Visual Perception

Question 1

Akinetopsia:

Answer 1

• Inability to perceive motion even though other aspects of vision seem normal
  
  • Can see difference in position (object that was here is now over there), but doesn’t see the object moving

Question 2

Retina

Answer 2

◦ Light sensitive tissue lining back of eyeball

◦ Fovea (center of retina)

Question 3

Cornea and lens

Answer 3

◦ Focus incoming light
◦ Muscle around lens tightens to bulge lens to focus nearby objects
◦ Muscle around lens relaxes to flatten lens to focus far away objects

Question 4

Photoreceptors:

Answer 4

Located on retina

Rods and Cones

Question 5

Rons

Answer 5

◦ Sensitive to low levels of light
◦ Can distinguish different intensities of light
◦ Can’t distinguish colour
◦ More rods than cons farther away from fovea

Question 6

Cones

Answer 6

◦ Less sensitive than rods
◦ Need more incoming light to operate
◦ Sensitive to colour differences
◦ 3 different types, each respond to different wavelengths
◦ Important for acuity
• Ability to see detail
◦ In fovea, cons far out number rods (no rods at all in center of fovea)

Question 7

Bipolar cells

Answer 7

Intermediate cells that are stimulated by photoreceptors which then excite ganglion cells

Question 8

Ganglion cells

Answer 8

Spread uniformly across retina, but axons converge to form optic nerve

Question 9

Lateral Geniculate Nucleus (LGN)

Answer 9

◦ Info from optic nerve sent here first, then transmitted to occipital lobe
◦ Located in thalamus

Question 10

Lateral Inhibition

Answer 10

Once stimulated, cells inhibit activity of neighbouring cells

Question 11

Edge enhancement

Answer 11

Lateral inhibition highlights a surfaces edge because cells in the middle will be inhibited more than cells at the edge

Question 12

Single Cell Recording:

Answer 12

• Animal is immobilized and has electrodes placed outside optic nerve or brain
  
  • Various patterns on a computer flashed in front of animals eyes
  • Used to define a cell’s receptive field (size and shape of area in visual that the cell responds to)

Question 13

Receptive Fields:

Answer 13

Hubel and Wiesel discovered existence of specialized neurons, each with a different type of receptive field and different kind of visual trigger

Question 14

Center-surround cells

Answer 14

◦ Center has one response, surrounding ring has opposite response
◦ If both center and surrounding are stimulated, they cancel each other out

Question 15

Edge detectors

Answer 15

◦ Fire at maximum only when a stimulus has an edge in a specific orientation (i.e. horizontal, vertical)
◦ Will still fire when they detect a stimulus orientated in a different way, but not as strongly

Question 16

Parallel Processing: Area V1

Answer 16

◦ Site on occipital lobe where axons from LGN first reach cortex
◦ Contains cells to detect every kind of stimulus (horizontal, vertical…etc)

Question 17

Parallel Processing: Area MT

Answer 17

Neurons are acutely sensitive to direction and speed of movement

Question 18

Parallel Processing: V4

Answer 18

Neurons most sensitive to certain colour and certain shapes

Question 19

P Cells

Answer 19

• Provide main input for LGN’s parvocellular cells

* Specialized for spatial analysis and detailed analysis of form

Question 20

M Cells

Answer 20

• Provide input for LGN’s magnocellular cells

* Specialized for detection of motion and perception of depth

Question 21

Ventral Stream:

Answer 21

What Stream
• Occipital lobe-> temporal lobe
• Crucial for identification of visual objects
• Damage can cause visual agnosia
◦ Inability to recognize objects in visual field

Question 22

Where System/ Dorsal Stream:

Answer 22

• Occipital lobe-> parietal lobe
  
  • Crucial for locating object in space
  • Damage can result in difficulty reaching out for objects

Question 23

Binding Problem:

Answer 23

• Task of reuniting various elements of a scene that are initially addressed by different systems in different parts of the brain

Question 24

Spatial Position:

Answer 24

• Various brain areas all keep track of where an object is

* i.e. where a circle is, where the blueness is, where motion was detected, where things were still

Question 25

Neural Synchrony:

Answer 25

• If neurons detecting 2 different attributes are firing together, then they must be detecting the same object
  
  • i.e. vertical line moving down stimulates neurons detecting orientation, and neurons detecting movement, therefore the are detecting the same object

Question 26

Attention:

Answer 26

• Attention important aspect in binding different features of a stimulus together
  
  • Synchronized neural firing observed when paying attention to a stimulus, not observed in neurons activated by an unattended stimulus

Question 27

Conjunction Errors

Answer 27

◦ Correctly detecting the features present in a visual display, but making mistakes about how the features are bound together
◦ i.e. Someone shown blue H and red T but reports seeing a blue T and red H

Question 28

Gestalt Psychologists:

Answer 28

• Suggested that organization of perception of visual world is contributed by perceiver
• Explains why perception of a stimulus can differ from the stimulus itself
• Ie. Necker cube
◦ Hand drawn cube that can be viewed in 2 different ways (reversible)

Question 29

Figure/Ground Organization:

Answer 29

Determination of what is the figure (object) and what is the ground

Question 30

Proximity/Similarity:

Answer 30

• Perception guided by principles such as proximity and similarity
  
  • If you see 2 objects that are close together and resemble each other, you assume these elements are part of the same object

Question 31

Perceptual Constancy:

Answer 31

• We perceive the constant properties of objects in the world even though the sensory information we receive about these attributes changes whenever our viewing circumstances change
  
  • i.e. object getting bigger as you get closer, but still knowing that its is still the same size

Question 32

Size Constancy

Answer 32

Correctly perceiving the sizes of objects in the world despite changes in retinal image size created by changes in viewing distance

Question 33

Shape Constancy

Answer 33

Correctly perceive shapes of objects despite changes in the retinal image created by shifts in viewing angle

Question 34

Brightness Constancy

Answer 34

Correctly perceive the brightness of objects whether they’re illuminated by dim or bright light

Question 35

Unconscious Inference:

Answer 35

• Unconscious calculation done to perceive elements correctly
  
  • Size of image on retina x distance between you and object = size
  • Also occurs for shape and brightness constancy
  • Is the reason you misinterpret optical illusions

Question 36

Binocular Cues:

Answer 36

Distance Cues

Binocular Disparity

Question 37

Distance cues

Answer 37

Features of stimulus that indicate an object’s position

Question 38

Binocular disparity

Answer 38

◦ Difference between 2 eyes’ views

◦ Provides info about distance relationships in the world

Question 39

Monocular Cues:

Answer 39

• Depth cues that depend only on what each eye sees by itself
  
  • Depends on adjustment that the eye must make to see the world clearly
  • Lots of adjustment for nearby objects, little adjustment for objects far away

Question 40

Pictorial cues

Answer 40

Creating an impression of depth on a flat surface (i.e. in pictures)

Interposition
Linear Perspective

Question 41

Interposition

Answer 41

Blocking of your view of one object by another object

Question 42

Linear Perspective

Answer 42

Pattern in which parallel lines seem to converge as they get farther and farther away

Question 43

Motion Parallax

Answer 43

Projected images of nearby objects move more than those of distant ones

Question 44

Optic Flow

Answer 44

Pattern of stimulation across visual field also changes as you move toward object