18&20. size & shape constancy

Question 1

Law of size constancy?

Answer 1

We tend to perceive an object to be a fixed size regardless of the distance to the object (i.e., regardless of the visual angle)

Question 2

Holway & Boring experiment – what principle were they trying to test?

Answer 2

Law of size constancy –> can we account for distance when we perceive size?

Question 3

Holway & Boring experiment – how was it set up?

Answer 3

• subjects sat at the corner of 2 hallways
• saw a test circle that changed in distance (10-120ft) and size, but was always 1 degree of visual angle & a comparison circle (10ft away)

Question 4

Holway & Boring experiment – what did participants do?

Answer 4

• had to make the comparison circle the same size as the test circle

Question 5

Holway & Boring experiment – results?

Answer 5

There is a linear relationship between the distance to test circle and the size of comparison circle

IE –> participants judged distance right and perceived size accurately

Question 6

Holway & Boring experiment – (pt 2) what did they change? Why?

Answer 6

• got rid of all depth cues
• turned of lights –> gets rid of most cues
• look through peep hole
  –> no binocular cues, no motion parallax
• test if depth cues are the cause of size constancy

Question 7

Holway & Boring experiment – (pt 2) –> results/ conclusion?

Answer 7

• “Law” of visual angle
• judgements of size (without any depth cues) are based only on visual angle
• NO size constancy –> graph is flat line
• size constancy can’t happen without depth cues!!

Question 8

Why are the moon and sun perceived as approx. the same size? What “law” explains this?

Answer 8

• there is almost NO good depth information that far away in the sky/space
• Law of visual angle
  –> both take up approx. the same visual angle, so we perceive them as the same size

Question 9

Size-distance invariance def? What is it?

Answer 9

• Relationship!!
• the perceived size of an object DEPENDS ON its perceived distance, and vice versa.

Question 10

Emmert’s Law def? What “object” does it involve? What depth property does it relate to?

Answer 10

Object: retinal after images!
Property: size-distance invariance

• perceived size of afterimage changes (proportionally) based on distance of surface its “projected” on
• if you look at a wall far away, afterimage is big
• look at a desk up close, after image is small
• shows that we take depth into account when perceiving object size

Question 11

How does depth perception affect size constancy? (negatively)

Answer 11

• if we misperceive depth, we misperceive size
• we judge size based on depth
• causes “failures” of size constancy, or illusions

Question 12

6 examples of “failures” of size constancy caused by misperceived depth? (illusions) (1 is sorta repeated)

Answer 12

1. Ames room (2 versions)
2. Moon illusion
3. Ponzo illusion
4. Ponzo variant with fMRI
5. Muller - Lyer illusion
6. Outside rear-view mirror illusion

Question 13

Ames room –> what happens? why do we misperceive depth? What are the results?

Answer 13

• objects look like they’re all the same distance, leading to misperception of relative size
• depth cues eliminated through peep hole
• all “rectangular” shapes are actually trapezoidal, so its angled back but you perceive it as perpendicular to you
• you think objects on the left side are much smaller than objects on the right side

Question 14

Ames room –> difference between version 1 and version 2?

Answer 14

Version 1:
- DIFF. retinal size
- same apparent distance
- kid looks small on one side, huge on other

Version 2:
- SAME retinal size
- same apparent distance
- mom looks same size as kids

Question 15

Moon illusion –> what happens? best explanation for why?

Answer 15

• moon appears much bigger at horizon than peak
• perceive distance at horizon to be much bigger
• very difficult to study and prove, so we still don’t know for sure

Question 16

Ponzo illusion –> what is it? Why does it happen?

Answer 16

• 2 of the same object (taxi, RR X sign, moon, etc) are placed on a railroad track, one “above” the other
• due to depth cues like linear perspective, texture gradient, and relative height, you think the “top” object is farther away
• top object looks far, perceive it as big
• lower obj. looks close, perceive as small

Question 17

Ponzo variant with fMRI –> what is it? What did they conclude?

Answer 17

• Uses depth cues to make 2 checkered circles (with equal retinal images) seem diff. sizes
• they showed that the brain activity is V1 was greater for the circle that was perceived as farther and bigger

conclusion:
- we actually do perceive it as bigger, and devote more brain activity towards it

Question 18

Muller-Lyer illusion –> what is it?

Answer 18

• 2 lines (red and green) are exactly the same retinal image size
• add Vs facing away from the red line and facing towards the green line
• makes the red seem bigger than green

Question 19

Muller-Lyer illusion –> best explanation for why it happens?

Answer 19

• the red line with Vs facing away from it looks like the far corner of a room
• this corner would be the farthest away from you
• the green line with Vs facing inwards looks like the edge of a box protruding towards you
• this corner would be closest to you
• you perceive the line of the “far away wall” as longer than the “close up box”

Question 20

Outside mirror illusion –> what is it? What problem would it cause?

Answer 20

• the outside mirror is convex, so it makes objects seem smaller than they really are
• it assumes that you use familiar size to judge distance to objects you see
• if you see a small object in the mirror, you’d think you’re farther away than you really are, since the mirror is making it seem smaller than it really is

Question 21

Shape constancy def?

Answer 21

• we perceive the shape of objects correctly, regardless of the retinal image shape, which changes due to changing orientation
• tendency to perceive an object’s shape as constant despite changes in retinal image due to changing orientation.

Question 22

Shape-slant invariance def?

Answer 22

• relationship between perceived shape and perceived slant
• perceived shape of object DEPENDS ON its perceived slant, and vice versa
• shape of an object can be determined by COMBINING info about the shape of ret. image and slant of its surface

**If no slant information –> no correct shape information

Question 23

Anamorphic projection meaning? Why do we do it?

Answer 23

• an image that is seen “correctly” only from a specific viewpoint
• implying a failure of shape constancy
  –> if shape constancy was working, you wouldn’t need to change the shape, or you could see it correctly from any view point
• ex. road signs –> you only read it at an extreme slant

Question 24

When does shape constancy fail?

Answer 24

1. extreme slants
   
   • anamorphic projections –> road signs
2. if you perceive slant wrong
   
   • Ames room (don’t perceive slant of back wall)
   • examples of street art that you see 3D

Question 25

Tabletop illusion –> what is it? why does it happen? success/failure? What illusion is it sorta similar to?

Answer 25

• shape constancy is working, but causes an illusion!
• the retinal image of 2 table tops are exactly the same, but they appear very different
• we take slant into account, and perceive the length and width of the tables very differently
• while the retinal projections are the same, it doesn’t really matter, because IRL, the tables would be different sizes
  –> same as 3 car illusion that kept getting “bigger” but was the same