Depth and size part 1 Flashcards
Why do we perceive depth and size?
Depth and targets of action (catching)
Size and object recognition (judging size is important for survival)
What are the 3 cues we used to perceive depth?
oculomotor cues
monocular cues
Binocular cues
What is the challenge of depth and size perception?
How to recover 3D object in space from 2 D image on retina
confusion between size and depth
What causes confusion between size and depth?
smaller things that are closer create the same image on retina as large things that are farther
What are the two oculomotor cues?
Accommodation
Convergence
What is convergence? What does it tell us?
Inward movement of eyes when we focus on something
Muscle position gives a clue about distance
for a far object the eyes are straight and for a close object they turn in
What is accommodation?
Shape of lens changes when we focus on objects at different distances
What happens to the lens and eye muscles when we focus on something far away?
lens is flat and muscles are relaxed
What happens to the lens and eye muscles when we focus on something close?
Lens is pulled by muscles and gets fatter and rounder
What is a monocular cue?
depth cue available to one eye
What are the two types of monocular cues?
Pictorial and motion cues
What are pictorial cues?
Sources of depth info available in still image
What are motion cues?
Sources of depth information only available due to motion
What are the 7 types of pictorial cues?
Occlusion
Relative height
Familiar and relative size
Perspective convergence
Atmospheric perspective
Texture gradient
Shadows
What are the two types of motion cues?
Motion parallax
Deletion and accretion
What are the two types of depth?
Relative and actual depth
What is relative depth compared to actual depth?
Depth of objects compared to eachother –> relative depth
Distance from observer –> actual depth
Which cues indicate relative depth?
Occlusion
Deletion and accretion
Relative height
Atmospheric perspective
Which cues indicate actual depth?
Relative size
texture gradients
motion parallax
Accommodation
Convergence
What is occlusion?
When one object partially covers another it must be closer
What is relative height?
Objects closer to the horizon line appear more distant
Just below and above horizon like = farthest away
What is familiar size? Give example
Distance information based on our knowledge of object size. Comparing objects that we know are different size but appear the same so one must be closer
i.e tennis ball and soccer ball
What is relative size?
For objects of equal size, closer one takes up more of visual field. We know the size is the same but they look different (i.e two soccer balls)
What is perspective convergence?
Parallel lines appear to come together in distance
What is atmospheric perspective?
Distance objects are fuzzier and hve a blue tint
What is texture gradient? Example?
Equally spaced elements are more closely packed as distance increases
grass
What do shadows indicate?
where objects are located
What is motion parallax? Who has to be moving?
close objects glide past rapidly but distant objects appear to move more slowly. When we are moving
What is deletion and accretion?
Objects are covered (deletion) or uncovered (accretion) as we move relative to them or they move relative to us
What is the binocular depth cue?
Binocular disparity
What is stereoscopic depth perception? How does it compare to monocular depth perception?
depth perception created from input from both eyes
The experience is very different from monocular depth perception –> we feel it more whereas monocular just tells us about it being further away
What is a toy that uses stereoscopic depth perception? explain how it works
view-master that puts a different copy of an image in each eye and the brain interprets the difference as depth
What is binocular disparity? What is the trick to see it?
Difference in images on left and right retinas that brain determines depth from. Finger trick closing left and right eye
What are corresponding points on retina?
Objects on horopter fall on corresponding points on retina (same relative location on both eyes)
What are noncorresponding points?
Objects off horopter fall on noncorresponding points
What is the horopter>
circular arch around thing you are looking at
What are the two angles of disparity?
Cross disparity and uncrossed disparity
What is crossed disparity and where would bill be placed relative to julie?
Bill nearer than julie. Bill will be on the right of julie in the left eye and on the left of julie in the right eye
What is uncrossed disparity and where would bill be placed relative to julie?
Bill farther than julie
Bill will be on the right of julie in the right eye and on the left of julie in the left eye
What does angle of disparity tell us?
Difference in location of 2 things
What are the two types of disparity?
Absolute disparity
Relative disparity
What is absolute disparity?
angle from corresponding point that determines distance from horopter
Does absolute disparity change with gaze?
yes
Give an example of absolute disparity? Being further from the horopter does what to the angle?
If dave is farther from the horopter than bill, his absolute disparity would more more than bill
What is relative disparity?
difference in disparities between two objects which determines the distance between objects
Does relative disparity change with gaze?
no
Give an example of relative disparity?
Relative disparities between julie and bill does not change if you switch who you are looking at –> same distance
What is stereopsis?
perception of depth due to binocular disparity only (not colour)
How does a random dot stereogram work?
you detect the difference in images as depth
What are the 3 types of stereograms?
random dot stereograms
animated stereogram
autostereogram
What is the correspondence problem?
How do we match up points in the two retinal images? What in the left eye corresponds to the right eye image
What can we use to solve the correspondence problem?
Use features of objects such as colour (often use monocular cues)
What do we do when we don’t have colour (or anything else) to solve the correspondence problem?
within each local area of the image, try all possible matches, pick the one that minimizes the difference (best match)
What is the relationship between depth and size?
A small close object and a large distant object can have identical visual angles and retinal images.
We would need distance to figure out size or visa versa
Explain the Boring experiment (basic)?
Person looks at comparison circle then has to judge how near or far test circles are compared to the comparison circle. Test stimuli are picked so they create the same size image on the retina
They were also asked to guess the size of the test circles under different conditions
What were the 4 conditions in the boring experiment?
- full depth cues
- One eye only (no binocular disparity)
- viewed through peephole (no motion parallax from moving yourself)
- drapes in hallways (no shadows)
What were the results of the study?
People were good in the first 2 conditions (full cues and one eye only)
But were bad in the last two conditions
They found that size perception depends on depth perception
What is size constancy? How is visual angle affected by closer and father things?
same size objects at different depths form different images on retina (and different visual angles) yet we perceive them as having the same size
Father = smaller
Closer = bigger
What is the equation the brain uses for the relationship between size and difference? What are the symbols?
Size-distance scaling
S= K(RxD)
S is perceived size, R is size of retinal image and D is perceived distance
What does the size-distance scaling equation tell us?
If either the size or distance increases, the perceived size increases
What is the ponzo illusion?
3 cars that are the same size (same size retinal image) on the page, but have different perceived size due to different perceived depth. One that looks closer is thought to be smaller
What is the ames room?
room with weird dimensions that makes one person look very big. You can only look through a peephole (one eye, no motion parallax). The brain incorrectly thinks the people are at the same distance and that the different retinal images must mean that one person is large.
Where do we perceive depth in the brain (start of depth perception)?
Binocular depth cells/disparity-selective cells in V1
What do disparity tuning curves for cells in V1 show?
We have cells with different tuning curves that respond best to different disparities between eyes. Some neurons respond best to things on horopter and some respond best to other disparities
What are the two pathways involved in depth perception?
The ventral (what) pathway and the dorsal (where) pathway
What do the dorsal pathway do for depth perception?
Absolute disparity for guiding action. Need to know how far something is from you for action
What does the ventral pathway do for depth perception
relative disparity for identifying objects. How components of objects relate to eachother
