Midterm 2: Topic Depth and Size (Part 1,2,3) Flashcards
Why perceive depth and size?
Depth and targets of action
size and object recognition
how do we perceive depth
oculomotor cues
monocular cues
binocular cues
The challenge of depth and size perception
Distal stimulus is 3D object in space
Proximal stimulus is 2D projection on retina
what is convergence
Inward movement of eyes when we focus on nearby objects
Our eyes have to turn inward (close up)
our eyes have to be parallel (far away)
what is accommodation
Shape of the lens changes when we focus on objects at different distances
Muscles relax and lens flatten (to see far away)
Muscles tighten and lens become more rounded (to see close up)
what is relative depth
Depth of objects compared to each other
what is actual depth
Distance from observer
Occlusion
When one object partially covers another
The object doing the covering must be closer
Relative Height
Objects closer to the horizon line appear more distant
Objects further from the horizon line would appear closer
Familiar size
Distance information is based on our knowledge of object size
Example: a tennis ball is smaller than a soccer ball so if they are the same size then that means the tennis ball has to be closer
relative size
For objects of equal size, closer one takes up more of visual field
Perspective convergence
Parallel lines appear to come together in distance
Atmospheric perspective
Distance objects are fuzzier and have a blue tint
Texture gradient
Equally spaced elements are more closely packed as distance increases
how do shadows impact depth
Shadows indicate where objects are located
Motion parallax
Close objects glide past rapidly but distant objects appear to move more slowly
Things close to us will move very quickly while things in the distant move more slowly
Example: on a train, the close up of the city (benches and people) move by very quickly but the buildings and mountains in the back do not move as quickly
Deletion and accretion
Objects are covered (deletion) or uncovered (accretion) as we move relative to them or they move relative to us
what is Stereoscopic depth perception
Depth perception created by input from both eyes
Binocular disparity
Difference in images on left and right retinas
The image gets focused on different locations of retina compared to the other eye
what is Corresponding & non-corresponding retinal points
Objects on horopter fall on corresponding points
Objects off horopter fall on non-corresponding points
Helps our brain know that different objects are not all the same distance away
what is disparity
difference in location
How far away on surface of retina an image is
Where things are relative to horopter
Crossed disparity
A is nearer than B
A is on the right side in the left eyes view and on the left side in the right eyes view
Uncrossed disparity
A is farther from B
A is on the left side in the left eyes view and is on the right side of the right eye view
absolute disparity
Angle from corresponding point
Determines distance from horopter
Changes with gaze
bigger the disparity angle the further away from horopter
Relative disparity
Difference in disparities between objects
Determines distance between objects
Unchanged with gaze
difference in depth perception between two objects in a scene
what is Stereopsis
Detecting differences in alignment of an image due to it being closer or further away
2 images entering the same eye creates this effect
Perception of depth due to binocular disparity
what is the correspondence problem
refers to the challenge the brain faces in stitching together the images from both eyes to create a single, unified perception of the world.
can use colour to match up stimuli or within each local area of the image pick the one that minimizes differences
what is the relationship between depth and size
size perception depends on depth perception.
what is Size constancy
Same size objects at different depths form different size images on retina (and different visual angles)
Size-distance scaling equation
S = K(R × D)
Ponzo illusion
Same size on page, but different perceived size, due to different perceived depth
Hijacking of the size-distance relationship
Ames room
3D room with weird dimensions
Can only look into room through a small hole
Brain has this built assumption that all walls in rooms are parallel
2 people standing at different ends of the room will look different sizes because our brain is tricked into thinking they are the same distance away from us
what are Disparity-Selective Cells
Disparity-selective cells respond most strongly when they receive slightly different inputs from the left and right eyes
These cells are tuned to different levels of disparity.
areas involved in depth perception
Dorsal (where) stream is for:
Absolute disparity
Guiding action
Ventral (what) stream is for:
Relative disparity
Identifying objects
Anaglyph (stereoscopic movies)
Uses colored lenses to delivery one image to each eye
Displacement of the red and blue create depth perception in movies
Polarized lenses (stereoscopic movies)
Uses polarized lenses to deliver one image to each eye
One eye gets vertically polarized lens and the other gets horizontal polarization
Active shutter (stereoscopic movies)
Uses LCD lenses to open and close each lenses in turn
Downside is the glasses are very expensive
Interference filter technology (stereoscopic movies)
Wavelength multiplex visualization
Each eye will see a specific set of wavelengths with specific glasses
Parallax barrier autostereoscopic (stereoscopic movies)
Use tiny barriers to allow one image to reach each eye
Used in Nintendo 3DS
Only works when eyes are at certain distance away from screen
2 versions of an image intertwined
