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Sensing the
world around us
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sound

The movement of air molecules brought about by a source of
vibration
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eardrum

The part of the ear that vibrates when sound waves hit it
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cochlea

A coiled tube in the ear filled with fluid that vibrates in response
to sound
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Basilar membrane

A vibrating structure that runs through the center of the cochlea,
dividing it into an upper chamber and a lower chamber and
containing sense receptors for sound
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Hair cells

Tiny cells covering the basilar membrane that, when bent by
vibrations entering the cochlea, transmit neural messages to the
brain
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The physical aspects of sound

Sound is actually the physical movement of air molecules in
regular, wavelike patterns caused by a vibrating source

When the lowest notes are playing on ,the speaker moves in
and out

The speaker pushes air molecules into waves with the same
pattern as its movement

Strength of the wave pattern weakens considerably during their
travels
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
All other sources that produce sound work in essentially the
same fashion

Air or some other medium, such as water is necessary to make
the vibrations of the object reach us
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Frequency

Frequency is the number of wave cycles that occur in a second

The audio speaker moving when low notes are played because
of a primary characteristic of sound called frequency

At very low frequencies there are relatively few wave cycles per
second

Low frequencies are translated into a sound that is very low in
pitch
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pitch

Pitch is the characteristic that makes sound seem ‘high’ low.

The lowest frequency that humans are capable of hearing is 20
cycles per second

Higher frequencies are heard as sounds of higher pitch

At the upper end of the sound spectrum, people can detect
sounds with frequencies as high as 20,000 cycles per second
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Amplitude

Is a feature of wave patterns that allows us to distinguish between
loud and soft sound

Amplitude is the spread between the up-and down peaks and
valleys of air pressure in a sound wave as it travels through the air

Waves with small peaks and valleys produce soft sounds’

Those with relatively large peaks are valleys produce loud sounds

We are sensitive to broad variations in sound amplitude

The range is measured in decibels
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Theories of sound

Place theory of hearing

Frequency theory of hearing
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How are our brains able to sort out
wavelengths of different frequencies and
intensities?

So, why do we hear the difference between notes in a song
instead of just monotone notes? This is attributed to
the frequency theory of hearing. The frequency theory of
hearing states that the frequency of the auditory nerve's
impulses corresponds to the frequency of a tone, which allows
us to detect its pitch.
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
The way it works is that sound waves cause the entire basilar membrane
to vibrate at different rates, which, in turn, causes the neural impulses to
be transmitted at different rates.

Basically, when we hear a musical note, it causes specific vibrations in
our ears that lets us hear that specific pitch.

Lower notes vibrate at slower speeds, while higher notes vibrate at
higher speeds. As pitch increases, nerve impulses of the same frequency
are sent to the auditory nerve.

This means that a tone with a frequency of 700 hertz produces 700 nerve
impulses per second. It is the speed in which the neural signals move
along the brain that determine the pitch.
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Place theory of hearing

The place theory of hearing is used to explain how we
distinguish high-pitched sounds that possess a frequency that
exceeds 5,000 hertz. According to the place theory of hearing,
we can hear different pitches due to specific sound frequencies
causing vibrations in specific parts on the basilar membrane of
the cochlea. In other words, different parts of the cochlea are
activated by different frequencies.
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
Each location on the basilar membrane possesses a particular characteristic
frequency.

For example, a sound that measures 6,000 hertz would stimulate the spot
along the basilar membrane that possesses a characteristic frequency of
6,000 hertz.

The brain detects the pitch based on the position of the hair cells that
transmitted the neural signal.
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Auditory cortex

After an auditory message leave the ear, it is transmitted to the
auditory cortex of the brain through a complex series of neural
interconnections

Neuron that respond to specific types of sounds

Specific sort of sound features( clicks and whistles)

About sound’s location
Perceptual organization
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
Gestalt psychology was founded by German thinkers Max
Wertheimer, Wolfgang Kohler, and Kurt Koffka and focused on how
people interpret the world.2 The Gestalt perspective formed partially
as a response to the structuralism of Wilhelm Wundt, who focused
on breaking down mental events and experiences to the smallest
elements.

