Binocular Vision: Lecture 15: Stereopsis-2

Question 1

Binocular Disparity (1)

1. What kind of Disparity does the Binocular Visual System Process?
2. Binocular Disparity tells us an object’s relative position in space…
3. Binocular Disparity does not tell us what?
4. Fusional Eye Movements are made to reduce what?
   a. Stereopsis is in response to what?

Answer 1

1. RELATIVE DISPARITY (not absolute)
2. …if it’s closer to us or farther away from us compared to other objects
3. the absolute position of any particular object
4. Absolute or Relative Disparity
   a. to Relative Disparity ALONE

Question 2

Binocular Disparity (2)

1. If all targets in the VF are given Identical Non-Zero disparities, What would happen?
2. In order to see depth, we must compare what?

Answer 2

1. No Object(s) will be seen to stand out in depth.

2. we have to compare differences in disparity at different spatial locations.

Question 3

Vertical Disparity

1. Unequal Image Magnification b/w the 2 eyes along the Vertical Meridian produces what?
2. When both eyes see an object on the midline, what will appear to be the same for both eyes?
   a. The Angular size of the object will also be what?
3. If the object is moved to the right or left of the midline, it will be what?

Answer 3

1. Horizontal Disparity
2. the Vertical Size
   a. be the same.
3. be Nearer to one eye than the other. The Vertical Angular Size will be Different for the 2 Eyes. This is called VERTICAL GEOMETRIC DISPARITY

Question 4

Orientation Disparity

1. Differences in the orientation of targets presented to each eye may yield what?
2. This perception is due to what?

Answer 4

1. a Percept of Tilt in Depth

2. due to Gradually changing degree of horizontal disparity b/w the 2 targets resulting from the differing orientations

Question 5

Motion Parallax and Stereopsis (1)

1. Motion parallax and stereopsis are both produced by what?
   a. This suggests what?
2. Motion parallax shares many of the properties of Stereopsis. We are only half as sensitive to motion parallax. Based on Experiemental findings…?

Answer 5

1. by Slight shifts in the retinal Image
   a. possible shared physiological mechanisms
2. MOTION PARALLAX and STEREOPSIS have DIFFERENT MECHANISMS

Question 6

Motion Parallax and Stereopsis (2)

1. Show each eye Vertical sine-wave grating stimuli of slightly different spatial frequencies.
   a. The different spatial frequencies create what?
2. The simpler explanation is that the difference in grating spatial frequency is similar to what?

Answer 6

1. a. Horizontal Binocular Disparities b/w corresponding bars of the 2 gratings and produces apparent tilting of the plane.
2. to the geometric effect noted in ANISEIKONIA cuz one grating is magnified or minified with respect to the other

Question 7

Stereoacuity (1)

1. What is it?
2. humans are capable of detecting a shift of one eye’s image (that is, a binocular disparity) of only how much?
3. Stereoacuity is a FORM of what?

Answer 7

1. the smallest depth difference we can see (A Depth discrimination threshold). It’s usually measured in a lab using the method of constant stimuli or a staircase procedure.
2. 4’’ to 5’’ ARC
3. of HYPERACUITY

Question 8

Stereoacuity (2)

1. What can be calculated for an avg interpupillary distance?
   a. So, you can’t see depth for objects more than how far away?
   b. Objects beyond this limit will appear to be?
2. Binocular Thresholds via DISPARITY are better than the Monocular Threshold (i.e., using only monocular cues to depth) by a Factor of what?

Answer 8

1. the Geometric limit can be calculated to occur when the fixation distance equals 1,320 m or 0.8 MILE
   a. more than 0.8 miles away.
   b. to be at the same distance
2. of 20 times

Question 9

Stereoacuity (3)

1. Stereoacuity Thresholds tend to improve with what?
2. Effect on Luminance Disparity: The Dimmer the background Luminance, the Less what?
3. Stereoacuity for targets that ISOLATE BLUE CONE FUNCTION is poorer/better than for targets that stimulate the Red and Green Cone Systems.
4. We are much more sensitive to depth if we are allowed to view the target for how long?

