Lecture 16 Size and Depth Flashcards
What are corresponding retinal points?
points on the retina that would overlap if the eyes were superimposed on each other
What is binocular disparity?
refers to the difference in images from 2 eyes
What is the horopter?
an imaginary sphere that passes through the point of focus
Objects on the __________ fall on corresponding points on the retinas.
horopter
What can we infer when two objects fall on the horopter?
they are approximately the same distance away from the observer
Objects that are not on the horopter fall on _________________ points.
non-corresponding
What kind of images do non-corresponding points make?
disparate images
The degree to which disparate images deviate from corresponding points is the ___________ and can be represented by a calculation referred too as the _______________.
absolute disparity; angle of disparity
TRUE or FALSE: object that fall in front of/behind the horopter (i.e. fall on non-corresponding points) create disparate images in each of our eyes
TRUE
What is crossed disparity? Does it occur in front of or behind the horopter?
- occurs whenever an object is CLOSER to the observer than where they are looking
- in front of the horopter
What is uncrossed disparity? Does it occur in front of or behind the horopter?
- occurs whenever an object is FARTHER away from the observer than where they are looking
- behind the horopter
Describe an example of crossed disparity.
- observer is looking directly at Julie
- Bill is in front of Julie
- The image of Bill is on the ‘inside’ side of Julia’s image, in each eye of the observer
Describe an example of uncrossed disparity.
- The observer is looking directly at Julie
- Bill is behind Julie
- The image of Bill is on the ‘outside’ of Julie’s image, in each eye of the observer
The _____________ of the disparity (________ or ___________), along with the ___________ of disparity, helps us judge where things are in space.
nature; crossed; uncrossed; angle
What does determining whether disparity is crossed or uncrossed tell us?
whether something is behind or in front of our point of focus (i.e. the horopter)
Because objects that are _______________ the horopter create larger angles of disparity, this information tells us how far away something is from the horopter.
farther away from
TRUE or FALSE: Objects closer to the horopter create larger angles of disparity.
FALSE: objects FARTHER away = LARGER angle of disparity
What is stereopsis?
depth information provided by binocular disparity
What are random-dot stereograms?
have 2 identical patterns of ‘noise’ with one ‘piece of information’ shifted in position
What are stereoscopes?
viewers which use 2 pictures from slightly different viewpoints
review slide 11
slide 11
What is one challenge to relying on stereopsis on its own to extract depth information?
the correspondence problem
What is the correspondence problem?
- challenges stereopsis being used on its own to extract depth information
- the problem of how we ‘line up’ what’s happening in one retina with what’s happening in the other (e.g. determining whether an object falls on corresponding points)
Review slide 13 - 15
slide 13 - 15
What is one possible solution to the correspondence problem?
- visual system could rely on the specific features of objects to help ‘keep track’ of what is creating an image/where
- e.g. encoding not only where points on the retina are being stimulated, but also some associated feature (e.g. colour) may help with this problem
Review slides 17-18
slide 17-18
What are binocular depth cells? What is another name for them? Where are they found?
- respond best to a specific degree of absolute disparity between images on right and left retinas
- aka. disparity selective cells
- found in V1, dorsal, ventral streams
What do disparity tuning curves plot?
neural response as a function of disparity
review slide 20
slide 20
Describe the selective rearing experiment that demonstrated the existence and function of binocular neurons.
- cats reared by alternating vision between 2 eyes
- had few binocular neurons
- unable to use binocular disparity to perceive depth
Review diagram on slide 21
slide 21
What is the visual angle?
refers to the angle of an object relative to the observer’s eye
There are ______ degrees around the circumference of the eye. 1 degree = ____/360 of this circumference. That equates to an image of about ______ mm.
360; 1/360; 0.3
TRUE or FALSE: As things get closer, the visual angle decreases.
FALSE: increases
What does the thumb method of determining visual angle of an object tell us?
When the thumb is at arm’s length, whatever its width covers has a visual angle of about 2 degrees.
Why does the moon’s disk almost exactly cover the sun during an eclipse?
sun and moon have same visual angles
Can you use visual angle alone to judge size? Why or why not? What is the evidence for this?
- visual angle alone is not accurate for judging distance
- bc stimuli have smaller/larger visual angles as they get farther away/closer
- evidence from holway and boring experiment where they presented a luminous test circle down a right corridor, and a luminous comparison circle down the left –> could not accurately adjust test circle size when depth cues removed
What is the formula proposed for size-distance scaling?
- S = K(R x D)
- S = perceived size
- K = a scaling constant
- R = retinal size
- D = perceived distance
Why is an object perceived to remain a constant size as it moves farther away?
bc as the retinal size gets smaller, our perception of the distance increases
According to the S=RxD formula, what happens when you create an afterimage and move your eyes across the room vs when you look at something distant?
- visual angle will remain constant as you move eyes across room
- perceive afterimage as larger if looking in the distance
- this is because retinal size is constant, but distance varies, which conforms to predictions based on S=RxD
What is the Muller-Lyer Illusion? What is one proposed explanation for it?
- straight lines with inward fins appear shorter than straight lines with outward fins
- involves misapplied size-constancy scaling (of a form that works in 3D but is misapplied for 2D objects)
(i.e. if equivalently sized images are formed on retina, and one is judged to be farther away, it will be perceived as LARGER)
TRUE or FALSE: outside corners appear closer and inside corners appear further away.
TRUE
What is the conflicting cues theory?
- our perception of line length depends on two factors: 1) the actual length of the vertical lines 2) the overall length of the figure
- the conflicting cues are integrated into a compromised perception of the length
What does our perception of line length depend on?
- the actual length of the vertical lines
- the overall length of the figure
What is the Ponzo illusion? What might cause this illusion to occur?
- horizontal rectangular objects are placed over railroad tracks in a picture
- the far rectangle appears larger than the close rectangle but both are the same size
- may be due to misapplied size-constancy scaling (same retinal image formed, yet perceived to be at diffrent distances, will be perceived as being different actual sizes)
What is the Ames room?
- 2 people of equal size appear very different in size in an Ames room
- the room is constructed so that the shape looks like a normal room when viewed with one eye
- the actual shape has the left corner twice as far away as the right corner
How does size-distance scaling explain the Ames Room?
size-distance scaling (S=RxD)
- observer thinks room is rectangular, so the 2 people would be same distance away from observer
- woman on right has SMALLER VISUAL ANGLE (R)
- PERCEIVED DISTANCES (D) are the SAME
- therefore, PERCEIVED SIZE (S) on the RIGHT IS SMALLER
How does relative size explain the Ames room?
- perception of size depends on size relative to other objects
- one person fills the distance between the top and bottom of the room
- other person only fills part of the distance
- therefore, person on right appears taller
