M2 Lecture 11: Feb 19 Flashcards
what is Accommodation
The process by which the eye changes its focus (in which the lens gets fatter as gaze is directed toward nearer objects) – useful < 2-3 meters
what is Convergence
The ability of the two eyes to turn inward, often used to focus on nearer objects.
what is Divergence:
The ability of the two eyes to turn outward, often used to focus on farther objects.
what are the binocular cues
accommodation, convergence and divergence
what is Binocular summation:
The combination (or “summation”) of signals from each eye in ways that make performance on many tasks better with both eyes than with either eye alone
what is Binocular disparity:
The differences between the two retinal images of the same scene
Disparity is the basis for what
stereopsis
what is stereopsis
a vivid perception of the three-dimensionality of the world that is not available with monocular vision
what is Corresponding retinal points:
A geometric concept stating that points on the retina of each eye where the monocular retinal images of a single object are formed are at the same distance from the fovea in each eye
what is Vieth–Müller circle (Horopter):
The location of objects whose images lie on the corresponding points. The surface of zero disparity.
Objects on the horopter are seen as what
single images when viewed with both eyes.
Objects significantly closer to or farther away from the horopter fall where
on noncorresponding points
Objects significantly closer to or farther away from the horopter fall on noncorresponding points in the two eyes and are seen as how many images
2
what is Diplopia:
Double vision. If visible in both eyes, stimuli falling outside of Panum’s fusional area will appear diplopic.
what is Panum’s fusional area:
The region of space, in front of and behind the horopter, within which binocular single vision is possible.
what is Crossed disparity
The sign of disparity created by objects in front of the plane of the horopter
Images in front of the horopter are displaced how
to the left in the right eye and to the right in the left eye.
what is Uncrossed disparity:
The sign of disparity created by objects behind the plane of the horopter.
Images behind the horopter are displaced where
to the right in the right eye and to the left in the left eye.
Different binocular neurons in V1 encode all categories of retinal disparity (zero, crossed (near), and uncrossed (far)).
These neurons are organised how
into columns
Different binocular neurons in are V1 encode all categories of retinal disparity (zero, crossed (near), and uncrossed (far)).
These neurons allow perceiving what
depth within Panum’s fusional area.
what is Stereoscope
A device for presenting one image to one eye and another image to the other eye.
explain how 3D glasses work
For movies to appear 3D, each eye must receive a slightly different view of the scene (just like in real life).
Early methods for seeing movies in 3D involved “anaglyphic” glasses with a red lens on one eye and a blue lens on the other.
Current methods use polarized light and polarizing glasses to ensure that each eye sees a slightly different image.
what is 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
the question is Do we need to recognize objects to have stereopsis?
what is Random dot stereogram (RDS):
A stereogram made of a large number of randomly placed dots.
RDSs contain what cues to depth
no monocular
Stimuli visible stereoscopically in RDSs are cyclopean stimuli, what is cyclopean
Referring to stimuli that are defined by binocular disparity alone.
what is Free fusion:
The technique of converging (crossing) or diverging (uncrossing) the eyes in order to view a stereogram without a stereoscope
(for RDS) If the “object” on the right eye is positionned to the left of the object on the left eye (if there is crossing), the object will be perceived where
in front of the background (and vice-versa).
what is 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.
-> the retinal input is constant, but the percept changes!
What tracks the percept
Patterns in V1-V3!
V1 tracks more what than the percept
the eye
Logically speaking, motion perception shouldn’t require anything else than what
the ability to perceive successive still frames.
what is Akinetopsia
A rare neurophysiological disorder in which the affected individual has no perception of motion.
Akinetopsia can be caused by what
can be caused by lesion of areas MT/MST
e.g. of Akinetopsia (just an example to solidify the issue)
A 47-year-old man reported seeing streams of multiple, frozen images trailing in the wake of moving objects. As soon as motion ceased, the images collapsed into each other. he compared his vision to a scene lit by a flashing strobe, except that stationary elements were perceived normally. In fact, if nothing was in motion and he held perfectly still, his vision was entirely normal. The moment anything moved, however, it left a stream of static copies in its path. For example, while out for an evening stroll, he saw a pack of identical dogs lined up behind his West highland terrier. Driving was impossible because he was confused by multiple snapshots of cars, streets, and signs. Moving lights were followed by a long comet trail»
what is Apparent motion
The illusory impression of smooth motion resulting from the rapid alternation of objects that appear in different locations in rapid succession.
