Transcript Slide 1

Chapter 6
Object Perception
Object recognition
0.1 sec to identify many objects.
 We typically don’t encounter things
tachistoscopically; but we instead scan.
 Fixations last typically about .25 sec.

Challenges in object recognition
Occlusion (desk, screen)
 Upside down
 Picture of a chair vs. chair
 Far chair in room vs. toy chair on desk

Two types of theories for object
recognition
Recognition by components (Biederman)
 View-based recognition (Bülthoff, Tarr, et
al.)

Geons:
Distinguishable from almost any
perspective.
 Recognizable even with occlusions.

Pros and cons of geon theory

Explains why it is hard to recognize
objects from unusual angles.
No physiological evidence.
 Sometimes recognition is viewpoint
dependent.
 Doesn’t explain recognition of individuals.
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View-based recognition

People have preferred viewing angles for
familiar objects.

Less consensus on preferred viewing
angles for novel objects.

Recognition is slower the greater the
deviance from preferred viewing angle.
Impact of rotation on recognition

James Stone (1998) showed ameboid images.
Impact of rotation on recognition

James Stone (1998) showed ameboid
images.

Guy Wallis (1998) five head shots in
apparent rotation.
Learning to see
The young woman – old woman illusion
 James Elkins experiences with moth
hunting
 Face - woman illusion
 High contrast images

Perceptual learning
(p. 230)
 Panel A: Orientation discrimination
 Panel B: Vernier acuity (The degree to
which a pair of fine lines can be aligned to
each other.)
 Panel C: Orientation of 3-line bars
(followed by mask)
 Panel D: Face recognition in the presence
of noise.
Perceptual learning
Chicken sexing
 Perception of high contrast images (p.
232)

 Pre-training:
55% for faces; 13% for others.
 Post-training: 93% for faces; 87% for others.
Inferotemporal cortex

Single cell recording reveals:
 Few
neurons that prefer oriented lines.
 Neurons with large receptive fields.
 Neurons that are sensitive to “diagnostic”
features, such as eyes of a face.
 Neurons that are occlusion insensitive.
 Neurons that are object size invariant.

Dolan: Viewing gray-scale images
facilitates interpreting high contrast
versions of those images.

Tovee, Rolls, and Ramachandran, (1996).
Monkeys shown black & white, then grayscale, then black & white again. IT cells
were more active the second time around.
Kobatake, Wang, & Tanaka, (1998).
Monkeys shown a target, then after a delay
the target with three other objects.

Monkeys improved with practice to be able
to perform with longer delays.
IT cells changed firing patterns.
Face Recognition
Much worse when contrast is reversed.
 Much worse when inverted.
 The top half of a face is harder to
recognize, when the face is hybridized.
 Anger is the most distinctive of the six
basic facial expressions (sadness,
happiness, anger, fear, surprise, and
disgust).

Prosopagnosia

Two types of strategies to cope:
 Configural:
patients base their judgements on
the overall similarity of the faces’
configuration.
 Featural processing: patients base their
judgements on parts of the face, rather than
the whole.
Greebles

http://mail.cog.brown.edu/~tarr/projects/gr
eeble_poster.html

They have symmetric body parts, families,
and genders.
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Becoming a greeble expert.
Greebles

Expert recognition: As good with general
categories as with specific categories.
 Bird
and black-capped chickadee
 Sex, family, and individual identity
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People can become greeble experts after
thousands of trials.
Become a Greeble expert
The better a person is at greeble
recognition, the more than fMRIs look like
facial fMRIs.
 The ‘face’ area appears to be deployed in
the inspection of even novel greebles.
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Attention and object recognition
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Attention reduces variability in perception.
 Prinzmetal,
et al., show that distractors
increase trial-to-trial variability in color
assessments.
Attention changes an object’s appearance
 Attention can increase sensitivity of
appearances.

Spotlight versus object attention
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Edgly, Driver, and Rafal (1994)
Attention and object recognition

Egly, Driver, and Rafal (1994) suggest that
attention is object-based.

The gorilla and girl with umbrella examples
also suggest that vision is not a spotlight,
but is object-based.
Change Blindness

See demos from Rensink at University of
South Dakota.
Imagery and Vision
Cheves Perky (1910). Confusability of
imagination and vision
 fMRI has shown that some of the same
brain regions are active during both vision
and imagining, including V1. (Kosslyn, et
al., 1999)

Imagery and Vision
Cheves Perky (1910). Confusability of
imagination and vision
 fMRI has shown that some of the same
brain regions are active during both vision
and imagining, including V1. (Kosslyn, et
al., 1999)
 TMS to V1 shows that response times on
this task are slowed by ~200msec. About
the same for both imagery and vision.

What does visual imagery look
like?
Compare doctored pictures with mental
images.
 Rate them for similarity on a scale 1-7
when simultaneously present.
 Rate them for similarity on a scale 1-7
when successively present.
 Images look like vision, except with high
frequency detail removed.
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Perceptual Aspects of Reading

Alexia = inability to read acquired late in
life.
 Letter
by letter alexia appears to be due to a
visual processing deficit.

The number of saccades and fixation
times depends on reading ability and
difficulty of material.
Basic facts on reading saccades
Saccades occur on average 0.25 sec.
 Range of 0.1-0.5 sec.
 Distance of 2 – 18 letters.
 90% of saccades among English readers
are left to right.
 By making text fill one spot, it is possible
to increase reading rates 3-4 times.
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Word superiority effect
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Letters can be better recognized in the
context of words, than in isolation.

Thus, it appears that words are processed
holistically, rather than individually.
Reading through a window
One letter at a time: 90% accuracy on
words.
 7-9 letters (so entire words could be seen),
words were read error-free, but more
slowly than normal.
 Four words at a time, reading was still
slower than normal.

Contextual influences

Expectations shape reading. Unexpected
words involve longer fixations.
Spaces in reading
Spaces are not necessary for reading. In
fact, you can learn to read about as
accurately and with comprehension with
as without them.
 Fixation points were largely unchanged
with the removal of spaces.
 Insertion of spaces in the wrong place lead
to slowed processing.

Spaces and meaning

Booth, Epelboim, and Steinman (1996).
 Meaning
Normal spacing
No spacing
versus interword spaces.
Meaningful
100%
<100%
Meaningless
<<100%
<<100%
Temporary failures of
processing
What happens in the face of extreme
ambiguity?
 Bruner and Potter (1964), studied
perception of defocused images.
 If you start with more defocused images,
recognition is slowed.

 Hypothesis:
People always conjecture
something and then persevere.
Age and recognition of defocused
images
Adults are 50% faster than children in
recognition.
 Adults shape their guesses in a
continuous way; children change their
guesses randomly at each stage.
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