Read on Twitter
#Illusions
As we call them!
It means that what we perceive & what in reality is out there can b different
But bigger point is:
What really out there may not even b an absolute reality!
But we will not know
There's a limit to our perception & many a times it's distorted completely
As we call them!
It means that what we perceive & what in reality is out there can b different
But bigger point is:
What really out there may not even b an absolute reality!
But we will not know
There's a limit to our perception & many a times it's distorted completely
1
Here I'll take visual illusions
What eyes see & mind interprets IS NOT what is out there.
No matter how much u prepare urself u will witness limitation of human way of looking at things
Literally!
There r different combinations of alterations at play, in any particular case
Here I'll take visual illusions
What eyes see & mind interprets IS NOT what is out there.
No matter how much u prepare urself u will witness limitation of human way of looking at things
Literally!
There r different combinations of alterations at play, in any particular case
2
Still we can try n classify them in different categories for sake of understanding.
Visual Illusions r distortion of perception of:
A Motion/Time
B Brightness/contrast
C Color
D Geometric
E Spatial/Size
F Cognitive (Gestalt effects)
G Facial
H Others/Auditory
Still we can try n classify them in different categories for sake of understanding.
Visual Illusions r distortion of perception of:
A Motion/Time
B Brightness/contrast
C Color
D Geometric
E Spatial/Size
F Cognitive (Gestalt effects)
G Facial
H Others/Auditory
3
Footsteps illusion (FI)
Object's background has profound effect on its perceived speed
Illusion consists of a yellow & blue bar that move over B&W, striped background
Although the bars move at constant rate, they appear to accelerate & decelerate in antiphase with each other
Footsteps illusion (FI)
Object's background has profound effect on its perceived speed
Illusion consists of a yellow & blue bar that move over B&W, striped background
Although the bars move at constant rate, they appear to accelerate & decelerate in antiphase with each other
4
Edges of light ‘foot’ merge with light bars & r only visible when they traverse dark bars
So half of time there really is no motion cue &perception goes into default-NO motion
Same for Dark
Edge information is only contained in color & magnocellular motion system cannot see it
Edges of light ‘foot’ merge with light bars & r only visible when they traverse dark bars
So half of time there really is no motion cue &perception goes into default-NO motion
Same for Dark
Edge information is only contained in color & magnocellular motion system cannot see it
5
2 Motion Blindness (Troxler effect)
Fixate on the centre (watch the flashing green spot)
Note that yellow spots disappear once in a while: singly, in pairs or all three simultaneously, right?
In reality, the 3 yellow spots are continuously present!
2 Motion Blindness (Troxler effect)
Fixate on the centre (watch the flashing green spot)
Note that yellow spots disappear once in a while: singly, in pairs or all three simultaneously, right?
In reality, the 3 yellow spots are continuously present!
6
If you fixate steadily, all structures are imaged continuously on their retinal location
This leads to local adaptation in the retina (Troxler effect- fatigue)
By adding temporal modulation (rotation), background noise is increased.
So Troxler disappearence is more pronounced.
If you fixate steadily, all structures are imaged continuously on their retinal location
This leads to local adaptation in the retina (Troxler effect- fatigue)
By adding temporal modulation (rotation), background noise is increased.
So Troxler disappearence is more pronounced.
7
3 Motion Silencing
Rotating ring consists of many coloured discs
Fixate on central cross
Notice anything special? Well, the ring changes rotation direction
When ring stops it becomes obvious that all small disks change their colour
But it is barely noticable during rotation!
3 Motion Silencing
Rotating ring consists of many coloured discs
Fixate on central cross
Notice anything special? Well, the ring changes rotation direction
When ring stops it becomes obvious that all small disks change their colour
But it is barely noticable during rotation!
8
This effect was published in 2011 by Jordan W. Suchow and George A. Alvarez from Harvard University
It subsequently won “Best Illusion of the Year Contest”
Explanation is that processing global motion presents an overload, which impairs coding of the local details.
This effect was published in 2011 by Jordan W. Suchow and George A. Alvarez from Harvard University
It subsequently won “Best Illusion of the Year Contest”
Explanation is that processing global motion presents an overload, which impairs coding of the local details.
