Chapter 5:
Perceiving Objects and Scenes
The Puzzle of Object and Scene Perception
• The stimulus on the receptors is ambiguous.
– Inverse projection problem: An image on
the retina can be caused by an infinite
number of objects.
• Objects can be hidden or blurred.
– Occlusions are common in the
environment.
Figure 5-1 p96
Figure 5-2 p96
Figure 5-3 p97
Figure 5-4 p97
Why Is It So Difficult to Design a
Perceiving Machine?
• The stimulus on the receptors is ambiguous.
– Inverse projection problem: An image on
the retina can be caused by an infinite
number of objects.
• Objects can be hidden or blurred.
– Occlusions are common in the
environment.
Figure 5-5 p98
Figure 5-6 p98
Figure 5-7 p98
Why Is It So Difficult to Design a
Perceiving Machine? - continued
• Objects can be hidden or blurred
Figure 5-8 p99
Figure 5-9 p99
Why Is It So Difficult to Design a
Perceiving Machine? - continued
• Objects look different from different
viewpoints
– Viewpoint invariance: the ability to
recognize an object regardless of the
viewpoint
– This is a difficult task for computers to
perform
Figure 5-10 p99
Perceptual Organization
• Approach established by Wundt (late 1800s)
– States that perceptions are created by
combining elements called sensations
– Structuralism could not explain apparent
movement
– Stimulated the founding of Gestalt
psychology in the 1920s by Wertheimer,
Koffka, and Kohler
– The whole differs from the sum of its parts.
• Perception is not built up from sensations,
but is a result of perceptual organization.
Figure 5-11 p100
Figure 5-12 p100
Figure 5-13 p100
Figure 5-14 p101
Figure 5-15 p101
Perceptual Organization - continued
• Illusory contours- contours that appear real
but have physical edge
Figure 5-16 p102
Gestalt Organizing Principles
• Principles of perceptual organization.
– Good continuation - connected points
resulting in straight or smooth curves
belong together
• Lines are seen as following the smoothest path
– Pragnanz - every stimulus is seen as
simply as possible
– Similarity - similar things are grouped
together
Figure 5-17 p102
Figure 5-18 p102
Figure 5-19 p103
Gestalt Organizing Principles - continued
• Proximity - things that are near to each other
are grouped together
• Common fate - things moving in same
direction are grouped together
• Common region - elements in the same
region tend to be grouped together
• Uniform connectedness - connected region of
visual properties are perceived as single unit
Figure 5-21 p103
Figure 5-22 p103
Figure 5-18 p102
Figure 5-22 p103
Figure 5-23 p104
Figure 5-24 p104
Perceptual Segregation
• Figure-ground segregation - determining what
part of environment is the figure so that it
“stands out” from the background
– Properties of figure and ground
• The figure is more “thinglike” and more
memorable than ground.
• The figure is seen in front of the ground.
• The ground is more uniform and extends
behind figure.
• The contour separating figure from
ground belongs to the figure (border
ownership).
Figure 5-25 p105
Figure 5-26 p105
Perceptual Segregation - continued
• Factors that determine which area is figure:
– Elements located in the lower part of
displays
– Convex side of borders
Figure 5-27 p105
Figure 5-28 p106
Subjective Factors That Determine
Which are is Figure
• Gestalt psychologists believed that
experience and meaning play a minor role in
perceptual organization.
• Gibson Experiment showed that figureground can affected by meaningfulness of a
stimuli.
Figure 5-30 p107
Figure 5-31 p107
Figure 5-32 p108
Perceiving Scenes and Objects in
Scenes
• A scene contains:
– background elements.
– objects organized in meaningful ways with
each other and the background.
• Difference between objects and scenes
– A scene is acted within
– An object is acted upon
Perceiving Scenes and Objects in
Scenes - continued
• Research on perceiving gists of scenes
– Potter showed that people can do this
when a picture is only presented for 1/4
second
– Fei-Fei used masking to show that the
overall gist is perceived first followed by
details.
