3 - Visual Direction (Exam 1)

Question 1

What 3 sources of information are required to determine the location of target?

Answer 1

1. Relative position
2. Absolute distance
3. Egocentric point of reference

Question 2

How is relative position of a target determined?

Answer 2

Retinocentric/oculocentric direction
Monocular distance cues
Stereopsis

Question 3

How is absolute distance of a target determined?

Answer 3

Vergence eye movements
Monocular distance cues
Vertical disparity

Question 4

What is the egocentric point of reference?

Answer 4

Position of the eye with respect to head and body

Cyclopean eye

Question 5

What is retinocentric (oculocentric) direction?

Answer 5

Location expressed relative to the fovea of the viewing eye - specific to each eye

Question 6

What is the Cartesian coordinate system?

Answer 6

Numeric values assigned to oculocentric direction

Fovea has oculocentric direction of ZERO

Question 7

What was shown by Hering’s window experiment?

Answer 7

The perceived location of targets can differ significantly from their physical locations depending on the viewing situation.

Question 8

What is the relationship between inputs and outputs of the visual system?

Answer 8

Physical inputs of oculocentric directions are processed to produce perceived output of directions relative to a virtual reference point.

Question 9

How many fundamental laws of visual direction are there?

Answer 9

Four

Question 10

What is the first law of visual direction?

Answer 10

The perceived direction of all targets are judged from the cyclopean eye

Question 11

How many parts of Law II of visual direction are there

Answer 11

two parts

Question 12

What is part a of the second law of visual direction?

Answer 12

All targets perceived on the primary visual line will be perceived as on a primary visual direction

Question 13

What is part b of the second law of visual direction?

Answer 13

If two target lie on the same visual line they will be perceived as in the same visual direction

Question 14

How many parts of Law III of visual direction are there?

Answer 14

two parts

Question 15

What is part a of the third law of visual direction?

Answer 15

All targets on secondary visual lines will be perceived as on secondary visual directions which connect to the cyclopean eye

Question 16

What is part b of the third law of visual direction?

Answer 16

The angle between the primary and secondary visual line in a given eye is equal to the perceived angle between the primary and secondary visual direction.

Question 17

How many parts of Law IV of visual direction are there?

Answer 17

one part

Question 18

What is the fourth law of visual direction?

Answer 18

Under binocular conditions, every visual line in one eye has a corresponding visual line in the other eye that shares the same visual direction.

Question 19

Will two separate targets that resolve at the fovea be resolved in the retinal periphery?

Answer 19

Sometimes

If the separation between two targets is large enough, it will be resolved at the fovea and in the periphery

Question 20

What is 1 example of corresponding points?

Answer 20

The foveas of each eye.

Question 21

What is the horopter?

Answer 21

The locus of all targets in space that stimulate corresponding points

Question 22

What is the difference between the theoretical horopter (Veith-Muller Circle) and the empirical horopter?

Answer 22

The Veith-Muller Circle is circular

The empirical horopter is elliptical

Question 23

What does the horopter pass through in each eye?

Answer 23

The fixation point and nodal point of each eye

Question 24

If targets are located off the horopter, what types of points will be stimulated?

Answer 24

Non-corresponding points

Question 25

What is Panum's Fusional Space?

Answer 25

A 3D volume of space around the empirical horopter in which targets that stimulate non-corresponding retinal points appear single

Question 26

How is version angle calculated?

Answer 26

Average of left and right eye positions in orbit relative to axis parallel to the median plane (straight ahead)

Question 27

How is headcentric direction computed for targets on the Horopter?

Answer 27

Average of oculocentric directions plus the version angle

Question 28

How is headcentric direction computed for targets off the Horopter but within Panum's Fusional Space?

Answer 28

The same as headcentric direction for targets on the horopter (average of oculocentric directions plus the version angle)

Question 29

How is headcentric direction computed for targets off the Horopter and outside Panum's Fusional Space?

Answer 29

Headcentric direction is separate for OD and OS | Each eye individually is the oculocentric direction plus the version angle

Question 30

In what way does the image move compared to the occluder with an esophoria?

Answer 30

Moves against occluder motion

Question 31

In what way does the image move compared to the occluder with an exophoria?

Answer 31

Moves with occluder motion

Question 32

How is diplopia different from confusion?

Answer 32

Diplopia is when a target is perceived in two different headcentric visual directions Confusion is when two dissimilar targets are perceived in a one single headcentric visual direction

Question 33

What is a sensory mechanism that avoids diplopia and confusion?

Answer 33

Suppression | Only the image from one eye is seen so two images are not possible