Answer 9

1. with Practice (Learning)
2. the Less our sensitivity to Depth, and our percept of depth degrades
3. POORER
4. for a longer time.

Question 10

Stereoacuity (4)

1. We get our best stereoacuity with exposure times of how long?
   a. Which disparities take longer to detect: Fine or Coarse Disparities?
2. If RE and LE targets are presented with a Temporal Asynchrony, is stereopsis Impaired?
3. Can the Retinal Periphery detect fine differences in position?

Answer 10

1. of about 1 Second
   a. FINE DISPARITIES
2. No…only if the Asynchrony is over about 100 ms in duration
3. No.

Question 11

Stereoacuity (5)

1. Stereothresholds are elevated at Contrast Threshold so that it’s difficult to see Stereopsis at what?
2. Stereothresholds decrease by a factor of what?
3. When does blur have a much greater EFFECT on stereoacuity?

Answer 11

1. at VERY LOW CONTRAST
2. of the Square Root of the Contrast Stimulus
3. when it’s a MONOCULAR BLUR

Question 12

Stereoacuity (6)

1. A Target can move up to what degrees per Second w/o degrading stereoacuity?
2. Stereothresholds are not affected by what?

Answer 12

1. up to 2-3 degrees per second

2. by Fixational Eye Movements

Question 13

Stereoacuity (7)

1. Oscillating a target in depth degrades dynamic stereoacuity thresholds if the oscillations are SLOWER than what?
2. If the reference and Test targets are too widely what?
   a. It becomes difficult to compare them for what?
3. If the targets are too close together (how much), what happens to stereoacuity?

Answer 13

1. than 1 Hz
2. too widely separated (> 50’ ARC).
   a. for a relative difference in depth, and Stereoacuity Suffers
3. (s also Degraded, and the impression of a depth difference b/w the 2 stimuli suffers

Question 14

Fine vs. Coarse Stereopsis

1. Fine Stereopsis: Responds to what?
   a. Fine stereopsis is mainly found where?
   b. Supported by what system?
   c. This system provides for what?
2. Coarse Stereopsis: Mainly responds to what?
   a. When is it active?

Answer 14

1. to higher spatial frequencies (Fine Details), retinal disparities less than 30 arc minutes, and to stationary or slowly moving targets
   a. in Foveal Vision
   b. by the Parvocellular System
   c. for high quality stereopsis (patent stereopsis) and may also contribute to fine disparity vergence control
2. to lower spatial frequency targets (large objects), operates w/Larger retinal disparities (30-600 arc minutes), and moving targets
   a. in both Foveal and Peripheral vision, and may also be related to coarse disparity vergence control. Supported by the Magnocellular system

Question 15

Chromostereopsis (1)

1. Stereopsis is primarily a function of what?
2. Color can also deceive the visual system into seeing what?
   a. Blue light has a shorter wavelength, dispersion of light by the eye’s crystalline lens causes what?

Answer 15

1. of the Achromatic channels of the magno and parvo pathways
2. stereopsis
   a. causes blue light to be refracted more than red light, an effect called longitudinal chromatic aberration

Question 16

Chromostereopsis (2)

1. The lines of sight are decentered slightly nasally from the visual axes, producing differential prismatic effects for what?
2. Red and Blue Lights viewed at the same fixation distance will not be focused at the same lateral position on the retina. The image of red objects will be displaced how?
3. Red and blue objects will have a relative disparity introduced by what?
   a. This will cause the red object to appear where?

Answer 16

1. for red and blue light
2. nasally relative to blue objects (transverse Chromatic Aberration)
3. by the Differential Refraction of the lens.
   a. to appear CLOSER to you than the blue object

Question 17

Stereomotion

1. We are sensitive to depth when a target moves how?
   a. We are not very sensitive to depth with motion when?
2. The Sole stereomotion that we can see even MODERATELY well occurs when an object moves how?

Answer 17

1. horizontally
   a. toward and away from us (Stereomotion)
2. moves towards us, directed toward our NOSE (LOOMING)