Lecture 03 Visual Perception

Question 1

Perception

Answer 1

• Picking up sensory information from external environment
• Process into perceptual experience

Question 2

Human Eye

Answer 2

• Photoreceptors
• Ganglion cells

Question 3

Photoreceptors

Answer 3

• Rods
• Cones

Question 4

Rod Cells

Answer 4

• Monochromatic
• Sensitive

Question 5

Cone Cells

Answer 5

• Colors
• Sharpness

Question 6

What are the differences between rod and cone cells

Answer 6

• Distribution
• Connection

Question 7

Ganglion Cells

Answer 7

Rod convergence: light sensitivity, less acuity

Question 8

Neural Processing

Answer 8

Found early stage in the eyes
- Lateral inhibition
- Edge enhancement

Question 9

Lateral Inhibition

Answer 9

Stimulation of a cell inhibit the activity of neighboring cells

Question 10

Edge Enhancement

Answer 10

Chevreul illusion or staircase illusion

Question 11

Visual Pathway

Answer 11

1. Retina
2. Pre-optic tracts: separated left and right eyes
3. Optic chiasma
4. Post-optic tracts: combined left and right eyes
5. Lateral geniculate nuclei (LGN)
6. Visual cortex

Question 12

Retinotopic Mapping

Answer 12

RETINAL cells correspond to points of
surface of the visual cortex

Question 13

Receptive field

Answer 13

Visual space that correspond to retinal region
- at Fovea

Question 14

3 Specialized Neurons

Answer 14

• Dot detectors
• Edge detectors
• Movement detectors

Question 15

Parallel Processing

Answer 15

Different steps are processed simultaneously
- MT: speed and movement
- V4: share and color

Question 16

V1 & V2

Answer 16

Early stage processing
- Color
- Form

Question 17

V3

Answer 17

Form and shapes but not color

Question 18

V4

Answer 18

Color and line orientation

Question 19

V5

Answer 19

Visual motion

Question 20

Medial temporal cortex (MT)

Answer 20

Speed and movement

Question 21

Two Visual Pathways

Answer 21

• Ventral
• Dorsal

Question 22

Ventral Stream

Answer 22

Occipital-Parietal: What
- Object identification
- Visual agnosia

Question 23

Dorsal Stream

Answer 23

Occipital-Temporal: Where
- Object location
- Visually guided action
- Optic ataxia

Question 24

Visual Agnosia

Answer 24

Inability to recognize object
- No difficulty in object orientation or reaching

Question 25

Optic Ataxia

Answer 25

Difficulty in reaching - No object identification

Question 26

Visual Illusions

Answer 26

Vision-for-action (how pathway) should not be affected by visual illusions

Question 27

Ebbinghaus illusion

Answer 27

- Verbal judgement → stronger illusion effect - Grasping → weaker illusion effect

Question 28

3D object sensitivity

Answer 28

Ventral pathways damage doesn't affect

Question 29

The Holistic Processing of Faces Brain Part

Answer 29

TMS on parietal cortex (dorsal) disrupts

Question 30

Color Vision

Answer 30

- Hue – colors - Saturation – vividness (amount of white) - Brightness (value) – intensity of light-to-drak

Question 31

Color Vision Functions

Answer 31

- Recognize - Categorize objects E.g., under- or overripe fruits

Question 32

Trichromatic Theory

Answer 32

- Three types of cone receptors 1) Short-wavelength (blue) 2) Medium-wavelength (yellow- green) 3) Long-wave length (orange-red) - Perceived color is determined by relative stimulation levels

Question 33

Opponent-process Theory

Answer 33

1. Red-green channel 2. Blue-yellow channel 3. Achromatic channel (white-black) - Negative afterimage [link] cannot be explained by the trichromatic theory - Adaptation of presented color -> higher sensitivity of opponent color in white light - Opponent color cannot be seen together (e.g., bluish yellow or reddish green). - Color blindness for both color in a channel

Question 34

Color Constancy

Answer 34

- Surface or object is perceived as having the same color when the illuminant (light source) is changed - Color perception does not depend solely on the wavelengths of the light

Question 35

Familiarity effect

Answer 35

- Chromatic adjustment method/Chromatic adaptation - Over-adjustment

Question 36

Scene Illumination

Answer 36

- Reflected wavelength is influenced by light source - Light source estimation is accurate -> High color constancy - The Dress: White/gold or blue/black 1) Ambiguous light source 2) Depend on how observers assume light source

Question 37

Form Perception: Gestalt Approach

Answer 37

- Perceptual organization principle - Figure-ground organization - Law of prägnanz (good figure) - Innate and intrinsic

Question 38

Organization and Features

Answer 38

1. Bottom-up process - Marr’s Computational Approach - Biederman’s Recognition-by Components Theory 2. Top-down process

Question 39

Marr’s Computational Approach

Answer 39

1. Primal sketch – 2-D description 2. 2.5-D sketch – depth and orientation 3. 3-D model representation – shape and relative position

Question 40

Biederman’s Recognition-by Components Theory

Answer 40

GEON: Basic shapes (geometric ions)

Question 41

Top-down Process

Answer 41

- Incoming signals from cortex to primary visual cortex. - Strong effects for ambiguous figures - Interactive-iterative framework

Question 42

Depth Perception

Answer 42

- Transformation of 2-D retinal images to 3-D representations. - Ambiguous information - Cues

Question 43

Cues

Answer 43

1) Monocular cues 2) Binocular cues 3) Oculomotor cues

Question 44

Monocular Cues

Answer 44

"Pictorial cues" - Interposition - Linear perspective - Familiar size - Blur - Texture gradient - Motion parallax

Question 45

Binocular Cues

Answer 45

Binocular disparity - Stereopsis: ability to perceive in 3-D - Decrease with distance

Question 46

Oculomotor Cues

Answer 46

- Vergence: Eye Rotation - Accommodation: Eye focus

Question 47

Vergence

Answer 47

Eye Rotation

Question 48

Accommodation

Answer 48

Eye focus

Question 49

Size Constancy

Answer 49

Distance -> different retinal images * Haber & Levin (2001) * Invariant size - e.g., bicycle * Variable size - e.g., TV * Unfamiliar - e.g., ovals

Question 50

Helmholtz’s theory of unconscious inference

Answer 50

Humans unconsciously made inference based on retinal image size and distance

Question 51

Accuracy of Size judgment

Answer 51

- Invariant size > Variable size > Unfamiliar