Sensation
and
Perception
Modules
18, 19 , 20
What we’ll sense and perceive…
in this chapter:
 Sense:
 especially vision and hearing
 smell, taste, touch, pain, and
awareness of body position
 How do the sense organs and
nervous system handle incoming
sensory information?
 How does the brain turn sensory
information into perceptions?
 Why is our style of creating
perceptions better at perceiving
the real world than at decoding
tricky optical illusions?
Sensation vs. Perception
Sensation
“The process by which our
sensory receptors and
nervous system receive and
represent stimulus energies
from our environment.”
The brain
receives input
from the
sensory organs.
Perception
“The process of organizing
and interpreting sensory
information, enabling us
to recognize meaningful
objects and events.”
The brain makes
sense out of the
input from
sensory organs.
Making sense of the world
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?
Do you see a
painting or a 3D
bottle?
What’s on the
bottle?
Kids see eight to
ten dolphins.
Why do you think
kids see
something
different than
adults?
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”
From Sensory Organs to the Brain
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
Sensation-Perception
 The strange case of Dr. P
Visual Agnosia
seeing without "knowing"
 Helen Sellers
Prosopagnosia
face blindness
http://abcnews.go.com/GMA/Books/video/heather-sellers-battle-faceblindness-11906989
Fusiform area
Face recognition
Face blindness
Prosopagnosia
Greek:
“prosopon” ( face)
“ag nosia” (not knowing)
What if face recognition ok, but emotion
inputs are disconnected?
CAPRAS SYNDROME:
My wife is an imposter!!
Oliver Sacks
Prosopagnosia
face blindness
https://www.youtube.com/watch?v=k5bvnX
YIQG8
Sensation-Perception
 Agnosias show both sides of “-”
Sensation transduction/assembly
Perception recognition/meaning
 Importance of S-P research
 ancient philosophical riddle: What is reality?
 clinical and practical applications
Sensory disorders
Problems of daily living (e.g. accidents)
3 Approaches to Sens-Percep
1. Psychophysical
2. Physiological
3. Cognitive
Psychophysics
 Quantifying sensation
How much energy needed before detection?
What does "twice" as loud mean?
 Gustav Fechner (1860)
Absolute threshold (50% likelihood of being
detected)
Thresholds
The absolute threshold refers
to the minimum level of
stimulus intensity needed to
detect a stimulus half the time.
Anything below
this threshold
is considered
“subliminal.”
Psychophysics
 Gustav Fechner (1860)
JND= Just Noticable Difference
Q: What is the JND for light?
Q: What is the JND for sound?
Any general law for intensity scaling?
Weber's Law:
Intensity = constant proportion of initial stimulus
Weber Fraction
e.g., JND for light = 1/60 watts
General scaling of "intensity“
Fechner:
Stevens (1960s):
Use #JNDs above absolute
“Power Law”
Magnitude ratings
Fit mathematical curves
Best fitting exponent for each sense
When Absolute
Thresholds are not
Absolute
Signal detection theory
refers to whether or not we
detect a stimulus, especially
amidst background noise.
This depends not just on
intensity of the stimulus but
on psychological factors
such as the person’s
experience, expectations,
motivations, and alertness.
17
Signal Detection Theory (SDT)
 Detection is rarely absolute because
Stimulus certainty varies
Motivation varies
(e.g., noise)
(e.g., boredom)
 Signal Detection Theory (SDT)
Hits + / +
Correct Rejections
Misses - / +
False Alarms + / -
-/-
Signal Detection Theory (SDT)
Detection rate controlling response bias
 Takes into account statistical nature of
detection
 Takes into account psychological factors
affecting detection
Signal Detection Theory (SDT)
In medical diagnosis which signal detection
outcome is most critical?
a) Hits
b) Misses
c) False Alarms
d) Correct rejections
Signal Detection Theory (SDT)
In the judicial system which signal detection
outcome is most critical?
a) Hits
b) Misses
c) False Alarms
d) Correct rejections
Sensory Adaptation
 Entering movie theatre (vision)
 Visiting friend's apartment (smell)
 Change detection is evolutionarily critical
Why don't visual images fade?
 Saccades
eye movements
Pritchard (1961)
Martinez-Conde et al. (2006)
Sensory Adaptation
 Even visual perception of emotional
expressions show evidence of sensory
adaptation….
Gaze at the angry face on the left for 20 to 30 seconds,
then look at the center face (looks scared, yes?). Then
gaze at the scared face on the right for 20 to 30
seconds, before returning to the center face (now looks
angry, yes?). (From Butler et al., 2008.)
http://www.forbes.com/pictures/eimh45mfkh/mocha-cookie-crumble/
500
grams
of fat.
