2 – object recognition a visual scene consists of objects: creatures, faces, enemies, food

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?

CATS CHASE RATS CATS CHASE BATSSHE RAN FAR SHE BAN EARSHE RAN FAST SHE RAN EASTHIS NAME IS BOB HIS NAME IS ROB

More context effects

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

Then Ss were asked to repeat what they heard.

Modal response: FA FA 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 Disks pass through each other

Clink 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 Implication

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)

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) but could copy objects (right).

(Patient L.H., Farah, 2004)

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

Objects Faces

Upright Good Good

Inverted Fairly Good Bad

(Yin, 1969)

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 R P B R ambiguity

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)