PSYC 230 CHP 13- Size and Depth Perception

Accommodation

The lens changes shape to focus on near vs. far objects.

Vergence

The inward/outward rotation of the eyes.

Monocular Pictorial Cues

Depth cues available from one eyes and from still images.

Monocular Depth Cues

Visual cues that allow depth perception even without binocular vision.

Occlusion: When does it happen?

One object blocks part of another, making the blocker appear closer.

Relative Height

Objects higher in the visual field (for things on the ground) are perceived as farther away.

Relative size

If two objects are known to be the same size, the smaller retinal image is judged as farther.

Familiar size

Knowledge of typical object size helps judge how far away it must be to produce its retinal size.

Linear perspective

Parallel lines appear to converge as they extend into the distance (e.g., railroad tracks).

Texture gradients

A textured surface appears denser and less detailed with distance.

Atmospheric perspective

Far objects look blurrier, hazier, or bluer due to scattering of light in the atmosphere.

Shadows and shading

The shape and depth of objects are inferred from:

-direction of shadows

-light–dark transitions (shading)

-These give clues about 3D form and location.

Motion parallax

As you move your head/body, near objects move faster across your retina than far ones. Strong cue for depth.

Deletion

When an object moves in front of another, parts of the background become covered.

Accretion

When an object moves away and reveals parts of the background that were previously hidden (uncovered).

Optic flow

The pattern of motion across the retina created by your movement through the world.

Helps determine direction of movement and speed.

Steropsis

the sense of depth that we perceive from the visual system’s processing of the comparison of the two different images from each retina.

Binocular Disparity

The small differences in the retinal images due to the eyes’ horizontal separation.

3D movies

presents two different images (one to each eye) using polarization or color filters, creating simulated binocular disparity.

The Horopter and Corresponding Points

The imaginary surface where objects fall on corresponding retinal points, producing zero disparity and appearing at the same depth.

Corresponding locations on the two retinae

Points on each retina that map to the same visual direction in the brain. When both eyes view objects lying on the horopter, the images fall on these equivalent locations.

Stereograms

Pairs of 2D images that create depth through binocular disparity when each eye sees a different version.

Wheatstone Stereograph

A historical device using mirrors to present two separate images to each eye, producing a 3D effect.

Anaglygh

A red–cyan or red–blue image viewed with colored glasses that separate the images for each eye, creating depth.

Random-dot sterograms

Images made of random dots that contain hidden depth revealed only through disparity; proves that stereopsis can occur without recognizable objects.

Random-dot Stereograms as Anaglyphs

Using color filters (red/cyan glasses) to reveal the disparity in RDS images.

Virtual Reality

presents separate images to each eye in real-time, using binocular disparity + head tracking to create immersive 3D environments.

Forced Perspective Illusions

Manipulating size, angles, and distance in photos/architecture to make people or objects appear larger, smaller, closer, or farther than they are.

Development of Stereopsis

Binocular depth develops in early infancy (around 3–5 months) as the visual system learns to match images from both eyes.

Strabismus

Misalignment of the eyes.

-If untreated early, the brain may suppress one eye’s input, preventing normal stereopsis from developing.

Size-distance invariance

Perceived size depends on both retinal size and perceived distance.

-If distance seems larger, the brain interprets the object as bigger.

Size Constancy

Perceive objects as maintaining the same physical size, even when the retinal image changes with distance.

The Ponzo Illusion

Converging lines trick the brain into thinking the top object is farther away, so it looks larger even with the same retinal size.

The Müller-Lyer Illusion

The Moon Illusion

Arrows pointing inward vs. outward change perceived length of identical lines, influenced by depth cues.

Ebbinghaus Illusion

A circle looks larger or smaller depending on the size of surrounding circles due to context-driven size comparison.

The Ames Room Illusion

A distorted, trapezoidal space that looks normal from one fixed viewpoint. Because the true distances are hidden, people in different corners appear dramatically larger or smaller than they really are.

• The illusion happens because the brain assumes the space is rectangular and misjudges distance, disrupting size constancy.

Binocular Suppression

When each eye receives a very different image, the brain suppresses one image at a time, causing alternating perception.