9
Turi &Burr 2013 report
1 There's speed threshold(0.2 rps {depending on absolute spatial arrangement})
2 crowding-Fact that recognition of target in periphery is difficult when surrounded by other stimuli/where small details r more difficult to detect when more details r nearby)
Turi &Burr 2013 report
1 There's speed threshold(0.2 rps {depending on absolute spatial arrangement})
2 crowding-Fact that recognition of target in periphery is difficult when surrounded by other stimuli/where small details r more difficult to detect when more details r nearby)
10
4 Rotating snakes (Akiyoshi Kitaoka)
It demonstrates strong rotation of “wheels”(originally snakes) occurring in relation to eye movements
On steady fixation the effect vanishes
With certain luminance relations, wheels can turn in opposite direction (Atala-Gérard &Bach 2017)
4 Rotating snakes (Akiyoshi Kitaoka)
It demonstrates strong rotation of “wheels”(originally snakes) occurring in relation to eye movements
On steady fixation the effect vanishes
With certain luminance relations, wheels can turn in opposite direction (Atala-Gérard &Bach 2017)
11
Neurological basis of this illusion needs detailed explanation but in brief..
There r direction sensitive neurons in macaque visual cortex
4 colors firing them in sequence can give sense to motion.
Black>Blue>White>Yellow
Or(achromatic version)
Black>Dark Grey>White>Light Grey
Neurological basis of this illusion needs detailed explanation but in brief..
There r direction sensitive neurons in macaque visual cortex
4 colors firing them in sequence can give sense to motion.
Black>Blue>White>Yellow
Or(achromatic version)
Black>Dark Grey>White>Light Grey
12
Any static stimuli with color pair like-
Black/Blue
Blue/White
White/Yellow
Yellow/Black
Will give sense of rightward motion
Pairs like-
Blue/Black
White/Blue
Yellow/White
Black/Yellow
Will give sense of leftward motion
For greyscale
Change Blue>Dark Grey & Yellow>Light Grey
Any static stimuli with color pair like-
Black/Blue
Blue/White
White/Yellow
Yellow/Black
Will give sense of rightward motion
Pairs like-
Blue/Black
White/Blue
Yellow/White
Black/Yellow
Will give sense of leftward motion
For greyscale
Change Blue>Dark Grey & Yellow>Light Grey
13
Just shades of grey (alternating black n white stripes)...& mind perceives motion!
Just shades of grey (alternating black n white stripes)...& mind perceives motion!
14
5 Pinna-Brelstaff illusion
Fixate at Centre point.
While 2 rings expand/shrink, there's "perceived" relative motion of 2 rings to each other.
There's another variant of this with stronger effect by Pierre Bayerl
5 Pinna-Brelstaff illusion
Fixate at Centre point.
While 2 rings expand/shrink, there's "perceived" relative motion of 2 rings to each other.
There's another variant of this with stronger effect by Pierre Bayerl
15
6 Motion Artefact/ Waterfall effect
In Aristotle “De Somnis” (in Parva Naturalia, transl by Beare JI, 1931) ch2 (search for ‘rivers’)
Lucretius looked at stationary leg of horse in middle of flowing river & noted that it seemed to b moving in opposite direction to the flow
6 Motion Artefact/ Waterfall effect
In Aristotle “De Somnis” (in Parva Naturalia, transl by Beare JI, 1931) ch2 (search for ‘rivers’)
Lucretius looked at stationary leg of horse in middle of flowing river & noted that it seemed to b moving in opposite direction to the flow
16
If u stare at movement in particular direction, subsequently viewed stationary scenes appear to move in opposite direction
Motion after-effect is by adaptation in neurons that respond to moving contours in the image
In absence of motion, cells tuned produce equal responses
If u stare at movement in particular direction, subsequently viewed stationary scenes appear to move in opposite direction
Motion after-effect is by adaptation in neurons that respond to moving contours in the image
In absence of motion, cells tuned produce equal responses
17
This is called "induced motion"
Even if u see this for as briefly as for 3 cycles from 1 eye & then subsequently watch stationary object from OTHER eye...even then u will find opposite motion in stationary object.
This is called "interocular transfer"
This is called "induced motion"
Even if u see this for as briefly as for 3 cycles from 1 eye & then subsequently watch stationary object from OTHER eye...even then u will find opposite motion in stationary object.
