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Depth Perception
Problem
2D images fall onour eyes
but we perceivea 3D world!
Solution
Depth PerceptionMonocular Cues
&Binocular Cues
Binocular Cues
Clues to relative distance of differentobjects
Retinal DisparityDiff between the twoDiff between the two
images images Closer the object = the
larger the disparity
ConvergenceDegree to which eyesDegree to which eyes
face inwardface inwardCloser the object = the greater convergence
Binocular CuesRetinal/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
http://www.netaxs.com/~mhmyers/rds-ex.htmlStereograms
Perceptual ConstancyObjects 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.
Relative SizeRelative Size
InterpositionInterposition
If two objects are similar in size, we perceive the one that casts a smaller
image to be farther away
If one object partially blocks our view of another object, we
perceive it as closer
Monocular Cues
Relative ClarityRelative Clarity
Relative BrightnessRelative Brightness
We perceive hazy objects to be farther
away than those objects that appear
sharp and clear
Nearby objects reflect more light to our eyes,
so dimmer objects appear to be farther away and brighter
objects seem closer
Monocular Cues
Texture GradientTexture Gradient
Linear PerspectiveLinear Perspective
Indistinct (fine) texture signals an
increasing distance, while coarse texture
signals a close distance.
Monocular Cues
Parallel lines appear to converge in the distance. The more the lines converge, the greater their
perceived distance.
Relative HeightRelative Height
Relative MotionRelative Motion
We perceive objects that are higher in our field of vision to be farther away
than those that are lower.
Monocular Cues
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.
What Cues Do You See?
Optical Illusion: PonzoThe 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 distanceTexture 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-to-day 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.
Stroboscopic Motion – rapid sequencing of visual images
Motion Perception: Stroboscopic
Perceptual Organization
Max Wertheimer(1880-1943)
““The whole is different thanThe whole is different thanthe sum of its parts.”the sum of its parts.”
Gestalt PsychologyDescribed principles by which
we organize sensationsinto perceptions.
We combine bottom-up info with top-down knowledge to
createcreate perceptionhttp://www.thepsychfiles.com/2007/10/episode-31-lemon-slices-and-a-new-face-on-mars-gestalt-principles-at-work/
Principles of Gestalt Psychology
Proximity (group nearby figures together)
Similarity (group figures that
are similar)
Figure & Ground(organization of the visual
field into objects (figures) that stand out from their
surroundings (ground))
Principles of Gestalt PsychologyContinuity
(perceive continuous patterns)
Closure (fill in gaps)
Connectedness (spots, lines and areas are seen as unit when connected)
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
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To an East African, the woman sitting is balancing a metal box on her head, while the family is
sitting under a tree.
The predominating norms, behavior patterns, artifacts, institutions, and attitudes of a group of people. In addition, past learning shapes perception.
Observer Characteristics: ExpectationsPreconceptions 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
Olny srmat poelpe can.I cdnuolt blveiee that I cluod
aulaclty uesdnatnrd waht I was rdanieg. The
phaonmneal pweor of the hmuanmnid, aoccdrnig to rscheearch at
CmabridgdeUinervtisy, 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 rghitpclae
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. Amzanighuh? Yaeh and I awlyas tghuhot
slpeling was ipmorantt!
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We interpret what we see based on the context in which we see it (first and last letter of word).
Expectations: Context EffectsDear 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
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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.
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(a)Lochness monster or a tree trunk;
(b) Flying saucers or clouds?
Expectations: Perceptual Set
Expectations: Perceptual Set• Sine Wave Speech
– http://www.lifesci.sussex.ac.uk/home/Chris_Darwin/SWS/
– http://www.mrc-cbu.cam.ac.uk/people/matt.davis/sine-wave-speech/
• Backmasking– http://jeffmilner.com/backmasking.htm– http://www.youtube.com/watch?
v=Qwiba6_LYP0
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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.454H:3-4Demo
– 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.