ep chapter 05-m
TRANSCRIPT
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Sensation and Perception
Chapter 5
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Sensation and Perception
DefinitionsSensing the World: Thresholds
Sensory Adaptation
Vision
The Stimulus Input: LightEnergy
The Eye
Visual InformationProcessing
Color Vision
Perceptual Organization
Form Perception
Depth Perception
Perceptual Constancy
Perceptual Interpretation
Sensory Deprivation
and Restored Vision
Perceptual Adaptation
Perceptual Set
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Sensation & Perception
How do we construct our representations of the external
world?
To represent the world, we must detect physical energy
(a stimulus) from the environment and convert it into
neural signals. This is a process called sensation.
When we select, organize, and interpret our sensations,
the process is calledperception.
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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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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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Our sensory and perceptual processes work together
to help us sort out complex images.
Making Sense of Complexity
The Forest Has Eyes, Bev Doolittle
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Psychophysics
A study of the relationship between physicalcharacteristics of stimuli and our psychological
experience with them.
Physical WorldPsychological
World
Light Brightness
Sound Volume
Pressure Weight
Sugar Sweet
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Exploring the Senses
What stimuli cross our threshold for
conscious awareness?
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Thresholds
AbsoluteThreshold: Minimum stimulation needed to
detect a particular stimulus 50% of the time.
Proportionof
YesResponses
0.00
0.50
1.0
0
0 5 10 15 20 25
Stimulus Intensity (lumens)
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Sensing the World Around Us
Absolute threshold
The smallest intensity of
a stimulus that must bepresent for it to be
detected
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Subliminal Threshold
Subliminal Threshold: When
stimuli are below ones
absolute threshold for
conscious awareness.
KurtScholz/Superstock
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Puzzles of Perception
Can we ever perceive what is happening
below our usual sensory threshold?
Can we pick up signals from world or fromother people without using our usual
sensory channels at all?
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Perceiving without Awareness
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Priming
A method used to insure unconscious processes, inwhich a person is exposed to information and is
later tested to see whether the information affectsbehavior or performance on another task or inanother situation
Findings suggest simple primes influence perception, memory, thinking,
and decision-making.
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Perception vs. persuasion
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Although subliminal priming can influencejudgments and preferences, research doesntsupport its success in major levels ofpersuasion.
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Extrasensory perception
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ESP
The ability to perceive something without ordinary sensory information
Has not been scientifically demonstrated
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Difference threshold
The smallest difference in stimulation thatcan be reliably detected by an observer whentwo stimuli are compared
Also called the Just Noticeable Difference(JND)
Also known as Webers Law
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Sensory Adaptation
Diminished sensitivity as a consequence of constant
stimulation.
Put a band aid on your arm and after awhile
you dont sense it.
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Vision
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Transduction
In sensation, the transformation of stimulus energy
(sights, sounds, smells) into neural impulses.
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Visible
Spectrum
The Stimulus Input: Light Energy
BothPhotos:ThomasEisner
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Physical Characteristics of Light
1. Wavelength (hue/color)
2. Intensity (brightness)
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Wavelength (Hue)
Different wavelengths of light result
in different colors.
400 nm 700 nm
Long wavelengthsShort wavelengths
Violet Indigo Blue Green Yellow Orange Red
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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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The Eye
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Parts of the eye
1. Cornea: Transparent tissue where light enters the
eye.
2. Iris: Muscle that expands and contracts to change
the size of the opening (pupil) for light.
3. Lens: Focuses the light rays on the retina.
4. Retina: Contains sensory receptors that process
visual information and sends it to the brain.
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The Lens
Lens: Transparentstructure behind the pupil
that changes shape to focus
images on the retina.
Accommodation: The
process by which the eyes
lens changes shape to helpfocus near or far objects on
the retina.
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Retina
Retina: The light-sensitive inner
surface of the eye,
containing receptorrods and cones inaddition to layers of
other neurons(bipolar, ganglion
cells) that processvisual 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 eyes cones cluster.
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Photoreceptors
E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969
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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 in the visual cortex respond to specific
features, such as edges, angles, and movement.
RossKinnaird/Allsport/Get
tyImages
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Shape Detection
Specific combinations of temporal lobe activity occur
as people look at shoes, faces, chairs and houses.
Ishai,Ungerleider,MartinandHaxby/NIMH
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Trichromatic theory
Young (1802) and vonHelmholtz (1852) bothproposed that the eye
detects 3 primarycolorsRed, blue, and green
All other colorsderived bycombination
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ColorBlindness
Ishihara Test
Genetic disorder in which people are blind to green orred colors. This supports the Trichromatic theory.
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Afterimages
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