Object Perception (Recognizing the things we see)

SnowflakeLightening 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 ProcessesBottom-up > grabs control (attention) Controlled Processes (Attention)Top-down > uses memory sets and expectations > affects perception Interaction between the two processes!

RED YELLOW BLUE GREEN RED GREEN YELLOW BLUE YELLOW GREEN BLUE RED BLUE RED GREEN YELLOW RED GREEN BLUE YELLOW Stroop Task

RED BLUE GREEN YELLOW YELLOW BLUE RED GREEN BLUE YELLOW GREEN RED GREEN BLUE YELLOW RED BLUE 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) 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!

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.