This is called "interocular transfer"
18
Moirées Scanimation
In flip book, u draw a scene, where from page to page something moves
Then you rapidly flip through the pages. The rest is done by our brain: from just few phases of motion it creates a seeming continuous motion percept.
This is known as the “φ-phenomenon”
Moirées Scanimation
In flip book, u draw a scene, where from page to page something moves
Then you rapidly flip through the pages. The rest is done by our brain: from just few phases of motion it creates a seeming continuous motion percept.
This is known as the “φ-phenomenon”
19
gif on tweet 13 is same illusion.
8 Roger's Palisade illusion
In below clip u will perceive bending of spokes at bottom.
Shape distortion can occur in still pics too.
In bike race finish, arrow release in archery...
gif on tweet 13 is same illusion.
8 Roger's Palisade illusion
In below clip u will perceive bending of spokes at bottom.
Shape distortion can occur in still pics too.
In bike race finish, arrow release in archery...
20
Explanation is surprisingly very simplistic.
It's result of the motion and the persistence of vision!
However it applies to camera still pics too!
This pic is not touched in any way!!
http://www.archery-interchange.net/f12/look-what-happens-release-18242/
Explanation is surprisingly very simplistic.
It's result of the motion and the persistence of vision!
However it applies to camera still pics too!
This pic is not touched in any way!!
http://www.archery-interchange.net/f12/look-what-happens-release-18242/
21
Reverse Spoke illusion
The wheel defined by the dark-bright sectors is rotating clockwise and the spokes are rotating counter-clockwise?
Look again... The spokes stay put! Rather, each spoke makes a tiny shift in one direction and then slowly (subliminally) moves back.
Reverse Spoke illusion
The wheel defined by the dark-bright sectors is rotating clockwise and the spokes are rotating counter-clockwise?
Look again... The spokes stay put! Rather, each spoke makes a tiny shift in one direction and then slowly (subliminally) moves back.
22
When 1 analyses step-by-step gray levels next to spokes, there r 2steps where any given spoke 1st merges with preceding sector on 1side then with succeeding sector. Since in this transition spoke’s identity is lost and thus it (seemingly) changes position, it's seen as moving
When 1 analyses step-by-step gray levels next to spokes, there r 2steps where any given spoke 1st merges with preceding sector on 1side then with succeeding sector. Since in this transition spoke’s identity is lost and thus it (seemingly) changes position, it's seen as moving
23
10 Wagon wheel effect/ stagecoach-wheel effect/stroboscopic effect
Spoked wheel appears to rotate differently from its true rotation
Wheel can appear to rotate more slowly, stationary, or in opposite direction
This last form of the effect is called the reverse rotation effect
10 Wagon wheel effect/ stagecoach-wheel effect/stroboscopic effect
Spoked wheel appears to rotate differently from its true rotation
Wheel can appear to rotate more slowly, stationary, or in opposite direction
This last form of the effect is called the reverse rotation effect
24
Display needs to be presented discontinuously
It may not b visible but Wheel here is (or anything in a movie or TV) moving in jerks.
If these jerks occur fast enough (20/sec) our visual system, namely its motion department, interpolates the intervening missing position
Display needs to be presented discontinuously
It may not b visible but Wheel here is (or anything in a movie or TV) moving in jerks.
If these jerks occur fast enough (20/sec) our visual system, namely its motion department, interpolates the intervening missing position
25
This interpolation relies on “nearest neighbour” principle
Thus, if displacement of wheel spoke from frame to frame is so large, that it's closer to (former) next spoke than to its (former) original, our visual system assumes that the opposite motion direction.
This interpolation relies on “nearest neighbour” principle
Thus, if displacement of wheel spoke from frame to frame is so large, that it's closer to (former) next spoke than to its (former) original, our visual system assumes that the opposite motion direction.
26
11 Sigma motion
Move ur finger along it from left to right with a speed such that you travel the distance in about 2 seconds, while following the finger with your gaze. When you hit the right speed, you should perceive a smooth rightwards motion of the stripes.
11 Sigma motion
Move ur finger along it from left to right with a speed such that you travel the distance in about 2 seconds, while following the finger with your gaze. When you hit the right speed, you should perceive a smooth rightwards motion of the stripes.
27
While you perceive the illusory motion, your eyes do a “smooth pursuit motion” with occasional backwards saccades, altogether known as oculokinetic nystagmus.
