Illusions as key to reality, in space and time Flashcards

1
Q

what are the fundamental steps of information processing

A

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

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2
Q

illusions in scientific study

A

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

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3
Q

properties of spatial vision

3 properties

A
  • two-dimensional
  • image = static
  • basic properties: brightness & colour & patterns
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4
Q

what is black & white?

A

the amount of light

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5
Q

how should we interpret visual systems?

A

as a measurement device (like a ruler)

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6
Q

how many shades of grey can you discriminate?

A

5,000 perceptual shades of grey

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7
Q

perceptual colour space

A

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

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8
Q

measurement of discrimination thresholds

A

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

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9
Q

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

A

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

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10
Q

what is the outside world represented in?

A

retintopic maps of neurons with centre-surround receptive fields

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11
Q

what do spatial filters with opponency receptive fields do?

A

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

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12
Q

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

A

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

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13
Q

inside the black squares in the Herman grid:

A

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

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14
Q

white bars in the Hermann grid:

A

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

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15
Q

white intersections of the Hermann grid

A

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

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16
Q

what is contrast illusion?

A

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

17
Q

the logic of aftereffects: adaptation

A
  • green-red stimulus > response jumps up and the gradually returns to resting levels
  • NOTE: this encodes only changes (in time)
18
Q

the logic of aftereffects: opponency

A
  • red-green are subtracted from each other
  • NOTE: this is contrast enhancement
19
Q

logics of aftereffects: perceived aftereffect

4 points

A
  • opposite in time = successive colour contrast
  • red-adapted regions turn green
  • green-adapted regions turn red
  • NOTE: contrast enhanced in the time domain
20
Q

the third dimension: depth

what needs to be done by the third dimension?

A

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

21
Q

the third dimension: depth

multiple cues can be used:

4 points

A
  • size, perspective, occlusion
  • texture, contrast, shading
  • using two eyes
  • motion parallax
22
Q

depth cues: pictorial cues

A

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

23
Q

depth cues: binocular

A

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

24
Q

how does steropsis work?

A

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

25
why is stereopsis exploited?
stereopsis is expolited to produce depth impressions in projected/printed pictures e.g. * lenticular cards * magic eye
26
depth cue: relative size | the size constancy effect
the size constancy effect is sometimes beleived to be the basis of the Ponzo illusion
27
# real world size illusions: the ames room The Ames Room
in the ames room, the size of objects is perceived distorted, because the misleading geometry generates an incorrect frame of reference
28
# space and time give an example of space and time (astronomer)
* 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)
29
# motion correspondence problem what is motion correspondence problem?
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
30
SUMMARY: | 4 POINTS
* 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