Depth and Size Perception

Oculomotor cues

Cues based on our ability to sense the position and state of our eyes

Monocular cues

Cues based on the visual information available within one eye

Binocular cues

Cues that depend on visual information within both eyes

What are the two main oculomotor cues?

• Binocular convergence - the adjustment of the lens for focus on near or far objects.

• Accommodation - the process of changing the shape of the lens to focus on objects at different distances.

What are the three main monocular cues?

Accommodation, Pictorial cues, and Movement-based cues

What are the 7 main pictorial cues?

Occlusion, Relative height, Familiar and relative size, Perspective convergence, Atmospheric perspective, Texture gradient, and Shadows

What are the two main movement-based cues?

• Motion parallax - apparent movement of objects at different distances appears different when the observer moves

• Deletion and accretion - the process of objects being obscured or revealed as they move relative to each other, providing depth information.

Binocular Disparity

Because the left and right eyes are offset relative to each other, they see the world from slightly different viewpoints.

What does the lens of the eye create?

The lens of the eye creates an image of the outside world on the retina, but this image is flipped up/down and left/right.

Absolute Disparity

Whichever object is fixated on has zero absolute disparity/ the left and right images of this object fall onto corresponding parts of the retina

The Horopter

It is a plane containing all points that will fall on corresponding parts of the two retinas.

Correspondence Problem

challenge of determining which parts of the images from each eye correspond to the same object in the external world, crucial for depth perception.

• objects being different colours makes association become unambiguous

What is the relationship between Depth & Size?

Depth and size are closely related. How big an object appears can affect how far away it appears and vice versa

What two factors determined the perceived size of an object?

Its angular size and Its perceived depth

Angular Size

the visual angle an object subtends. The closer an object is to person, the larger its angular size.

Size Constancy

phenomenon where an object’s apparent size does not depend on its physical distance. achieved by observer considering both the size of retinal image and distance of object

• S = K x (RxD)

• S = apparent size of object, K = constant; R = retinal image size; D = distance from observer.

Size Illusions

Most caused by causing people to mistake the distance to an object so that it appears larger or smaller than it really is.

• if object appears closer than it is = appears smaller

Holway and Boring (1941)

how depth cues influence size judgments.

• intersection of 2 corridors = view test circle and comparison circle = adjust size of comparison to match test

• 1 = observer used binocular disparity, motion parallax and shadows

• 2 = used one eye = no remove binocular disparity cues

• condition 3 = peephole = no motion parallax cues

• condition 4 = peephole + drapes = no shadows

• sufficient depth cues = accurately estimated. No cues = apparent size of test is based on retinal image = further away perceived as smaller than they were

Accurate Size Estimates

occur only when distance to the object can be estimated accurately.

relative disparity

the difference in images received by the left and right eyes, which provides depth information.