Sensation &
Perception
basic terminology
Sensation
Information coming into our brain from our sensory
receivers
Perception
The way the brain organizes and interprets the data
received by our senses
Can you have sensation without perception?
Prosopagnosia
Complete sensation in the absence of perception
Example of Prosopagnosia: FACE BLINDNESS
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.”
• Bottom-up processing is also known as
"small chunk" processing and suggests that
we attend to or perceive elements by starting
with the smaller, more fine details of that
element and then building upward until we
have a solid representation of it in our minds.
• If you're the type of person who understands
concepts and ideas by starting with the
details and then working your way up to the
main idea of overall concept, then you're a
bottom-up processor.
Top-Down Processing
• Information processing guided by higher-level
mental processes as we construct
perceptions, drawing on our experience and
expectations.
• Top Down Processing explains how our
expectations and prior experiences guide our
perceptions.
THE CHT
• Top-Down Processing is also known as
"large chunk" processing and states that we
form perceptions (or focus our attention) by
starting with the larger concept or idea (it
can even be the concept or idea of an object)
and then working our way down to the finer
details of that concept or idea.
• If you're the type of person who learns new
ideas and concepts (or forms impressions)
by starting first with the high-level aspects
and then working your way down to the fine
details, then you're a top-down processor.
Bottom Up Vs. Top Down
• What do you see?
Bottom Up vs. Top Down
What do You See?
Top-Down Processing
• Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it
deosn't mttaer in waht oredr the ltteers in a wrod
are, the olny iprmoetnt tihng is taht the frist and lsat
ltteer be at the rghit pclae. The rset can be a total
mses and you can sitll raed it wouthit a porbelm.
Tihs is bcuseae the huamn mnid deos not raed
ervey lteter by istlef, but the wrod as a wlohe.
Sensation vs. Perception
What do you see?
Sensation vs. Perception
What do you see?
Making Sense of Complexity
“The Forest Has Eyes,” Bev Doolittle
How many faces do you see?
Thresholds
Absolute Threshold
Minimum stimulation needed to detect a particular
stimulus 50% of the time.
Subliminal Messages
Messages presented below absolute thresholds –
not consciously perceived
“Subliminal Messages”
• Some have argued that humans still “pick up”
these messages that influence our
“unconscious.” Do these messages have
suggestive powers?
• Skeptics argue “Subliminal Messages” are
heavily influenced by top down processes.
• Example: Feeling “hungry” during subliminal
advertisements.
Mr. Subliminal
Subliminal Message In Beer Ad?
Subliminal Messages In Money
Subliminal Message In
“The Lion King?”
Difference Threshold
Amount of change needed to notice that a change
has occurred.
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?
Sensory Adaptation
Diminished sensitivity as a consequence of
constant stimulation.
Put a band aid on your arm and after awhile
you don’t sense it.
The EYE
vision
The Eye
Structures of the eye
Cornea - Protective covering over the pupil.
Iris - Muscle in front of the lens that constricts to
shut out light or relaxes to let in light through the
opening known as the pupil. Regulates the amount
of light passing through the pupil.
Pupil - The hole through which light enters the eye.
Lens - A flexible transparent structure in the eye that
changes its shape to focus light on the retina. Light
enters through the lens and pupil.
Structures of the eye – cont’d
Retina - Surface at the back of the eye containing rods
and cones.
Rods - Receptors that are adapted for vision in dim
light.
Cones - Receptors for color, detail, and daytime vision.
Optic nerve - The nerve that carries impulses from the
retina to the brain.
Blind Spot - The point where on the optic nerve, there
are no visual receptors so no image can be seen.
Biology of Vision: Know the Steps
Behind the pupil, the lens focuses the light rays into
an image on the back surface of the eye called the
retina where the image is focused. The retina is like
a movie screen.
Biology of Vision: Know the Steps
•
Image coming through activates photoreceptors in
the retina called rods and cones (process information
for darkness and color).
•
The rods and cones set off chemical reactions they
form a synapse with bipolar cells which change light
energy into neural impulses.
•
These neural impulses go to the optic nerve (bundle
of neurons that take information from retina to the
brain) and eventually get to the visual cortex in the
occipital lobe.
Opponent Process Theory of Color
Vision
http://www.yorku.ca/eye/afterima.htm
Opponent Process Theory of Color Vision (Hering).
Three sets of color receptors (cones) in the visual system.
Stimulation of one member of a set produces the
sensation of the corresponding color. Through
disassimilation (red, yellow, white) and restitution (blue,
green, and black.)
• Cone receptors are combined in three pairs- blue/yellow;
red/green; black/white.
• This produces the afterimage effect
Trichromatic Theory of Color
Vision
•
Theory
•
– The results from many experiments led to the formation of the Young-Helmholtz
theory of color vision. This theory states that three receptors in the retina of the
eye are responsible for the perception of color by the brain. Each receptor is
sensitive to a single color: red, green or blue. The combination of these three
colors can form any visible color in the spectrum. This theory is more commonly
known as the trichromatic theory of color vision.
Color Blindness
– This theory paved the way to understanding color blindness. According to the
Encyclopedia Britannica, the existence of several kinds of color blindness can be
explained as the lack of function of one or more sets of the cones. If one set of
cones is not operating correctly, dichromatism occurs (also known as partial
color blindness). In rarer circumstances, an individual can suffer from
monochromatism, or complete color blindness
• Thomas Young’s research found that human’s
see color because of three cones. Stimulation in
the form of wavelengths of light must occur in all
three cones before one sees color. When two
wavelengths are mixed the colors are not
matched.
• Three colors are all that is
needed to provide the colors
on the color spectrum
Opponent Process Theory
Gaze at the middle of the flag.
When it disappears, stare at the dot and report
whether or not you see Britain's flag.
What just happened is called a NEGATIVE AFTERIMAGE