The stimulus is just a rapid phase reversal of a bar pattern (black becomes white, white becomes black, etc)
While you perceive the illusory motion, your eyes do a “smooth pursuit motion” with occasional backwards saccades, altogether known as oculokinetic nystagmus.
The stimulus is just a rapid phase reversal of a bar pattern (black becomes white, white becomes black, etc)
28
12 Spine Drift Illusion
Here u see an array of “spines” with a gap demarcating a square in the middle. Does the central square appear to float, to move relative to the background?
If so, you are perceiving seeming movement- Kitaoka’s “Spine Drift” illusion.
12 Spine Drift Illusion
Here u see an array of “spines” with a gap demarcating a square in the middle. Does the central square appear to float, to move relative to the background?
If so, you are perceiving seeming movement- Kitaoka’s “Spine Drift” illusion.
29
Whenever central &peripheral spines r parallel/180°, there's no illusion of differential movement; when they’re at 90°, the illusion occurs.
When retinal motion is at 45°, retinal image is poor in contrast.
It's known that reduced contrast reduces perceived speed(Thompson82)
Whenever central &peripheral spines r parallel/180°, there's no illusion of differential movement; when they’re at 90°, the illusion occurs.
When retinal motion is at 45°, retinal image is poor in contrast.
It's known that reduced contrast reduces perceived speed(Thompson82)
30
So when movement is in 45°-direction the image seems to lag
When central square & surround differ in their spine directions by 45°, eye-movement induced retinal motion blur (in 1 of 2), causing differential contrast reduction & thus a seeming shift bw central square & surround
So when movement is in 45°-direction the image seems to lag
When central square & surround differ in their spine directions by 45°, eye-movement induced retinal motion blur (in 1 of 2), causing differential contrast reduction & thus a seeming shift bw central square & surround
31
13 Biological motion
When images r static then mind draws no sense from them but as soon as motion is kicked in then it becomes meaningful.
13 Biological motion
When images r static then mind draws no sense from them but as soon as motion is kicked in then it becomes meaningful.
32
14 Flash lag effect
Rotating bar is accompanied by a flash at 1 end of bar
Flash APPEARS to lag slightly behind the position of the bar
It's coz of neural delay.
It takes 10th of sec to process the image from point of stimulus to perception point
So mind compensates for delay
14 Flash lag effect
Rotating bar is accompanied by a flash at 1 end of bar
Flash APPEARS to lag slightly behind the position of the bar
It's coz of neural delay.
It takes 10th of sec to process the image from point of stimulus to perception point
So mind compensates for delay
33
If an object is moving then visual system can predict where the object should be after the neural delays
Since perceived position of moving object is shifted forward, it is perceived ahead of the flash (which is also projected ahead in time but lags true motion projection)!
If an object is moving then visual system can predict where the object should be after the neural delays
Since perceived position of moving object is shifted forward, it is perceived ahead of the flash (which is also projected ahead in time but lags true motion projection)!
34
15 Enigma
It truly is Enigma.
If u stare in centre for a while then u will scintillating activity.
U will also notice circular rotation in the rings.
Honestly..this is not gif. It's still image!!
No moment is inbuilt in image.
It's all in ur mind.
Eye moments & color combo!!
15 Enigma
It truly is Enigma.
If u stare in centre for a while then u will scintillating activity.
U will also notice circular rotation in the rings.
Honestly..this is not gif. It's still image!!
No moment is inbuilt in image.
It's all in ur mind.
Eye moments & color combo!!
35
16 Freezing rotation illusion
It arises when a figure is continuously rotating in front of a back&forth rotating ground
Term “freezing rotation” designates the decrease in the perceived rotation speed of a figure when the figure and the ground are turning in equal directions
16 Freezing rotation illusion
It arises when a figure is continuously rotating in front of a back&forth rotating ground
Term “freezing rotation” designates the decrease in the perceived rotation speed of a figure when the figure and the ground are turning in equal directions
36
17 4-Stroke Motion illusion/ Reverse Phi illusion
This gif has only 4 frames
Bike repeatedly moves forward (frames 1-2 & 3-4)
& in-between these forward shifts it moves backward (frames 2-3 & 4-1)
But each backward shift is accompanied by a reversal in contrast
17 4-Stroke Motion illusion/ Reverse Phi illusion
This gif has only 4 frames
Bike repeatedly moves forward (frames 1-2 & 3-4)
& in-between these forward shifts it moves backward (frames 2-3 & 4-1)
But each backward shift is accompanied by a reversal in contrast
37
Effect of contrast reversal in human mind is to reverse the direction of perceived motion
So here, instead of appearing to move backwards from frames 2-3 and 4-1, the motorcycle still appears to move forward as backward motion is compensated by reversal of contrast
Effect of contrast reversal in human mind is to reverse the direction of perceived motion
So here, instead of appearing to move backwards from frames 2-3 and 4-1, the motorcycle still appears to move forward as backward motion is compensated by reversal of contrast
38
18 Motion binding
2 pairs of lines appear to move independently of each other, perpendicular to the motion of the other set of lines.
