
horizontal; thus the organ can tell you the angle of the head in
geometric coordinates! If one of the bony particles, called
otoconia, should slip out of position you may experience a form
of dizziness when you bend over that is called benign
paraoxysmal positional vertigo (sometimes the "paraoxysmal" is
left out). A doctor will tell you how to bend your head to
reposition the otoconia and return to normal or it may slip back
on its own in a few months. You can find more about
vertigo here.
Understanding the vestibular part of the inner ear helps to
explain why we get so dizzy when we spin, a joy that
diminishes with age. If you are a parent of toddlers, know that
when you reach middle age they will be just the age to delight
in carnival rides, and of course you will be invited to join them
after a large, greasy lunch. A noble calling, parenthood.
We judge motion by comparing what the eyes see with what the

vestibular organs sense about our body movement. If the
vestibular apparatus says that we're not moving, then any
movement sensed by the eyes must be outside the body. (The
brain discounts the appearance of movement caused by eye
movement itself.) Then the brain tells the eyes just how to move
to keep track of the moving object. If we're moving and the
world is moving, too, we need to keep track of the objects while
adjusting for our body's movement. The eyes and the
semicircular canals have to work together on this. However, if
you twirl around and set the fluid of one or two pairs of the
semicircular canals into motion and then stop suddenly, you
fool the brain into thinking the world is spinning. The reason is
that the vestibular fluid is moving as though you're moving, so
the eyes are moved to track objects.
This eye movement, called nystagmus, makes the world seem to
spin. You can produce the same effect by drinking alcohol,
which lowers the specific gravity of the fluid of the
semicircular canals and stimulates the vestibular hair cells as
though you're moving. Again the world spins. OR you can squirt
ice water into the ear canal to produce convection in the
semicircular canals. This produces a very powerful spinning
sensation, a vigorous nystagmus, and--frequently--vomiting. We
did this when I was a lab instructor in a medical school
neuroscience course as a grad student. You have to keep a bowl
near the poor medical student's mouth. (Remember that the med
student was a volunteer. I volunteered once for an anoxia
experiment in physiology class and learned what sudden loss of
consiousness is like. Brighter students know better than to
volunteer.
Questions (Please answer one.)
1. Describe the roles of vision and the vestibular apparatus in a
coordinated act in sports, such as a second baseman's double
play, a pole vault, or a turnaround jump shot. What are the
differences and similarities in the roles of the two senses?
2. Our sense of balance involves another sense besides vision
and vestibular function, called proprioception. Test your

balance at this site or that one. Why do you think that three
senses are necessary for balance?
3. Which of these illusions involve the vestibular system?
The Very Broad Problem of Pain
When did pain begin? We can trace the evolutionary origin of
some receptors--for light and sound, for example--but
irritability is a defining feature of life. We might better ask
when we began identifying irritability as pain. Few people say
that invertebrates have a sense of pain. Fish, birds, and reptiles
may have pain without the emotion. Mammals have the full
sensory and emotional repertoire.
When does pain begin? Certainly by the time of circumcision in
newborn boys. Conscious pain may not be present before 26
weeks of gestation. That is not a scholarly site and may be
partisan, but reliable evidence indicates that pain seems not to
be present at 24 weeks in humans.
Is pain normal? Pain is a sense that is also a disease. There are
many sensory impressions we can categorize as symptoms of an
underlying disorder, but pain occurs as a disorder in its own
right. Pain is pre-attentive; we rarely have to search to decide
whether it’s present, yet it is often elusive and hard to
localize—famously so for children.
The Specifics
Where does it hurt? Pain appears to become conscious when
messages of tissue injury reach the cerebral cortex. For pain,
the focus is on somatosensory cortex, which contains a body
map of areas represented in the brain; the insula; and anterior
cingulate cortex.

How does it hurt? Specialists distinguish two or three kinds of
pain by their origin, with a fourth appearing on the horizon:
nociceptive, neuropathic, and inflammatory (sometimes grouped
with nociceptive) pain—and maybe another category
of central or psychogenic pain should be added. (There is some
evidence that chronic pain may turn out to be psychogenic, but
there are genetic hypotheses, too.) The pain of combat
injuries justifiably dominates many current discussions of pain,
but the complexities lie beyond the scope of our textbook.
· Nociceptive pain: e.g., stubbing your toe, often acute
· Neuropathic pain: e.g., multiple sclerosis, always chronic
· Inflammatory pain: e.g., postoperative pain
Anatomists distinguish two peripheral pathways that carry pain
signals from the body to the brain. One, the Aδ system, consists
of myelinated nerve fibers that transmit signals at around 10
meters per second. We perceive this pain as sharp and
localized.
A second pathway is the unmyelinated C-fiber system that
carries signals much more slowly at about 1 meter per second.
We feel this pain as dull and diffuse. Most of the pain that
arises from our internal organs is of this type. This system
shows a “windup”phenomenon by which repeated stimulation
produces a steadily increasing response that leads eventually
to allodynia and central sensitization, which is important in
fibromyalgia and chronic fatigue syndrome.
On the skin, both kinds of pain exist. You can perceive the
difference when you hit your thumb with a hammer. You
become aware of a sharp pain just in time to think “Oh, no”
before the dull, aching pain of the C-fibers hits you.
The two pathways are variously labeled as “first”, or lateral;
and “second”, or medial, pain sensation. First pain sensation is
a discriminative sensory modality resembling touch that
terminates at the somatosensory cortex. Unlike touch, second

