Illusions as key to reality, in space and time

Question 1

what are the fundamental steps of information processing

Answer 1

key steps of information processing is converting the outside (physical) world into internal (psychological) events: encoding

Question 2

illusions in scientific study

Answer 2

illusions play a major role in the scientific study of sensory systems

Question 3

properties of spatial vision

3 properties

Answer 3

• two-dimensional
• image = static
• basic properties: brightness & colour & patterns

Question 4

what is black & white?

Answer 4

the amount of light

Question 5

how should we interpret visual systems?

Answer 5

as a measurement device (like a ruler)

Question 6

how many shades of grey can you discriminate?

Answer 6

5,000 perceptual shades of grey

Question 7

perceptual colour space

Answer 7

arrange colours according to similarty e.g. colour circle/rainbow

Question 8

measurement of discrimination thresholds

Answer 8

3M different colours would have to be measured by a 24 bit computer display as it can measure 16M

Question 9

what is the important perceptual measure in comparison to its surround?

Answer 9

the important perceptual measure is not absolute but relative stimulus intensity, in comparison to its surround, which is known as (simultaneous) contrast

Question 10

what is the outside world represented in?

Answer 10

retintopic maps of neurons with centre-surround receptive fields

Question 11

what do spatial filters with opponency receptive fields do?

Answer 11

spatial filters with opponency receptive fields enhance contrast, reduce redundancy and compress images

Question 12

what are the grey spots in the Hermann grid beleived to be the result of?

Answer 12

grey spots in the Hermann grid are believed to be the result of opponency filtering (excitation - inhibition)

Question 13

inside the black squares in the Herman grid:

Answer 13

no stimulation of excitatory centre and inhibitory surround: no overall excitation so its perceived as dark

Question 14

white bars in the Hermann grid:

Answer 14

only small parts of the inhibitory surround are stimulated: excitation dominates inhibition > bright

Question 15

white intersections of the Hermann grid

Answer 15

larger parts of the inhibitory surround are stimulated: small overall excitation > apparent reduction of brightness

Question 16

what is contrast illusion?

Answer 16

enhancement of colour differences in space when presented next to each other

Question 17

the logic of aftereffects: adaptation

Answer 17

• green-red stimulus > response jumps up and the gradually returns to resting levels
• NOTE: this encodes only changes (in time)

Question 18

the logic of aftereffects: opponency

Answer 18

• red-green are subtracted from each other
• NOTE: this is contrast enhancement

Question 19

logics of aftereffects: perceived aftereffect

4 points

Answer 19

• opposite in time = successive colour contrast
• red-adapted regions turn green
• green-adapted regions turn red
• NOTE: contrast enhanced in the time domain

Question 20

the third dimension: depth

what needs to be done by the third dimension?

Answer 20

the third dimension needs to be reconstructed from the flat images captured by the eyes

Question 21

the third dimension: depth

multiple cues can be used:

4 points

Answer 21

• size, perspective, occlusion
• texture, contrast, shading
• using two eyes
• motion parallax

Question 22

depth cues: pictorial cues

Answer 22

awhen a wide range of depth information can be directly extracted from a static monocular (single eye) image

Question 23

depth cues: binocular

Answer 23

when the combination of information from the two eyes allows precise depth measurements through steropsis

Question 24

how does steropsis work?

Answer 24

retinal projection of object on opposite side of the fovea (disparity) indicates its depth relative to the plane of fixation

Question 25

why is stereopsis exploited?

Answer 25

stereopsis is expolited to produce depth impressions in projected/printed pictures e.g.
* lenticular cards
* magic eye

Question 26

depth cue: relative size

the size constancy effect

Answer 26

the size constancy effect is sometimes beleived to be the basis of the Ponzo illusion

Question 27

real world size illusions: the ames room

The Ames Room

Answer 27

in the ames room, the size of objects is perceived distorted, because the misleading geometry generates an incorrect frame of reference

Question 28

space and time

give an example of space and time (astronomer)

Answer 28

• an astronomer may see two stars next to each other: spatial distance (SPACE)
• she might see a star appearing, disappearing, reappearing: temporal interval (TIME)
• she might see a moving star: change in space and time (MOTION)

Question 29

motion correspondence problem

what is motion correspondence problem?

Answer 29

challenge that the visual system faces in determining which elements in a visual scene correspond to the same moving object over time
* difficult when multiple objects are moving at diffferent speeds & directions

Question 30

SUMMARY:

4 POINTS

Answer 30

• when we perceive things different from what they actually
  are, we call it illusion
• illusions can be seen in static images, in space, and in time
• they can be used as scientific tool to understand perception
• understanding illusions is used in a wide range of applications