Transcript Sensation and Perception True or False???

Sensation and Perception
True or False???
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2.
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On a clear, dark night most of us can see
a candle flame 30 miles away.
Advertisers are able to shape our buying
habits through subliminal messages.
Constant eye movements prevent our
vision from being seriously disrupted.
So, what is Sensation & Perception?
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Sensation
 The physical energy we detect (with our
senses) from the environment and encode
as neural impulses (what we sense and
send to the brain)
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Perception
 How we select, interpret and organize
our sensations (how the brain interprets
it)
Sensation and Perception
(Work together)
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Bottom-Up Processing (Sensation)
 Sense receptors detect stimuli and send to
the brain
 the brain then integrates sensory information
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Top-Down Processing (Perception)
 information processing guided by higher-level
mental processes
 How we interpret sensations based on
expectations and previous experiences
Top Down Processing
Aoccdrnig to rscheearch at Cmabridge
Uinervtisy, it deosn’t mttaer in what oredr
the ltteers in a word are, the olny
iprmoetnt tihng is that the frist and lsat
ltteer be at the rghit pclae. The rset can
be a total 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.
Top Down Processing
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How were you able to immediately make
sense of these scrambled words?
Our experience and expectations enable
us to immediately perceive the scrambled
letters as meaningful words and
sentences.
 IOW: Higher level processes guide our
perceptions.
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Failures of Perception
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Prosopagnosia: complete sensation but
incomplete perception (“face blindness”)
– Can sense visual information, but can’t
recognize it (can’t relate stored knowledge to
sensory input)
– Damage to temporal lobe area (recognition)
Sensation- Basic Principles
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Psychophysics
 study of how physical energy relates to
our psychological experience (Or: study of
interaction between sensations we receive
and our experience of them.)
 Light- brightness
 Sound- volume
 Pressure- weight
 Taste- sweetness
Gustav Fechner
Pioneer in Psychophysics
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1801-1887 (U. of Leipzig)
Theory: consciousness and
matter coexist
Mind / body: two aspects
of fundamental unity
Stared at sun! Afterimage
of blue and yellow
Mathematical relationship
b/n force of stimuli and
intensity of sensation
Sensation- Thresholds
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Absolute Threshold
 minimum amount of stimulus one can detect
50% of the time
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Difference Threshold
 minimum difference between two stimuli
required for detection 50% of the time (the
smallest change in stimulus needed to detect
that change)
 AKA- just noticeable difference (JND)
Absolute threshold
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“An absolute threshold is not absolute…”
What factors might affect the absolute
threshold?
 Repetition
 Fatigue
 Competing stimuli
 Expectation
Sensation- Thresholds
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Weber’s Law- percentage or ratio of
difference between objects remains
constant for JND, even when weight or
dimensions change
 light intensity- 8%
 weight- 2%
 tone frequency- 0.3%
Sensation- Thresholds
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Signal Detection Theory
 predicts how and when we detect the presence of
a stimulus (signal) amid competing stimuli (noise,
objects etc.)
 assumes that there is no single absolute threshold
 Factors influencing detection (response criteria)
 experience
 expectations
 motivation
 level of fatigue
Vision: Sensory Adaptation
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Sensory adaptation- diminished sensitivity
to stimulus as a consequence of constant
exposure
Eyes: constant quiver to ensure enough
continual stimulation to eye’s receptors
 Otherwise full visual image is lost
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Vision- Stabilized Images
on the Retina
Sensation- Thresholds
100
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Percentage
of correct
detections
75
50
Subliminal
stimuli
25
0
Low
Absolute
threshold
Intensity of stimulus
Medium
Subliminal
 When stimuli are
below one’s
absolute
threshold for
conscious
awareness
1957
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James Vicary
1/3000 second
Repetition
Sales increase
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Popcorn= 57%
Coke = 18%
6 week study
Falsified results
Gateway to subliminal
marketing, then
images,“sexploitation”
“Priming Effect”
Feel what we do not know and cannot
describe (shapes our perceptions a tiny bit
without our awareness)
 subliminal images: Imperceptibly brief
stimulus
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What’s the reasoning…?
The average
American will see
over 6 million ads in a
lifetime…
 Appeal to the
subconscious will
make consumer feel
more positively about
a product
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Vision
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How do we transform particles of light
into meaningful images?
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Transduction
 conversion of one form of energy to
another
 in sensation, our sensory systems
transform stimulus energies into neural
impulses
Vision
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Two physical characteristics of light help
determine how we visually sense them…
1. Wavelength
 the distance from the peak of one wave to the peak of
the next (determines hue)
 Hue: color we see determined by wavelength of light
2. Intensity
 amount of energy in a light wave determined by
amplitude
 brightness
 or loudness
Wavelengths and Color
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From shortest to longest…
Violet
Indigo
Blue
Green
Orange
Red
(We turn our eye towards an object and the
reflected light coming from the object enters
our eye.)