pain sensation brings in an affective or emotional component to
pain that makes it aversive. It projects to the anterior cingulate
cortex and insula. Another terminus of the second pathway is
the insular cortex that lies beneath the lateral fissure. Brain
imaging has suggested that the insula may be responsible for
empathic pain, which is our tendency to recoil from witnessing
someone else’s pain.
Scaling of Pain
Why does pain hurt? We all know that a little pain is very
different from a lot of it. Without trivializing the horror of
serious pain, let’s admit that we can enjoy hot food but we hate
a burned tongue. What makes pain worse?
· Stimulus intensity: Different regions of somatosensory
cortex encode stimulus intensity differently.
· Anticipation: Anticipation of pain can heighten the response to
pain. However, expecting the pain to be less may make it less—
without a placebo!
· Duration: Pain is likely to worsen with prolonged stimulation.
· Heredity: Man or woman, redhead or brunette—your pain
betrays your genes. However, gender differences are not
necessarily genetic in origin. Psychogenic pain associated with
the “neurotic triad” on the MMPI—hypochondriasis, depression,
hysteria—breaks down by gender as well.
There are many ways of measuring pain. On the one hand, pain
sensation increases with stimulus intensity and unpleasantness
increases with sensory magnitude. This much was proved in the
days of Fechner.
·
http://www.thblack.com/links/RSD/JPainSymptMngmt2005_29_
14_PainMeasurement1945-2-2000.pdf
· http://www.uni-
leipzig.de/~psycho/fechner/generalinfo/PDFs/JBaird.pdf
·
http://journals.lww.com/psychosomaticmedicine/Abstract/1976/

03000/Signal_Detection_Theory_and_the_Psychophysics_of.2.a
spx
· https://www.theguardian.com/science/2017/jan/25/how-
doctors-measure-pain
· https://sanlab.psych.ucla.edu/wp-
content/uploads/sites/31/2015/05/Eisenberger2012NRN.pdf
·
http://abcnews.go.com/Health/Technology/story?id=116729&pa
ge=1
Needless to say, the study of pain has a long history.
(More here, there and yonder.)
The problem for psychophysics is to distinguish discriminative,
“first” magnitudes from affective, “second” magnitudes. In a
hospital, scaling poses a different kind of task. Patients may
minimize their pain out of bravado or exaggerate it to get more
drugs. Scales are needed for patients with dementia and
for young children. While the McGill Pain Questionnaire is in
widespread use, the search for a truly objective scale is still
going on. The McGill form looks like this and that.
The Gate-Control System and Other Controls
Watch this video of Ronald Melzack’s explanation of his
research. (If you would like to read more about his neuromatrix
model, try this article.)
The gate-control model describes two mechanisms for blocking
a pain signal, once when it enters the spinal cord (click on
“play” or try this animation) and again when the brain inhibits
pain input. See if you can pinpoint the synaptic changes that
suppress pain.
Pain is also reduced by the brain’s secretion of substances that
resemble marijuana and opium.
The control of attention provides another powerful way to
reduce pain. Who has not tried to distract a child from the pain

of a fall by directing his or her attention to a toy or a piece of
candy? For adults, love can accomplish the same end. Although
pain was once treated as a body sense, it is increasingly being
regarded as a “mind sense”.
Placebos
Our expectations may increase or decrease pain. The
anticipation of a shot may intensify the pain that a child feels
from an injection, while the color of a pain-killing pill may
allay the soreness of overexertion, as this week’s lab exercises
demonstrate. Placebos can have powerful effects. This radio
interview and that one describe the phenomenon further.
Questions (please answer one)
1. What flaws do you see in the following pain scales?
a. A hospital’s 1 to 10 scale. Patients are asked to rate
their pain from 1 to 10 in severity.
b. The Schmidt Sting Pain Index.
2. Is the placebo effect confined to drugs? Can you think of an
example in your own life of a placebo effect from something
other than a drug?
3. What is pain to you--a sensory signal like touch? A state of
consciousness generated by the brain? A disorder or disease? It
seems like everyone is thinking about this, but you don't need
research if your own experience offers an answer.
Vision senses electromagnetic energy-- light--while hearing
senses mechanical energy in the form of sound. Sound waves
must beat upon the eardrum, and its vibrations must be
transmitted across tiny bones called the ossicles, to

set fluid in the cochlea vibrating. When hair cells within the
cochlea pick up the vibrations and stimulate fibers of the
auditory nerve—transduction!—we hear sound. You might
visit this site for a quick review of the ear.
Now two big questions of psychophysics arise: How do sounds
vary in intensity and loudness? How do they vary in frequency
and pitch?
Sound & Decibels
First we want to understand how our sensory loudness varies
with sound intensity. We can measure sound intensity as air
pressure changes, since sound is alternating waves of
compression and rarefaction. We would be dealing with
fractions of a Pascal, which is a unit of pressure. However, the
threshold for hearing is so low that it's near the pressure of
sunlight on the eardrum or the random motion of molecules
because of heat. At the other end, we can hear sounds so intense
that they may rupture cells in the ear--altogether, a pressure
range of about 10,000,000,000,000 to 1. That's at least thirteen
powers of ten. In any case, rather than using such large
numbers, it's easier to count one unit of sound intensity for each
power of ten added to the air pressure. Letting units stand for
powers of ten is a logarithmic scale, the Bel (or more usefully,
tenths of Bels called decibels). And how big is a decibel? Just
click on a triangle or “enter” or scroll down to the green bars to
find out.
There was just a bit of sleight-of-hand there. How did we go
from Pascals to decibels? There are several ways of measuring
sound. It’s common to express the threshold of hearing as
0.0002 dynes/cm2. But that’s a unit of force. Psychologists
stopped expressing the threshold in force units about 40 years
ago because pressure is what we’re really talking about;
pressure is force per unit area. So our hearing threshold is now
20 μPascals, or simply 20 μPa. Acoustical engineers talk about
sound pressure level, or SPL. It’s a somewhat arbitrary pressure
that corresponds to an average youngster’s threshold. We
measure sound levels above or below that in decibels. In

