Sensation & Perception
Chapter 4
Psyc103~019
Jen Wright
TR 12:30-1:15
perception
• Perception seems like the sort of thing that should
be straightforward…
– There is a physical world out there to be perceived
– We need to be able to perceive it in order to survive
• But, in truth, perception is a funny thing…
– We often fail to see what’s right in front of us
– And we often see things that aren’t actually there
what is perception?
• How do we explain this?
– To explain this we need to understand the
nature of perception.
• Let’s start by identifying the difference
between sensation and perception.
• Sensation – simple awareness due to the
stimulation of a sensory organ.
– A) True
– B) False
• Sensation involves transduction
• What is transduction?
– A) physical signals turned into neural signals
– B) neural signals turned into physical signals
– C) sent from sensory organs to the central nervous
system
– D) A & C
•
•
Perception – the organization, identification,
interpretation of sensation (transduced signals)
in order to form a mental representation.
Two different theories of perception:
1. Bottom-up processing
–
Physical features of stimulus alone drive perception
2. Top-down processing
–
Knowledge, expectations, desires, and thoughts of perceiver
drive perception
bottom-up
=
top-down
Thoughts,
beliefs, desires,
expectations,
past experiences
?
• Research suggests that:
– A) we build mental representations that accurately (and
impartially) reflect the world.
– B) we don’t build mental representations that accurately (and
impartially) reflect the world.
 Rather, our interpretation goes into the very construction
of the mental representation itself.
• The goal of perception is not to create a replica of the
experienced world in our heads.
• Instead, perception is a dynamic and ongoing construction
project
– short-lived models of the external world are being continuously
built
– designed for the current perceptually guided tasks of the viewer
• What we perceive depends as much on our goals,
expectations, and beliefs as it does on transduction.
– A) True
– B) False
perceptual constancy
– A) sensory signals change  perception of the
object does not change
– B) sensory signals change  perception of the
object changes
Our perception is
altered based not
on changes in
sensory stimuli but
based on beliefs.
top down processing (“seeing as”)
• Attention matters
Shift in focus results in
shift in perception.
Image 1
• Context matters
Image 3
Image 2
Image 4
• Image #1
– A) 13
– B) B
• Image #2
– A) man playing saxophone
– B) woman’s face
• Image #3
– A) “liar”
– B) man’s face
• Image #4
– A) donkey
– B) seal
• Environment (culture) matters
• Which line looks longer?
A
B
A
B
T/F: The experience of this illusion is universal to all human beings.
False! Members of Zulu and San do not experience the same illusions.
• Which of the following
faces looks messed up?
• Both right-hand faces
have eyes and mouth that
are upside down.
– So, why does the bottom
face look so much worse?
• Because of our
– Experience
– Expectations
perceptual expectations
perceptual expectations
perceptual expectations
• The conclusion is that:
• A) our sensory systems are misreporting
information about the real world to our brains.
• B) our brains are “interpreting” (rather than
straightforwardly “translating”) incoming sensory
information.
• C) neither
• Top down processing occurs for all forms of
sensory perception
– Perception of heat/cold
– Perception of weight
– Perception of tastes, sounds
• And even in our (higher-order) social perception
social perception
• Symmetrical, well-balanced
faces are perceived as more
attractive.
• They are also perceived as
• more intelligent, funny,
interesting, desirable,
competent, sexual,
successful….
– “beautiful is good” phenomenon
social cognition
• The processes by which we use available sensory
information to form impressions of other people,
to classify them according to their attributes.
• What determines what classifications we use?
• Purposes of the perceiver
– We use concepts to determine how people will affect the pursuit of our
goals.
• Accessibility in memory
– Experience may make some classifications more accessible than others.
• Availability of stereotypes
– fixed set of characteristics we tend to attribute to group members.
• Social context
– The social context strongly influences the ways we label people and their
behavior.
• The power of social context to
influence perception.
• Violinist in DC Metro Station
– Joshua Bell
• Considered one of the best violinists in the
world
– Played a violin worth $3.5 million
– People pay over $100/seat to see him
play
• He collected only $32 from over 1000
people
– http://www.youtube.com/watch?v=hnOPu0_YWhw
social categories
• Stereotypes as concepts
– top-down activation
• Shooting of Amadou
Diallo
– Pure accident?
– Outright racism?
• Automatic influence of
racial stereotype?
– Police saw him as
“armed and dangerous”
Guns–Tools Task (Payne, 2001)
Identify quickly flashed objects, half
tools and half guns.
Half were preceded by a black face, half
by a white face.
Faces prime social categories.
Participants must rapidly choose
gun or tool during the visual
mask.
200ms
200ms
300ms
Decide gun
or tool
Guns–Tools Task (Payne, 2001)
.40
Black
White
.30
Prime
.20
.10
200ms
.00
False "Tool"
200ms
300ms
Decide gun
or tool
False "Gun"
African American prime causes significant
increase in mistakenly reporting “gun”
when tool was shown
other studies
• People primed with elderly stereotype will perceive
hills to be steeper and distances longer.
• People primed with stereotype of obesity perceived
people to be less intelligent, more lazy.
• Priming with gender influences perception of artistic
pieces and writing.
• Priming of stereotypes facilitate specific
interpretations of behavior.
• People can be primed to act consistently with stereotypes
that don’t otherwise apply
– A) True
– B) False
• People can be primed to see things that are consistent with
their stereotypes even when they don’t exit
– A) True
– B) False
• Change blindness – the phenomenon of a person
viewing a visual scene and failing to detect large changes
in the scene.
• So, what is going on?
• Could be that our (short-term) visual memory is
relatively impoverished.
– we only form a representation of that which we are actually
paying attention to.
• Could be that our visual memory is richer than that of
which we are conscious.
What do we really see?
•
•
•
•
•
•
http://viscog.beckman.uiuc.edu/flashmovie/15.php
Video clip: BB counting experiment
Video clip: different person
http://viscog.beckman.uiuc.edu/djs_lab/demos.html
Gradual changes to scenes
http://nivea.psycho.univparis5.fr/Mudsplash/Nature_Supp_Inf/Movies/Movie_List.
html
• http://www.psych.ubc.ca/~rensink/flicker/download
Exam 01
30
25
20
15
Series1
10
5
0
A
B
C
D
F
Version
1
Descriptive Statistics
didn't attend
Minimum Maximum
54
37.00
95.00
Std.
Mean Deviation
76.3889 12.23306
attended
32
78.3438 10.21656
N
60.50
96.00
Version
2
Version
3
17
32
3
20
26
5