Sensation and Perception
Sensation & Perception
To represent the world, we must detect physical energy (a
stimulus) from the environment and convert it into neural
signals. The process by which sensory systems and the
nervous system receive stimuli from the environment is
sensation.
When we select, organize, and interpret our sensations, the
process is called perception.
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.”
Top-Down Processing
Information processing guided by higher-level
mental processes as we construct perceptions,
drawing on our experience and expectations.
THE CHT
Making Sense of Complexity
Our sensory and perceptual processes work
together to help us sort out complex images.
“The Forest Has Eyes,” Bev Doolittle
Can you read this?
 Ancordicg to a reaesrch at Carbmidge Univeristy, it
dosen't maettr in waht odrer the letters in a wrod
are. The olny improtant tihng is taht the fsrit and lsat
lteter be in the rihgt pcale.
 The rset can be a toatl mses and you can slitl raed it
wiuhott proelbm. Tihs is becuase the huamn mnid
deos not raed eevry letter by iestlf, but the wrod as a
whloe.
Exploring the Senses
What stimuli cross our threshold for
conscious awareness?
Absolute Threshold: Minimum stimulation
needed to detect a particular stimulus
50% of the time.
Absolute Thresholds
 VISION:
Candle Flame
seen at _________ on a
clear night
 HEARING: Tick of a
watch under quiet
conditions at________
 TOUCH: A bee’s wing
falling on your cheek
from
__________above
 30 miles
 20 feet
 One centimeter
Absolute Thresholds
 SMELL: __________
 1 drop
of perfume diffused into
a three-room apartment
 TASTE: __________
of sugar in two gallons of
water
 1 teaspoon
Psychophysics
A study of the relationship between physical
characteristics of stimuli and our psychological
experience with them. How we detect events in our
environment using our sensory systems
Physical World
Psychological
World
Light
Brightness
Sound
Volume
Pressure
Weight
Sugar
Sweet
Subliminal Threshold
Subliminal Threshold:
When stimuli are below
one’s absolute threshold for
conscious awareness.
Kurt Scholz/ Superstock
Weber’s Law
Two stimuli must differ by a constant minimum
percentage (rather than a constant amount), to be
perceived as different.
Minimum amount needed to notice difference
Quarters/Envelope/Shoes Activity
The Point?
 Difference thresholds
grow with the
magnitude of the
stimulus
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.
Marker Activity
 Sniff a marker and rate your perception of the
intensity of the aroma from 1 to 20.
 Sniff the marker six times. Each time rate your
perception of the intensity of the aroma.
This is sensory adaptation! Much like getting
used to being in a cold pool of water.
Both Photos: Thomas Eisner
The Stimulus Input: Light Energy
Visible
Spectrum
Wavelength (Hue)
Hue (color) is the
dimension of
color determined
by the
wavelength of the
light.
Wavelength is the
distance from the
peak of one wave
to the peak of the
next.
Wavelength (Hue)
Violet
Indigo
400 nm
Short wavelengths
Blue
Green
Yellow
Orange
Red
700 nm
Long wavelengths
Different wavelengths of light result
in different colors.
Intensity (Brightness)
Intensity:
Amount of
energy in a
wave
determined by
the amplitude.
It is related to
perceived
brightness.
Intensity (Brightness)
Blue color with varying levels of intensity.
As intensity increases or decreases, blue color
looks more “washed out” or “darkened.”
The Eye
Parts of the eye
1.
2.
3.
4.
Cornea: Transparent tissue where light enters
the eye.
Iris: Muscle that expands and contracts to
change the size of the opening (pupil) for light.
(colored portion of our eye)
Lens: Focuses the light rays on the retina.
(creates nearsightedness or farsightedness)
Retina: Contains sensory receptors that process
visual information and sends it to the brain.
The Lens
Lens: Transparent
structure behind the
pupil that changes shape
to focus images on the
retina.
Accommodation: The
process by which the
eye’s lens changes shape
to help focus near or far
objects on the retina.
Retina
Retina: The lightsensitive inner
surface of the eye,
containing receptor
rods and cones in
addition to layers of
other neurons
(bipolar, ganglion
cells) that process
visual information.
Optic Nerve, Blind Spot & Fovea
Optic nerve: Carries neural impulses from the eye to the
brain.
Blind Spot: Point where the optic nerve leaves the eye
because there are no receptor cells located there.
Fovea: Central point in the retina around which the eye’s
cones cluster.
http://www.bergen.org
Test your Blind Spot
 Blind spot testers:
 Close your right eye
 Use your left eye to look at the face on the right side of
the paper
 You should be able to see the face on your left with your
peripheral vision
 Now SLOWLY move the paper away from and towards
your face while focusing on the face on the right
 At some point, the left face will disappear. That is your
blind spot!
Photoreceptors
E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969
Bipolar & Ganglion Cells
Bipolar cells receive messages from
photoreceptors and transmit them to ganglion
cells, which converge to form the optic nerve.
Visual Information Processing
Optic nerves connect to the thalamus in the
middle of the brain, and the thalamus connects to
the visual cortex.
Shape Detection
Ishai, Ungerleider, Martin and Haxby/ NIMH
Specific combinations of temporal lobe activity
occur as people look at shoes, faces, chairs and
houses.
Visual Information 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.
Color Vision
Trichromatic theory: Young and von Helmholtz
suggested that the eye must contain three receptors
that are sensitive to red, blue and green colors.
Try this Activity. You will have about 3 seconds to read the
following statement..
tHecoWgAvecOla
thEcoWgAvecOla
TheCowGaveCola
Want to try again?
Try reading the statement below from right to
left. You will have about 3 seconds to read it.
Then write it down!
“.tar eht was tac ehT”
Did you write “The cat was the rat”?
If you did you were incorrect. The correct answer is:
“The cat SAW the rat”
Let play it again one more time.
You get three seconds to look
Very carefully, then write it
down! Without Blurting Out!
CONES – Receptors for color vision that work best in the
daylight. Located in the Retina which receives focused light.
RODS – Receptors for night and side (peripheral) vision.
At left, Rods & cones under the microscope
After image experiment. Focus on the center of the circle without moving your
eyes for 30 seconds. Then look at the surrounding area. You will see an after
image.
Opponent Colors
Gaze at the dot in middle of the flag for about 30
seconds. When it disappears, close your eyes and report
whether or not you see Britain's flag.
VISUAL DYSFUNCTIONS (cont.) Most common problem;
Females 0.05%
cannot see red or green. Males 8%
Do
animals
see
color?
Animals
have
rods &
cones
which
allow
them to
see color.
This bull
must be
seeing
red!
Color Test One
Look at the pictures below. Do you see a puzzle piece in the picture on the left? If you do,
you have normal color vision. The picture on the right will give you an idea of how the
color picture would look to someone that is totally colorblind. It is the same picture using
shades of grey. Without the colors as a reference the image in the picture disappears.
Red Deficient
Red Deficient
Green Deficient
Color Blindness/Color Deficient
Genetic disorder in which people are blind to
green or red colors. This supports the
Trichromatic theory.
Ishihara Test