physics, a 10-decibel increase means a tenfold increase in sound
pressure. With SPL, a 20-dB increase represents a tenfold
increase in pressure.
Decibels take some getting used to. You can ratchet the
discussion down a notch in complexity at this earlier site or up
a notch at this website if you wish.
Either way, it's useful to acquaint yourself with how sound
works in hearing. Hearing is basically a mechanical sense like
touch and balance. You can find a brief account here or an
overall review in this excellent presentation (optional, of
course). The former lasts 6 1/2 minutes and the latter almost
two hours, but even the long one is worth the time, if you have
it. It covers disorders as well as normal function, and why
hearing aids will be cool to wear in a couple of years. Just skip
the first eight minutes of introduction!
The physical intensity of a sound registers as the subjective
impression of loudness, while a sound’s frequency creates the
impression of pitch.
Two Mechanisms for Pitch Discrimination
How do we tell one sound frequency from another? We do it by
telling the brain either which nerve fibers in the cochlea are
firing or how the fibers are firing. The latter process uses phase
locking.
Phase-Locking
Phase-locking is a mechanism for responding to higher sound
frequencies that all tend to stimulate the apical end of the
basilar membrane. One nerve fiber can't respond thousands of
times per second to, say, a 5,000 Hz tone, but many fibers
acting together can! If each fiber in the eighth cranial nerve
responds to a different sound wave in a series (say the second or
fifth wave) and to a particular part of that wave (say the rising
part or the trough), the pattern of response among all of the
nerve fibers will be distinct for each frequency. On that basis
the brain can distinguish among sound frequencies.
In other words, phase refers to the part of a sound wave to
which a nerve fiber responds (indirectly, of course, since it has

to be stimulated by hair cells). The time of stimulation doesn't
matter. It's the phase that is important. Here's an analogy: If you
always go to bed at 10 p.m., your sleep is time-locked to each
day-night cycle. If you travel to Tokyo or Moscow you will find
yourself trying to sleep at odd times of the day that correspond
to 10 p.m. stateside. Instead, if you always go to bed when it is
sunset, your sleep is phase-locked to each day-night cycle. If
you move to Tokyo or Moscow, your sleep won't be as badly
disrupted.
Music
Musical ability appears early. Peretz and Zatorre mention that
infants begin to sing by their first birthday and reach
competence by five. Music appears as a social interaction; it
may support attachment and contribute to group bonding.
It is hard to say what distinguishes music from other sounds,
but we can usually tell the difference. There are good sounds
and bad sounds, and then there is music. You can watch a
video about the physics of music, but it won't tell you what
music is, though music’s resemblance to speech may provide a
clue, since a kind of music is present in speech when its ups and
downs occur in minor thirds.
Melody
Melody is the part of music in which the pitch changes, note
after note. We can change the pitch by varying the resonance of
a musical instrument or the human voice. (You can review
resonance at sites one, two, three, four, and five.)
Not surprisingly, your ability to appreciate melodies depends on
your ability to discriminate different pitches. (Test
yourself here (cancel the sign-in) or there.) Closely related to
melody is harmony, or the pleasantness of different pitches in
combination.
One challenge for psychology is to explain why one melody is
more pleasant than another. This is partly a matter of
consonance. Dissonant pitches may draw our attention or be
unpleasant, but they are not constant across cultures. Cultures
differ in the musical scales they use, which tell the listener what

pitches to expect in a melody. If you doubt this predictive value
of a scale, watch this amazing demonstration of the pentatonic
scale (3 minutes). Melodies from other cultures tend to sound
out of tune or off-key. Exposure to different kinds of music has
good effects if it's started early; later, it alienates. We don't like
music of older or younger people, either. Millennials aren't keen
on classical music, as a rule, and some people just don't like
music at all.
Of course our attitudes have changed over time as well; for
example, we no longer fear the Devil’s Interval*.
There are individual variations in the ability to respond to
melodies that also vary with culture. Absolute pitch provides
one example. It is rare in Western cultures, though not beyond
learning. Its appearance varies with culture and language.
Whereas the average Westerner might distinguish just the do-re-
mi notes of a scale, the person with absolute pitch
may discriminate among 70 pitches and be able to identify by
letter each note of the scale, no matter which instrument plays
it.
Rhythm
Besides melody, the other important part of music is the
rhythm, which is time-based. The rhythm is the beat, while
tempo is the overall speed, or the number of beats per minute.
Some writers have played up the resemblance between a musical
beat and the human pulse rate (about 72 per minute) as
significant; but rhythm might have other origins. As with
melody, the listener’s expectations are an important part of our
enjoyment of rhythm. After the predictable rhythms of
centuries-old dances like the Schottische or a minuet, the
syncopation of ragtime is a refreshing surprise, when a note
appears earlier than we expected it. (Does syncopation
improve this lullaby?) Even more complicated rhythms arise in
Latin music such as salsa (continued here), enlivened by an
Afro-Cuban clave rhythm that may sound complicated to
northern ears. Clap your hands as you listen to the clave beat to
test your understanding of it.

Beyond generating (and violating) expectations, an amazing
feature of rhythm is its ability to synchronize our movement,
which is sometimes called entrainment. The effect is so
powerful that it raises a chicken-and-egg question: Is music the
cause or the result of our desires—to move in synchrony, to
bond, and thereby to feel intense emotion?
Are North Americans rhythm-challenged**? There’s one test of
rhythm here and a limited test of rhythm memory at this site if
you scroll to the bottom.
Putting It Together
The psychology of music has a long history with few significant
discoveries. We still don’t know for sure what role music plays
in behavior. This topic began with the link between personality
and music. The evidence is limited and uncertain and these
kinds of correlations reveal little of the way music works in our
lives. You are welcome to test yourself further at this site.
Speech Perception
You can quickly review the subtopic of speech perception with
try-it-yourself demonstrations at this site. Three phenomena
worth knowing about are the following:
· The segmentation problem of distinguishing one word from
another. Listen to yourself say "We were away a year ago." Now
look at a site that shows such a sentence's sound pattern. (It's
near the bottom of the Web page.) There are no word
boundaries! This is typical of our speech.
· Categorical perception
· The phonemic restoration effect
Questions (Answer any two.)
1. There can't be sounds without frequencies, but are there
sounds without pitch?
2. As you know, one important feature of sound is its frequency.
Are you able to hear the 10,000 Hz sound?
· http://www.skidmore.edu/~hfoley/Perc9.htm#ch9demo2
· http://www.youtube.com/watch?v=igGroIcga3g
· http://www.youtube.com/watch?v=bWpSePfbTxc (ineradicable
error in grammar)

