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Introduction to Sensation and
Perception: Vision
Module 11
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Sensation Overview
Sensing the World:Some Basic Principles Thresholds Sensory Adaptation
Vision The Stimulus Input: Light Energy
The Eye Visual Information Processing Color Vision
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Sensation Sensation
a process by which our sensory receptors and nervous system receive and represent stimulus energy
Perception a process of organizing and interpreting
sensory information, enabling us to recognize meaningful objects and events
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6Illustration from Sensation and Perception, Fourth Edition, by Stanley Coren, Lawrence
M. Ward, and James T. Enns, copyright © 1994 by Harcourt, Brace, and Company, reprinted by permission of the publisher.
Figure 5.14: Categorizing Perceptions: What Do You See Here?
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From Sensation and Perception, Fourth Edition by Stanley Coren, Lawrence M. Ward, and James T. Enns, p. 393; Copyright c 1994. Reprinted with permission of John Wiley & Sons, Inc.
Figure 5.19: Another Version of Figure 5.14
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Bottom-up Processing
Analysis of the stimulus begins with the sense receptors and works up to the level of
the brain and mind.
Letter “A” is really a black blotch broken down into features by the brain that we perceive as an
“A.”
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Feature Analysis – Bottom-Up
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Top-Down Processing
Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience
and expectations.
THE CHT
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Divide class in half
• Number margin 1-10
• Show half first description, the other half the second.
• Answer questions.
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• You are going to look briefly at a picture and then answer some questions about it.
• Do not dwell on the picture. Look at it only long enough to “take it all in” once.
• After this, you will answer YES or NO to a series of questions.
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Group B close your eyes
• “A” description is on the next slide
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Group A
• The picture is a rough sketch of a poster for a costume ball.
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Group A close your eyes
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Group B
• The picture is a rough sketch of a poster for a trained seal act.
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Ready to look at the picture?
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Picture
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In the picture was there . .
1. A car?2. A man?3. A woman?4. A child?5. An animal?6. A whip?7. A sword?8. A man’s hat?9. A ball?10. A fish?
It depends on the description of the picture you read!
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What does this say?
•你的媽媽是這麼胖
• You have no idea because you have no higher level experience to guide your perception.
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Top down example
Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn’t mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a total mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.
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Psychophysics
A study of the relationship between physical characteristics of stimuli and
our psychological experience with them.
Physical World Psychological World
Light Brightness
Sound Volume
Pressure Weight
Sugar Sweet
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Name the color of the font in which each word is presented as rapidly as you can
Source: Stroop, J.R. (1935). "Studies of Interference in Serial Verbal Reactions." Journal of Experimental Psychology, 18, 643-662.
The Stroop Task
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ThresholdsAbsolute Threshold: Minimum stimulation needed
to detect a particular stimulus 50% of the time.
Pro
port
ion
of
“Yes”
Resp
on
ses
0.0
0
0
.50
1.0
0
0 5 10 15 20 25 Stimulus Intensity (lumens)
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Sensory ThresholdsVision
A candle flame seen at 30 mi. on a clear, dark night
Hearing The tick of a watch under quiet conditions at 20 ft.
TasteOne teaspoon of sugar in 2 gallons of water
Smell1 drop of perfume diffused into the entire volume of a 3 room apartment
TouchThe wing of a bee falling on your cheek from a height of 1 cm
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Why Does the “Absolute” Threshold Vary?
- Signal Detection• Sensitivity:
– Intensity of the signal.– Capacity of sensory systems.– Amount of background stimulation, or “noise.”
• Response criterion reflects one’s willingness to respond to a stimulus.– Influenced by motivation and expectancies.
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Subliminal ThresholdSubliminal Threshold:
When stimuli are below one’s absolute
threshold for conscious awareness.
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Thinking Critically: Can Subliminal Stimuli Influence Your Behavior?• What am I being asked to believe or
accept?– Subliminal stimuli can influence behavior.
• What evidence is available to support the assertion?– Can have at least a temporary impact on
judgment and emotion.– No evidence as to the effectiveness of
subliminal advertising or value of subliminal self-help tapes.
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Thinking Critically: Subliminal Stimuli Influence (cont’d.)
• What conclusions are most reasonable?– Subliminal perception does occur, but has no
potential for “mind control.”– Subliminal effects are usually small and short-
lived.– Effects mainly affect simple judgments and
general measures of overall arousal.
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Subliminals
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• http://www.ted.com/talks/michael_shermer_on_believing_strange_things.html
• http://www.youtube.com/watch?v=Gv6-ZAM5gds
• http://jeffmilner.com/backmasking/index.html
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Judging Differences Between Stimuli
• Difference Threshold or Just-Noticeable Difference (JND)
• JND = Smallest detectable difference in stimulus energy.
• JND determined by two factors:– How much of a stimulus was there to begin
with?– Which sense is being stimulated?
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Weber’s Law (AP only)
• Law States That JND = KI– K is the Weber’s constant for a particular
sense (each sense has its own K value.)– I is the amount, or intensity, of the stimulus.
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Sensory Adaptation
Diminished sensitivity as a consequence of constant stimulation.
Put a band aid on your arm and after awhileyou don’t sense it.
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Now you see, now you don’t
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Transduction
In sensation, the transformation of stimulus energy (sights, sounds, smells) into neural impulses.
