Depth Perception part 1

Question 1

Name the 5 Mechanisms of perception

Answer 1

1) convergence of the eyes
2) Accomodation of the lens
3) Binocularity : Stereopsis spatial disparity fusion / Matching

4 Neural Mechanism- activation/ Inhibition Location sesitivity

5)Depth cues and cue intergration

Question 2

convergence

Answer 2

inward movement of the eyes when we focus on nearby objects

Question 3

accommodation

Answer 3

the term for the adaptation of the lens of the eye

the lens breaks the light wave which is emitted from the object these waves are then absorbed by the receptor cells in the retina

the closer the object the more the lens needs to be thicker. adaption of the lens can be corrected by prescribing concave or convex lenses

Question 4

what is the Horopter

Answer 4

denotes a half circle in the visual field of the observer.

Question 5

binocular depth information, objects that do not fall on the horopter fall on noncorresponding points

these points make disparate images AD and RD ?

Answer 5

Absolute Disparity

concerns one object the amount of disparity indicates how far an object is from the horopter

Relative Disparity

Is the difference between the absolute disparity of two objects.

Question 6

stereopsis

Answer 6

depth information provided by binocular disparity

Question 7

false fusion

Answer 7

occurs in near space when two pictures are presented seperately to each eye in the stereoscope

Sherrington 1906

panums limit is the distance at which fusion occurs

Question 8

occlusion is over known as

Answer 8

over lap

interposition

always involves the violation of the contours of the overlapped object

Question 9

size reduction

Answer 9

even in the absense of explicit viewpoint perspective the adult viewer seems - with a sequence of objects - to perceive the smallest object as furthest away

Question 10

convexity and concaveity

Answer 10

£D perception can be produced with black andwhite shading or light which comes above or below

the variation of the objects surface is also called texture gradient

Question 11

atmospheric perspective

Answer 11

space further away is depicted in lighter colours and contours are more blurry than those in the forground

Question 12

view point perspective

Answer 12

discovered in the renaissance in europe by using a grid which worked like a transparent layer over reality

viewpoint perspective is created by diagonal spatial axes which converge in a viewpoint.

Question 13

Motion paralax

Answer 13

occurs when the observer or the scene is moving.

objects nearer to the observer hae to travel further and faster across the retina.

thus we can deduce the slower the moveing object - the further away.

Question 14

ISI

Answer 14

Inter stimulus Interval

the time between two stimuli

if very short then the obderver simply sees two dots

if the ISI is too long the observer sees one dot flash and then one dot flash

but if the ISI is Intermediate then the viewer sees APPARENT MOTION

Question 15

Perception of causality

Answer 15

Pure percieved motion can also be interpreted in meaningful ways

HEIDER + SIMMEL 1944 made a film with geopmetric objects moving

participants were instructd to write down what happened

Anthropomorphic interpretations of movement perception

Question 16

Anthropomorphic interpretations of

Answer 16

movement perception

Question 17

Perception of causality

Answer 17

MICHOTTE 1946

showed people films of little blocks interacting

further research suggests that not every person would interpret these visual cues as meaning full

Ie BERRY MISOVICH ini 1994

Question 18

rigidity assumption

Answer 18

using moving lights as cues , participants can interpret moving dots as being from a human form with as little as 6

infants can also do this

Question 19

Binocular depth Cells

Answer 19

or disparity selective cells have been found that respond best to binocular disparity

These cells respond best to a specific degree of absolute disparity between images on the right and left retinas.

Question 20

Disparity tuning curve

Answer 20

a graph showing the response time a neuron on the x (verticle) axis and the degree of horizontal disparity on the y axis.

this shows more spikes per second for the near objects indicating that the neuron is specialized for near objects

Question 21

BLAKE AND HIRSCH and their pirate cats

Answer 21

in 1975

cats were reared for 6 months by alternating vision between two eyes daily

the cats were found to not develop many binocular neurons

cats were unable to use binocular disparity to percieve depth

they developed esotropic (inward) and Exotropic (outward) squints

Question 22

linear size of an object ie its actual size is reffered to as S . what is the visual angle ?

Answer 22

V

the visual angle V determines the size of the retinal image

this it the factor that perception scientists care about

Question 23

size- distance scaling equation-

Answer 23

s = A (RxD)

Percieved size S is the result of the angle A

real object size - R
object distance - D

the changes in distance and retinal size balance each other out

Question 24

size constancy

Answer 24

object size estimation

• remains tied to the realobject despite various changesin distance

this breaks down when contextual depth cues are removed and poeple are only alowed a peep hole view of the object its self

HOLWAY + BORING 1941

Question 25

MULLER-LYER Illusion

with the two lines with arrows pointing in and out

the two lines look different lengths but they are not

why?

Answer 25

Why does this length illusion occur?
Misapplied size-constancy (Gregory, 1966)
Size constancy scaling that works in 3-D is misapplied to 2-D objects.
Observers unconsciously perceive the fins like corners, as if they were corners belonging to buildings.

Question 26

Gregory 1966

Answer 26

Misapplied size-constancy (Gregory, 1966)
Size constancy scaling that WORKS in 3-D is MISAPPLIED to 2-D objects.

Observers unconsciously perceive the fins like corners, as if they were corners belonging to buildings.

Question 27

what are the problems with Gregorys explanation for the mis applied size constancy (the corner of a building makes one line seem far away, and thus bigger)

Answer 27

The “dumbbell” version shows the same perception even though there are no “corners.”
Still, one could argue that the circles resemble weights for weight lifting

Question 28

Muller-lyer three dimensional illusion ?

Answer 28

The illusion ( with the line and the arrows pointing in and out) also occurs in a 3-D display with the line not actually present.

Question 29

Muller-lyer illusion

potentially most plausible explanation

Answer 29

Another possible explanation:
Conflicting cues theory - our perception of line length depends on:
The actual length of the line
The overall length of the figure
The conflicting cues are integrated into A

COMPROMISED LENGTH PERCEPTION

Question 30

the Ames room

Answer 30

Two people of equal size appear to be of very different in size in this room.
The room is constructed so that:
The shape looks like a normal room when viewed with one eye.
On the next slide, a photo has been taken through the peephole showing what the participants in the experiment were perceiving.

Question 31

the Ames room

two explanations -

Answer 31

size distance scaling
Observer thinks the room is normal.
Women would be at same distance.
Woman on the left has smaller visual angle (R).
The participant computes an assumed distance (D’), but the true distance D is larger and thus the perceived size (S) is smaller

relative size - Perception of size depends on size relative to room height (spatial context)

Question 32

Moon illusion

where the moon appears to be larger when it is low in the sky and close to the ground

Answer 32

APPARENT DISTANCE THEORY - horizon moon is surrounded by depth cues, while moon higher in the sky has none.
ANGULAR SIZE CONTRAST THEORY- the moon appears smaller when surrounded by larger objects. (the heavens!)

Actual explanation may be a combination of a number of cues such as atmospheric perspective.