Figure 5-33 p109
Perceiving Scenes and Objects in
Scenes - continued
• Global image features of scenes
– Degree of naturalness
– Degree of openness
– Degree of roughness
– Degree of expansion
– Color
• Such features are holistic and perceived
rapidly
Figure 5-35 p110
Regularities in the Environment:
Information for Perceiving
• Physical regularities - regularly occurring
physical properties
– Oblique effect - people perceive
horizontals and vertical more easily than
other orientations
– Uniform connectedness - objects are
defined by areas of the same color or
texture
Regularities in the Environment:
Information for Perceiving – continued
• Physical regularities - regularly occurring
physical properties
– Homogenous colors and nearby objects
have different colors
– Light-from-above heuristic - light in natural
environment comes from above us
Figure 5-36 p111
Figure 5-37 p111
Figure 5-38 p112
Regularities in the Environment:
Information for Perceiving - continued
• Palmer experiment
– Observers saw a context scene flashed
briefly, followed by a target picture.
– Results showed that:
• Targets congruent with the context were
identified 80% of the time .
• Targets that were incongruent were only
identified 40% of the time.
Figure 5-39 p113
Figure 5-40 p113
Role of Inference in Perception
• Theory of unconscious inference
– Created by Helmholtz (1866/1911) to
explain why stimuli can be interpreted in
more than one way
– Likelihood principle - objects are perceived
based on what is most likely to have
caused the pattern
• Modern researchers use Bayesian inference
that take probabilities into account
Figure 5-41 p113
Connecting Neural Activity and Object
Perception
• Grill-Spector Experiment
• FFA in each participant was monitored.
• On each trial, participants were shown either:
– a picture of Harrison Ford’s face.
– a picture of another person’s face.
– a random texture.
– All stimuli were shown for 50 ms followed by a
random-pattern mask.
– Participants were to indicate what they saw.
• 60 pictures of each type were presented.
Identifying an Object: Is That Harrison
Ford?
• Grill-Spector experiment
– Region-of-interest approach: the FFA for
each person was determined first by:
• Showing participants faces and nonfaces
• Finding the area that responded
preferentially to faces
Connecting Neural Activity and Object
Perception - continued
• For trials that only included Harrison Ford’s
face, results showed that FFA activation:
– was greatest when picture was correctly
identified as Ford.
– was less when picture was identified as
other object.
– Showed little response when there was no
identification of a face
• Neural processing is associated with both the
presentation of the stimulus and with the
response to the stimulus.
Figure 5-43 p115
Figure 5-44 p115
Brain Activity and Seeing
• Experiment by Sheinberg & Logothetis
• Monkey was trained to pull two levers:
one for a sunburst one for a butterfly
• Binocular rivalry was used - each picture
shown to one eye at the same time
• Neuron in the IT cortex that responded
only to the butterfly was monitored.
• Firing was vigorous for only the butterfly
Figure 5-45 p116
Brain Activity and Seeing - continued
• Experiment by Tong et al.
– Binocular rivalry used again with people
– Picture of a house shown to one eye and a
face to another
– Participants pushed button to indicate
perception.
– fMRI showed an increase in activity in
• Parahippocampal place area for the
house
• Fusiform face area for the face
Figure 5-46 p117
Reading the Brain
• Experiment by Kamitani & Tong
– Gratings with different orientations were
presented to participants.
– Responses from fMRI voxels were
measured.
– Activity patterns across voxels varies by
grating orientation.
– An orientation decoder was used to
analyze the voxel activity.
• The decoder could accurately predict
which orientation had been presented.
Figure 5-47 p117
Figure 5-48 p118
Figure 5-49 p118
Are Faces Special?
• Fusiform face area (FFA) - responds only to
faces
• Amygdala (AG) - activated by emotional
aspects of faces
• Superior temporal sulcus (STS) - responds to
where the person is looking and to mouth
movements
• Frontal Cortex (FC) - activated when
evaluating facial attractiveness
Figure 5-50 p119
Figure 5-51 p120
Figure 5-52 p120
Infant Face Perception
• Understanding what an infant sees using
preferential looking effect.
• Human faces are among the most important
stimuli in an infants environment.
Figure 5-53 p121
Figure 5-54 p121
Figure 5-55 p122