Modified from:
http://www.appsychology.com/Book/Biological/perceptio
n.htm
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The way we interpret the information we sense
The way we interpret the world in many ways dictates
our sense of reality.
Even if our senses are keen (like superman on crack), if
our perception is skewed we will not understand the
information we sense.
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Thresholds are the idea that our senses have limits.
Absolute threshold - the smallest amount you can just
sense something (about half of the time.)
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Example 1: If the guy sitting next to you in class farts,
and you take a whiff and smell it, but the next whiff do not
smell it, then kind of smell it again- the fart is at your
absolute threshold for smell.
• Example 2: If you can just barely hear a
sound- then it is at your absolute threshold
for sound.
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Difference threshold (or just noticeable difference) the smallest amount of change needed in a stimulus
before we notice the change
Example: Ok, picture this- you are watching TV (Family
Guy or Gilmore Girls- take your pick) and your parents
are singing Backstreet Boys in the next room. You grab
the controller and raise the volume one bar, but you still
can't hear Peter Griffin and his offensive anti-Semitic
rhetoric.
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The change in volume was under your difference
threshold (or just notice difference). In fact, you need
to raise the volume four bars until you can tell the
difference in amplitude.
So the difference threshold for your hearing is
somewhere between the three and four bars on your TV.
There are several theories that psychologists have that show
us how we perceive the world. These theories are not in
opposition to each other (like McDonalds and Taco Bell- they
are more like McDonalds and The Gap- just different).
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This theory examines how outside influences effect our
perception. This theory attempts to predict what we will
pay attention to among competing stimuli.
For example, they believe that one's absolute threshold
depends on your motivation to sense, tiredness, and a whole
host of other issues.
They question why a new mother will sleep through traffic
but awaken upon hearing the smallest whimper from their
newborn.
• Picture yourself at a noisy
party, and someone says your
name 10 feet away. You will
probably notice that sound
above all the others (called the
cocktail party effect) because
you are motivated to hear your
own name.
When we perceive the world through top-down processing we are
using our experience to fill in the gaps in front of us.
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Take a look at the following sentence
I _ant t_
e_t
s_om_
c_tt_n
ca_dy.
Our schemas often cause us to form a perceptual set (a
predisposition to perceive something in a certain way).
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For example, Beavis and Butthead have a well known perceptual set;
sex. Every time someone in their word says the word "tool" or "hard",
they see it as sexual. Their schemas for sex are so encompassing that
they create this perceptual set so that everything in their lives is seen
through the eyes of sexuality.
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In the 1970's, many parents were concerned aboutbackmasking in
music (when you play the music backwards, secret satanic messages are
revealed). Now in reality, there is nothing but jumbled noise, but the
parents created a perceptual set, expecting to hear devil messages, so
what did they hear? What they expected. –
http://jeffmilner.com/backmasking/
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This type of processing usually occurs when we are
unfamiliar with an object.
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This type of processing is slower, but also prone to less
errors than top-down.
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Instead of using our experience to decipher an object
(like in top-down) we use the features of the object
itself. We actually examine the object at its basic core
structure.
Try to picture a five year old who has just learned to
read try to decipher
I _ant t_

e_t
s_om_
c_tt_n
ca_dy.
They would examine every line and curve because they do
not have the experience to do what you or I would do.
Psychologist love tackling issues dealing with how we see
the world.
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They examine issues like the figure-ground
relationship which deals with how we distinguish what
objects in our vision we want to examine (figure) and what
parts are just background (ground).
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In the following pictures what do you see? Which is the
background and which is the figure?
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Gestalt psychologists were a group that explored some of
the above issues.
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In particular they were concerned with how and why we
GROUP objects together.
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They stated that humans can't help but perceive stimuli in
groups rather than individual or isolated elements.
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Gestalt thinkers are obsessed with the notion that we group
these objects together in our lives and create groups that are
larger than the sum of their parts. If you asked me to sit down
and write down all of the feeling that encapsulate the feeling of
love I have for my kids, I may spend days writing. But even
after I finished the list, it will NOT equal my feelings. My
feelings of love (group) are larger than all the individual reasons
I have to love. It's kinda cool when you think about it.
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Proximity: Objects that are close together are more likely
to be perceived as belonging in the same group. If you see
two people walking down the hallway next to each other,
you will probably perceive them as friends.
