Depth perception

Depth Perception

Monocular Cues
Binocular Cues
Visual Illusions
Clinical Relevance

D
e
p Objectives
t
h
p  deals at first with some general theory about visual
e
r depth cues (oculomotor, monocular and binocular
c cues) from the psychological point of view.
e
p  details about some possibilities to convey depth
t
i and shape surface in computer based visualization
o
n

Gauri S. Shrestha, M.Optom 2

D
e
p Introduction
t
h
p  we have developed perceptual systems capable of
e representing three dimensional environment with
r
c sufficient accuracy to guide our behavior.
e
p  The human visual system is able to reconstruct
t
i depth information from flat images through
o
n combination of a set of many different impulses,
cues and patterns
 Distance estimations, hints about an object's
surface and other visual cues are essential for all
of us

D
e
p General theory of depth cue
t
h
p  Oculomotor cues are, as the name suggests, possibilities
e for depth estimation by controlling the eye axes and the
r lens focus using the eye muscles.
c  Convergence and accommodation are counted among that
e
p kind of cues which interact with each other in depth
t perception.
i  The angle of convergence of the two eyes and their
o accommodative states are one source of scaling
n information
 They must be supplemented by other cues even at close
ranges.
 Thus they are considered to be minor cues in depth
perception.


D
e
p Monocular vs. Binocular Cues
t
h
p  Monocular Depth Cues
e
r  Cues perceived as strong with one eye as with two eyes
c  Binocular Depth Cues
e
p  Cues that must be viewed with both eyes
t Greatly enhance depth perception
i 
o
n


D
e
p Monocular Depth Cues
t
h
p  Pictorial Depth Cues
e  Size
r
c  Linear Perspective
e  Texture
p
t  Interposition
i  Clarity
o  Lighting and Shadow
n
 Motion Parallax
 Accommodation
 Aerial perspective


D
e
p Pictorial Depth Cues -Size
t
h
p  Larger objects are interpreted
e as being closer
r
c  Relative Size- If objects are
e thought to be the same size, the
p
t one that appears smaller is
i perceived as being farther
o away
n
 Familiar Size-Used viewing
objects of a known size.
Object distance determined
based on previous knowledge
of its size

D
e
p Relative size
t
h
p
e
r
c
e
p
t
i
o
n


D
e
p Relative height
t
h
p  Points that are situated
e
r closer to the horizon
c seem to be more
e
p distant than points that
t
i are farther away from
o the horizon.
n


D
e
p Pictorial Depth Cues-
t
h Linear Perspective
p  Related to relative size
e
r  Sense of depth is experienced due to our
c
e conception that objects have a constant
p shape and size
t
i
o
n


D
e
p Pictorial Depth Cues -Texture
t
h
p  Smaller, densely packed objects appear far away
e
r  Larger, loosely packed objects appear closer
c  Observer assumes all objects are the same size
e
p  Smaller images are perceived as being farther away
t
i
o
n


D
e
p Pictorial Depth Cues -texture
t
h
p
e
r
c
e
p
t
i
o
n


D
e
p Pictorial Depth Cues -Interposition
t
h
p  One object blocks view of another
e
r  Blocked object is perceived as being farther
c
e away
p
t
i
o
n


D
e
p Pictorial Depth Cues -Clarity
t
h
p  Objects that appear clear are
e interpreted as being closer than
r
c those objects that appear hazy
e  Fog, smoke, rain and smog act as
p
t interposing elements that make
i obscured objects seem farther
o
n away


D
e
p Pictorial Depth Cues -Lighting
t
h and Shadow
p  With Light falling on an object, it casts a shadow
e
r  The shadow is interpreted as falling behind the
c
e object-creating a sense of depth
p
t
i
o
n


D
e
p Monocular Depth Cue:
t
h Motion Parallax
p  Kinetic Depth Cue
e
r  Produced by relative
c motion of two or more
e objects
p
t  Near Object Fixation
i Far objects move with
o 
n head movement
 Distant Object Fixation
 Near objects move
opposite of head
movement


D
e Monocular Depth Cue
p
t
h Motion Parallax
p  Whenever we move, the images projected by
e
r objects located at different distances move across
c our retina with different speed whereby nearby
e
p objects tend to cross the retinal image plane faster
t
i than the distant objects.
o
n


D
e
p Monocular Depth Cue
t
h Accommodation
p  Accommodation is necessary to clearly view near
e
r objects
c
e  The signal to accommodate contains information
p regarding the distance of viewed objects
t
i
o
n


D
e
p Aerial perspective
t
h
p  Over very long distances in the natural
e
r environment the color of surfaces tends to become
c bluer. (aerial perspective)
e
p  The outlines of far away objects become blurred
t
i and the contrast gets reduced
o
n


D
e
p Binocular Depth Cues
t
h
p  Binocular cues are the most important category of cues
e that potentiates humans to experience a three dimensional
r
c world.
e  The term binocular cues refers to the fact that both eyes
p
t are required to gain depth information from the projected
i image of the real world.
o
n  They are
 Stereopsis
 Corresponding retinal points

 Retinal Disparity

 Convergence

D
e
p Stereopsis
t
h
p  Retinal locations of images
e signal the distance of the
r
c object being seen
e  Corresponding points-two
p
t retinal points that
i correspond to the same
o
n direction in space (foveas)
 Retinal Disparity-distance
between corresponding
points and the image
location


D
e
p Stereopsis
t
h
p  Retinal Disparity
e
r  Disparity provides information about spatial depth
c when the images of an object fall upon different retinal
e areas in the left and right eyes
p
t  Allows visual system to determine distance of object
i
o  It is the function of IPD as well
n  Depth is perceived when non corresponding point is
stimulated


