2 – Object Recognition
A visual scene consists of objects: creatures, faces, enemies, food
Object recognition is complex – not merely a comparison of stimulus to memory.
Several factors affect object recognition:
Light and Shadow
Motion can facilitate object recognition.
In fact, some objects are recognizable only when in motion.
Examples
www.cogsci.uci.edu/~ddhoff/Sphere3.html (Donald Hoffman)
michaelbach.de/ot/mot_biomot/index.html (Michael Bach)
www.biomotionlab.ca/Demos/BMLwalker.html (Nicholas Troje)
(G. Johansson, 1973)
Motion can also inhibit object recognition.
apparent motion rapid sequence of still objects misperceived as one moving object
Examples
animation
neon lights
Animations
www.yorku.ca/eye/balls.htm
dragon.uml.edu/psych/circles_0029_red.html
psy2.ucsd.edu/~sanstis/Stuart_Anstis/Apparent_Motion.html
(Wertheimer, 1912)
Object recognition can be impeded by figure-ground confusion
Context Effects
is read as “THE CAT” even though “H” and “A” are identical.
context effect perception of stimulus is altered by surrounding stimuli
Thus, perception depends on
bottom-up processes
guided by stimulus
looks like A or H
top-down processes
guided by knowledge
should be A or O
 must be A.
More examples
EGG
FUN
Poelpe dsilkie radeing snetenecs wtih rarergaend lteerts.
Can you read this handwritten word?
More context effects
CATS CHASE RATS
CATS CHASE BATS
SHE RAN FAR
SHE BAN EAR
SHE RAN FAST
SHE RAN EAST
HIS NAME IS BOB
HIS NAME IS ROB
Context effects allow perception of a missing stimulus.
Example (from a magazine ad)
L ke y ur b ain, the n w L nd Rov r autom tic ly adj sts to anyth ng.
Context effects can create perceptual errors.
Example
Who is standing behind Bill Clinton?
Another context effect
Experiment
On each trial, S saw underlined letter that appeared alone or as part of word.
K
DARK
S was asked to read the underlined letter.
All letters appeared simultaneously and disappeared simultaneously.
Letters presented so briefly that identification was hard.
Result: Accuracy was greater when letter appeared as part of a word.
(Reicher, 1969)
Another context effect
Experiment
Ss listened to audiotape of sentences with missing sound.
The eel was on the axle.
The eel was on the shoe.
After each sentence, Ss repeated what they heard.
Results: Ss unknowingly “replaced” the missing sound.
The wheel was on the axle.
The heel was on the shoe.
(Warren, 1970)
Seeing-Hearing Context Effect
Experiment
Ss viewed video of person saying
FA
FA
FA
FA
while listening to audio of BA
BA
BA
BA
FA
FA
Then Ss were asked to repeat what they heard.
Modal response: FA
FA
That is, they believe they “heard” what they actually saw, not what they actually heard.
Video (3:39)
www.youtube.com/watch?v=G-lN8vWm3m0
(McGurk & MacDonald, 1976)
Another seeing-hearing context effect
Demo michaelbach.de/ot/mot_bounce/index.html
Experiment
Ss viewed video of two disks.
Each disk moved along a linear path at constant speed.
The disks simultaneously reached the center point.
At that moment, Ss heard a “clink” on some trials.
Results:
Modal Self-Report
No Clink
Clink
Disks pass through each other
Disks collide.
(e.g., Metzger, 1934)
Subliminal Perception
Prototypical Experiment
S saw briefly presented word, followed by mask
S cannot identify word.
Later, S was asked to choose the word from a list
Results: Accuracy slightly greater than chance
Conclusion
Under precisely controlled conditions, subliminal perception is a real phenomenon
(e.g., Cheesman & Merikle, 1984)
Subliminal Perception Outside the Lab
Experiment
Ss were asked to listen to music audiotapes with embedded message.
½ Ss given tape labeled “Memory” and were told that message improves memory.
½ Ss given tape labeled “Self-Esteem” and were told that message boosts self-esteem.
Deception: For half of the tapes of each kind, the label did not match the message.
One month later, Ss returned for tests.
Results
Type of message (memory vs. self-esteem) had no effect on Ss memory or self-esteem.
Yet some Ss reported improvement that matched label, not message (placebo effect).
Conclusion
No subliminal perception
(Greenwald, Spangenberg, Pratkanis, & Eskenazi, 1991)
agnosia
disorder in which patients cannot assign meaning to visually-perceived object
But vision and visual perception are normal
Case Study – Doctor showed patient a bell
Doctor
Patient
What is this?
