Depth Perception
Problem
Solution
2D images fall on
our eyes
but we perceive
a 3D world!
Depth Perception
Monocular Cues
&
Binocular Cues
Binocular Cues
Retinal Disparity
Diff between the two
images
Closer the object = the
larger the disparity
Convergence
Degree to which eyes
face inward
Closer the object = the
greater convergence
Clues to relative distance of different
objects
Binocular Cues
Retinal/Binocular disparity: Images from the two eyes
differ. Try looking at your two index fingers when
pointing them towards each other half an inch apart
and about 5 inches directly in front of your eyes. You
will see a “finger sausage” as shown in the inset.
http://www.michaelbach.de/ot/sze_Frankfurter/index.html
Stereograms
http://www.netaxs.com/~mhmyers/rds-ex.html
Perceptual Constancy
Objects remain unchanged as their
image on the retina changes
•
•
Shape Constancy
Size Constancy – looking at the same
size objects close and far away
– Close Object –> projects larger
image on our retina.
– Far Object –> projects smaller
image on our retina.
• Example: as a person walks
away from you their retinal
image decreases in size.
However, we know that they
are just getting farther away
not shrinking in size.
If two objects are similar in
size, we perceive the one
that casts a smaller image
to be farther away
Relative Size
If one object partially blocks
our view of another object,
we perceive it as closer
Interposition
Monocular Cues
We perceive hazy
objects to be farther
away than those objects
that appear sharp and
clear
Relative Clarity
Relative Brightness
Nearby objects reflect more
light to our eyes, so
dimmer objects appear to
be farther away and
brighter objects seem
closer
Monocular Cues
Indistinct (fine) texture
signals an increasing
distance, while coarse
texture signals a close
distance.
Texture Gradient
Parallel lines appear to
converge in the distance.
The more the lines
converge, the greater
their perceived distance.
Linear Perspective
Monocular Cues
We perceive objects that are
higher in our field of vision
to be farther away than
those that are lower.
Relative Height
Objects closer to (in front of )a
fixation point move faster and
in opposing direction to those
objects that are farther away
from (behind) a fixation point,
moving slower and in the same
direction.
Relative Motion
Monocular Cues
What Cues Do You See?
Optical Illusion: Ponzo
The distant monster (below, left) and the top red bar (below,
right) appear bigger because of size constancy and the monocular
distance cues of linear perspective and texture gradient.
Linear Perspective - parallel lines appear to converge in the distance.
The more the lines converge, the greater their perceived distance
Texture Gradient – indistinct (fine) texture signals an increasing
distance, while coarse texture signals a close distance
Size Constancy - If 2
objects cast identical
retinal images (i.e.,
they are the same
size), the object
appearing further
away is perceived as
larger and so the
brain perceptually
enlarges the image
Optical Illusion: Horizontal- Vertical Illusion
The vertical line appears longer
than the equally long horizontal
line because of size constancy
and the monocular distance cue
of relative height
Relative height – Objects at the
top of our visual field appear to
be more distant.
Size constancy - If 2 objects cast
identical retinal images (i.e.,
they are the same size), the
object appearing further away is
perceived as larger and so the
brain perceptually lengthens the
vertical line.
Optical Illusion: Muller-Lyer
• (a) Outward pointing arrows signify
that the top horizontal line is farther
and thus looks longer; while (b)
inward pointing arrows signify that
the horizontal line is closer and thus
looks shorter.
• The illusion is not cross-cultural.
Non-Western subjects, and
particularly subjects whose day-today surroundings are usually not
rectangular (few buildings, doors,
walls) are much less likely to be
affected by it
Motion Perception: Phi Phenomenon
Phi Phenomenon: When lights flash
at a certain speed they tend to
present illusions of motion. Neon
signs use this principle to create
motion perception.
Motion Perception: Stroboscopic
Stroboscopic Motion – rapid sequencing of visual
images
Perceptual Organization
“The whole is different than
the sum of its parts.”
Gestalt Psychology
Max Wertheimer
(1880-1943)
Described principles by which
we organize sensations
into perceptions.
We combine bottom-up info
with top-down knowledge to
create perception
http://www.thepsychfiles.com/2007/10/episode-31lemon-slices-and-a-new-face-on-mars-gestaltprinciples-at-work/
Principles of Gestalt Psychology
Figure & Ground
(organization of the visual field
into objects (figures) that stand
out from their surroundings
(ground))





Similarity
(group figures that
are similar)
mom
mom
mom
mom
mom

Proximity
(group nearby figures together)
Principles of Gestalt Psychology
Connectedness
(spots, lines and areas
are seen as unit
when connected)
Continuity
(perceive continuous
patterns)
Closure
(fill in gaps)
Proximity
• Perceiving objects close to
each other as forming a group.
• Looking at the picture, since
the horizontal rows of circles
are closer together than the
vertical columns, we perceive
two vertical lines. Since the
first two columns and the last
two columns have less space
between them than the center
two columns, we perceive two
groups of two columns.
Closure
• The principle of closure applies
when we tend to see complete
figures even when part of the
information is missing.
• Closing up or completing figures
that are not, in fact, complete
• We see three black circles covered
by a white triangle, even through it
could just as easily be three
incomplete circles joined together.
• Our minds react to patterns that are
familiar, even though we often
receive incomplete information. It is
speculated this is a survival instinct,
allowing us to complete the form of
a predator even with incomplete
information.
Continuation
• Perceiving smoothly flowing or
continuous forms rather than
disrupted or discontinuous ones.
• As seen in the example, we
perceive the figure as two crossed
lines instead of 4 lines meeting at
the center.
