11 introduction to sensation and perception: vision module 11

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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

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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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