Object Perception

(Recognizing the things we see)

Snowflake Lightening bolt

Different objects may look similar

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.

Recognition by components:Biederman’s geons

Properties of geons:

1) Geons can be distinguished from one another in any orientation.

2) Geons can be recognized when partially occluded (obscured).

What do you see?

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.

Are these photos all of the same horse?

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)

(Gold, Bennett, Sekuler, 1999)

Better performance after practice

Priming effect on Ambiguous figures

Top-down vs. bottom-up processes

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.

Face-inversion effect

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)

Look for a Red Triangle!

Look for a Red Triangle!

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.

Change blindness is an example of inattentional blindness, an impairment in the perception of

unattended objects.