Lecture 17

Question 1

What is the correspondence problem?

Answer 1

the question of how we ‘line up’ what’s
happening in one retina with what’s happening in the other (e.g. determining
whether an object falls on corresponding points)

Question 2

What is one possible solution to the correspondence problem?

Answer 2

the visual system to
rely on the specific
features of objects to
help ‘keep track’ of
what is creating an
image/where

Question 3

What are binocular
depth cells or disparity selective cells?

Answer 3

Neurons have been found that respond best to
binocular disparity

Question 4

What are disparity tuning curves?

Answer 4

plot neural response
as a function of disparity

Question 5

Describe visual angle

Answer 5

Visual angle refers to the angle
of an object relative to the
observer’s eye

• There are 360 degrees around
  the circumference of the eye
• 1 degree = 1/360 of this
  circumference
• That equates to an image of
  about 0.3 mm

Question 6

Describe the Holway and Boring study (first phase)

Answer 6

Holway and Boring (1941): Presented a luminous test circle down the right
corridor, and a luminous comparison circle down the left

• Comparison circle was always 10 feet away
• Test circles ranged from 10-120 feet
• Participants were asked to adjust the diameter of the comparison circle to match the test circle
• In the first phase, participants were presumably able to adjust the comparison circle to accurately match the test circle by relying on various depth cues
  (binocular disparity, shading, etc.), in addition to visual angle

Question 7

Describe the Holway and Boring study (second phase)

Answer 7

In the second phase, the various depth cues were systematically eliminated
(view though one eye to eliminate binocular disparity, dim lighting to reduce
shadows, etc.)

• When those various depth cues were eliminated, the responses produced by
  participants suggested they began relying on visual angle alone to judge size
• Because this is not an accurate way to judge distance (because stimuli have
  smaller/larger visual angles as they get farther away/closer), accuracy in the
  second phase was very poor

Question 8

Describe the results of Holway and Boring’s study

Answer 8

The dashed
line marked physical size is the
result that would be expected if the
observers adjusted the diameter of
the comparison circle to match the
actual diameter of each test circle.
The line marked visual angle is the
result that would be expected if the
observers adjusted the diameter of
the comparison circle to match the
visual angle of each test circle.

Question 9

What is the size-distance scaling formula?

Answer 9

S = R x D

S = perceived size
R = retinal size
* D = perceived distance

Question 10

What other things influence size perception?

Answer 10

texture gradients (pictures on the left), relative size (pictures on the right)

Question 11

Describe the Muller - Lyer illusion

Answer 11

The Müller-Lyer illusion: Straight lines with
inward fins appear shorter than straight lines
with outward fins

• Lines are actually the same length
• One proposed explanation for this illusion
  involves misapplied size-constancy scaling
  (of a form that works in 3-D but is misapplied
  for 2-D objects

Question 12

How is the illusion perceived?

Answer 12

• Observers unconsciously perceive the fins as belonging to outside and inside
  corners
• Outside corners seem closer (appear to ‘jut
  out’), and thus are treated as such
• Inside corners seem further away (appear to
  ‘recede’), and are treated that way
• If equivalently sized images are formed on the retina, and one is judged to be
  farther away, it will be perceived as larger (thus, the
  ‘inside corner’ is judged
  as larger because it is perceived as being an equivalent size but farther away)

Question 13

Describe conflicting cues theory

Answer 13

• Another proposed explanation is the conflicting cues theory, which states that our perception of line length depends on two factors:

1. The actual length of the vertical lines
2. The overall length of the figure
   * The conflicting cues are integrated into a
   compromised perception of the length
   (e.g. might apply for version at right?)

Question 14

Describe the Ponzo illusion

Answer 14

• The Ponzo illusion: Horizontal rectangular
  objects are placed over railroad tracks in a
  picture
• The far rectangle appears larger than the
  closer rectangle but both are the same size
• Misapplied size-constancy scaling may offer
  an explanation (same retinal image formed,
  yet perceived to be at different distances, will
  be perceived as being different actual sizes)

Question 15

Describe the Ames room

Answer 15

• Two people of equal size appear very different in
  size in an Ames room
• The room is constructed so that the shape looks
  like a normal room when viewed with one eye
• The actual shape has the left corner twice as far
  away as the right corner

Question 16

How can size distance scaling be used to describe the Ames room?

Answer 16

• Size-distance scaling offers another plausible explanation here
  S = R x D
• Observer thinks the room is rectangular, which would mean the Women would
  be the same distances away (from the observer)
• Woman on the right has smaller visual angle (R)
• The perceived distances (D) of the two women
  are the same
• Therefore, the perceived size (S) of the women
  on the right is smaller

Question 17

What is the relative size expalanation of the Ames room?

Answer 17

Another possible factor relates to relative size
* Perception of size depends on size relative to other objects
* One woman fills the distance between the top and bottom of the room
* The other woman only fills part of the distance
* Thus, the woman on the right appears taller

Question 18

What is the moon illusion?

Answer 18

the fact that it appears larger on the horizon than
when it is higher in the sky (despite having the same visual angle)

Question 19

Describe apparent distance theory

Answer 19

horizon moon
surrounded by depth cues but moon higher in the sky has none

• While the visual angle of the
  moon is the same, the perceived
  distance is different (horizon is
  perceived as farther away than
  the sky), resulting in a difference
  in perceived size (S = R x D)

Question 20

Describe frontal eyes in animals

Answer 20

Animals with frontal eyes that have
fields which significantly overlap
afford good stereoscopic depth
perception

Question 21

Describe lateral eyes in animals

Answer 21

Animals with lateral eyes have
poor stereoscopic depth perception
(but gain a more panoramic view)

Question 22

Describe the Granrud study

Answer 22

Granrud (1985): Showed infants objects A and B during the familiarization

period, then objects C and D during the test period
* Hypothesized that showing infants a larger
version of the same toy they had
previously seen (object C) would be
perceived as being closer if they relied on
familiar size to judge distance (and
remembered object B)
* Reach behaviour supported their
prediction