• Even though the circle is not joined
together, we still perceive a circle
due to the principle of closure
Similarity
• The principle of similarity
states that things which share
visual characteristics such as
shape, size, color, texture,
value or orientation will be
seen as belonging together.
• In the example, the two filled
lines gives our eyes the
impression of two horizontal
lines, even though all the
circles are equidistant from
each other.
• In the example, the larger
circles appear to belong
together because of the
similarity in size.
Observer Characteristics: Experience / Culture
The predominating norms, behavior patterns, artifacts,
institutions, and attitudes of a group of people. In addition, past
learning shapes perception.
To an East African, the woman sitting
is balancing a metal box on her head,
while the family is sitting under a tree.
24
Observer Characteristics: Expectations
Preconceptions about what we are supposed to perceive
may also influence perception by causing us to delete,
insert, transpose, or otherwise modify what we see.
• Perceptual familiarization/generalization - strong tendency
to see what we expect to see even if our expectation
conflicts with external reality.
• Perceptual set - a readiness to perceive a stimulus in a
particular way.
• Schemas -mental framework that organizes and interprets
information
• Context Effects - immediate context of a figure influences
one’s perception of it.
Expectations: Context Effects
We interpret what we see based on the context in which we see it
(first and last letter of word).
Olny srmat poelpe can.
I cdnuolt blveiee that I cluod
aulaclty uesdnatnrd waht I was
rdanieg. The
phaonmneal pweor of the hmuan
mnid, aoccdrnig to rscheearch at
Cmabridgde
Uinervtisy, it deosn’t mttaer in
what oredr the ltteers in a word
are, the
olny iprmoatnt tihng is that the frist
and lsat ltteer be in the rghit
pclae
The rset can be a taotl mses and
you can still raed it wouthit a
porbelm.
This is bcuseae the huamn mnid
deos not raed ervey lteter by istlef,
but
the word as a wlohe. Amzanig
huh? Yaeh and I awlyas tghuhot
slpeling was ipmorantt!
26
Expectations: Context Effects
Dear Mother and Dad:
Since I left for college I have been remiss in writing and I am sorry for my thoughtlessness in not having written
before. I will bring you up to date now, but before you read on, please sit down. You are not to read any further unless
you are sitting down, okay?
Well, then, I am getting along pretty well now. The skull fracture and the concussion I got when I jumped out the
window of my dormitory when it caught on fire shortly after my arrival here is pretty well healed now. I only spent two
weeks in the hospital and now I can see almost normally and only get those sick headaches once a day. Fortunately, the
fire in the dormitory, and my jump, was witnessed by an attendant at the gas station near the dorm, and he was the one
who called the Fire Department and the ambulance. He also visited me in the hospital and since I had nowhere to live
because of the burntout dormitory, he was kind enough to invite me to share his apartment with him. It’s really a
basement room, but it’s kind of cute. He is a very fine boy and we have fallen deeply in love and are planning to get
married. We haven’t got the exact date yet, but it will be before my pregnancy begins to show.
Yes, Mother and Dad, I am pregnant. I know how much you are looking forward to being grandparents and I
know you will welcome the baby and give it the same love and devotion and tender care you gave me when I was a
child. The reason for the delay in our marriage is that my boyfriend has a minor infection which prevents us from
passing our premarital blood tests and I carelessly caught it from him. I know that you will welcome him into our family
with open arms. He is kind and, although not well educated, he is ambitious. Although he is of a different race and
religion than ours, I know your often expressed tolerance will not permit you to be bothered by that.
Now that I have brought you up to date, I want to tell you that there was no dormitory fire, I did not have a
concussion or skull fracture, I was not in the hospital, I am not pregnant, I am not engaged, I am not infected, and there
is no boyfriend. However, I am getting a “D” in American History, and an “F” in Chemistry and I want you to see those
marks in their proper perspective.
Your loving daughter, Sharon
Expectations: Perceptual
Familiarization/Generalization
28
Expectations: Schemas
• Provide punctuation that will make the following
words meaningful:
• TIME FLIES I CANT THEYRE TOO FAST
• The apostrophes come easily, but the rest is difficult.
TIME FLIES. I CAN’T. THEY’RE TOO FAST. It
still does not seem to make sense because we’re too
familiar with the slogan, “Time flies” in which
“time” is a noun and “flies” is a verb. Tell students to
read “time” as the verb and “flies” as the noun. It
now makes perfect sense.
29
Expectations: Perceptual Set
(a) Lochness monster or a tree trunk;
(b) Flying saucers or clouds?
30
Expectations: Perceptual Set
• Sine Wave Speech
– http://www.lifesci.sussex.ac.uk/home/Chris_Da
rwin/SWS/
– http://www.mrccbu.cam.ac.uk/people/matt.davis/sine-wavespeech/
• Backmasking
– http://jeffmilner.com/backmasking.htm
– http://www.youtube.com/watch?v=Qwiba6_LY
P0
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Observer Characteristics: Cognitive Style
•
COGNITIVE STYLE: Way of processing the
stimuli within the environment, which affects how
we see the world. Pg. 454 H:3-4 Demo
–
–
Field-dependent approach = perceive the environment
as a whole and do not clearly distinguish in their minds
the shape, color, size, or other qualities of individual
items. No details. “Levelers”
Field-independent approach = perceive the elements of
the environment as separate and distinct from one
another and to draw each element as standing out from
the background. A lot of details. “Sharpeners”
Observer Characteristics
•
•
•
VALUES: What we deem as important will shape
our perceptions.
PERSONALITY: Person’s unique pattern of
thoughts, feelings, and behaviors affect perception.
MOTIVATION: Our desires and needs strongly
shape our perceptions. People in need are more
likely to perceive something that they think will
satisfy that need.