Sensation and Perception True or False???
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Transcript Sensation and Perception True or False???
Sensation and Perception
True or False???
1.
2.
3.
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?
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)
Perception
How we select, interpret and organize
our sensations (how the brain interprets
it)
Sensation and Perception
(Work together)
Bottom-Up Processing (Sensation)
Sense receptors detect stimuli and send to
the brain
the brain then integrates sensory information
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
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.
Failures of Perception
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
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
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
Absolute Threshold
minimum amount of stimulus one can detect
50% of the time
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
“An absolute threshold is not absolute…”
What factors might affect the absolute
threshold?
Repetition
Fatigue
Competing stimuli
Expectation
Sensation- Thresholds
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
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
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
Vision- Stabilized Images
on the Retina
Sensation- Thresholds
100
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
James Vicary
1/3000 second
Repetition
Sales increase
–
–
–
–
–
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
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
Vision
How do we transform particles of light
into meaningful images?
Transduction
conversion of one form of energy to
another
in sensation, our sensory systems
transform stimulus energies into neural
impulses
Vision
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
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
Accommodation- the lens changes shape
to help focus near or far objects on the
retina
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
Rods (120 million!)
peripheral retina / peripheral vision
detect black, white and gray
twilight or low light
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…
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?
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
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
Blind Spot- point at which the optic nerve
leaves the eye- creates “blind spot”
because no receptor cells located there
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
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
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
Visual Information
Processing
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)
Parallel Processing
Parallel Processing
Facial recognition = 30% of cortex
Neural networks: synchronized integration
– 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??
http://www.neitzvision.com/
Visual Information
Processing
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
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
Helps explain monochromatic and
dichromatic color deficiency (and
afterimage)
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
Thus theory of 2 visual systems in brain:
One for conscious perceptions
A second that guides our actions