Vision part 3 Flashcards
Vergence
Eye convergence for near objects, divergence for distant ones.
Ciliary muscles adjust lens shape for focus.
Accomodation
The _____ system keeps tract of degree of accommodation, and uses this cue to infer depth
Nervous
Absolute depth perception (unlike pictorial cues, can put absolute estimate of object’s distance )
Vergence limit: Reliable up to ~2m. After that, no divergence.
Accommodation limit: Active up to ~6m (beyond this is optical infinity)
Stereopsis
Rich impression of depth that we get from seeing with both eyes.
Binocular Disparity
The slight difference in the images perceived by each eye due to their horizontal separation, which the brain uses to calculate depth and perceive a three-dimensional view of the environment.
Vieth-Müller Circle
- imaginary geometric circle in visual space that passes through the point of fixation and the optical centers of both eyes.
The points in the Vieth-Müller Circle show the theoretical locations of objects that produce corresponding retinal points in both eyes, resulting in …
no binocular disparity and appearing at the same depth as the fixation point
The fixation point P is reflected on the _____
Fovea
A point that falls on the Vieth-Muller circle will be projected …
Exactly in the same point in both eyes.
A point that falls outside the Vieth-Muller circle will be projected…
At a different point in each eye
The principle of corresponding or non corresponding retinal points is used to infer ____
Depth
Horopter
Spatial region in visual space where objects project images onto corresponding retinal points in both eyes.
Objects on the horopter appear to be at the same depth as the point of fixation and are perceived without ….
Binocular disparity
In theory, for every point outside the horopter, we should have…
Double vision
The horopter can take different shapes depending on the viewing conditions, such as the distance of fixation. It includes the … under idealized conditions.
Vieth-Müller Circle
Panum’s fusional area
Region in visual space around the horopter where slight binocular disparities can still be fused by the brain to produce a single, unified perception of depth.
Objects outside Panum’s fusional area may appear as _____(diplopia)
Double
Crossed disparity occurs when an object is ____closer/farther to you than the point of fixation.
Closer
When the object is in front of the horopter (crossed disparity), the image of the object falls on the ____ side of the retina in both eyes.
outer (temporal)
Why is crossed disparity called that ?
from the left eye’s view, the object is located to the right of the fixation point, and from the right eye’s view, it is located to left of the fixation point
Uncrossed disparity
When an object is farther away from you than the point of fixation.
When the object is behind the horopter (uncrossed disparity), the image of the object falls on the _____ side of the retina in both eyes.
inner (nasal)
Why is uncrossed disparity considered “uncrossed” ?
From the left eye’s view, the object is located to the left of the fixation point, and from the right eye’s view, it is located to the right of the fixation point.
Different binocular neurons in V1 encode all categories of retinal _____ (zero, crossed (near), and uncrossed (far)).
Disparity
Binocular neurons in V1 perceiving depth within ____ _____ area.
Panum’s fusional
Neurons with a 0 disparity preference
No difference between retinal image of left and right eye, its firing rate will increase when there is NO disparity
- most neurons have this disparity tunning
Tuned near neurons prefer…
A little crossed disparity
Tuned far neurons prefer…
A little uncrossed disparity
Far neurons prefer
Uncrossed disparity
Near neurons prefer
Crossed disparity
There is a gradual decrease of perception away from the ______
Horopter
Stereoscope
A device for presenting one image to one eye and another image to the other eye.
For movies to appear 3D, each eye must receive a slightly different ____
View
“anaglyphic” glasses
Red lens for one eye, blue for the other
- Used for early 3D movies
Current methods for 3D glasses
- Polarized light and polarizing glasses to ensure that each eye sees a slightly different image
Polarized light = each image is the same color, but the polarity (orientation of light wave) differs
Correspondence problem
In binocular vision, the problem of figuring out which bit of the image in the left eye should be matched with which bit in the right eye.
2 hypotheses of object integration
- Our visual system perceives the object before integrating it in each eye and send this information forward to combine the images
- The visual system is made so that image from each eye is automatically integrated before recognizing the object
Random dot stereogram
- Visual pattern consisting of two images made up of random dots.
- When viewed with both eyes (using stereoscopic vision), the two images create the illusion of a three-dimensional shape or object floating in space.
Generation of a random dot stereogram
- 2 similar random-dot patterns are created.
- A section of 1pattern is shifted slightly horizontally (left or right) relative to the corresponding section in the other pattern.
Disparity in a random dot stereogram
1.The horizontal shift creates binocular disparity when the two images are viewed together.
2.This disparity mimics the differences in the images seen by the left and right eyes in real-world 3D viewing.
Perception of a random dot stereogram
1.When each eye views one image (e.g., using a stereoscope or by crossing/uncrossing the eyes), the brain fuses the two patterns.
2.The shifted section appears as a 3D object or surface due to the brain’s interpretation of the disparity.
If the square from the left eye view is to the right of the square in the right eye view, there will be _____uncrossed/crossed disparity
Crossed (objects seen as more near)
If the right square is to the right of the square of the left eye view, there will be _____uncrossed/crossed disparity
Uncrossed (object seen as more far)
Binocular rivalry
The competition between the two eyes for control of visual perception, which is evident when completely different stimuli are presented to the two eyes.
Most time there is no double vision for objects outside panum fusional area, because…
The visual system supresses the image that is coming from one of the eye for a couple of seconds, then switches to the other side (binocular rivalry)
Right object recognition hypothesis
We cannot recognize certain stimuli with only 1 eye, so it is the 2nd hypothesis : The visual system is made so that image from each eye is automatically integrated before recognizing the object
