object perception (recognizing the things we see)
TRANSCRIPT
Similar objects may look very different
chairs
coffeepots
sunglasses
Challenges of object recognition
1) How can we recognize objects when we can’t see all the parts?
2) How can we distinguish among objects that share common features?
3) How can we recognize group membership of objects that look very different?
Recognizing 3-D objects
How can we recognize the same object in multiple orientations?
• Recognition by components.
• View-based recognition.
Properties of geons:
1) Geons can be distinguished from one another in any orientation.
2) Geons can be recognized when partially occluded (obscured).
View-based recognition
1) Recognition of 3-D objects depends upon multiple, stored views of objects.
2) Object recognition occurs when a current pattern matches a stored pattern.
Learning to see
When you encounter the same object again and again, the way you perceive that object can change.
(Practice effect)
What’s happening?Fine-tuning your visual system
(plasticity of the brain)
Top-down vs. Bottom-up Processes
Automatic Processes Bottom-up
> grabs control (attention)
Controlled Processes (Attention) Top-down
> uses memory sets and expectations> affects perception
Interaction between the two processes!
RED YELLOW BLUE GREENRED GREEN YELLOW BLUEYELLOW GREEN BLUE REDBLUE RED GREEN YELLOWRED GREEN BLUE YELLOW
Stroop Task
RED BLUE GREEN YELLOWYELLOW BLUE RED GREENBLUE YELLOW GREEN REDGREEN BLUE YELLOW REDBLUE YELLOW RED GREEN
The temporal (‘WHAT’) pathway and object recognition
Inferotemporal (IT) cortex is involved in object recognition
(WHAT)
(WHERE)
Faces: Special objects
People are very good at reading faces for information about age, gender, and emotional state.
We are experts at recognizing faces.
We are so good that an upside face is difficult to recognize.
Development of Face Perception
9 minutes old: face patterns preferred
Staring Time (sec)
0 10 20 30
36 hours: imitate expressions
1 to 3 months old: parent recognition
Prosopagnosia: Failure of face recognition
People with prosopagnosia can describe a face, but cannot recognize whose face it is.
Oliver Sacks (The Man who Mistook his Wife for a Hat)
Are faces special?
Greebles
Greebles are computer-generated creatures that differ by gender, family membership, and individual identity.
(Gauthier & Tarr, 1999)
People trained to identify greebles show increased activation of “face” areas of the brain when
recognizing new greebles.
Maybe “face” area is really an “expert” area.
Still a hot topic for debate!(Kanwisher vs. Gauthier)
Attention and object recognition
Objects in the environment compete for attention.
Brightly coloured objects may “pop-out” at us, and capture attention from the bottom up
(e.g., red coat in a black and white film)
A purposeful search for an object involves top-down attentional processing
(e.g., looking for a friend in a crowd).
Object-based attention
When you attend to an object it increases the neural processing of that object and enhances recognition.
Attention acts as an amplifier.
Attention operates at the level of an entire object, not just a certain spatial location.
Object-based attention: (Egly, Driver, Rafal, 1994)
Fixation Cue (Prime) Test
• • •
• • •
Valid
• • •
Invalid(same object)
Invalid(different object)
Sequence of events
Attention can induce blindness
When our attention is diverted, we may fail to see an object change in a scene.