Now put frequency and amplitude together to find out which
frequencies you are most sensitive to at this website. Try to
judge the frequencies to which you are most sensitive and share
the result with us. You might want to confirm your results
at this site. How did you make your decision?
3. Going through the following links in order, would you say
that you have perfect musical memory? Perfect rhythm
perception? Perfect pitch discrimination? Perfect (absolute)
pitch? What turned out to be your strongest auditory skill, and
why?
· http://www.nidcd.nih.gov/tunetest/Pages/Default.aspx (cancel
the sign-in)
· http://www.classicfm.com/discover/music-quizzes/keep-time-
test/
· http://tonedeaftest.com/
· http://www.audiocheck.net/blindtests_abspitch.php
4. Music isn't always entertainment. In surgery and religion
what is more important: melody or rhythm (or both)? Why?
*You've heard it in the music of Black Sabbath and other
groups. Or listen to the first two notes of the Simpson’s theme
or play C followed by F♯ (G♭ ) on this piano keyboard.
**Unstable web page. It seems to stabilize when you use this
link and right-click on the page as if to "save" it, then hit
"cancel" to return to the page.
5. Depth Perception and Attention

Unlocked: Monday, September 4, 2017 12:00 AM EDT -
Sunday, September 17, 2017 11:59 PM EDT.
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Please respond to Question 1 or Question 2.
In this week's learning resources, the follow-on page for the
article on depth perception might escape notice. The link to the
second page, on binocular depth cues, is at the bottom, labeled
1:77.
However, there's a clearer account of depth perception in this
textbook chapter.
As primates, we enjoy binocular vision*, or stereopsis. Our two
eyes have overlapping visual fields that allow us to judge
distance better than animals who lack binocular vision, such as
rabbits. You can find much more about stereopsis (when you
have time and if you have the inclination) at the following sites:
· http://www.vision3d.com/stereo.html
· http://mysite.du.edu/~jcalvert/optics/stereops.htm
· http://nzphoto.tripod.com/sterea/3dvision.htm
You have already encountered the notion that each object
projects an ambiguous image onto the retina, which permits
different interpretations, as in the illustration at left. To
understand binocular depth perception, keep two further points
in mind: Images in the two retinas are slightly different and
these differences provide a cue to depth.
Binocular Disparity: The Most Powerful Depth Cue?
Binocular disparity is simply the notion that the eyes receive
different views of near objects but not of distant objects, so the
disparity between the retinal images of the left and right eye
provide information about how far away something is.
Understanding how it works is the hard part.
How Binocular Disparity Works
Recall that the visual cortex contains a map of each retina,
whereby each point in the left retina has a corresponding retinal

point in the right retina. Corresponding retinal points will
appear in the same place in the cortical map. Further, any object
that you fixate on will be projected onto corresponding retinal
points.
For any object that we fixate on, there is a circle of objects that
will also be imaged on corresponding retinal points. This circle
is the horopter. Objects that are not on the horopter will be
imaged on noncorresponding retinal points. The more distant
these objects are from the horopter, the greater the difference
will be between their images in the two eyes. This difference
between the left and right retinal images is binocular disparity.
You can demonstrate it yourself. If you hold your thumb a few
inches in front of you and close first one eye and then the other,
leaving the other eye open, you will notice that the right eye
sees more of the right side of your thumb and the left eye sees
more of the left side of your thumb. This disparity decreases as
you move your thumb farther away. Since you are fixating on
your thumb it must lie on the horopter, yet corresponding points
on your retinas do not show quite the same images. This
produces an effect similar to what we experience with objects
off the horopter.
Binocular disparity is a depth cue. If an object lies off the
horopter it must be closer to you or farther from you than is
your point of fixation. The degree of difference between the two
retinal images for this object is binocular disparity. It can be
measured as degrees of visual angle.
A Small Experiment
Here's a quick way to demonstrate how important the
correspondence of points on the two retinas is. Keep both eyes
open. Gently, gently push on the outside of your right eye with
your finger while you're looking at something with pattern. You
should feel no pain; if you feel pain, back off and press more
gently. Do you see two images? If so, good. If not, try focusing
on a closer object.
Do you see a double image? When objects are projected onto
noncorresponding points in the two eyes, double vision is the

result. Does it make sense that the double image disappears
when you close either eye? The muscles that move the eye are
among the fastest in the body. They're called the extrinsic
ocular muscles; there are six of them. They are controlled by
three cranial nerves: the oculomotor [N. III], trochlear [N. IV],
and abducens [N. VI].
Now suppose one of the cranial nerves that controls eye
movements is damaged. What will the patient experience?
Right--just what you experienced when you pushed on your
eyeball. It's called diplopia, or double vision. It occurs
whenever the image of what you're looking at no longer falls
exactly on the same retinal location in each eye. (You may
smell a rat here. You just produced double vision by creating
non-corresponding points of vision, which should create
stereopsis. Is this a contradiction? It turns out that the brain
interprets small disparities as depth; large disparities are
interpreted as double vision.)
Rembrandt was Stereoblind
Many people, perhaps as many as one in ten**, lack
stereoscopic vision to some extent despite normal vision in both
eyes. Such people are said to be stereoblind, but it's not an all-
or-none condition; the causes and the severity vary. Most
affected people aren't even aware of the deficit until they try to
visualize depth in random dot stereograms. Instead, they rely on
other depth cues to drive and reach for things. Babe Ruth may
have been stereoblind! Binocular vision is useless as a depth
cue for really distant objects, anyway. It's fine for catching a
football but not for judging the distance of a football 100 feet
away. You can find out more at these sites:
·
http://www.boston.com/news/nation/articles/2004/09/16/an_eye
_on_rembrandt/
·
http://www.abc.net.au/science/articles/2004/09/16/1198105.htm
Question 1
To further evaluate the role of binocular disparity as a depth

