Lecture 16

Question 1

What is a cue approach to depth perception?

Answer 1

A cue approach to depth
perception focuses on information
in the retinal image that is correlated
with depth in the scene

• We learn the connection between
  cue and depth (e.g. occlusion)
• Association becomes automatic
  through repeated exposure

Question 2

What are oculomotor cues?

Answer 2

based on sensing
the position of the eyes and muscle
tension

Question 3

Describe convergence

Answer 3

inward movement of
the eyes when we focus on nearby
objects

Question 4

Describe accommodation

Answer 4

the shape of the
lens changes when we focus on
objects at different distances

Question 5

Describe monocular cues

Answer 5

information that
can be based on the image from a
single eye

Question 6

Describe pictorial cues

Answer 6

sources of depth information that come from 2-D images, such as
pictures

Question 7

Describe occlusion

Answer 7

when one object partially covers another

Question 8

Describe relative horizon

Answer 8

• Objects below the horizon (an imaginary horizontal line that is at the same level as the observer,
  or ‘eye-level’) that are higher in the field of vision are more distant (motorcycle 2 vs. motorcycle 1)
• Objects above the horizon that are lower in the visual field are more distant (cloud 4 vs. cloud 5)

Question 9

What is relative size?

Answer 9

when objects are
equal size, the closer one will take
up more of your visual field

Question 10

Describe perspective convergence

Answer 10

parallel lines appear to come together in the
distance

Question 11

Describe atmospheric perspective

Answer 11

distance objects appear more ‘fuzzy’
* Occurs because the farther away something is, the
more air/particles we have to look through to see it

• Farther objects also tend to appear more ‘blue’ (for
  the same reason the sky looks blue, i.e. our
  atmosphere preferentially scatters short wavelengths
  and looking ‘through’ more of increases the
  ‘blueness’ this imparts on our perpeption

Question 12

Describe texture gradient

Answer 12

equally spaced elements are more
closely packed as distance increases

Question 13

Describe shadows

Answer 13

helps enhance depth by indicating
where objects/features are located

Question 14

Describe motion parallax

Answer 14

close objects in
direction of movement glide rapidly
past but objects in the distance
appear to move slowly

Question 15

Describe deletion and accretion

Answer 15

• Deletion and accretion: objects are covered or uncovered as we move relative to them
• Deletion refers to covering an object
• Accretion refers to uncovering an object

Question 16

What is stereoscopic depth perception?

Answer 16

constructed based on input provided to
both eyes

the basis for how 3D glasses typically
work
* This has been accomplished by presenting different images to each eye using
various techniques (e.g. shutters, red/blue filters, polarized lenses, etc.)

Question 17

Describe corresponding retinal points

Answer 17

points on the retina that would overlap if the eyes were
superimposed on each other

Question 18

Describe binocular disparity

Answer 18

the difference in images from two eyes

Question 19

What is the horopter?

Answer 19

an imaginary sphere that passes through the point of focus
* Objects on the horopter fall on corresponding points on
the retinas
* e.g. both Julie and the tree fall on the horopter, therefore
we know that they each fall on corresponding points
on the retinas
* This also tells us that they are both approximately the
same distance away from the observer

Question 20

Describe non-corresponding points

Answer 20

Objects that are not on the horopter fall on non-corresponding points

• These points make disparate images
• The degree to which these images deviate from corresponding points is the
  absolute disparity (and can be represented by a calculation referred to as the
  angle of disparity)

Question 21

Describe crossed disparity

Answer 21

whenever an object is closer to the observer
than where they are looking (in front of the horopter)

Question 22

Describe uncrossed disparity

Answer 22

whenever an object is farther away from the
observer than where they are looking (behind the horopter)

Question 23

Describe binocular disparity

Answer 23

1. Determining whether disparity is crossed or
   uncrossed tells us whether something is behind
   or in front of our point of focus (i.e. the horopter)
2. Because objects that are farther away from the
   horopter create larger angles of disparity, this
   information tells us how far away something is
   from the horopter

• All taken together then, the nature of the disparity
  (crossed or uncrossed), along with the angle of
  disparity, helps us judge where things are in space

Question 24

What is stereopsis?

Answer 24

depth information
provided by binocular disparity

Question 25

What are stereoscopes?

Answer 25

viewers which use two pictures from slightly different viewpoints

Question 26

Describe random-dot stereograms

Answer 26

Random-dot stereograms have two identical patterns of ‘noise’ with one ‘piece of information’ shifted in position