Topic 4 - Visual Illusions Flashcards

1
Q

Oculomotor cues

A

based on sensing the position of the eyes and muscle tension

  • Ocular convergence
  • Accommodation
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2
Q

Ocular convergence

A

inward movement of the eyes when we focus on nearby objects

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3
Q

Accommodation

A

change in the shape of the lens when we focus on objects at different distances

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4
Q

Monocular depth cues

A

Only come from one eye

Pictorial cues and motion-produced cues

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5
Q

Pictorial Cues

A

sources of depth information that come from 2-D images, such as pictures

Includes:
Occlusion
Relative height
Relative size
Familiar Size
Perspective convergence
Atmospheric perspective
Texture gradient
Shadows
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6
Q

Occlusion

A

When one object partially covers another

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7
Q

Relative height

A

objects below the horizon that are higher in the field of vision are more distant

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8
Q

Relative size

A

when objects are equal size, the closer one will take up more of your visual field

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9
Q

Familiar size

A

distance information based on our knowledge of object size

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10
Q

Perspective convergence

A

parallel lines appear to come together in the distance

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11
Q

Atmospheric perspective

A

distance objects are fuzzy and have a blue tint (on a clear day)

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12
Q

Texture gradient

A

equally spaced elements are more closely packed as distance increases

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13
Q

Shadows

A

indicate where objects are located

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14
Q

Motion parallax

A

close objects in direction of movement glide rapidly past but objects in the distance appear to move slowly

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15
Q

Deletion and accretion

A

objects are covered or uncovered as we move relative to them

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16
Q

Binocular depth cues

A

Two eyes cues

Includes binocular disparity and stereopsis

17
Q

Stereoscopic depth perception

A

depth perception created by input form both eyes

18
Q

Strabismus

A

misalignment of the eyes

19
Q

Binocular disparity

A

difference in the images on the left and right retinas

  • Corresponding retinal points - points on retina that would overlap - a surface called the horopter
  • Noncorresponding points - images that are not on the horopter
  • Absolute disparity - angle between noncorresponding points, angle of disparity
  • Crossed disparity - eyes see object on the opposite side of visual field to side eye is on
  • Uncrossed disparity - eyes see object on same side of visual field to side eye is on
  • Relative disparity - difference between absolute disparity of two objects
20
Q

Steropsis

A

depth information provided by binocular disparity (perceptual)

Stereoscope uses two pictures from slightly different viewpoints (one to each eye)
- Random-dot stereogram - has two identical patterns with one shifted in position

21
Q

Correspondence problem

A

How does the visual system match images from the two eyes? – Matches may be made by specific features of objects

This may not work for objects like random-dot stereograms, A satisfactory answer has not yet been proposed

22
Q

Depth perception in other species

A

Animals use same cues

Frontal eyes needed for binocular disparity
Lateral eyes provide a wider view

23
Q

Experiment by Tsutsui et al.

binocular depth perception

A
  • Monkeys matched texture gradients that were 2-D pictures and 3-D stereograms.
  • Recordings from a neuron in the parietal lobe showed: >Cell responded to 2D pictorial cues, Cell also responded to 3D binocular disparity
24
Q

Binocular depth cells, disparity selective cells

A

These cells respond best to a specific degree of absolute disparity between images on the right and left retinas (have a tuning curve)

25
Experiment by Blake and Hirsch | binocular disparity and depth perception
- Cats were reared by alternating vision between two eyes every other day for 6 months - no chance of binocular disparity - Results showed that they: had few binocular neurons due to cortical plasticity and were unable to use binocular disparity to perceive depth
26
Experiment by DeAngelis et al. | binocular disparity and depth perception
- Monkey trained to indicate depth from disparate images - Disparity-selective neurons were activated by this process (in V1) - Experimenter used micro-stimulation to activate different disparity-selective neurons - Monkey shifted depth judgment to the artificially stimulated disparity
27
Experiment by Holway and Boring | Perceiving size
- Observer was at the intersection of two hallways ○ A luminous test circle was in the right hallway placed from 10 to 120 feet away ○ A luminous comparison circle was in the left hallway at 10 feet away ○ On each trial the observer was to adjust the diameter of the test circle to match the comparison ○ Test stimuli all had same visual angle (angle of object relative to the observer’s eye) ○ Part 1 of the experiment provided observers with depth cues - Judgments of size were based on physical size ○ Part 2 of the experiment provided no depth information – Judgments of size were based on size of the retinal images (i.e., visual angle)
28
Visual angle
Angle of an object relative to the observer's eye
29
Size constancy
Perception of an object’s size remains relatively constant - This effect remains even if the size of the retinal image changes (or distance from the observer changes) Size-distance scaling equation – S = K (R x D) - The changes in distance and retinal size balance each other
30
Size-distance scaling - Emmert's Law
Retinal size of an afterimage remains constant - Perceived size will change depending on distance of projection (if you look at something further away, the afterimage will appear larger and vice versa)
31
Muller-Lyer Illusion
Straight lines with inward fins appear shorter than straight lines with outward fins, lines are actually the same length Misapplied Size Constancy Scaling - what works in 3D is misapplied in 2D - Problems with this theory Conflicting cues theory - perception depends on actual length of vertical lines in combination with overall length of the figure - compromise of perception
32
Ponzo illusion
Horizontal objects are placed over railroad tracks in a picture, upper object appears larger - Misapplied size constancy scaling
33
Ames Room
Reasons: Size-distance scaling - Observer thinks the room is normal, People would be at same distance – Person on the left has smaller visual angle (R) – Due to the perceived distance (D) being the same their perceived size (S) is smaller Relative Size - Perception of size depends on size relative to other objects. – One woman fills the distance between the top and bottom of the room. – The other woman only fills part of the distance – Thus, the woman on the right appears taller
34
Moon illusion
The moon appears larger on the horizon than when it is higher in the sky Apparent-distance theory - horizon moon is surrounded by depth cues while moon higher in the sky has none - Horizon is perceived as further away than the sky - called “flattened heavens” Angular size-contrast theory - the moon appears smaller when surrounded by larger objects, Thus, the large expanse of the sky makes it appear smaller