cue, consider that you are looking at your friend's face in a
photograph. You are thus viewing an object that produces
retinal images with no binocular disparity. Does zero binocular
disparity give you any information about the depth (or distance)
of your friend the way that viewing your friend in real life
does? Now imagine you are viewing your friend outside in real
life. Would stereopsis help you distinguish a friend at 300
meters' distance from another at 320 meters? Would it help to
tell you that the moon is closer than the stars?
Attention
Attention magnifies important things and filters out trivial
things. We don’t analyze everything we see fully, but anything
that's important or that appears unexpectedly gets extra
analysis yet there are people who can’t pay attention to two
things at the same time. Studying the resources that we devote
to objects and people tells us about perception.
Eye movements provide a clue to what’s happening with
attention. We move our eyes when we view a scene. Actually
our eyes are always moving very quickly when we're awake;
ocular microtremor, 60-80 Hz movements of both eyes, prevents
the formation of a stabilized retinal image that would
overbleach the rods and cones and make us blind. When we scan
a scene we use different eye movements called saccades.
Shouldn't saccades make the world seem to jump around by
suddenly changing where the images are focused on the retina?
Yet apparently these movements help to stabilize the scene.
(You can read more about eye movements here).
When attention is directed at one object it must ignore another.
We sacrifice understanding of some parts of a scene in order to
understand another part more thoroughly. Here are some
examples similar to what you will find in the readings:
· Change blindness. You can find different kinds of change
blindness (see WARNING*) here and there.
· Inattentional blindness
· Emotion-induced blindness (also called attentional
rubbernecking). Click on different components of the "story

map" to progress to the demo.
· Attentional blink.
Question2
Suggest an example of how others manipulate our attention.
You might think of catching someone's attention--or dampening
it--by flirting, hijacking our emotions in film, fooling us with
stage magic, or pick an example you prefer. What does your
example show about attention?
*This demo may be disturbing or dangerous for people who are
susceptible to seizures set off by flickering lights. If viewing
the demo makes you feel euphoric or uncomfortable it is best to
terminate viewing. The demo is not of worldshaking importance
anyway, so don't spend more than a few minutes at this!
The readings for this week will make it clear that the eye does
not project an image upon the mind like a projector on a screen.
Photoreceptor activation would not make sense to us. What we
see is actively constructed.
First, there is lateral inhibition, which enhances contrast and
helps us to see edges. The contrastiness of the image depends
on sideways connections between cells in the retina,
exerting lateral inhibition.
In lateral inhibition, the more active a cell is, the more it
inhibits its neighbors. Image contrast is enhanced first when
illuminated cells inhibit cells in the dark that were less active to
begin with. It is enhanced further by the release from inhibition
of illuminated cells that lie next to cells that are in the dark.
Consequently, at a border between intense illumination and
less-intense illumination there is extra-strong inhibition of cells
on the dark side of the border and unusually weak inhibition of
cells on the light side of the border. Both the light intensity and
the distance of a cell from the light-dark border determine its
activity level.

Lateral inhibition is the basis for the black spots in
the Hermann grid.
Mach bands are a real-life illustration of lateral inhibition. For
other examples you might try
· http://www.yorku.ca/eye/machband.htm
· http://scienceblogs.com/mixingmemory/2006/07/01/cool-
visual-illusions-mach-ban/
· http://home.pacifier.com/~ppenn/machband.html
In the second illustration down at this site, you'll find arrows
that point to where the Mach bands are. Mach bands should
prove to you that what you experience as sight contains more
contrast than the real world actually offers. You’ll find more
about how lateral inhibition produces Mach bands at this site.
The organization of the image also depends on receptive
fields. A receptive field can be defined for any neuron in the
visual system. All of the photoreceptors whose activity can
influence that neuron make up the neuron's receptive field, as
you can see in this animation or that one. In the visual system,
the receptive field is always defined as a patch of retinal
surface--i.e., a group of neighboring photoreceptors. For a
bipolar cell, the receptive field is all of the rods or cones that
can activate or inhibit the bipolar cell. For a ganglion cell
(which receives input from bipolar cells), the receptive field is
all of the photoreceptors that activate/inhibit all of the bipolar
cells that can activate the ganglion cell. These
are organized into on-center/off-surround or off-center/on-
surround fields by the way that bipolar neurons are connected to
ganglion cells and by lateral inhibition.
We assemble our mental pictures out of what our eyes tell us,
but our eyes are in constant motion, called saccades, and vision
is blacked out during each movement. Each eye is attached to
six little muscles that are the fastest in the body. They’re called
the extraocular muscles because they’re outside the eye; inside

the eye there is the contractile ciliary body that pulls on the lens
as you accommodate to near objects. But Prof. Rolfs explains
it more completely in just a few minutes. You can explore more
about eye movements at this site or drag the cursor circle with
your mouse to observe the working of the muscles.
We’ll have to leave to other psychology courses our
extraordinary sensitivity to gaze, as important in basketball as
in flirting. You can see how noticeable it is by moving your
cursor across this image. You might keep gazing in mind when
we reach the topic of face recognition.
Finally, constancy appears in several visual processes,
in size, shape, color, and lightness judgments. Constancy keeps
our subjective impressions unchanged while an object
undergoes familiar physical changes. In this illusion about
lateral inhibition, the border where lateral inhibition is evident
creates a false impression of a lightness difference as well.
You cannot turn a perceptual constancy off. The brain
constructs our perceptions out of ambiguous data provided by
the retina. The strategies we use are the ones that have kept us
alive as a species, but they can be fooled. Take a look at
Session 2 of these animations (with sound--click "start" on the
first screen, then click on the upper right image square in the
next window) to get an idea of our limits.
Questions (Answer one.)
1. How is lateral inhibition important for detecting edges?
2. How much can you tell about someone from their eyes? "I
looked the man in the eye. I found him to be very
straightforward and trustworthy….I was able to get a sense of
his soul." —George W. Bush, after meeting Russian President
Vladimir Putin, June 16, 2001
3. Information about the motion, color, form, luminance, and
size of objects arrives in separate channels at the visual cortex.
This information is routed along two major paths called the
Where pathway and the What pathway, or the dorsal and ventral
streams, that are discussed in the embedded NOBA textbook

