Chapters 5 & 6
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.
 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
 https://www.youtube.com/watch?v=vwCrxomPbtY
 http://www.cbsnews.com/news/face-blindness-when-
everyone-is-a-stranger-20-03-2012/
 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.
What am I
seeing?
Bottom-up
processing:
taking sensory
information and
then assembling
and integrating it
Top-down
processing:
using models,
ideas, and
expectations to
interpret sensory
information
Is that
something I’ve
seen before?
Top-down
Processing
You may start
to see
something in
this picture if
we give your
brain some
concepts to
apply:
“tree”
“sidewalk”
“dog”
“Dalmatian”
 What
do you see?

study
of the relationship
between physical
characteristics of stimuli and
our psychological experience
of them
Light- brightness
Sound- volume
Pressure- weight
Taste- sweetness
Absolute
Threshold:
minimum stimulation
needed to detect a
particular stimulus.
Usually defined as
the stimulus needed
for detection 50% of
the time.
 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?
 Stimuli

you cannot detect 50% of the time
Below one’s absolute threshold
 What
does the research say?
 http://jeffmilner.com/backmasking/
https://www.youtube.com/watch?v=L6pgoqZpfUU
 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 minimum percentage



light intensity- 8%
weight- 2%
tone frequency- 0.3%
•
The JND is always large when the
stimulus intensity is high, and small
when the stimulus intensity is low
2 stimuli must differ by a constant proportion
– Example: Think volume of tv or radio
–
•
(if the volume is low, then you only need to increase it
a little to notice the difference, in contrast, if the
volume is high, then you need to decrease it a
significant amount to notice it)
– http://www.youtube.com/watch?v=zo7FpI8MmmE
 Sensory
Adaptation: diminished sensitivity
with constant stimulation.
 Ocean
 Bad Smell
 Ads- cut in, zoom, fade out
 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
ROY G. BIV:
Starts from
longer to shorter
wavelengths.
R=longest;
V=shortest
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 process of sensation
can be seen as three
steps:
Reception--
the stimulation of
sensory receptor
cells by energy
(sound, light,
heat, etc)
Transduction-transforming
this cell
stimulation into
neural impulses
Transmission-delivering this
neural
information to
the brain to be
processed
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.
2.) Behind the pupil, the lens, a
transparent structure, changes its
curvature in a process called
accommodation, and focuses the light
rays into an image on the light-sensitive
back surface called the retina: where
image is focuses.


Light from the candle passes through the cornea
and the pupil, and gets focused and inverted by
the lens. The light then lands on the retina, where it
begins the process of transduction into neural
impulses to be sent out through the optic nerve.
The lens is not rigid; it can perform accommodation
by changing shape to focus on near or far objects.
The images we “see” are not made of light;
they are made of neural signals which can be
produced even by pressure on the eyeball.
Once neural signals
enter the optic nerve,
they are sent through
the thalamus to the
visual cortex.
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 seeing and turns image right side up.

When light reaches the back of the retina, it triggers chemical changes
in the receptor cells, called rods and cones. The rods and cones in turn
send messages to ganglion and bipolar cells and on to the optic nerve.

Rods help us see the black and white actions in our peripheral view and
in the dark. Rods are about 20 times more common than cones, which
help us see sharp colorful details in bright light.
 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
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
 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

Turning light into the mental act of seeing:
light waveschemical reactionsneural
impulsesfeaturesobjects
and one more step...

Parallel processing refers to building perceptions
out of sensory details processed in different areas
of the brain. For example:
Feature
Detectors: neurons in the
visual cortex respond to specific
features
 shape
 angle
 movement
 Trichromatic
 Young
(three color) Theory
and Helmholtz
 three different retinal color receptors
 red
 green
 blue
We see the color of an orange because it
absorbs all light except the wavelengths
that our brain interprets as orange.
You could note that the red, green and
blue don’t actually refer to the
appearance of the cones; they are the
colors to which these three cones react.
People who
suffer redgreen
blindness have
trouble
perceiving the
number within
the design
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
Opponent-Process Theory Test
The dot, the dot, keep staring at the dot in the center…

 Human
Beings maintain
Color Constancy:
perceiving familiar
objects as having
consistent color, even if
lighting changes to alter
the wavelength given
off by the object.
 http://www.brainbashers.com/showillusion.asp?129
We
only retain
color constancy
when the context
remains the same.
Same color will
look different
when compared
in different
contexts.