Topic 10: Depth & Size Perception Flashcards
Cue Approach to Depth Perception
the approach to explaining depth perception that focuses on identifying information in the retinal image that is correlated with depth in the scene
some of the depth cues that have been identified are overlap, relative height, relative size, atmospheric perspective, convergence, and accommodation
Occlusion
depth cue in which one object hides or partially hides another object from view, causing the hidden object to be perceived as being farther away
a monocular depth cue
Oculomotor Cues
depth cue that depends on our ability to sense the position of our eyes and the tension in our eye muscles
accommodation and convergence are oculomotor cues
Monocular Cues
depth cue, such as overlap, relative size, relative height, familiar size, linear perspective, movement parallax, and accommodation, that can work when we use only one eye
Pictorial Cues
monocular depth cue, such as overlap, relative height, and relative size, that can be depicted in pictures
Relative Height
a monocular depth cue
objects that have bases below the horizon appear to be farther away when they are higher in the field of view
objects that have bases above the horizon appear to be farther away when they are lower in the field of view
Familiar Size
a depth cue in which judgment of distance is based on knowledge of the sizes of objects
Epstein’s coin experiment illustrated the operation of the cue of familiar size by showing that the relative size of coins influenced perception of the coin’s distances
Relative Size
a cue for depth perception
when two objects are of equal size, the one that is farther away will take up less of the field of view
Perspective Convergence
the perception that parallel lines in the distance converge as distance increases
Atmospheric Perspective
a depth cue
objects that are farther away look more blurred and bluer than objects that are closer because we look through more air and particles to see them
Texture Gradient
the visual pattern formed by a regularly textured surface that extends away from the observer
this pattern provides information for distance because the elements in a texture gradient appear smaller as distance from the observer increases
Motion Parallax
a depth cue
as an observer moves, nearby objects appear to move rapidly across the visual field whereas far objects appear to move more slowly
Deletion
a cue that provides information about the relative depth of two surfaces
deletion occurs when a farther object is covered by a nearer object due to sideways movement of an observer relative to the objects
Accretion
a cue that provides information about the relative depth of two surfaces
occurs when the farther object is uncovered by the nearer object due to sideways movement of an observer relative to the objects
a cue that provides information about the relative depth of two surfaces
deletion occurs when a farther object is covered by a nearer object due to sideways movement of an observer relative to the objects
Stereoscopic Vision
two-eyed depth perception involving mechanisms that take into account differences in the images formed on the left and right eyes
Stereoscopic Depth Perception
the perception of depth that is created by input from both eyes
Strabismus
misalignment of the eyes, such as crossed eyes or walleyes (outward looking eyes), in which the visual system suppresses vision in one of the eyes to avoid double vision, so the person sees the world with only one eye at a time
Binocular Disparity
occurs when the retinal images of an object fall on disparate points on the two retinas
Corresponding Retinal Points
the points on each retina that would overlap if one retina were slid on top of the other
receptors at corresponding point send their signals to the same location in the brain
Horopter
an imaginary surface that passes through the point of fixation
images caused by a visual stimulus on this surface fall on corresponding points on the two retinas
Noncorresponding Points
two points, one on each retina, that would not overlap if the retinas were slid onto each other
also called disparate points
Absolute Disparity
the visual angle between the images of an object on the two retinas
when images of an object fall on corresponding points, the angle of disparity is zero
when images fall on noncorresponding points, the angle of disparity indicates the degree of noncorrespondance
Angle of Disparity
the visual angle between the images of an object on the two retinas, when images of an object fall on corresponding points, the angle of disparity is zero
when images fall on noncorresponding points, the angle of disparity indicates the degree of noncorrespondence
Crossed Disparity
disparity that occurs when one object is being fixated, and is therefore on the horopter, and another object is located in front of the horopter, closer to the observer
Uncrossed Disparity
disparity that occurs when one object is being fixated, and is therefore on the horopter, and another object is located behind the horopter, farther from the observer
Relative Disparity
the difference between two objects’ absolute disparities
Stereopsis
the impression of depth that results from binocular disparity
the differences in the position of images of the same object on the retinas of the two eyes
Random-Dot Stereogram
a pair of stereoscopic images made up of random dots
when one section of this pattern is shifted slightly in one direction, the resulting disparity causes the shifted section to appear above or below the rest of the pattern when the patterns are viewed in a stereoscope
Stereoscope
a device that presents pictures to the left and right eyes so that the binocular disparity a person would experience when viewing an actual scene is duplicated
the result is a convincing illusion of depth
Correspondence Problem
the problem faced by the visual system, which must determine which parts of the images in the left and right eyes correspond to one another
another way of stating the problem is: How does the visual system match up the images in the two eyes?
