Attention - Depth and Size Perception

30 important questions on Attention - Depth and Size Perception

What is the relationship between Depth & Size

Depth & Size are closely related
How big an object appears can affect how far away it appears
How far away an object appears can affect how big it appears

What happens when you perceive an object as closer than it actually is?

It will seem smaller

What are the 2 main oculomotor cues?

Binocular convergence & Accomodation
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What is binocular convergence?

When you look at an object that is near, your eyes converge - they can’t be aligned.
The degree of convergence gives you an indication of how close an object is.

What are monocular cues?

Cues based on our ability to sense the position and state of our eyes

What are the 3 main monocular cues?

Accomodation, Pictorial cues & Movement-based cues

What are the Pictorial Cues?  (7 Main Pictorial Cues)

F - Familiar and relative size
A - Atmospheric Perspective
T - Texture Gradient
P - Perspective Convergence
R - Relative Height
O - Occlusion
S -  Shadows

How does this picture explain F in FATPROS?

F
  • You know how tall/big a car roughly is
  • Thus, by its size, you can estimate how far an object is

How does this picture explain A in FATPROS?

A
  • There is fog in the photo – It is hard to see objects
  • By estimating how hard it is to see an object, you can estimate how far an object is

How does this picture explain T in FATPROS?

T
  • As the texture becomes more high frequency (smoother), the grass appears to be further away

How does this picture explain P in FATPROS?

P
  • The road markers don’t appear to be parallel; They appear to be converging
  • By estimating the degree of convergence, you can estimate how far an object is

How does this picture explain O in FATPROS?

O
  • The car is occluded by the truck
  • Objects that are occluded by another object are further away  

How does this picture explain S in FATPROS?

S
  • You can use the distance of the shadow from the object to give an estimation of how far the object is above the background

What are the Movement-Based Cues?

  1. Motion Parallax
  2. Deletion and accretion

What is Motion Parallax?

By estimating how fast an object seems to be moving/going past you, you can estimate how far away it is from you

What is Deletion and Accretion? Use a train example


When the train is moving, some objects will occlude another object
When a object is hidden from another object, it is known as deletion

When that object re-appears again, it is known as accretion
By looking at deletions and accretions, we can understand the occlusion relationship and tell which objects are further away

Whichever object is fixated on has ________ absolute disparity

Zero

What is a horopter?

A plane containing all points that will fall on corresponding parts of the two retina

How is the correspondence problem solved?

The objects in the visual scene have to be made distinct from each other by colour or by shape - Only then will it be disambiguous

What are the 2 factors that determines the perceived size of an object?

Angular Size and Perceived Depth

What is angular size? What is the relationship between distance and angular size?

The visual angle an object subtends. The closer an object is to a person, the larger its angular size.

What is size constancy?

  • Size Constancy is the phenomenon where an object's apparent size does not depend on it’s physical distance

  • When an object is far away, it appears to be the same size as when it is closer, even though its visual angle is much larger in the latter case

How does an observer achieve size constancy?

An observer needs to consider both the size of the retinal image and the distance to the object

Formula of size constancy

S = K x (R x D)

What are size illusions caused by?

Caused by people mistaking the distance to an object

What did Holway and Boring investigate?

How observers accurately estimate the size of objects - they investigated how depth cues influence size judgements

When is it easier to determine the distance of the object?

When we have more depth cues

Explain Holway and Boring's experiment


  • Observer sat at an intersection of two corridors and could view a test circle in one corridor and comparison circle in the other corridor.
  • Their task was to adjust the size of the comparison circle to match the size of the test circle.
  • The test circles were of different sizes but were presented at different distances so that their angular size was always the same.

What did the observers in Holway and Boring's experiment use to determine the depth of the test patch? (4 separate groups of participants)


In condition 1 -  binocular disparity, motion parallax and shadows

In condition 2 - observers viewed the test circle with 1 eye to remove binocular disparity cues (leaving only motion parallax and shadows)

In condition 3 - observers viewed the test circle through a peephole with 1 eye to remove motion parallax cues (leaving only shadows)

In condition 4 - Nothing; observers viewed the test circle through a peephole with 1 eye + drapes were used to remove the shadows

When can objects be accurately estimated?

When there are sufficient depth cues

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