What is the Relationship
Between Perception
and Sensation?
Perception brings meaning
to sensation, so perception
produces an interpretation of
the external world, not a
perfect representation of it
Copyright © Allyn and Bacon 2006
What is the Relationship Between
Perception and Sensation?
Percept : What we perceive
The meaningful product of perception –often an
image that has been associated with concepts,
memories, emotions, and motive
The primary goal of perception is to get an
accurate ‘fix’ on the world – to recognize friends,
foes, opportunities, and dangers.
Copyright © Allyn and Bacon 2006
The Machinery of
Perceptual Processing
• Feature Detectors
Cells in the cortex that specialize in extracting certain
features of a stimulus
• Binding Problem
The physical processes used by the brain to combine
many aspects of sensation to a single percept
• Example: Recognizing a face
• This is one of the major unsolved mysteries in psychology
Bottom-Up and
Top-Down Processing
• Bottom-Up Processing
Analysis that stress features of the stimulus,
rather than internal concepts
• Example: Noticing a flower in a field
• If your attention is drawn to a flower in a field, it
may be simply that the flower is more visually
outstanding than the surrounding field….you didn’t
have to think about it
Bottom-Up Processing
• In bottom-up
processing, the
resulting percept
is determined by
stimulus
features.
– Color, size,
shape…
Bottom-Up and
Top-Down Processing
• Top-Down Processing
• --Expectations
--Memories
--Knowledge
--Cultural background
--and other cognitive factors
….influence perception
Top-Down Processing
• Top-down processing is also known as
conceptually driven processing.
• Top-down does not emphasize
stimulus features
Olny srmat poelpe can raed tihs. I cdnuolt
blveiee taht I cluod aulaclty uesdnatnrd
waht I was rdanieg. The phaonmneal
pweor of the hmuan mnid, aoccdrnig to a
rscheearch at Cmabrigde Uinervtisy, it
deosn't mttaer in waht oredr the ltteers in
a wrod are, the olny iprmoatnt tihng is
taht the frist and lsat ltteer be in the rghit
pclae. The rset can be a taotl mses and
you can sitll raed it wouthit a porbelm.
Tihs is bcuseae the huamn mnid deos not
raed ervey lteter by istlef, but the wrod as
a wlohe.
• Even though the second letter in each word is
ambiguous, top down processing allows for
easy disambiguation based on the context.
Top-Down Processing
• Your dog has been lost
for three days, and you
cannot stop thinking
about him.
• When you hear a dog
bark, you assume that
it is your dog.
Perceptual Constancy
Ability to recognize the same object
A
dog
is
running
at
you
–
you
under different conditions, such as
don’t perceive
it as growing
changes
in light, distance,
or location
larger
Copyright © Allyn and Bacon 2006
• Shape Consistency:
Explains why we do not see
people morphing in shape as
they walk past us and we see
them from a different
perspective.
• Color Consistency:
Explains why a shirt will look
the same shade of blue in dim
light or sunlight
Copyright © Allyn and Bacon 2006
Perceptual Ambiguity and
Distortion
Ambiguous figures
Images that are capable of
more than one
interpretation
Illusions
The incorrect interpretation
of a stimulus pattern
(shared by others in the same
perceptual environment)
Copyright © Allyn and Bacon 2006
Perceptual Illusions
Do you see
or
?
Copyright © Allyn and Bacon 2006
Theoretical
Explanations for
Perception
Copyright © Allyn and Bacon 2006
The Gestalt Approach
• Gestalt Psychology
The theory that humans tend to create patterns and see
the ‘wholes’ and not simply the parts
• Example: People see a square and not four straight lines
connected…a school of fish…a melody
• Divides the perceptual experience into two parts.
• 1. Figure
Part of a pattern that commands attention
• 2. Ground
Part of a pattern that does not command attention; the
background
The Gestalt Approach
Closure
Tendency to fill in
gaps in figures and
see incomplete
figures as complete
The Gestalt Laws of Perceptual
Grouping
• Max Wertheimer (1923)
These laws suggest how our
brains prefer to group
stimulus elements together to
form a percept
The Gestalt Laws of Perceptual Grouping
Similarity
Proximity
Continuity
Common fate
Prägnanz
• Similarity
We tend to group similar
objects
• Proximity
We tend to group objects
together when they are
near each other.
• When you walk through
the cafeteria at lunch, you
see many people seated at
tables.
• You perceive those
individuals who are
sitting near each other as
being friends with one
another.
• You are demonstrating
Law of
Proximity
the
• Continuity
– We prefer perceptions of connected
and continuous figures over
disconnected and disjointed ones
• Common Fate
– We tend to group similar objects
together that share a common motion or
destination
• Prägnanz
• We perceive the simplest pattern
possible
• This is what makes things such as
proofreading
a text sotodifficult
Reality
is reduced
its simplest
form
Law of Pragnanz and the ‘face’ on
Mars
• People mentally
process visual
information that…
– is symmetrical
– contains the
simplest shapes
possible
– contains the
fewest number of
shapes
Perceptual Set
Readiness to detect a particular stimulus in a
given context.
We tend to perceive what we expect to
perceive.
Copyright © Allyn and Bacon 2006
More Perceptual Sets
More Perceptual Sets
• Repeat these words:
Folk
Soak
Joke
What is the white part of an egg called?
The egg white, or albumen
Copyright © Allyn and Bacon 2006
Context Effect
Setting is important
A person may not immediately
recognize someone in a different
setting
Interpreting Depth
• The human visual system interprets depth in
sensed images using both physiological and
psychological cues.
• Some physiological cues require both eyes
to be open (binocular), others are available
also when looking at images with only one
open eye (monocular)
• Binocular Cues
Information taken in by
both eyes that aids in depth
perception
 Retinal Disparity
 Images from the two eyes
differ
 The closer the object, the
larger the disparity
 Binocular Convergence
 When you look at an object
that is closer than 25 feet,
your eyes must converge on
the object to perceive it as a
single object clearly in
focus.
Hold a finger about 12
inches away
Look at it with one eye,,
then the other
The Visual Cliff Experiment
• Gibson and Walk
found that all
species tested can
perceive and avoid a
sharp drop by the
time they take up
independent
locomotion (About
6 months in
humans)
Experiments also prove depth
perception occurs in infants
as young as 2 WEEKS!
Watch Joseph Campos- Visual
Cliff Experiment at
Monocular Cues
Information about depth
that relies on the input
of one eye
 Relative Size
The smaller image of two
objects of the same size
appears more distant
 Interposition
Closer object blocks
distant object
 Relative Clarity
Hazy object seen as more
distant
 Texture
coarse = close
fine = distant
Relative Height
• Higher objects are farther
away
Relative Motion
As we move, objects at different
distances change their relative
positions in our visual image,
with those closest moving
most
Linear Perspective
The converging of parallel lines
indicates greater distance, as
in looking down a road
Light and Shadow
Dimmer objects seem more
distant.
Monocular Cues and Perception
A
B
Which box appears bigger, A or B?
Copyright © Allyn and Bacon 2006
Learning-Based
Inference
The view that perception
is primarily shaped by
learning, rather than
innate factors
Examples: You infer a
birthday party when you
see lighted candles on a
cake
Copyright © Allyn and Bacon 2006