Download Ch06 Lecture Part II

6
Binocular Cues
6
•Binocular summation: An advantage in detecting a stimulus
that is afforded by having two eyes rather than just one
Retinal Disparity
6
Introduction to Space Perception (cont’d)
• The two retinal images of a three-dimensional world
are not the same!
6
Stereopsis from Binocular Disparity
• Retinal locations
– Corresponding/Noncorresponding locations on two retinas
• Binocular Disparity
– Images fall on non-corresponding locations
– Basis of stereopsis; a vivid perception of the threedimensionality of the world that is not available with
monocular vision.
10°
10°
5°
0° 5°
10°
10°
5°
0° 5°
1
6
The Vieth-Müller Circle
6
Relative Disparity
Relative Disparity: Left Eye
6
Relative Disparity: Right Eye
• Horopter
– Set of points in space
that give rise to zero
disparity
– Objects on horopter fall
on corresponding retinal
locations
6
2
6
Binocular Disparity and Distance
6
Binocular Disparity and Relative Depth
6
Panum’s Area
• Objects lying off of the horopter – project to different
retinal locations
– Binocular disparity
– Amount – distance from horopter
6
Crossed vs. Uncrossed Disparity
• Panum’s Fusional Area
– Area surrounding horopter
– Able to fuse images to form single image
• Outside of Panum’s area – Diplopia (double vision)
– Inability to fuse images
3
6
Binocular Vision and Stereopsis (cont’d)
6
A Stereo Photo
6
Random Dot Stereogram
• Stereoscope: A device for presenting one image to
one eye and another image to the other eye, creating
a single, three-dimensional design
• Similar devices:
– View Masters
– Red/Green glasses
– Polarized glasses
– LCD goggles
• Free fusion: The technique of converging (crossing)
or diverging the eyes in order to view a stereogram
without a stereoscope
6
Free Fusion
4
6
Binocular Vision and Stereopsis (cont’d)
6
• Random dot stereograms can only be seen with
binocular cues; they contain no monocular depth cues
• Correspondence problem: Figuring out which bit of
the image in the left eye should be matched with
which bit in the right eye
• Evidence: We are not matching “objects” from each
retinal image
• In order to use retinal disparity
• Must solve correspondence problem
– Must match parts of images between the two eyes
– Must be based on earlier process (before perceptual
objects)
– Aids in forming objects?
6
Correspondence Problem
The Correspondence Problem (Part 1)
• Depth from random dot stereograms (no objects)
– Don’t need “objects” to solve correspondence
problem
6
The Correspondence Problem (Part 2)
5
6
Single Image Random Dot Stereograms
SIRD
• Magic Eyes
– Multiple solutions to correspondence problem
– Multiple ways to match images between eyes
– One solution
• No disparity between image points
• Perceive flat surface
– Other way
• Disparity between image points
• Perceive dinosaurs
6
Binocular Neurons
6
Disparity-Sensitive Neurons
• Input from two eyes must converge onto the same cell
– Binocular neurons
• Many binocular neurons respond best when the retinal
images are on corresponding retinal locations: Neural basis
for the horopter
– RFs -- corresponding retinal locations
• Other binocular neurons respond best when similar images
fall on different retinal locations
– RFs – non corresponding retinal locations
– Tuned to particular binocular disparity
– Specific location in space (relative to fixation)
6
6
Binocular Vision and Stereopsis (cont’d)
6
• Some people do not experience stereoscopic depth
perception because they have stereoblindness
Binocular Vision and Stereopsis (cont’d)
• 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
– An inability to make use of binocular disparity as a
depth cue
– Can result from a childhood visual disorder, such
as strabismus, in which the two eyes are
misaligned
– Lack disparity selective neurons?
6
Binocular Rivalry
6
Binocular Rivalry
7
6
Size Perception
6
• Two factors needed to determine perceived size
– Size of retinal image
– Distance of object
Illusions of size
• Which pair of lines are the same length?
• What happens when misperceive distance?
– Illusions of size
6
An Explanation of the Ponzo Illusion?
6
Another Illusion
8
6
Size Constancy
• Same object at different distances
– Different size retinal images
– Still perceive object to be same size
• Size constancy
– Why? -- Take distance into account
6
Size-Distance Scaling
• S = K(R x D)
– S - perceived size
– K - constant
– R - size of retinal image
– D - perceived distance
• R and D “trade-off”
– As D gets larger, R gets smaller (product the same)
– As R gets larger, D gets smaller (product the same)
9
6
Emmert’s Law
• Perceived size of afterimage
– Depends on distance of “surface”
– Retinal image stays the same
• Area on the retina -- bleached photoreceptors
• Stays constant
6
Ames Room Movie
10