this matching of the images is involved in determining depth perception using the we of binocular disparity
Binocular Depth Cells
a neuron in the visual cortex that responds best to stimuli that fall on points separated by a specific degree of disparity on teh two retinas
also called a disparity-selective cell
Disparity Turning Curve
a plot of a neuron’s response versus the degree of disparity of a visual stimulus
the disparity to which a neuron responds best is an important property of disparity-selective cell, which are also called binocular depth cells
Frontal Eyes
eyes located in front of the head, so the views of the two eyes overlap
Lateral Eyes
eyes located on opposite sides of an animal’s head, a sin the pigeon and the rabbit, so the views of the two eyes do not overlap or overlap only slightly
Echolocation
locating objects by sending out high-frequency pulses and sensing the echo created when these pulses are reflected from objects in the environment
echolocation is used by bats and dolphins
Visual Angle
the angle of an object relative to an observer’s eyes
this angle can be determined by expanding two lines from the eye, one to one end of an object
because an object’s visual angle is always determined relative to an observer, it’s visual angle changes as the distance between the object and observer changes
Size Constancy
occurs when the size of an object is perceived to remain the same even when it is viewed from different distances
Size-Distance Scaling
a hypothesized mechanism that helps maintain size constancy by taking an object’s perceived distance into account
according to this mechanism, an object’s perceived size, S, is determined by multiplying the size of the retinal image, R, by the object’s perceived distance, D
Emmert’s Law
a law stating that the size of an afterimage depends on teh distance of the surface against which the afterimage is viewed
the farther away the surface, the larger the afterimage appears
Muller-Lyer Illusion
an illusion in which two lines of equal length appear to be of different lengths because of the addition of “fins” to the ends of the lines
Misapplied Size Constancy Scaling
a principle, proposed by Richard Gregory, that when mechanisms that help maintain size constancy in the three-dimensional world are applied to two-dimensional pictures, and illusion of size sometimes results
Conflicting Cues Theory
a theory of visual illusion proposed by R.H. Day, which states that our perception of line length depends on an integration of the actual line length and the overall figure length
Ponzo Illusion
an illusion of size in which two objects of equal size that are positioned between two converging lines appear to be different in size
also called the railroad track illusion
Ames Room
a distorted room, first built by Adelbert Ames, that creates an erroneous perception of the sizes of people in the room
the room is constructed so that two people at the far wall of the room appear to stand at the same distance from an observer
in actuality, one of the people is much farther away than the other
Moon Illusion
an illusion in which the moon appears to be larger when it is on or near the horizon than when it is high in the sky
Apparent Distance Theory
an explanation of the moon illusion that is based on teh idea that the horizon moon, which is viewed across the filled space of teh terrain, should appear farther away than the zenith moon, which is viewed through the empty space of the sky
this theory states that because the horizon and zenith moon have the same visual angle but are perceived to be at different distances, the farther appearing horizon moon should appear larger
Angular Size Contrast Theory
an explanation of the moon illusion that states that the perceived size of the moon is determined by the sizes of the objects that surround it
according to this idea, the moon appears small when it is surrounded by large objects, such as the expanse of the sky when the moon is overhead
Binocularly Fixate
directing two fovea’s to exactly the same spot
What is absolute distance judgment?
“egocentric” localization (you <–> object)
What is relative distance judgment?
requires object-relative localization (object <–> object)
What is occlusion?
if object A covers part of object B, then A is seen as closer than B
What is shading and shadows?
indicates which surfaces are facing the light source and which are not
What is atmospheric perspective?
greater absolute distance makes objects appear fuzzier, bluer
Leonardo da Vinci suggested application in painting (“thus if one is to be five times as distant, make it fives time bluer”)
What is relative size?
same size object farther away produces smaller visual angle
What is familiar size?
knowledge of object’s actual size influences perception of its distance
What is linear perspective?
apparent convergence of receding parallel lines at a vanishing point
What is relative height?
below the horizon, higher objects appear farther away; above the horizon, lower objects appear farther
What is texture gradient?
texture elements appear smaller and more densely arranged as they get farther away
higher-order depth cue: made up of linear perspective + relative size
What are pictorial depth cues?
occlusion
shading & shadows
atmospheric perspective
relative size
familiar size
linear perspective
relative height
texture gradient
What are motion-based depth cues?
motion parallax
deletion
accretion
What is motion parallax?
as observer moves perpendicular object (side-to-side), nearby objects appear to move past more rapidly than faraway objects
What is deletion?