D
e
p Retinal Disparity
t
h
p  Uncrossed Retinal Disparity
e Images fall nasal to
r
c fixated object
e  Object is farther than
p
t fixated object
i  Crossed Retinal Disparity
o
n  Images fall temporal to
fixated object
 Object is closer than
fixated object
 Stereopsis is the perception
of depth produced by
binocular retinal disparity Shrestha, M.Optom
Gauri S. 23

D
e
p Stereopsis
t
h
p  More important while viewing near objects
e
r  Within arm’s length
c  Binocular disparity provides depth perception only
e
p if it is not too great
t
i  Panum’s Fusional Area-area on the retina that
o corresponds to binocular fusion
n
 Physiological diplopia-occurs when images fall on
retinal positions that signal grossly different
directions


D
e
p Demonstration
t
h
p  Hold one index finger 15 cm from nose
e
r  Hold other index finger at arms length
c
e  Focus on near finger
p
t  Notice diplopia
i
o  Bring far finger closer to you
n
 Notice diplopia disappears
 THIS IS PANUM’S AREA


D
e
p Another way to look at it
t
h
p  Every retinal point has a
e corresponding point in the other
r eye
c
e  Horopter-a plot of
p corresponding points for a given
t
i distance
o  curved plane due to the
n curvature of the retina
 Objects relatively close to
the horopter can be fused
Objects are within Panum’s
fusional area
 Provides stereopsis for

these objects Gauri S. Shrestha, M.Optom 26

D
e
p Disparity Detectors
t
h
p  Binocular Cortical Neurons are maximally
e
r responsive to stimuli at a specific distance
c
e  The same stimulus placed at different distances,
p elicits a less vigorous response
t
i
o
n


D
e
p Convergence
t
h
p  We constantly converge and diverge our eyes
e
r  The amount of convergence required to view a
c
e specific object provides information concerning
p the distance of that object
t
i  It is not understood how this information is
o
n incorporated into conscious depth perception


D
e
p What Are Visual Illusions?
t
h
p  Erroneous Perceptions
e
r  Commonly result from pictorial depth cues to
c
e judge the size of unfamiliar objects
p
t
i
o
n


D
e
p Size Constancy
t
h
p  The apparent size of
e
r an object does not
c normally change with
e
p viewing distance
t
i  Our visual system
o
n compensates for
differences in retinal
image size by taking
into account the
relative distance

D
e
p Size Illusion
t
h
p  Occurs when judgments of distance are erroneous
e
r  Size Constancy fails
c
e  Examples of Visual Illusions:
p
t  Corridor Illusion
i
o  Moon Illusion
n
 Müller-Lyer Illusion


D
e
p Corridor Illusion
t
h
p  Illustration
e
r  Size Constancy fails due to monocular depth cues:
c
e  Top line looks farther away
p
t  Top line seems larger
i
o  Two lines are actually the same size
n


D
e
p Corridor Illusion
t
h
p
e
r
c
e
p
t
i
o
n


D
e
p Moon Illusion
t
h
p  Moon appears larger if
e viewed on the horizon
r
c  Moon appears smaller
e
p when viewed directly
t overhead in a clear sky
i
o  Why?
n  Moon does not appear to
be at the same distance
 On the horizon, moon
appears farther away
 Due to background

(trees, houses, fields,
etc.) Gauri S. Shrestha, M.Optom 34

D
e
p Müller-Lyer Illusion
t
h
p  Lines mimic the corner of a room
e
r  The line that appears to be an outgoing corner is
c
e judged as being farther away
p
t  Perceived as being a longer line
i
o  The line that appears to be an ingoing corner is
n judged as being closer
 Perceived as being a shorter line


D
e
p Müller-Lyer Illusion
t
h
p
e
r
c
e
p
t
i
o
n


D
e
p Clinically Relevant Topics
t
h
p  Stereopsis and Vision Development
e
r  Monovision Contact Lenses
c
e
p
t
i
o
n


D
e
p
t
h Stereopsis Clinically
p  Stereopsis Tested Clinically
e
r  Patient views flat surface with two identical figures
c
e separated by a small distance
p  Each eye views only one of the objects
t
i  Polaroid or Red-Green glasses
o
n  Minimum amount of disparity that allows patient to
appreciate depth is determined


D
e
p Stereo-acuity
t
h
p  Can be as small as 3 seconds of arc
e
r  A high degree of stereo-acuity depends on a
c normal complement of binocular neurons in the
e
p visual cortex
t  Anisometropia and Strabismus are two disorders
i
o of binocular vision that retard cortical neuron
n
development


D
e
p Monovision Contact Lenses
t
h
p  One eye for near, One eye for distance
e
r  Patient alternates between two eyes to view
c
e objects at various distances clearly
p
t  Blurred image is suppressed
i
o  Stereopsis is reduced because patient is not using
n both eyes simultaneously
 Monocular depth cues are still present


D
e
p When Will It Matter?
t
h
p
e  Stereopsis is more important for near work
r
c  Driving can be difficult for these patients
e
p  Patients must be advised of ↓ depth perception
t
i  Alternatives while driving:
o
n  Glasses to correct near eye while driving
 Distance only contact lenses for driving only


D
e
p Thank you
t
h
p
e
r
c
e
p
t
i
o
n


Depth perception

Recommandé

Recommandé

Contenu connexe

En vedette

En vedette (9)

Similaire à Depth perception

Similaire à Depth perception (11)

Plus de GauriSShrestha

Plus de GauriSShrestha (20)

Depth perception