…we live in the past in a very real way.
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• Link to pic…http://www.eaglemanlab.net/papers/StetsonetalNeuron2006.pdf
A time illusion…?
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VisibleSpectrum
The Stimulus Input: Light Energy
Bot
h P
hoto
s: T
hom
as E
isne
r
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Wavelength (Hue)
Hue (color) is the dimension of
color determined by the wavelength
of the light.
Wavelength is the distance
from the peak of one wave to the peak of the next.
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Wavelength (Hue)
Different wavelengths of light resultin different colors.
400 nm 700 nmLong wavelengthsShort wavelengths
Violet Indigo Blue Green Yellow Orange Red
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Intensity (Brightness)
Intensity: Amount of energy in a
wave determined
by the amplitude.
It is related to perceived brightness.
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The LensLens: Transparent
structure behind the pupil that changes
shape to focus images on the retina.
Accommodation: The process by which the eye’s lens changes shape to help focus
near or far objects on the retina.
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Retina
Retina: The light-sensitive inner
surface of the eye, containing
receptor rods and cones in addition to layers of other neurons (bipolar,
ganglion cells) that process
visual information.
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Optic Nerve, Blind Spot & Fovea
http://www.bergen.org
Optic nerve: Carries neural impulses from the eye to the brain.
Blind Spot: Point where the optic nerve leaves the eye because there are no receptor cells located there.
Fovea: Central point in the retina around which the eye’s cones cluster.
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The Eye
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Test your Blind Spot
Use your textbook. Close your left eye, and fixate your right eye on the black dot. Move the page towards your eye and away from
your eye. At some point the car on the right will disappear due to a blind spot.
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Retina’s Reaction to Light- Receptors
Rods peripheral retina detect black, white and gray twilight or low light
Cones near center of retina fine detail and color vision daylight or well-lit conditions
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Rod Serling from the B&W Twilight Zone, Rod = B & W
Cone = Color
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Photoreceptors
E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969
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Rods
Cones
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Bipolar & Ganglion Cells
Bipolar cells receive messages
from photoreceptors and transmit
them to ganglion cells, which
converge to form the optic nerve.
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Visual Information Processing
Optic nerves connect to the thalamus in the middle of the brain, and the thalamus
connects to the visual cortex.
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Feature Detection
Nerve cells/neurons in the visual cortex respond to specific features, such as edges, angles, and movement…. many
cortical cells respond most strongly to specific visual information
Link 8:42 Link 2:39
Ros
s K
inna
ird/
Alls
port
/ Get
ty I
mag
es
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A Feature detector
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Shape Detection
Specific combinations of temporal lobe activity occur as people look at shoes,
faces, chairs and houses. Face blindness link 5.05
Isha
i, U
nger
leid
er, M
artin
and
Hax
by/ N
IMH
Visual agnosia link
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Visual Information Processing
Processing of several aspects of the stimulus simultaneously is called parallel processing. The
brain divides a visual scene into subdivisions such as color, depth, form, movement, etc.
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Blindsight…..
• People that report that they are blind but have some startling abilities…
• Get line orientation correct.
• Put mail in a slot.
• Unable to estimate size butcan pick up objects.
• Navigate obstacles.
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Bizarre Psych Syndromes…
• Neglect• The best description
of the neglect syndrome is an indifference to the left side of the world
• Link at 4:48 More, More
• Drawing made by a neglect patient. Notice that the left half of the flower is missing. Many neglect patients will also only draw half of the flower when drawing from memory - even with their eyes closed. This implies that the patient has also lost the ability to "scan" the left side of the internal mental picture of the flower.
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Charles Bonet Syndrome
• ….people losing their sight will begin to see things such as flowers, birds, other people, buildings that they know are not real.
• Link 5:05
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Visual Information Processing
Trichromatic (three color) Theory Young and Helmholtz three different retinal color receptors
red green blue
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PhotoreceptorsRed
ConesGreenCones
Longwave
Mediumwave
Shortwave
BlueCones
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Relative Responses of Three Cone Types to Different
Wavelengths of Light
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What do colors look like to a dichromat?
• We are provided some insight by a rare person who was deuteranope in her left eye but color-normal in her right eye.
• Red, orange, yellow, green) all appeared to have the same yellow hue
• Blue and violet appeared to be blue.
• Blue-green appeared to be a neutral gray.
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Color Blindness
Ishihara Test
Genetic disorder in which people are blind to green or red colors. This supports the
Trichromatic theory.
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Opponent Process Theory
Hering proposed that we process four primary colors combined in pairs of red-green, blue-
yellow, and black-white.
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Opponent Colors
Gaze at the middle of the flag for about 60Seconds. When it disappears, stare at the dot and report
whether or not you see Britain's flag.
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ComplementaryAfterimages
ComplementaryAfterimages
Gaze at the middle of the flag for about 60Seconds. When it disappears, stare at the dot and report
whether or not you see America's flag.
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EXPLORING PSYCHOLOGY(7th Edition in Modules)
David MyersPowerPoint Slides
Aneeq AhmadHenderson State
University, Amy Jones, Bernstain, Garber editsWorth Publishers, © 2008
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Intensity (Brightness)
Blue color with varying levels of intensity.As intensity increases or decreases, blue color
looks more “washed out” or “darkened.”
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