Similarity: Objects that are similar in appearance are
more likely to be perceived as belonging to the same
group. If there are a small group of Latinos in your class,
you may think they all know each other because you view
them as similar (you may not be right of course).
Continuity: Objects that form a continuous form (such as a
trail or geometric figure) are more likely to be perceived
as belonging to the same group.
Closure: Objects that make up a recognizable image are
more likely to be perceived as belonging to the same group
even if the image contains gaps that the mind needs to fill
in. Just like top-down processing.
Remember, our eyes are like mirrors, reflecting
information to the back of our retinas. Even though the
object we are looking at may change on our retina, we still
know the object itself has not changed.
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That sounds confusing but look at these concepts:
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Size Constancy: Objects that are closer to us produce
bigger images on our retinas.
For example, if Mario Lopez
was standing 100 feet from
you, he would produce a image
on your retina. If he dances
closer to you, his image on
your retina will slowly
increase. But you know that
Mario (a.k.a. Slater) is not
really growing. His size is
kept constant in your mind,
even though the picture on
your retina changes in size.
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Shape Constancy: Objects viewed from different angles
will produce different shapes on our retinas, but we know
that the shape of the object remains constant.
Take a look at the doors to the
right. The one on the left looks
like a rectangle, The one in the
middle is shaped like a (what do
you call it.....) parallelogram? The
shape looks different in our
retinas, but our mind maintains
that the shape of the door
remains a rectangle.
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Brightness Constancy: We perceive objects as being a
constant color even as the light reflecting off the object
changes.
Kermit the frog is green in the daytime. As night comes
he will look gray, or even black as the light fades. But we
know that his color is always green even though it may
not look like so in our retina.
The concept of depth is one of the most studied aspects
of perception. Imagine what the world would look like if we
could not see depth (it would look 2 dimensional).
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Researcher E.J. Gibson
conducted a very famous
experiment called
the visual cliff
experiment to determine
when humans are able to
see depth. He placed an
infant onto one side of a
glass topped table that
creates the impression of
a cliff.
Gibson discovered that by the time the baby can crawl, it
will not crawl across the glass table, showing us that depth
perception does exist at young ages. The general consensus
is that babies develop depth perception at around three
months of age.
 The way babies (and adults) understand depth is by using
a bunch of tricks that are called monocular and binocular
cues.
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Monocular cues are tricks that we (and artists who draw a
lot) use to judge depth perception.
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What makes them monocular cues is that you need only
one eye to use them.
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So if you lost your eye in a tragic ping pong accident, the
following cues would still be at your disposal to see depth.
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Interposition: So if something is blocking something
else, the thing being blocked is farther away- kind of
in your face obvious.
If Justin Timberlake is standing in front of me and
blocking me from looking at Jessica Alba, I am going to
assume Justin is closer to me.
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Texture Gradient: Objects look smoother if they are
farther away and rougher if they are closer.
To look at Beyonce's face from thirty feet and it will
look smooth as pudding. But get right up on her face and
you will see crevices, bumps and imperfections all
over. Smooth=far away Rough=closer.
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Relative Size: If we know that two objects are around
the same size and one looks a lot bigger in our visual
field, you are going to assume it is bigger.
The Olsen twins are hanging out at your crib. Ashley
looks huge and Mary-Kate looks really small. You are
going to assume that Mary-Kate is farther away from
you than Ashley or has some type of eating disorderwhich is more likely?
Linear perspective: Parallel lines look like the are converging
over a distance.
Binocular cues are tricks we use to see depth using BOTH
your eyes.
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So if you are missing an eye, these will do you no good.
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Retinal Disparity: We have two eyes, so the brain gets
two images. The more similar the images are between
the two eyes, your brain will assume the object is
farther away. The more of a difference the images are
between the eyes, you brain will assume the object is
closer.
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Convergence: As an object comes closer to us, our eye
muscles must strain to stay focused on the object. The
brain receives feedback from the muscles controlling eye
movements and knows that the more the eye converges,
the closer the object must be.
It is true that our culture does affect the way we
perceive the world. Some cultures, for example, do not use
certain monocular cues (like linear perceptive). Take a look
at the figure below and quickly me which line is longer.
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People in western societies
tend to perceive the first
line as being longer even
though they are the same
length. If you come from a
culture that does not use
right angles (non carpentered
cultures) you would not be
fooled by such an illusion.