Visual space perception

Visual Space Perception
Wednesday, 4 June 14

1.The Problem ofVisual Space
Perception

The Physical World and the Perceptual World

• Physical World - exist outside observer

• Perceptual World

• Experienced by the observer

• Produced by activity in eye-brain system - when - patterned light simulates
the eye of observer

the eye of observer
• Consist of - view at a given moment

the eye of observer
• Consist of - view at a given moment
• 4D World - “3D Space” + Time

Geometrical Relationships

• Physical Space

• Physical Space
• Object can be displaced / rotated
without deformation

• Physical Space
without deformation
• Follows Euclidean Geometry -
Parallel Postulate - Parallel Lines do
not meet

• Physical Space
without deformation
not meet
• Points in space can be assigned
coordinates in Cartesian coordinate
system and distance between points
can be measured w.r.t origin

• Physical Space
without deformation
not meet
• Perceptual (Visual) Space

• Physical Space
without deformation
not meet
• Geometry of Physical space w.r.t.
Perceiver

• Physical Space
without deformation
not meet
Perceiver
• Direction and Distance in Polar
Coordinates

• Physical Space
without deformation
not meet
Perceiver
• Direction and Distance in Polar
Coordinates
• By specifying an origin that
corresponds to a perceiver - visual
space can be measured in terms of
angular direction and radial distance

• Relationships among Spaces - Perceived and Physical

• To maintain important distinction between

• physical objects (or scenes) and

• pattern of reﬂected light impinging on the retinal surface

• Physical Objects (or scenes) are described as distal stimuli and

• Impinging Patterns of light are described as proximal stimuli

• Impinging Patterns of light are described as proximal stimuli
• Perception refers to the process or act of perceiving, whose
content is the percept, the conscious experience of the distal
object or scene.

• Distal objects and scenes can be observed directly

• Perception cannot be observed directly

• Proximal stimulus patterns can be observed by

• projecting light from distal stimuli

• onto a surface - a screen or projection place that represents the retinal surface

• Each component of perceptual act - distal stimulus, proximal stimulus, percept,
response - can be described geometrically

• Each component of perceptual act - distal stimulus, proximal stimulus, percept,
response - can be described geometrically
• The relationship between adjacent components in a sequence may be described
by mapping the geometry of one component into geometry of the next
component

Distal - Proximal Relationships

• Projective Geometry: Geometrical Optics

• The light falling on an eye can come

• directly from an emitting source or

• after being refracted through a medium like air, water

• The 2D pattern of light reﬂected to an eye from 3D arrangement of objects
in the world is described by projective geometry

• The 2D pattern of light reﬂected to an eye from 3D arrangement of objects
in the world is described by projective geometry
• We apply geometrical analysis to light - it is called as Geometrical Optics

• To study perception - it is necessary to consider
only the rays that enter the eye of a viewer.

• Fig. shows the distal-proximal realtions for a
single eye

single eye
• The viewer is looking at house - a distal object

single eye
• Light is reﬂected everywhere - but the perceiver is simulated only by light that - enters the
eye

single eye
eye
• Light is represented by the rays that converge toward the nodal point of the eye and simulate
cells on the retina of the viewer.

single eye
eye
• The pattern of light simulating cells on retina constitutes the proximal stimulus

single eye
eye
• The pattern of light simulating cells on retina constitutes the proximal stimulus
• inverted w.r.t. orientation of distal object

• Proximal Geometry - Geometry of Perspective

• represented in a hypothetical projection
plane erected b/w the viewer
and the distal stimulus

• In above ﬁgure, the projection is on frontoparallel plane or picture
plane - a plane that is perpendicular to line of sight of the viewer

• the upright pattern in proximal stimulus is described by 2D
geometry of perspective

• the upright pattern in proximal stimulus is described by 2D
geometry of perspective
• In this pattern, the size of a distal object is represented according

“The Problem ofVisual Space Perception”

• To relate - the experienced qualities - of - visual space to speciﬁc
aspects of simulation - and - to processes occurring in the visual
space system

space system
• To simplify these tasks of identifying these components - visual
space perception is divided into two different ways

space system
• Binocular and Monocular Perception

space system
• Binocular and Monocular Perception
• Static and Kinetic Analysis

2. Spatial Localization :Visual Directions

Visual Directions

Visual Directions
• Visual directions experienced when viewing a
scene with two eyes

Visual Directions
scene with two eyes
• Eyes are in different positions in space

Visual Directions
scene with two eyes
• Eyes are in different positions in space
• When looking at a single point, the two eyes
must be oriented in slightly different directions

Monocular Localization of Directions

• MonocularVisual Field

• The portion of the world that is visible to a single
stationary eye deﬁnes the monocular visual ﬁeld

• Perimetry

• Perimetry
• Field of monocular vision

• Perimetry
• Field of monocular vision
• Blind spot

• BinocularVisual Field

• Superimposed monocular ﬁelds of
two eyes

• Superimposed monocular ﬁelds of
two eyes
• Max width = ~200º with 120º of
binocular ﬁeld

• Objective Directions:Visual Lines

• Visual Line - locus of distal points that stimulate a given point on
the retina of a single eye

• PrincipalVisual Line (PVL) - locus of distal points that stimulate the
center of foveola of a single eye

• PrincipalVisual Line (PVL) - locus of distal points that stimulate the
center of foveola of a single eye
• Line passing through the center of the foveola, the nodal point of
the eye and the ﬁxated point is Visual Axis

• Relationship between distal points and their representation in the
proximal stimulus for a single eye

• Subjective Directions: Visual directions

• Perceived visual directions are the subjective directions of points
in space (up, down, left, right)

• When eye is directed at a given point, the image of the point falls
on the center of the fovea

• When eye is directed at a given point, the image of the point falls
on the center of the fovea
• The subjective direction associated with this ﬁxation is called
PrincipalVisual Direction (pvd).

• Proximal - perceptual relations described by visual directions.
• Perceived directions are described relative to the principal visual direction (pvd)
• Point A appears to be ßº to the left and øº above pvd

• Vergence Movements

• Conjunctive eye movements that maintain a constant
convergence angle

• Conjunctive eye movements that maintain a constant
convergence angle
• Vergence Movements are disjunctive eye movements in which
the convergence angle changes i.e. the eye muscle move the
eyes equally inward or outward.

• tan y/2 = A / 2D
• ~ y = A/D for small y in radians

Binocular Localizarion

• Well’s Experiments

• Fusion

• Fusion
• Horopter andVieth-Muller Circle

• Fusion
• Horopter andVieth-Muller Circle
• Next -- 3. Fusion and Horopters

Visual space perception

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