I don’t know.
What is it for?
I don’t know.
agnosia  word finding difficulty
Describe it.
It’s metallic - about 15 cm tall.
agnosia  vision problem
[Rings bell.]
Oh, that’s a bell.
agnosia  auditory issue
What is it for?
It alerts people.
(Ghadiali, 2004)
Implication
Another agnosia case study
Doctor showed patient a rose
Doctor
Patient
What is this?
“A convoluted red form with a linear green attachment.”
Smell it.
“It’s a rose.”
“When leaving, the patient looked around for his hat. He reached out his hand
and took hold of his wife’s head and tried to lift it.”
(Patient Dr. P, Sacks, 1987)
Another agnosia case study
Patient
could not identify objects (left)
(Patient L.H., Farah, 2004)
but could copy objects (right).
Diagnosis of Agnosia
Patients asked to identify objects depicted in photos
(Images part of the Birmingham Object Recognition Battery)
Case study video (1:22)
www.youtube.com/watch?v=rwQpaHQ0hYw
Faces Are Special
Faces are remarkably similar (when matched for gender and skin color)
Yet we can distinguish between hundreds of faces.
Hypothesis: mind has mechanism (brain region?) devoted to face recognition.
This “faces-are-special hypothesis” is supported by several kinds of data.
Thatcher illusion distortion not noticed when face is inverted
implication: face perception is specially suited for upright faces
(Thompson, 1980)
Demo – Who are they?
Inverted Face Recognition
Experiment
Ss saw photos of famous faces and common objects.
Photos were upright or inverted.
Ss tried to identify face (e.g., Reagan) or object (e.g., house)
Accuracy and response time measured.
Results
(Yin, 1969)
Objects
Faces
Upright
Good
Good
Inverted
Fairly Good
Bad
prosopagnosia inability to recognize familiar face (but patients know it’s a face)
Patients with prosopagnosia cannot recognize famous faces like these
prosopagnosia provides further evidence that faces are special
recognize objects
recognize faces
some patients
yes
no
other patients
no
yes
Example
“A sheep farmer with prosopagnosia failed a facial recognition test in which he had to
identify a familiar face from unfamiliar faces. In contrast, he was able to recognize
familiar and unfamiliar sheep.” (Ghadiali, 2004)
(De Renzi, 1986; Farah, 1992)
Prosopagnosia test – Do you recognize these people?
www.faceblind.org
Another Prosopagnosia Test
All 3 top row photos
depict the same man.
Can you spot that man
in the bottom row?
courtesy of Ken Nakayama
In rare cases, prosopagnosia patients cannot recognize themselves in a mirror.
(Farah, 1992)
Yet patients can look at face photo and identify facial expression of emotion.
(e.g., Duchaine et al. 2003)
prosopagnosia experiment
Patient LF and 2 healthy controls looked at 10 famous face photos
While looking at each face, S heard five names (15 s each).
During this period, E measured skin conductance resistance (measure of emotion)
Then, S was asked to choose the correct name.
LF
controls
% of faces for which correct name was chosen
20% (chance)
100%
% of faces with highest SCR for correct name
60%
80%
Conclusion. Patient recognized face at some level outside his awareness.
(Not all patients with prosopagnosia show this covert recognition.)
(Bauer, 1984)
Prosopagnosia demo
courtesy of the
Exploratorium
Case Study
Dr. S (a professor who suffered a stroke)
Usually unable to recognize colleagues until they speak.
IQ = 147
(Temple, 1992)
Videos
Patient Terry (3:31)
www.youtube.com/watch?v=vwCrxomPbtY&list=UU943UnajVxe9SpFJpwxpLsQ&index=8
60 minutes 18 March 2012 part 1 (12:45) www.youtube.com/watch?v=dxqsBk7Wn-Y
British tutorial (3:09) www.youtube.com/watch?v=ZogbIvdgfzQ
Brain Games DVD - Perception (about 45 minutes – start at 1:54)
The End
CAT analog problem
bottom-up
top-down
percept
THE CAT
H A
H
H
HIS NAME IS BOB
B
PBR
ambiguity
R
Demo Two words will appear briefly in the box. Read them.
Note to instructor: hit “Enter” twice in rapid succession.
Object recognition is sometimes aided by light and shadow.
Example.
Which dimples are raised?
Why?
Light usually shines from above.
(image from O’Reilly www.oreilly.de/catalog/9780596007799/toc.html)