Transcript PSYCHOLOGY (8th Edition) David Myers

EXPLORING
PSYCHOLOGY
EIGHTH EDITION IN MODULES
David Myers
PowerPoint Slides
Aneeq Ahmad
Henderson State University
Worth Publishers, © 2011
Sensation and Perception
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Basic Concepts and Vision
Module 14
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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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Sensing the World: Some Basic
Principles
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 called perception.
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Sensing the World: Some Basic
Principles
Analysis of a stimulus that begins with the sense
receptors and works up to the level of the brain
and mind is referred to as bottom-up processing.
Top-down processing is guided by higher-level
mental processes, as when we construct
perceptions, drawing on our experience and
expectations.
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What’s Going On Here?
Our sensory and perceptual processes work
together to help us sort out complex images.
“The Forest Has Eyes,” Bev Doolittle
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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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Thresholds
Our awareness of faint stimuli illustrate our
absolute threshold – the minimum stimulation
needed to detect a particular stimulus 50% of the
time.
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Subliminal Threshold
Subliminal Threshold: When stimuli are below one’s
absolute threshold for conscious awareness.
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Subliminal Threshold
Can we be affected by stimuli too weak to be
noticed?
In some instances yes. An invisible word or image
can prime your response to a later question by
activating certain associations which predispose
your memory, perception, or response.
However, studies have shown that subliminal
messages in advertising are ineffective, as the
effect is subtle and fleeting.
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Difference Thresholds
The difference threshold is the minimum difference between
two stimuli required for detection 50 percent of the time.
Ernest Weber noted that two stimuli must differ by a
constant minimum percentage (rather than a constant
amount), to be perceived as different. Weber fraction: k =
dI/I. This is known as Weber’s Law.
Stimulus
Constant (k)
Light
8%
Weight
2%
Tone
3%
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Sensory Adaptation
The diminished sensitivity to an unchanging stimulus
is known as sensory adaptation.
This is why we seem to get used to an unpleasant
smell in a room or an annoying background sound.
After constant exposure to a stimulus, nerve cells fire
less frequently.
This allows us to focus on informative information
rather than being distracted by constant background
stimulation.
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Now you see, now you don’t
Why, then, if we stare at an object without flinching, does it
not vanish from sight? Because our eyes are constantly
moving, enough that stimulation constantly changes.
However, if you can stop the eyes from moving, images will
begin to disappear bit by bit, reappear, and disappear again.
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Vision
What strikes our eyes is
actually pulses of
energy that our eyes
perceive as color. It is a
thin slice of the of the
whole spectrum
of electromagnetic energy.
Visible
Spectrum
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The Stimulus Input: Light Energy
Two physical characteristics of light help
determine our sensory experience of them.
Wavelength: the distance from the peak of one
light or sound wave to the peak of the next.
Influences hue – the color we experience.
Intensity: the amount of energy in a light or
sound wave. Influences our perception of its
brightness.
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The Physical Properties of Waves
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The Eye
Light enters the eye through the cornea, which protects
the eye and bends light to provide focus, then passes
through the pupil, a small adjustable opening
surrounded by the iris, a colored muscle that adjusts
light intake. The iris dilates or constricts in response to
light intensity.
Behind the pupil is a lens that focuses incoming light
rays into an image on the retina, a multilayered tissue
on the eyeball’s sensitive inner surface. The lens focuses
the rays by changing its curvature in a process called
accommodation.
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The Eye
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The Retina’s Reaction to Light
Light makes its way
through the retina’s
outer layers to the rods
– retinal receptors that
detect black, white,
and gray – and cones –
retinal receptors that
detect fine detail and
give rise to color
sensations.
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Optic Nerve, Blind Spot & Fovea
Blind Spot: Point where the optic nerve leaves the eye
because there are no receptor cells located there.
Close your left eye, look at the black dot, and hold the page about a
foot from your face, at which point the car will disappear.
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Receptors in the eye
Rods and cones differ in their geography and in the
tasks they handle. Cones cluster in and around the
fovea, the retina’s area of central focus.
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Visual Information Processing
After processing by the retina, information travels to the bipolar
cells, and then to the ganglion cells, through their axons making
up the optic nerve and to the brain. Any retinal area relays
information to the visual cortex.
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Feature Detection
Feature detectors are nerve cells in the brain that respond
to specific features of a stimulus, such as shape, angle, or
movement.
Feature detectors in the visual cortex pass information to
other cortical areas where supercell clusters respond to
more complex patterns.
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The Telltale Brain
Looking at faces, houses, and chairs activates
different brain areas in this right-facing brain.
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Parallel 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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Summary of Visual Information
Processing
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Color Vision
We talk as if objects possess color, when in fact
they do not. We perceive an object as certain
color. How then, do we see the world in color?
Knowing that any color can be created by combining the
light waves of three primary colors—red, green, and
blue—Young and von Helmholtz inferred that the eye
must have three corresponding types of color receptors.
This is now known as the Young-Helmholtz Trichromatic
(three-color) theory and has been confirmed by further
research.
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Color Blindness
Genetic disorder in which people are blind to
green or red colors. This supports the
Trichromatic theory.
People who suffer red – green deficiency have trouble
perceiving the number within the design.
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Color Vision
The trichromatic theory can’t solve all of the mysteries
of color vision.
Ewald Hering studied the effect of afterimages and
determined that that there must be two additional color
processes, one responsible for red - versus - green
perception, and one for blue - versus - yellow.
This was later confirmed by the opponent-process
theory - the theory that opposing retinal processes
(red – green, yellow - blue, white - black) enable color
vision.
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Opponent Colors
Gaze at the middle of the flag for about 30
Seconds. When it disappears, stare at the dot and report
whether or not you see Britain's flag.
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