But then those squares pop up & suddenly 4 lines r moving in sync, appearing like the attached sides of a square moving in a circular motion!
18 Motion binding
2 pairs of lines appear to move independently of each other, perpendicular to the motion of the other set of lines.
But then those squares pop up & suddenly 4 lines r moving in sync, appearing like the attached sides of a square moving in a circular motion!
39
When 1 sees >2 sets of objects moving, brain lets motion of 1 set influence how we perceive motion of 2nd
Gap’s a clue 2 brain that 2 sets of lines r different
But cover up the corners &that piece of information is lost
Brain tries to link them together &all motion becomes 1
When 1 sees >2 sets of objects moving, brain lets motion of 1 set influence how we perceive motion of 2nd
Gap’s a clue 2 brain that 2 sets of lines r different
But cover up the corners &that piece of information is lost
Brain tries to link them together &all motion becomes 1
40
19 Breathing Square
This is very similar to motion binding
When corners r much hidden then Blue square behind looks like pulsating/ breathing
19 Breathing Square
This is very similar to motion binding
When corners r much hidden then Blue square behind looks like pulsating/ breathing
41
But honestly..nothing changes here as per size of blue square.
It's of same size throughout with uniform spin.
Still minds "perceives" variation in size of Blue square because of variability in amount of information available at 4 corners (hidden by 4 yellow squares)
But honestly..nothing changes here as per size of blue square.
It's of same size throughout with uniform spin.
Still minds "perceives" variation in size of Blue square because of variability in amount of information available at 4 corners (hidden by 4 yellow squares)
42
20 Kaleidoscope motion
What's motion of Red wheel?
Clockwise & jerky?
What's motion of blue Centre?
Anti-clockwise & jerky?
No! Jerks & blue Centre motion is all illusion!
There's only SMOOTH clockwise motion of Red wheel!
Blue is stationary!
20 Kaleidoscope motion
What's motion of Red wheel?
Clockwise & jerky?
What's motion of blue Centre?
Anti-clockwise & jerky?
No! Jerks & blue Centre motion is all illusion!
There's only SMOOTH clockwise motion of Red wheel!
Blue is stationary!
43
2 contrasting colors coupled by motion contrast (1 rotating vs other stationary) accentuates 2 contrasts so much that brain overcorrects for it & gets fooled in thinking reverse motion/brief halt of 1 relative to other.
It's simple but strong illusion.
2 contrasting colors coupled by motion contrast (1 rotating vs other stationary) accentuates 2 contrasts so much that brain overcorrects for it & gets fooled in thinking reverse motion/brief halt of 1 relative to other.
It's simple but strong illusion.
44
21 Dotted line motion illusion
It's difficult to show in image but if u move ur eyes rapidly from left to right or vice versa than oblique striped/dotted lines seem to move.
21 Dotted line motion illusion
It's difficult to show in image but if u move ur eyes rapidly from left to right or vice versa than oblique striped/dotted lines seem to move.
45
Explanation is simple. Sharp contrast gives rise to perception of motion!
Motion signal by the black-white border is stronger than the horizontal shift, thus the local motion detectors decode an oblique motion which is at odds with the global picture, hence the illusion
Explanation is simple. Sharp contrast gives rise to perception of motion!
Motion signal by the black-white border is stronger than the horizontal shift, thus the local motion detectors decode an oblique motion which is at odds with the global picture, hence the illusion
46
There r many versions of illusive motion based on same principles
eg. Tusi motion, pigeon neck, missing fundamental motion inversion, frequency doubling etc..
