Week 5: Perceiving objects part 2

Question 1

Perceptual consistency: what? (3 examples)

Answer 1

We perceive the constant properties of objects in the world
– Despite sensory information changing

	1. Size constancy
	2. Shape constancy
	3. Colour constancy

Question 2

1) Size consistency

Answer 2

Correctly perceive size on objects, despite changes in size created by viewing distance

Question 3

2) Shape consistency

Answer 3

Correctly perceive shapes of objects despite changes in viewing angle (e.g a closed or open door)

Question 4

3) Colour constancy

Answer 4

Correctly perceive same colour of an objects despite changes in the wavelengths

Question 5

Object comparison: How do we achieve perceptual constancy?

Answer 5

interpretation… Depth cues

Question 6

Depth cues (where?) (4)

Answer 6

Binocular

Oculomotor

Monocular

Motion

Question 7

Binocular cues

Answer 7

– Each eye has a different view of the world (stereopsis)

– Difference = binocular disparity

Question 8

Oculomotor cues

Answer 8

– Convergence: eyes turn inwards when we focus on close objects
– Accommodation: shape of lenses in the eye changes shape depending on an objects distance

Question 9

Monocular (pictorial) cues

Answer 9

– Interposition/occlusion
* Blocking of our view of one object by another (e.g. the people behind other people)

– Linear perspective:
	* Parallel lines seem to converge as they get farther from the viewer (e.g. the road)

– Texture gradients
	* As surface gets farther away, its texture appears finer and smoother (e.g. the cobblestones)

Question 10

Motion cues

Answer 10

– Motion parallax
* Nearby objects move more rapidly than far away objects (e.g. a car going right by you will look faster than a plane flying in the sky)

– Optic flow
* Images get larger as we approach them (e.g. a train)

Question 11

Summary so far

Answer 11

Summary

• Perceptual constancy (what?)
  ✓Size
  ✓Shape
  ✓Colour
• Depth cues (where?)
  ✓Binocular
  ✓Oculomotor
  ✓Monocular
  ✓Motion

Question 12

Agnosia

Answer 12

Failure to recognise objects
(deficit caused by brain damage)

Question 13

E.g. music professor (Dr. P)

Answer 13

Lost his ability to recognise objects and faces
– Able describe the features or components of an object, but unable to name object (i.e. visual system was not damaged)

e.g. the man who mistook his wife for a hat book

Question 14

Two subtypes of agnosia:

Answer 14

Apperceptive agnosia

Associative agnosia

(they stem from different brain regions)

Question 15

Apperceptive agnosia (and brain hemispheres)

Answer 15

Able to perceive features (e.g. colour)

UNABLE TO GROUP FEATURES TO NAME OBJECTS

Damage to posterior regions of the right hemisphere!

Question 16

Associative agnosia

Answer 16

Able to group (or combine) features

CAN’T ASSOCIATE FEATURES WITH STORED KNOWLEDGE OF OBJECT IDENTITY

Damage to temporal and occipital lobes in both left and right hemispheres.

Question 17

Implications

Answer 17

• both types of agnosia can perceive features

Apperceptive agnosia deficit of grouping features

Associative agnosia deficit with stored knowledge of object

Question 18

Face recognition

Answer 18

Involves holistic processing
- integrating info from an entire object
- holistic processing is supported by the face inversion effect (Thatcher illusion)

Question 19

Prosopagnosia (& brain region)

Answer 19

• poor face recognition (but good object recognition)

Face and object recognition involve different brain areas

Fusiform gyrus

Question 20

Summary

Answer 20

• Agnosia refers to a cognitive deficit to recognise and name objects
  – Apperceptive
  – Associative
• Face recognition differs from other forms of object recognition
  – Holistic processing
  – Prosopagnosia