chapter on vision that was assigned for week 3.
The dorsal stream provides us with "how" or "where"
information in the parietal lobe of the cerebral cortex of each
hemisphere; the ventral stream provides us with "what"
information--that is, it identifies what we see as recognizable
objects, using inferotemporal (IT) cortex on the bottom of the
temporal lobe.
Interruption of the dorsal stream results in optic ataxia. Damage
to inferotemporal cortex results in visual agnosia. You can also
try out dorsal-stream-without-ventral-stream function for
yourself with the odd experience of blindsightat this site.
Do you think blindsight illustrates more the operation of the
what pathway or the where pathway? Do these pathways seem to
operate with conscious awareness or without it. (If in
doubt, check it out. You can watch patient T.N. in this video.)
A threshold is an entrance; in psychology, it is the intensity a
stimulus must achieve to be sensed, either by a receptor or in
our awareness. Of course, thresholds are different for every
kind of sense--and sensory attribute--that you can imagine.
Absolute Thresholds
Psychology recognizes two kinds of threshold, absolute and
difference (or relative). The absolute threshold is the weakest
intensity that can be detected.
Remember from the previous discussion topic that what we see
is not always what is there physically and vice versa. That may
make it easier to understand why the absolute threshold is
defined as the fifty-percent level of detection. To experience the
reason for yourself, go outside late on a clear night and look for
the dimmest star you can see. Does it seem to be sometimes

there and sometimes not?
Some people will say they see a star on the slightest evidence,
while other people will wait to report one until they are certain.
If you can find the cluster of stars called the Pleiades, count the
number of stars you can see in it. Some will see four, others
seven. In fact, there are more than 20 stars in the Pleiades. Why
does the count vary? Obviously, some people see better than
others; but some will not wait to confirm a pinpoint of light
before counting it, while others will want to make sure they can
always see a star before counting it. This is typical of absolute
threshold tests. Near the threshold, the subject is never sure
whether a light--or any other stimulus in the test--is there or
not. Responses vary and make it appear that the idea of an
absolute threshold is vague.
Signal Detection Theory (SDT)
Most psychologists have dropped the concept of an absolute
threshold in favor of a measure from signal detection theory
called d' (read d-prime). Signal detection theory separates a
subject's response criterion from sensory detection so that both
may be measured. The response criterion is a person’s
willingness to report detection, while detection reflects the
observer’s sensitivity to a stimulus such as light or sound. In
the process of doing this, however, the simple notion of an
absolute threshold is lost.
SDT is a useful technique. It is used in psychology, medicine,
and engineering. Our resources avoid mathematical calculations,
but the whole thing rests on a solid foundation of statistics.
(Maybe only psychologists think of statistics as a solid
foundation.) You can learn more about it starting on p. 5 of this
presentation.
Are you amazed at the claims of wine experts to detect licorice
notes in a red wine? Are they really any better than novices?
SDT was used in this study to find out.
Difference Thresholds
The difference threshold is also called a difference limen or
relative threshold. It is the smallest change in a stimulus that

can just be detected. You can't see the motion of a clock's hour
hand; you may see motion in the minute hand of a large clock;
and you can certainly see the second hand move. The second
hand exceeds the difference threshold for motion detection.
An absolute threshold is typically defined against the condition
of no stimulation at all. A difference threshold is always a
change in existing or repeated stimulation. Both are defined as a
50% level of detection.
A Personal Experiment. A less obvious result can appear if you
test someone's two-point discrimination threshold for touch.
How far apart must two points be before a subject can feel the
two points separately? Bend a paper clip so that the two ends lie
close together, about two millimeters apart--the width of two
grains of table salt. Can you find any part of a friend's body
where two points rather than one can be felt? Now bend the
paper clip so that the clip ends lie 25 millimeters apart, roughly
an inch. Touch the clip ends to the shoulder, forehead, thigh,
and back. What do you find? Even if your data are fairly dull,
you should now be on very friendly terms with your
experimental partner. Time for a cup of coffee. Next, we’ll look
at how to measure difference thresholds using Weber’s law.
Scaling
Psychological magnitudes often don’t go up and down the same
way that physical magnitudes do. Actually, even scales in the
physical world can vary in how they measure the same stimulus.
Temperature is measured differently on the Fahrenheit and
Celsius scales. Compare marginal tax rate with income level:
The scales are very different. Your first $20,000 of earnings
isn’t taxed at the same rate as your neighbor’s top $200,000, is
it? Musical scales don’t indicate sound frequency very well,
either. Playing eight notes up the scale only doubles the sound
frequency (or you can see the difference graphically here.) In
fact, the subjective psychological impression called pitch
increases at a different rate from sound frequency. Response
expansion (pain of shock) and compression (brightness): They
reflect the mismatch between one scale and another.

Weber’s Law
This mismatch is what makes Weber’s law seem complicated.
Our sense organs, and therefore our subjective awareness,
change at a different rate than the physical stimulus does.
Here's the problem: Our sense organs can only respond with
action potentials, and action potentials aren't normally fired off
more than a few hundred times per second by a neuron*. That's
a problem because the intensity of light goes up to at least ten
billion (i.e., ten thousand million if you're British; 1010 if
you're an engineer) times absolute threshold; that is, the most
intense light we see is about ten billion times the weakest light.
We can't generate action potentials ten billion times per second,
or even a million times per second. How does the eye signal
changes in light intensity to the brain?
How Weber's Law Works
That's where Weber's law comes in: The retina
signals percentage increases to the brain. If the difference
threshold for light intensity is 0.3, or 30%, the retina will signal
an uptick in light intensity when there's a 30% increase. In that
way, the visual system doesn't max out its response before the
light is near its maximum intensity.
Fechner's Law and Stevens' Law
Weber's law was replaced by the more accurate Fechner's law; it
in turn gave way to Stevens' power law, which uses a technique
called magnitude estimation. This difference often appears in
psychophysical discussions, so if it's not clear, ask a question.
Magnitude estimation yields different results for different kinds
of sensory measurements. For example, little
increases in shock intensity tend to produce large increases in
our pain, while big changes in light intensity may produce only
small increases in brightness. It's important not to confuse the
scale of our psychological impressions (brightness, loudness,
pitch, pain, warmth, cold) with the physical stimulus scale
(light intensity, sound intensity, sound frequency, shock
intensity, and temperature, respectively).