=
2 Big Macs
Subliminal Perception
 Sub + Limen
 Advertising: e.g., "Joe Camel"
Big Tobacco & Subliminal Percep.
Subliminal Perception
Silverman (1988)
Use subliminal msg. to test Freudian ideas
“Dynamic Activation Method”
Tachistoscope
“Mommy and I Are One”
RESULT? Positive mood/wellbeing
“Beating Dad is OK”
RESULT? Dart throwing accuracy
 Begg et al (1993)
Rock band Judas Priest, lawsuit: “Do it!”
Experiment : backward song effect??
No comprehension.
No effect on behavior.
 Greenwald et al. (1991)
Self-esteem; Memory enhancement
Gave wrong tape to half of sample.
Measured actual self-steem, and memory
Believed it worked---even if wrong tape!!
NO effect on self-esteem, or memory.
Subliminal Perception
Krosnick et al. (1992)
subliminal prime (dead bodies vs flowers)
rate persons in photographs
Result? primes affected ratings
Yes, subliminal primes can work.
But very weak, very brief.
ESP
Unknown sensory systems?
Telepathy
Clairvoyance
Precognition
Does ESP exist?
 JB Rhine (Duke University): 1934 book
 Zenner Cards
Guess the symbols!
Telepathy
(sender)
Clairvoyance (face down)
Precognition (predict)
 Results:
RESULT: Yes, > chance! (5 vs 7.2)
Wow! Maybe ESP is real ???
ESP: Bem & Hornton (1994 )
 Gansfeld Procedure
Sensory masking
Talk aloud about what
floats through one’s
mind
Present 4 objects
Which one correct?
 Psych Bulletin (1994
32 correct rate! (> chance)
Bem (2011) “Feeling the Future”
Extrasensory Pornception
Neutral? Chance levels (no effect).
Erotic images?
53% accuracy!!
Bem (2011) “Feeling the Future”
No one has been able to replicate Bem’s
result. Maybe it was bad stats and overly
awed reviewers.
Sensory Systems
1) Sensory neurons: transduction
2) Nerves--> spinal cord--> brain
3) Thalamus (except smell)
4) Cortex  association areas
… retrieval, comparison,
categorization...recognition,
5) Recognition !
6) Do something.
Vision
Electromagnetic Radiation Spectrum
(e.g., Newton, Faraday, Maxwell...)
The Eye
“…To suppose that the eye, with all its
inimitable contrivances for adjusting the
focus to different distances, for
admitting different amounts of light, and
for the correction of spherical and
chromatic aberration, could have been
formed by natural selection, seems I
freely confess, absurd in the highest
degree. "
Darwin, 1859
The Eye
 Charles Darwin (Origin of Species)
So complex!! Challenge to evolution theory?
 Basic anatomy of the eye
The Eye
pupil
iris
Anatomy of the Eye
A
B
Anatomy of the Eye
Visual System
 Pupil
 Accommodation
ciliary muscles changing thickness of lens
Which has no rods?
A: OWL
B: CHIPMUNK
http://www.youtube.com/watch?v=a1Y73sPHKxw
Visual System
 Retina
("Duplex" vision).
1. Rods
B&W
125 million
high convergence (many converge on 1
ganglion cell)
v. sensitive to low light (eg, Owls)
Visual System
 Retina
("Duplex" vision).
2. Cones
Color vision
6 million
(3 cone types: RGB)
(all in the Fovea)
low convergence (1 to 1 ganglion cell)
chipmunks (no Rods)
Retina (cont'd)
 Fovea
small spot, middle of retina
cones only (no rods)
 Bipolar cells
 Ganglion cells
axons --> "optic nerve"
 Horizontal & Amacrine cells
"preprocessor"
Retina layers
Receptive Fields (center-surround)
Lateral antagonism
 firing of a cell inhibits firing of
adjacent cells
 permits coding of contrasts
 Explains Hermann Grid Ilusion...
Dark/Light Adaptation
 Rods
slow to adapt (30 minutes)
10,000x more sensitive to light
 Cones
fast to adapt (10 minutes)
focal vision back quickly
Visual Pathways
 Thalamus
LGN
(lateral
geniculate
nucleus)
 Midbrain
Superior
Colliculus
 Thalamus
LGN (lateral
geniculate
nucleus)
 Midbrain
Superior
Colliculus
Visual Pathways to the Brain
LGN (Lateral Geniculate Nucleus)
 parvocellular layer (90%)
form, texture, color
 magnocellular layer (10%)
depth, brightness, motion
6
5
4
3
Lateral
Geniculate
Nucleus
90% of retinal ganglion
cells send axons to LGN
Parvocellular
layers
2
1
Magnocellular
layers
Extrastriate Cortex (green)
Faces
Houses
Chairs
Houses and Chai