Sensation vs. Perception
 Sensation:
a process by which our
sensory receptors and nervous system
receive and represent stimulus energy
 Sensation is the raw data our brain takes
in from the environment.
Sensation vs. Perception
Perception: a process of organizing and
interpreting sensory information, enabling us to
recognize meaningful objects and events.
 Perception “makes sense” of sensation.
 Both involve one continuous process and
perceptual failure may occur at any level
whether at the sensory level or the perceptual
interpretation level.
 Example: Prosopagnosia
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Bottom Up vs. Top Down
Processing
Bottom Up Processing: analysis that begins with
the sense receptors and works up to the brain’s
integration of sensory information.
Involves making sense of raw sensation.
Top Down Processing: Information processing
guided by higher-level mental processes
As when we construct perceptions drawing on our
experience and expectations.
Our expectations and experiences shape how we
perceive information.
Prosopagnosia
 Is
a condition…
Bottom Up vs. Top Down
Bottom Up Vs. Top Down
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What do you see?
Bottom Up vs. Top Down
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OLD WITCH IN PICTURE
Psychophysics
 Psychophysics: study of the
relationship between physical
characteristics of stimuli and our
psychological experience of
them
Light- brightness
Sound- volume
Pressure- weight
Taste- sweetness
Sensation: Thresholds
 Absolute
Threshold:
minimum stimulation
needed to detect a
particular stimulus.
 Usually defined as the
stimulus needed for
detection 50% of the
time.
“Subliminal Messages”
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What does the research say?

http://jeffmilner.com/backmasking.htm
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http://www.nlpweekly.com/?p=527
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Homework
Sensation: Thresholds
Difference Threshold or (JND-Just
Noticeable Difference): the minimum
difference that a person can detect between
two stimuli. What does it take to tell two
similar stimuli apart?
 Weber’s Law: to perceive a difference
between two stimuli, they must differ by a
constant proportion
 light intensity- 8%
 weight- 2%
 tone frequency- 0.3%
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Sensation: Thresholds
Signal Detection Theory: predicts how
and when we detect the presence of a faint
stimulus (signal) amid background
stimulation (noise)
 Assumes that there is no single absolute
threshold
 What might a person’s detection of a
stimulus depend on?
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Sensory Adaptation

Sensory Adaptation: diminished sensitivity
with constant stimulation.
Ocean
Bad
Smell
Ads- cut in, zoom, fade out
Sensory Adaptation and
Vision
The Science of Energy and Sensation
Transduction- conversion of one form of
energy to another.
 Wavelength- the distance from the peak of
one wave to the peak of the next.
 Hue- dimension of color determined by
wavelength of light…color is matter of how far
wavelengths are apart.
 Intensity- amount of energy in a wave
determined by amplitude.

 brightness
 loudness
Human Vision Represents Narrow Part
of All Electromagnetic Energy
ROY G. BIV:
Starts from
longer to shorter
wavelengths.
R=longest;
V=shortest
Vision: Physical Property of
Waves
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)
Biology of Vision Step One:
Light Enters the Eye
1.) Light enters the eye through the
cornea: (transparent protector) and the
light passes through the pupil: (small
opening/hole). The size of the opening
(pupil) is regulated by the iris: the
colored portion of your eye that is a
muscular tissue which widens or constricts
the pupil causing either more or less light
to get in.
Biology of Vision Step Two: An
Image is Produced
2.) Behind the pupil, the
lens, a transparent
structure, changes its
curvature in a process
called accomodation,
and focuses the light rays
into an image on the lightsensitive back surface
called the retina: where
image is focuses.
Biology of Vision Step Three:
Chemical Reactions and Sight
3.) Image coming through activates
photoreceptors in the retina called rods and
cones. As rods and cones set off chemical
reactions they form a synapse with bipolar
cells which forms a synapse with ganglion
cells which fire action potentials along the
optic nerve: that carries this information to be
processed by the Thalamus: (sensory
switchboard) that sends information to the
visual cortex which resides in the occipital
lobe. The brain then constructs what you are
Parts of Retina
Blind Spot: part of retina where optic nerve
leaves the eye…no receptor cells are there.
Brain fills information in with info from other
eye.
 Fovea: central focal point of the retina, where
cones cluster.
 Cones: located near center of retina (fovea)
 fine detail and color vision
 daylight or well-lit conditions
 Rods: located near peripheral retina
 detect black, white and gray
 twilight or low light
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Rods & Cones
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
Errors In Vision
 Acuity:
the sharpness of vision
 Nearsightedness:
 nearby objects seen more clearly
 lens focuses image of distant objects in
front of retina
 Farsightedness:
 faraway objects seen more clearly
 lens focuses near objects behind retina
Errors in Vision

Normal
Vision
Farsighted
Vision
Nearsighted
Vision
Visual Involves Parallel Processing
Parallel vs. Serial: parallel means
simultaneous while serial means step by step.
Our brains process are often parallel processes
while computers work serially.
 Parallel Processing: simultaneous
processing of several dimensions through
multiple pathways. Different part of brain for:
 color
 motion
 form
 depth
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Parallel Processing
 Feature
Detectors: neurons in the
visual cortex respond to specific
features
 shape
 angle
 movement
How The Brain Perceives
Visual Information
Processing

Trichromatic (three color) Theory
 Young and Helmholtz
 three different retinal color receptors
red
green
blue
Color Deficient Syndrome
People who
suffer redgreen
blindness have
trouble
perceiving the
number within
the design
Visual Information
Processing
Opponent-Process Theory- opposing retinal
processes enable color vision. Example: Jesus
On Title Slide.
“ON”
“OFF”
red
green
green
red
blue
yellow
yellow
blue
black
white
white
black
Stare At This for 30 Seconds
Then Look At A White Surface