You can find another explanation of Stevens' power law here.
This website illustrates why Stevens' law is called a power law:
The magnitude of a subjective experience (S) is related to the
physical magnitude (I) raised to some power, a. If it's not clear
how magnitude estimation works, please raise a question.
Question: Please respond to either question 1 or question 2:
1. It's not always easy to tell absolute and difference thresholds
apart. Briefly explain your answer to each of the following
examples:
· Someone who takes an opioid drug like Oxycontin or fentanyl
for pain relief may find themselves taking more and more to
reach the same level of pain control. Would you say that the
absolute threshold for the drug effect is decreasing or the
difference threshold is increasing? .
· Entering a dark theater, you cannot see the seats and have to
wait a moment for them to become visible. When the seats are
not visible are they below your absolute threshold for visual
sensitivity or below your difference threshold?
· In story of the princess and the pea, how did the princess
differ from ordinary young women? Did she have a lower
absolute threshold for tactile pressure or a higher difference
threshold?
· If you walk to the kitchen to get an apple, the trip back to your
seat won’t seem different in length from the trip to the kitchen.
But if you travel to another city for the first time and return
home by the same route, you will think the return trip felt
shorter. Does this return trip effect illustrate an absolute
threshold or a difference threshold for perception of the trip
distance?
2. How would you actually use psychophysics?
Here’s an example from the magical world of spaghetti sauce.
(It lasts 17 ½ minutes but it offers an interesting look at
psychophysics.)
Psychologists are still at work on improving tomato taste.
Suggest a strategy based on measurement that might herald the
next big thing in tomato products.

Sweetness is an important factor in tomato taste that was bred
out of the plant in an effort to make them redder at market time.
How about replacing the lost sweetness in sauces with artificial
sweeteners? But then how do you decide how much to add
without going bankrupt?
Illustration credits:
http://retina.umh.es/webvision/psych1.html
http://www1.appstate.edu/~kms/classes/psy3203/Measure/Steve
nsFig2.gif
This is a course in sensation and perception. Sensation is
stimulation of our sense organs by external stimuli, while
perception is the organization of sensory information. Sensation
is bottom-up information conducted from the periphery to the
brain, and perception is top-down information that imposes an
interpretation on sensation.
In the two videos in this week’s Learning Resources (in Content
>> Course Content >> Week 1), Professor Kihlstrom makes two
major points: Sensation may change while perception remains
the same; and sensation may remain the same while perception
changes. That is, bottom-up and top-down understanding are not
just the beginning and end of a single process. It’s a dual
process.
There’s a duality in perception called “bottom-up” and “top-
down” processing. What we see depends on what the outside
world tells us, bottom-up, and also what we expect to see, top-
down.
Everything we see is ambiguous at first. Shapes, luminances,
distances and colors always can be duplicated by alternative
stimuli. Consequently, every percept is an interpretation,
a choice among alternatives.
Usually we “disambiguate” what we see too fast to be aware of

our analysis. Sometimes a pattern may be so blatantly
ambiguous that we alternate between interpretations, as with
the Necker cube and the Young-girl/Old-woman illusion*.
A raw sensation supplies “bottom-up” information. Our mental
interpretation is called “top-down”. In the Ponzo illusion
below, the equal length of the yellow bars is bottom-up
information. The unequal appearance of the bars that results
from our analysis of linear perspective is a top-down
perception**.
It is hard to turn off either bottom-up or top-down processes
when both are active. We find it hard to enjoy the bottom-up
delights of a dessert if they remind us of an illness that once
accompanied them; and despite knowing that only animals have
faces, we sometimes see top-down faces in inanimate objects.
Questions (please answer one)
· Can you think of a pure bottom-up or pure top-down
perception?
· How would you classify the perception of the difference
between living and nonliving? Is it bottom-up or top-down?
Explain your answer.
· Is it trivial to distinguish sensation and perception? Most
sensory input is ambiguous. Sometimes we confront sensory
stimuli that can’t be interpreted in one best way, but usually the
brain sets to work and we quickly dispel the fog. If we can’t do
that, we suffer and persist.
*These figures generate bistable perceptions; that is, we see one
or the other. Tristable alternations are also possible.
**Not convincing? Try this other illusion of perspective
(explanation here). Can you separate the bottom-up from the
top-down influences?
Note: Links in the discussion topics are optional; they will not
appear in tests, although the discussions are intended to clarify
the readings and videos in the syllabus and weekly Course
Content.

Class Project
Instructions
A class project that critically evaluates recent research on a
problem in sensation and perception should be submitted not
later than the deadline listed in the syllabus schedule, using
Eastern Daylight or Eastern Standard time, whichever is
appropriate for the time of year. Your project should bear your
name, a title, and references in APA format. Your project must
include at least one peer-reviewed reference. You are not
restricted to topics that appear in the assigned readings and
videos, but your project must be based on serious scholarship.
Although it is permissible to choose the same topic as another
class member, all work must be your own; this is not a
collaborative project.
The assignment may be fulfilled by a term paper of no more
than 1,600 words (about 6 to 8 pages not counting references,
but be guided by the word count in judging length, and stay
within 200 words of the target to avoid penalties) accompanied
by either of the following: a podcast in MP3 format of five
minutes' length or five MB file size; or a slide presentation
(e.g., PowerPoint) of about six slides. Your written portion will
be worth a maximum of 50 points, and the podcast or
PowerPoint that accompanies it will be worth a maximum of 10
points. Thus, the project as a whole will be worth 60 points. The
penalty for a late project is ten percent of the score on the
project.
Everyone needs to write a paper. Beyond that, pay attention
only to the part of the project description that concerns the

activity that interests you.
Written paper. As an example, the problem you choose might be
to identify the way we recognize faces. Your paper should state
the fundamental issues, pinpoint unanswered questions, and
evaluate recent research that aims to solve the problem. To
accomplish this, you will have to use one or more recent
research articles published within the last five years, along with
supplementary information that may be drawn from reputable
magazines like Scientific American or blogs from professionals
such as MindHacks.com. Avoid tabloid newspapers and blogs
by authors without appropriate credentials. You may use any of
a number of electronic databases to find research articles that
deal with your topic, including the library and the Internet.
(You may wish to consult with the library staff or your faculty
member to confirm whether a particular journal is peer-
reviewed.)
You should avoid simply repeating the articles in summary
form, but rather use them within the text of your paper to
illustrate important points. You are welcome to discuss your
choice of topic with your faculty member to make sure you are
on the right track.
The paper will be graded on content, organization, and writing
mechanics and style. The following rubric is used to assign
points associated with each main topic.
Grading Rubric for
Project: Written Paper
5
4
3
2
1
0
CONTENT

1. All topics were discussed in clear detail.
2. Author supported assertions correctly.
3. Ideas were inter-related coherently and logically.
4. Author creatively enhances the topic.
ORGANIZATION

5. An introduction previews main points of study
6. Body of paper develops and elaborates main ideas.
7. A conclusion summarizes main points.
WRITING MECHANICS and STYLE
8. Paper free of mechanical errors (e.g., misspellings, typos,
etc.)