Max Wertheimer noted that rapid sequences of perceptual events,
such as rows of flashing lights, create the illusion of motion even
when there is none. This is known as the phi phenomenon. Motion
pictures are based on this principle, with a series of still images
appearing in rapid succession to form a seamless visual
experience.
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
According to Gestalt psychology, the whole is different from the
sum of its parts. Based upon this belief, Gestalt psychologists
developed a set of principles to explain perceptual organization,
or how smaller objects are grouped to form larger ones.
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
Have you noticed how a series of flashing lights often appears to be
moving, such as neon signs or strands of lights? According to Gestalt
psychology, this apparent movement happens because our minds fill in
missing information. This belief that the whole is greater than the sum of
the individual parts led to the discovery of several different phenomena
that occur during perception
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
Some of the most basic perceptual processes can be described
by a series of principles

that focus on the ways we organize bits and pieces of
information into meaningful

wholes. Known as gestalt laws of organization, these principles
were set forth in the

Gestalt laws of organization: A series of principles that describe
how we organize bits and pieces of information into meaningful
wholes.
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
FIGURE 1 When the usual cues we use to distinguish figure from
ground are absent, we may

shift back and forth between different views of the same figure. If
you look at each of these

objects long enough, you’ll probably experience a shift in what
you’re seeing. In (a), you can

see either a vase or the profiles of two people. In (b), the shaded
portion of the figure, called a

Necker cube, can appear to be either the front or the back of the
cube.
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Gestalt law of organization


Law of Proximity: This law describes elements that are closely
placed together and thus perceived as a group. For example,
placing a particular shape without proximity , just as the Adidas
logo in figure 1, but still perceived as separate shapes.
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proximity
 .. .. .. .. .. .. .. .. .. .. .. .. ..
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
Law of Similarity: This law describes placing
similar objects with one another. It could be
perceived as a pattern or group. For example,
placing two distinct shapes in vertical
columns.
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similarity
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similarity
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
Law of Continuation: This is described as the
compelling movement of the eyes through an object
to another object. For example, in the image letter
below, the eyes are compelled to follow the curve in
the letter to the leaf.
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Law of continuity
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

Law of Closure: This is described as the
incompleteness or a space unenclosed in
an object. For example, the panda below
shows some incompleteness in its figure.
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
Law of Simplicity: Any
ambiguous stimuli have the
tendency to determined to
favor the simplest. An
example is shown below in
figure 7.

Law of Pragnanz: This is
described as the reduction
and organization of the reality
of an object to its simplest
possible form. Example is
shown below.
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Figure and ground
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
Although gestalt psychology no longer plays a prominent role in
contemporary psychology, its legacy endures. One fundamental
gestalt principle that remains influential is that two objects
considered together form a whole that is different from the
simple combination of the objects. Gestalt psychologists argued
that the perception of stimuli in our environment goes well
beyond the individual elements that we sense. Instead, it
represents an active, constructive process carried out within the
brain
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Bottom -up and top -down processing

Ca- yo- re-d t-is -en-en-e, w-ic- ha- ev-ry -hi-d l-tt-r m-ss-ng? It
probably won’t take you too long to figure out that it says, “

Can you read this sentence, which has every third letter
missing?”

