Depth and size perception

How are depth and size related?

How big an object appears can affect how far away it appears and how far away an object appears can affect how big it appears.

How do we perceive depth (3 cues)

-Oculomotor cues

-Monocular cues

-Binocular cues

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 ques

Binocular convergence and accommodation

Binocular convergence

how much yours eyes converge to see something, you are more cross eyed the closer the object is to your face

accommodation

your lens is thinner for points that are further away and thicker for point closer to you.

There are three main monocular cues

-Accommodation

-Pictorial cues

-Movement-based cues (MAP)

There are 7 main pictorial cues

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

Movement based cues include:

motion parallax, deletion and accretion

motion parallax

Objects closer to the viewer appear to move faster across the visual field than objects further away.

deletion and accretion

Deletion= a moving object is gradually hidden behind another object, accretion = a moving object gradually emerges from behind another.

Binocular disparity

each eye has a slightly different view of a scene

Relative disparity

position of objects projected on the retina - further away person will be on the more inner part of each retina

Does the point of fixation alter relative disparity

no

Does the point of fixation alter absolute disparity

yes

what is the horopter

a plane containing all points that will fall on corresponding parts of two retinas

correspondence problem

In binocular vision, it can be hard to identify which images in the left retinal images should match with the right retinal images, if there are identical objects. It can be solved by using colour which makes the objects distinguishable

The perceived size of an object is determined by two factors.

Its angular size and its perceived depth

Angular Size

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

Size constancy

is the phenomenon where an object's apparent size does not depend on is physical distance

To achieve size constancy an observer needs to consider

Both the size of the retinal image and the distance to the object.

Formula for size constancy

S=K x (R x D)

S = apparent size of an object

K = constant

R = size of retinal image

D = perceived distance to the object

If an object appears closer than it really is, it will appear

smaller than it really is.

If an object appears further away than it really is, it will appear

smaller than it really is

What did Holway and Borings experiment prove?

When there are sufficient depth cues, the size of the test patch can be accurately estimated. When there are not sufficient depth cues, the apparent size of the test patch appears more like the visual angle.

Accurate size estimates can occur only when

distance to the object can be estimated accurately

Who and when was the experiment that tested how observers accurately estimate the size of objects conducted?

Holway and Boring in 1941