Vision- Physical Properties of
Waves (from an atom to a mile…)
Short wavelength=high frequency
(bluish colors, high-pitched sounds)
Great amplitude
(bright colors, loud sounds)
Long wavelength=low frequency
(reddish colors, low-pitched sounds)
Small amplitude
(dull colors, soft sounds)
The spectrum of
electromagnetic
energy: (light that
we transduce into
color)
Vision
Match the following
a.
1.
2.
3.
4.
5.
Cornea
D
Pupil
A
Iris
B
Lens
C
Retina
E
b.
c.
Adjustable opening in
the center of the eye
Ring of muscle, color
portion of the eye
around pupil- controls
size of pupil opening
Transparent- behind
pupil, changes shape to
focus images on retina
Protects eye, bends
light to provide focus
e. Eyes light sensitive
inner surface- rods,
cones, neurons that
process visual info.
d.
Vision
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Accommodation- the lens changes shape
to help focus near or far objects on the
retina
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Retina- the light-sensitive inner surface of
the eye, containing receptor rods, cones
and layers of neurons that begin the
processing of visual information
(transduction)
Retina’s Reaction to
Light- Receptors
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Rods (120 million!)
 peripheral retina / peripheral vision
 detect black, white and gray
 twilight or low light
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Cones (6 million)
 near center of retina (Fovea)
 fine detail and color vision
 daylight or well-lit conditions
Rods and Cones
Making sense of our vision…
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So why is our peripheral vision more blurred
than our focused vision? (in front of us)
 Cones = center of retina (fovea: hotline to visual
cortex = fine detail)
 Rods = periphery of retina
How do you walk effectively on a trail on a very
dark night? Why?
 Why can a cat see better than us at night?
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Vision- Receptors
Receptors in the Human Eye
Cones
Rods
Number
6 million
120 million
Location in
retina
Center
Periphery
Sensitivity in
dim light
Low
High
Color sensitive?
Yes
No
From the eye to the brain…
Optic Nerve
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Rope-like axons
form ganglion
cells- carries
information from
the eye to the
brain (1,000,000
messages at
once!)
Close your left eye- move forward to a
spot in which the car disappears. What
is this called? How do we explain it?
Retina’s Reaction to Light
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Blind Spot- point at which the optic nerve
leaves the eye- creates “blind spot”
because no receptor cells located there
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Fovea- central point in the retina, around
which the eye’s cones cluster (contains
only cones- direct connection to visual
cortex through bipolar cells = fine detail)
Vision
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Acuity- the sharpness of vision
Nearsightedness- nearby objects are
more clear than distant objects because
distant objects in front of retina
Farsightedness- faraway objects are more
clear than near objects because the image
of near objects is focused behind retina
Vision
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Normal
Vision
Nearsighted
Vision
Farsighted
Vision
Pathways from the Eyes to
the Visual Cortex
Visual Information Processing
Retina: Brain tissue /
analyzes, encodes
info & routes to
Thalamus
 Process becomes
more complex as
continues
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Visual Information
Processing
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Feature Detectors
(Hubel and Wiesel, 1979)
 Specific parts of the
visual cortex respond
to specific features
(routed by
Thalamus)
 shape
 angle
 movement
Cell’s
responses
Stimulus
Parallel Processing
feature detection is integrated in visual cortex in
split second
 IOW: angle, shape motion, depth etc of object are
all processed in different parts of cortex and then
instantly combined to create whole visual image)
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Parallel Processing
Parallel Processing
Facial recognition = 30% of cortex
 Neural networks: synchronized integration
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– ¼ of second- neurons, parts of brain
collaborate at once(40 impulses per second)
= conscious recognition!
How does this explain Prosopagnosia?
Color Vision
 “Light
rays are not colored. Color,
like all aspects of vision, resides
not in the object but in the
theater of our brains.”
Isaac Newton, 1704
How’s Your Color Vision??
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http://www.neitzvision.com/
Visual Information
Processing
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Trichromatic (three color) Theory
 AKA: Young and Helmholtz theory
 three different retinal color receptors (cones)
 red
 green
 Blue
 Combination of these cones = all colors of
visible spectrum
 Can not explain monochromatic /
dichromatic color deficiency
Color-Deficient Vision
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Dichromatic
Monochromatic
Opponent-Process Theory- opposing retinal
processes enable color vision (in retina &
thalamus, some neurons turned on/off by
certain colors)
“ON”
“OFF”
red
green
green
red
blue
yellow
yellow
blue
black
white
white
black
Opponent-Process Theory
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Helps explain monochromatic and
dichromatic color deficiency (and
afterimage)
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Most theorize that we use a combination
of both major theories (need both to
explain color vision fully)
Visual Disabilities
Stroke, illness, surgery etc. can damage the
visual cortex thus…
 Stroke victim case studies who have lost sense
of visual movement
 Blindsight: sensation of vision is functional, but
no perceptual awareness
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Thus theory of 2 visual systems in brain:
One for conscious perceptions
A second that guides our actions