Cues of Depth Perception

Why is depth perception even a problem?

• Each eye has a two-dimensional view of the

world

• … a 2D projection of the 3D world onto the

retina

• This means that there are many possible 3D

scenes that could have led to any given 2D

image.

Binocular Disparity

The differences between the two retinal images of the same scene. Disparity is the basis for stereopsis, a vivid perception of the three-dimensionality of the world that is not available with monocular vision.

Binocular Depth Cue

A depth cue that relies on information from both eyes. Stereopsis is the primary example in humans, but convergence and the ability of two eyes to see more of an object than one eye sees are also binocular depth cues.

Monocular Depth cue

A depth cue that is available even when the world is viewed with one eye alone

Stereopsis

The ability to use binocular disparity as a cue to depth

Occlusion

A cue to relative depth order in which, for example, one object obstructus the view of part of another object

A foveated object is a—

“fixated” object. When our eyes fixate on the same place/object, it brings it onto each fovea and the object has no disparity—it falls onto the same place on each retina (the fovea)

Forced perspective

The deliberate creation of accidental alignments, often leading to misjudgements of size

Vergence eye posture

Degree to which the eyes deviate from having parallel optic axies; an oculomotor depth cue

Linear Perspective

Depth cue related to the apparent convergence of parallel lines in the two-dimentsional retinal image

Shading

the visual process by which the human brain interprets variations in light, shadow, and surface luminance to extract the three-dimensional (3D) shape, curvature, and depth of an object from a flat, two-dimensional image

Motion parallax

Depth cue related to the relative apparent movement magnitudes and or directions of near v. far objects when the observer is moving

Shape-slant invariance

Automatic compensation for (slant in) perceived depth when judging shape

Optic flow

The pattern of apparent motion of objects in a visual scene produced by the relative motion between the observer and the scene. Helps observer gauge their own movement in their environment

Accretion

The gradual reappearance of a moving object from behind occlusion

Horopter

Imaginary surface or distnace at which all objects have zero disparity

Crossed disparity

The specific difference between the two retinal images of some object that you are not fixating, yielding the percept that that non-fixated object is closer in depth than a different fixated object

Partial Occlusoin

One item (partially) blocking another from view; a depth cue indicating the relative distance of two items

aka Interposition

Anaglyph

An image composed to two overlaid images than can be separated using lens filters over each eye

Atmospheric perspective

Depth cue that functions because of the visual system heuristic that a scene is likely to be illuminated from above

Stereogram

The visual phenomenon where depth perception is enhanced and objects at the edges appear to move more compared to those at the center (the focus of expansion) when transitioning through a scene.

Telestereoscope

Device that boosts binocular disparity by virtually moving the eyes further apart

Size-distance invariance

Automatic compensation for perceived depth when judging size

Zero Disparity

when an object falls at corresponding points on the two retinas, that object has _____ disparity: the two eyes see it at the same location on their retinals (relative to fixation/the fovea)

Vieth-Müller circle

The circle defined by the two eyes and the fixated object

Crossed disparity

Objects closer than the horopter have _______ ________, meaning you would have to further cross your eyes to fixate them

Uncrossed disparity

Objects further away than the horopter have _______ ________

The greater the disparity between the retinal images.

The greater the distance in front of or behind the horopter—

Oculomotor cue

NOT from the retinal image;

Vergence Eye Posture

Movements occur when we rotate our eyes inward (converging the eyes) or outward (diverging the eyes) to focus on a near or far object; the degree to which your eyes converge

greater convergence → item is closer

Static monocular cues or Pictorial cues

• do not require motion

• occur in still images

Relative Height

where an item is positioned (relative to eye level or the horizon), NOT comparisons of heights of objects

Ex: items that are closer to the horizon/eye level are perceived as further away

items closer to the top of bottom are perceived as closer

Visual Angle

• Description of size on the the retinal that combines distance and real-world size

• The angle subtended by an object; the angle at the eye of the triangle formed by the eye and the items two extremes

Familiar size

we use the knowledge that we have about the size of regular objects to make judgements on their distance to us

ex: a super small basketball is a basketball that is far away

Relative size

We have no knowledge but can compare the size of an object relative to other objects to determine the size

Texture

Repeated, regular variation in structure or appearance