If perception were based primarily on breaking down a stimulus
into its most basic elements, understanding the sentence, as
well as other ambiguous stimuli, would not be possible. The fact
that you were probably able to recognize such an imprecise
stimulus illustrates that perception proceeds along two different
avenues, called top-down processing and bottom-up processing.
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
In top-down processing, perception is guided by higher-level
knowledge, experience, expectations, and motivations. You were
able to figure out the meaning of the sentence with the missing
letters because of your prior reading experience, and because
written English contains redundancies. Not every letter of each
word is necessary to decode its meaning. Moreover, your
expectations played a role in your being able to read the
sentence. You were probably expecting a statement that had
something to do with psychology, not the lyrics to a Fergie song
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
Top-down processing is illustrated by the importance of context
in determining how we perceive objects. Look, for example, at
Figure 4. Most of us perceive that the first row consists of the
letters A through F, while the second contains the numbers 10
through 14. But take a more careful look and you’ll see that the
“B” and the “13” are identical. Clearly, our perception is affected
by our expectations about the two sequences—even though the
two stimuli are exactly the same
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
However, top-down processing cannot occur on its own. Even
though top-down processing allows us to fill in the gaps in
ambiguous and out-of-context stimuli, we would be unable to
perceive the meaning of such stimuli without bottom-up
processing. Bottom-up processing consists of the progression of
recognizing and processing information from individual
components of a stimuli and moving to the perception of the
whole. We would make no headway in our recognition of the
sentence without being able to perceive the individual shapes
that make up the letters. Some perception, then, occurs at the
level of the patterns and features of each of the separate letters.
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
Top-down and bottom-up processing occur simultaneously, and interact with
each other, in our perception of the world around us. Bottom-up processing
permits us to process the fundamental characteristics of stimuli, whereas
top-down processing FIGURE 3 Although at first it is difficult to distinguish
anything in this drawing, keep looking, and eventually you’ll probably be
able to see the figure of a dog (James, 1966). The dog represents a gestalt,
or perceptual whole, which is something greater than the sum of the
individual elements. Top-down processing: Perception that is guided by
higher-level knowledge, experience, expectations, and motivations.

FIGURE 4 The power of context is shown in this figure. Note how the B and
the 13 ar
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
allows us to bring our experience to bear on perception. As we
learn more about the complex processes involved in perception,
we are developing a better understanding of how the brain
continually interprets information from the senses and permits us
to make responses appropriate to the environment (Buschman &
Miller, 2007).
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Perceptual constancy

Consider what happens as you finish a conversation with a
friend and he begins to walk away from you. As you watch him
walk down the street, the image on your retina becomes smaller
and smaller. Do you wonder why he is shrinking? Of course not.
Despite the very real change in the size of the retinal image, you
factor into your thinking the knowledge that your friend is moving
farther away from you because of perceptual constancy.
Perceptual constancy is a phenomenon in which physical
objects are perceived as unvarying and consistent despite
changes in their appearance or in the physical environment.
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
In some cases, though, our application of perceptual constancy
can mislead us. One good example of this involves the rising
moon. When the moon first appears at night, close to the
horizon, it seems to be huge—much larger than when it is high
in the sky later in the evening. You may have thought that the
apparent change in the size of the moon was caused by the
moon’s being physically closer to the earth when it first appears.
In fact, though, this is not the case at all: the actual image of the
moon on our retina is the same, whether it is low or high in the
sky
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
Instead, the moon appears to be larger when it is close to the
horizon primarily

because of the phenomenon of perceptual constancy. When the
moon is near the horizon, the perceptual cues of intervening terrain
and objects such as trees on the horizon

produce a misleading sense of distance. The phenomenon of
perceptual constancy

leads us to take that assumed distance into account when we view
the moon, and it

leads us to misperceive the moon as relatively large.
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
In contrast, when the moon is high in the sky, we see it by itself, and we don’t try

to compensate for its distance from us. In this case, then, perceptual constancy
leads

us to perceive it as relatively small. To experience perceptual constancy, try
looking at

When the moon is near the horizon, we do not see it by itself and perceptual
constancy leads

us to take into account a misleading sense of distance.

fel70207_ch03_088-129.indd 120 9/11/08 5:23:12 PM

121
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
the moon when it is relatively low on the horizon through a paper-towel tube; the

moon suddenly will appear to “shrink” back to normal size (Coren, 1992b; Ross
&

Plug, 2002; Imamura & Nakamizo, 2006).

Perceptual constancy applies not just to size (as with the moon illusion) but to

shape and color as well. For example, despite the varying images on the retina
as an

airplane approaches, flies overhead, and disappears, we do not perceive the
airplane
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Depth perception

As sophisticated as the retina is, the images projected onto it are
flat and two- dimensional.

Yet the world around us is three-dimensional, and we perceive it
that way.

How do we make the transformation from 2-D to 3-D?