I will now take examples of illusions based on
Group B: Luminence/Contrast
There r many versions of illusive motion based on same principles
eg. Tusi motion, pigeon neck, missing fundamental motion inversion, frequency doubling etc..
I will now take examples of illusions based on
Group B: Luminence/Contrast
47
22 Herman Grid Illusion (1870)
If u focus on any crossing then U will "see" dark patches in all street crossings except the ones which u r directly looking at!
22 Herman Grid Illusion (1870)
If u focus on any crossing then U will "see" dark patches in all street crossings except the ones which u r directly looking at!
48
Retinal ganglion cell's receptive field is indicated by red disk
When Ganglion cell's looking at grating with its centre(+) positioned at crossing, there r 4 bright patches in inhibitory surround
Ganglion cell looking at street only gets 2inhibitory patches, so higher spike!
Retinal ganglion cell's receptive field is indicated by red disk
When Ganglion cell's looking at grating with its centre(+) positioned at crossing, there r 4 bright patches in inhibitory surround
Ganglion cell looking at street only gets 2inhibitory patches, so higher spike!
49
23 Vanishing dots
Similar to Hermann Grid
There're 12 dots in this pic but u can't see them all at same time!
23 Vanishing dots
Similar to Hermann Grid
There're 12 dots in this pic but u can't see them all at same time!
50
When one of the dot's fixated, its center and surround r well discerned
The next dots, however, top, left or whatever, fall on a region of our visual field that has less resolution
There the black dot &white surround fuse, rendering the dot indistinguishable from the grid line
When one of the dot's fixated, its center and surround r well discerned
The next dots, however, top, left or whatever, fall on a region of our visual field that has less resolution
There the black dot &white surround fuse, rendering the dot indistinguishable from the grid line
51
24 Moiré Pattern
Interference patterns that can be produced when an opaque ruled pattern with transparent gaps is overlaid on another similar pattern
For the moiré interference pattern to appear, 2 patterns must not be completely identical, but displaced or rotated
24 Moiré Pattern
Interference patterns that can be produced when an opaque ruled pattern with transparent gaps is overlaid on another similar pattern
For the moiré interference pattern to appear, 2 patterns must not be completely identical, but displaced or rotated
52
The 2 patterns are superimposed, so light has to pass both patters (or be blocked, as the case may be). This involves a multiplication of the two transmittance values, and multiplication of patterns with similar spatial frequencies causes difference frequencies to appear
The 2 patterns are superimposed, so light has to pass both patters (or be blocked, as the case may be). This involves a multiplication of the two transmittance values, and multiplication of patterns with similar spatial frequencies causes difference frequencies to appear
53
25 Pulfrich (3D) effect
Get a pair of sunglasses & hold 1 glass over 1 eye
U shall b able to see depth in below animation
Balls moving R-L have different depth than balls movie L-R
More the speed, more the depth
25 Pulfrich (3D) effect
Get a pair of sunglasses & hold 1 glass over 1 eye
U shall b able to see depth in below animation
Balls moving R-L have different depth than balls movie L-R
More the speed, more the depth
54
Explanation lies in fact that processing of "seeing" via photoreceptors depend upon luminance
Rule is 10x darker=10ms slower
So perception of image from covered eye lags a little behind
So position on retina in 2 eyes r different giving rise to stereovision/3D
Explanation lies in fact that processing of "seeing" via photoreceptors depend upon luminance
Rule is 10x darker=10ms slower
So perception of image from covered eye lags a little behind
So position on retina in 2 eyes r different giving rise to stereovision/3D
55
This is basis of 3D cinema coming up!
Another fact is..that's why u should not wear dark glasses while driving.
Ur perception, hence reaction will b delayed by ms. Which can b crucial!
Bonus fun fact: Pulfrich who found this out was blind in 1 eye
So he himself cudnt verify!
This is basis of 3D cinema coming up!
Another fact is..that's why u should not wear dark glasses while driving.
Ur perception, hence reaction will b delayed by ms. Which can b crucial!
Bonus fun fact: Pulfrich who found this out was blind in 1 eye
So he himself cudnt verify!
56
26 Adelson's Checker Shadow
Which square is brighter- A or B?
Ur ans will b B. Ryt?
Area of the image labeled A appears to be a darker color than the area of the image labeled B on the 2D plane of the rendered 3D projection
26 Adelson's Checker Shadow
Which square is brighter- A or B?