background object is occluded by foreground object moving in front of it
What is accretion?
background object is uncovered by foreground object moving out of the way
What is accommodation?
crystalline lens changes shape to focus on objects
feedback from ciliary muscles provides information on lens curvature, and therefore distance
What is convergence?
rotation of eyes inward to cause image to fall on the fovea
smaller convergence angle = farther object; larger angle = closer
What is the interaction of depth cues?
depth cues rarely used alone; most used in conjunction with others
accuracy in estimating distance is an additive relation between depth cues
also, perception of depth is stronger with more cues
What is binocular (or retinal) disparity?
retinal images of an object fall on disparate points on each eye’s retina
What is stereopsis?
perception of depth based on retinal disparity alone
What is horopter?
imaginary surface passing through fixation point
is a distal stimulus lies on the horopter, then the proximal stimulus will fall on corresponding points on each retina (no disparity)
if a distal stimulus is not on the horopter, then the proximal stimulus produces disparity
the distance between points on each retina is called the degree (or angle) of disparity
the farther from the horopter, the greater disparity
What are random-dot stereograms?
each eye sees the same pattern of random dots, with one exception
central region in each pattern is shifted over; this creates retinal disparity
shifted region is perceived as floating above the background
What are single-image random-dot stereograms?
retinal disparity in “autostereograms” is produced in opposite way from random-dot stereograms
usually, two slightly different images are directed onto the same part of each retina
in SIRDSs, a single image is observed so that it falls on two different parts of each retina
What are the steps of viewing an autostereogram?
- have a small angle of convergence (e.g., look at a wall or distant object)
- look at autostereogram, but don’t change convergence; you should see two overlapping images
- change accommodation to bring images into focus, keeping convergence constant
- change convergence until repeating parts of the pattern line up horizontally
What is the correspondence problem?
how is it determined which dots (or visual features) in the left eye match with after dots (or visual features) in the right eye, to fuse the two images into one percept?
What are the proposed solutions to the correspondence problem?
matches are made only between elements that are similar (e.g., a black dot in the left eye can only match a black dot in the right eye)
however, no widely accepted solution has been created yet
What are the sensitive/critical periods in the development of depth perception?
in humans, binocular depth develops early: 3-5 months
collision info apparent as young as 2-3 weeks
pictorial depth cues used later: 6-7 months
depth information from shadows may not appear until ~3 years
What was the Holway & Boring size perception experiment?
task: adjust size of comparison circle to match that of various sized test circles, placed at different distances
visual angle of all test circles is one degree (same retinal size or visual angle)
normal viewing: if test circle was large (and far), observers chose large comparisons, too
depth cues eliminated: observers looked at test circles with one eye through a peephole
all stimuli had the same visual angle, so the size of the comparison matched the visual angle of the test circle, not the size of the test circle
What is size constancy?
as distance from a given object increases, retinal image becomes smaller, yet we do not perceive the object as getting smaller
distance taken into account when perceiving size: size-distance scaling
distance & depth cues (pictorial, accommodation, convergence, disparity) must be available, or errors will occur
illusions are often caused by misapplied size constancy (generally exist on paper; are rare in the real world)
What is the Muller-Lyer Illusion?
illusion is weaker in children and in people living in dome-shaped huts
“carpentered world” hypothesis: (a) like inside corner of a room, (b) like outside edge of a building
depth cues indicate (a) is relatively far away, (b) is relatively close
due to size constancy, (a) appears longer, (b) appears shorter
What is the moon illusion?
horizon moon seems to be much larger than zenith (overhead) moon
but moon’s retinal size, and actual distance are essentially constant
misjudgment of moon’s size is an illusion, resulting from a misperception of distance
if an object perceived to be (or actually) farther away has the same visual angle as an object perceived to be (or actually) nearer, the farther object will appear larger
What is the apparent-distance theory?
objects on the horizon, viewed across the filled space of the terrain, should appear to be farther away
objects at the zenith, seen through the empty space of the sky, should appear to be closer
What was Boring’s solution to the moon illusion?
eye elevation hypothesis: moving eyes upwards makes objects appear smaller
What is Emmert’s Law?
perceived size of an object having a constant visual angle is proportional to the (perceived) distance of the object
What was the solution to the moon illusion based on Claudius Ptolemy?
plants were objects that moved on sets of transparent heavenly spheres
“vault of the heavens” is flattened
the moon seems to travel along a flat sky
horizon appears farther away
result: zenith moon appears closer than horizon moon, due to size constancy its apparent size is thus smaller