The ability to view the world in three dimensions and to perceive
distance—a skill known as depth perception—is due largely to
the fact that we have two eyes.
binocular disparity
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
Because there is a certain distance between the eyes, a slightly
different image reaches each retina. The brain integrates the two
images into one composite view,

but it also recognizes the difference in images and uses it to
estimate the distance of an object from us.

The difference in the images seen by the left eye and the right
eye is known as binocular disparity
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binocular disparity

To get a sense of binocular disparity for yourself, hold a pencil
at arm’s length and look at it first with one eye and then with the
other. There is little difference between the two views relative to
the background.

Now bring the pencil just six inches away from your face and try
the same thing. This time you will perceive a greater difference
between the two view
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
the distance of objects that we view provides us with a means of
determining distance.

If we view two objects and one is considerably closer to us than
the other is, the retinal disparity will be relatively large and we
will have a greater sense of depth between the two.

However, if the two objects are a similar distance from us, the
retinal disparity will be minor, and we will perceive them as being
a similar distance from us
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
Binocular vision – seeing 3D with two eyes

There are two main binocular cues that help us to judge
distance:
•
Disparity – each eye see a slightly different image because they
are about 6 cm apart (on average). Your brain puts the two
images it receives together into a single three-dimensional
image. Animals with greater eye separation, such as
hammerhead sharks, can have a much greater depth perception
(as long as the view from both eyes overlaps the same scene).
This can be very useful when trying to catch fast-moving prey.
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•
Convergence – when looking at a close-up object, your eyes angle
inwards towards each other (you become slightly cross-eyed). The extra
effort used by the muscles on the outside of each eye gives a clue to the
brain about how far away the object is. If you hold your finger 20 cm in front
of your eyes, your muscles need to work a lot harder than when your finger
is 50 cm away.

These binocular cues are most effective for objects up to 6 m away. After
this, the amount of eye separation does not give a great enough difference
in images to be useful.
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Monocular cues
z In some cases, certain cues permit us to obtain a sense of depth and
distance with just one eye. These cues are known as monocular
cues.
 One monocular cue—motion parallax

is the change in position of an object on the retina caused by
movement of your body relative to the object.

For example, suppose you are a passenger r in a moving car, and
you focus your eye on a stable object such as a tree. Objects that are
closer than the tree will appear to move backward, and the nearer the
object is, the more quickly it will appear to move. In contrast, objects
beyond the tree will seem to move at a slower speed, but in the same
direction as you are. Your brain is able to use these

cues to calculate the relative distances of the tree and other objects.
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
t makes a smaller image on the retina is farther away than is the
one that provides a larger image—

an example of the monocular cue of relative size. But it’s not just
size of an object that provides information about distance; the
quality of the image on the retina helps us judge distance.


texture gradient
The monocular cue of texture gradient provides information
about distance because the details of things that are far away
are less distinct
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linear perspective

Finally, anyone who has ever seen railroad tracks that seem to
join together in the distance knows that distant objects appear to
be closer together than are nearer ones, a phenomenon called
linear perspective.

People use linear perspective as a monocular cue in estimating
distance, allowing the two-dimensional image on the retina to
record the three-dimensional world (Bruce, Green, &
Georgeson, 1997; Dobbins et al., 1998;

Shimono & Wade, 2002; Bruggeman, Yonas, & Konczak, 2007).
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Linear perspective
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Motion perception

When a batter tries to hit a pitched ball, the most important
factor is the motion of the ball. How is a batter able to judge the
speed and location of a target that is moving at some 90 miles
per hour?

The answer rests in part on several cues that provide us with
relevant information about the perception of motion. For one
thing, the movement of an object across the retina is typically
perceived relative to some stable, unmoving background.
Moreover,

.
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
if the stimulus is heading toward us, the image on the retina will
expand in size, filling more and more of the visual field. In such
cases, we assume that the stimulus is approaching—not that it
is an expanding stimulus viewed at a constant distance.

It is not, however, just the movement of images across the
retina that brings about the perception of motion. If it were, we
would perceive the world as moving every time we moved our
heads. Instead, one of the critical things we learn about
perception is to factor information about our own head and eye
movements along with information about changes in the retinal
image
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