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Sensation & Perception
Chapter 4Psyc103~019
Jen WrightTR 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 mattersShift in focus
results in shift in perception.
• Context matters
Image 1
Image 2
Image 3
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 AB
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)
Faces prime social categories.Participants must rapidly choose gun or tool during the visual mask.
Identify quickly flashed objects, half tools and half guns. Half were preceded by a black face, half by a white face.
200ms
200ms
300ms
Decide gunor tool
200ms
200ms
.00
.10
.20
.30
.40
False "Tool" False "Gun"
Black
White
Guns–Tools Task (Payne, 2001)
300ms
Prime
Decide gunor tool
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.univ-paris5.fr/Mudsplash/
Nature_Supp_Inf/Movies/Movie_List.html• http://www.psych.ubc.ca/~rensink/flicker/download
Exam 01
0
5
10
15
20
25
30
A B C D F
Series1
Version1
Version2
Version3
17 32 3
20 26 5
Descriptive Statistics
NMinim
umMaxim
um Mean
Std. Deviati
ondidn't attend 54 37.00 95.00 76.388
912.233
06
attended 32 60.50 96.00 78.3438
10.21656
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