Chapter 6

Question 1

Why is it important to be able to see the world in depth?

Answer 1

1. ability to tell how far away an object is

2. safety reasons

Question 2

What is the major problem the brain must overcome in order to see the world three-dimensionally?

Answer 2

Brain has to construct a 3-d perception (world) out of a 2-d retinal image

Question 3

Briefly describe the three areas of visual space as proposed by Cutting (1997)

Answer 3

personal space: arms reach (1.5 meters)
action space: quickly act
vista space: see but not quickly act

Question 4

Why do some animals have frontally placed eyes (e.g. humans), while others have laterally placed eyes (e.g. rabbits)? What are the “tradeoffs” involved with eye placement?

Answer 4

frontally: predators. important-see depth, give up field of view
laterally: prey. important-field of view, give up depth

Question 5

Briefly explain the “Ames room”

Answer 5

ames room: illusory room constructed to trick brain that each corner is same distance but they’re not. relies on retinal image size

Question 6

Briefly explain the “moon illusion”

Answer 6

moon illusion: moon looks bigger at the horizon-more depth cues at horizon then at the zenith

Question 7

Briefly explain motion parallax.

Answer 7

~ the difference in the apparent position of an object (fixation point) along two different lines of sight.
~In a moving vehicle (i.e. train) things outside the vehicle that are closer to us have a larger parallax and they appear to move rapidly in the opposite direction of travel
~ things that are farther away (i.e. mountains) have a smaller parallax and tend to move more slowly in the same direction of travel.

Question 8

What two major problems does the brain have to solve in order to see stereoscopically? How does the brain solve these problems?

Answer 8

1. ccompute retinal disparity: binocular neurons with visual fields in both eyes, bioncular cues/neurons
2. match up objects between the two eyes: spatial frequency

Question 9

Describe stereoscopic depth perception.

Answer 9

a method of perceiving distance in which the brain compares slightly different inputs from the two eyes
~ binocular depth cues
~ retinal disparity
~ allows us to see fine discriminatory details

~ our ability to determine distances between objects and see the world in three dimensions and this is completed through stereopsis, or perception of relative depth using binocular vision. Our eyes are separated laterally in the head, each eye gets a slightly different view of visual space and the retinal disparities

Question 10

Describe the oculomotor cues to depth.

Answer 10

oculomotor: eye muscle
brain gets kinesthetic cues from muscles associated with convergence and accomodation. monitor the strain as cues to depth. can get a copy of corollary discharge (efference copy)-motor signals sent to the brain
~The brain either measures these cues to calculate depth, OR simply monitors the motor signals being sent to the ocular muscles, which is called corollary discharge.

Question 11

Convergence occurs when…

Answer 11

the eyes rotate inward to focus on a point closer than they were previously looking.

Question 12

accommodation occurs when

Answer 12

the lens of the eye changes shape, by work of the ciliary muscle, to change its focus.

Question 13

Describe the static cues to visual depth

Answer 13

monocular cues w/o motion
occlusion/interposition
transparency
retinal image size
linear perspective
aerial perspective (things further away look blue)
texture gradients
shading
neon shading