9. Paper grammatically sound (proper sentence structure)
10. Citations and references in proper style (e.g., APA).
You may wish to submit a draft of your complete or near
complete paper to the Effective Writing Center (EWC) for
review and comment, prior to the due date of the paper. This
should be submitted well in advance of the due date, in order
for the EWC to respond and for you to make the necessary
corrections. Once you receive feedback from the EWC, you can
copy and paste it into a Word Document, then upload it into
LEO by the due date, for your instructor to view as necessary.
The EWC can help address questions regarding format,
structure, writing style, and appropriateness of references.
Podcastpresentation. The podcast should be targeted to the
public and should summarize and discuss the topic of your
written paper. It should not be a verbatim reading of your paper.
You will record your spoken comments with a microphone and
audio software, then upload your audio file to class. You will
need to create an audio story (approaching it the same way you
would any other story or essay) on your paper topic. The
podcast should be in MP3 format of five minutes' length or 5
mB file size. You may download free audio recording software

at http://www.audacityteam.org/
Grading Rubric for Project: Podcast (Audacity or substitute)
2
1
0
Information Content
Describes the topic fully and accurately
Describes the topic superficially or incorrectly
Description fails to correspond to the written description
Technical
Volume, transitions, and noise are effectively controlled
Uneven control of sound that occasionally interferes with
clarity
Missing intervals or unintelligible sound recording
Creativity
Narrative enhanced with special effects throughout the delivery
Narrative exhibits momentary enhancement
Narrative lacks creative enhancement
Spoken production
Clear, well-rehearsed delivery
Unrehearsed or unclear delivery
Unintelligible enunciation
Relevance
Meets requirements of the assignment in length or size
Comes acceptably close to meeting the requirements of the
assignment
Varies widely from the assigned requirements
PowerPoint presentation.The PowerPoint presentation should
summarize and illustrate the topic of your written paper.The
main purpose of this is to familiarize you with the most widely
used state-of-the-art presentation form, to augment information
in the paper, and to share your work with other class members.
The PowerPoint presentation should consist of a minimum of 6
slides of the area in your written report. If you do not have
access to PowerPoint, you may use free, publicly available

software such as Prezi or Open Office Impress instead.
Consider the following tips in preparing your presentation:
1. Your first slide should give your name and our class's name
and the term, along with the title of your presentation.
2. There should be about four or five points per slide
3. Use a standard font (Times Roman or Arial) and at least an
18-point font size with different sized fonts for main points and
secondary points
4. Use a font color that contrasts sharply with the background
5. Use graphs rather than charts and words, and always title
your graphs
6. Proof your slides for spelling and grammatical errors
7. Use a conclusion slide to summarize the main points of your
presentation and to suggest future avenues of research. You do
not need to list references.
8. Avoid ending your presentation abruptly—you might end
your slide with a quote, a simple question, or the next steps
Grading Rubric for Project: Slide Presentation (PowerPoint or
substitute)
2
1
0
Introduction
Topic, author, and date are clearly indicated
Introduction lacks some important information
Introduction is missing
Layout
Visually pleasing, with appropriate use of headings,
subheadings and white space
Appears cluttered and busy or distracting with large gaps of
white space or uses a distracting background
Confusing or unreadable
Text
Readable text with good placement and appropriate typeface.

Lengthy, busy, or full of distracting and inappropriate
embellishments
Missing, unreadable or inappropriate text
Creative enhancements
Graphics effectively supplement text
Graphics present, but irrelevant or inappropriately used
No enhancements
Relevance
Meets requirements of the assignment in length or size
Comes acceptably close to meeting the requirements of the
assignment
Varies widely from the assigned requirements
PROJECT RESOURCES
Resources for a slide presentation
The class project described in the Syllabus is a written paper
accompanied by either PowerPoint slides or a podcast. In this
topic we’ll take a look at PowerPoint. If you haven’t used it
before, of course your first question will be “What is
PowerPoint?”. It is versatile software from Microsoft that is
used to present text and graphics in slides. You can buy it at a
student discount from UMUC. There is also free software that
will do much the same job, sometimes in a different way.
There are versions of PowerPoint for the Mac and the PC, with
training for Microsoft Office here and there. If you prefer the
free route, you may download a PowerPoint clone such as
OpenOffice Impress from this site and find their other
products here.
Among the free options, a newly popular presentation tool is
Prezi, available at http://prezi.com/. For further help, try the
forums for PowerPoint and Prezi users:
http://www.msofficeforums.com/powerpoint/https://prezi.com/c
ommunity/
If you use an alternative to PowerPoint, please include a note in
your upload to tell me which software you used. The project
assignment in the Syllabus will ask you to turn in at least six

slides. The grading rubric will give you some ideas of what to
include in your presentation.
If you have trouble getting started, give some thought to a
strategy. The assertion-evidence style has attracted interest in
scientific and medical presentations.
Resources for a podcast
The class project described in the Syllabus is a written paper
accompanied by either PowerPoint slides or a podcast.
If you have not made a podcast before, welcome to sound
communication on the Internet! You can learn more at this
siteor that one. For example, here is the history of brain
research in ten 15-minute podcasts that you could have made
yourself. Your podcast should have at least a length of five
minutes or a file size of 5 mB in MP3 format. What is MP3? It’s
explained at this site and at that one. Using free Audacity
software, each minute of monaural recorded speech in MP3
format occupies about 1 mB in file size.

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