Ur ans will b B. Ryt?
Area of the image labeled A appears to be a darker color than the area of the image labeled B on the 2D plane of the rendered 3D projection
57
They r actually exactly the SAME color on the 2D plane of the image file!
To determine grayscale of checks, just measuring light coming from a surface (luminance) is not enough: cast shadow will dim a surface
Visual system uses several tricks to determine where the shadows r
They r actually exactly the SAME color on the 2D plane of the image file!
To determine grayscale of checks, just measuring light coming from a surface (luminance) is not enough: cast shadow will dim a surface
Visual system uses several tricks to determine where the shadows r
58
& how to compensate for them, in order to determine the shade of gray that belongs to the surface
1st trick is local contrast:
Light check in shadow is surrounded by darker checks. Thus, even though check is physically dark, it is light when compared to its neighbours.
& how to compensate for them, in order to determine the shade of gray that belongs to the surface
1st trick is local contrast:
Light check in shadow is surrounded by darker checks. Thus, even though check is physically dark, it is light when compared to its neighbours.
59
2nd trick is based on fact that shadows have soft edges
Visual system tends to ignore gradual changes in light level, so that it can determine the color of the surfaces without being misled by shadows
Here all edges r interpreted as changes in surface color ignoring shadow!
2nd trick is based on fact that shadows have soft edges
Visual system tends to ignore gradual changes in light level, so that it can determine the color of the surfaces without being misled by shadows
Here all edges r interpreted as changes in surface color ignoring shadow!
60
27 Wertheimer Koffka Ring
(This is subtle effect. May not b appreciable to all)
Which half of ring is darker?
Left....ryt?
By now u must have guessed it..
They r of same shade.
27 Wertheimer Koffka Ring
(This is subtle effect. May not b appreciable to all)
Which half of ring is darker?
Left....ryt?
By now u must have guessed it..
They r of same shade.
61
In the presence of separator, brightness difference without luminance difference is a standard case of simultaneous contrast.
This is due to retinal mechanism.
Without separator, a cortical phenomenon of 'filling-in' wins!
In the presence of separator, brightness difference without luminance difference is a standard case of simultaneous contrast.
This is due to retinal mechanism.
Without separator, a cortical phenomenon of 'filling-in' wins!
62
28 Induced Contrast Asynchrony
2 disks r pulsating within light n dark circles
Are they doing so simultaneously?
Continue watching for answer.
28 Induced Contrast Asynchrony
2 disks r pulsating within light n dark circles
Are they doing so simultaneously?
Continue watching for answer.
63
Brightness of is influenced by its surround luminance
LUMINANCE refers 2 physical properties-how many photos/sec r at a given location
BRIGHTNESS refers 2 subjective assessment
Modification of brightness by surround is “simultaneous contrast” phenomenon
credit @agshapiro2
Brightness of is influenced by its surround luminance
LUMINANCE refers 2 physical properties-how many photos/sec r at a given location
BRIGHTNESS refers 2 subjective assessment
Modification of brightness by surround is “simultaneous contrast” phenomenon
credit @agshapiro2
64
29 Pyramid (Vasarely) illusion
When there are many squares, an oblique light cross, like a large ‘X’, appears.
This cross does not really exist!
29 Pyramid (Vasarely) illusion
When there are many squares, an oblique light cross, like a large ‘X’, appears.
This cross does not really exist!
65
Refer to Hermann Grid explanation
Imagine a cell at a corner with its centre in the lighter patch, it will be inhibited by 1/4 surround from lighter patches & by 3/4 from darker patches
Voilà, the ganglion cells at the edges signal more brightness https://twitter.com/dr_gsharma/status/1232571055367024642?s=19
Refer to Hermann Grid explanation
Imagine a cell at a corner with its centre in the lighter patch, it will be inhibited by 1/4 surround from lighter patches & by 3/4 from darker patches
Voilà, the ganglion cells at the edges signal more brightness https://twitter.com/dr_gsharma/status/1232571055367024642?s=19
66
But story is a bit murkier here.
For all normal images this info from ganglion cells is integrated & heavy luminance distortion is removed.
Surprisingly, in current illusion, inverse transformation applied to correct this retinal convolution somehow "breaks down"!
But story is a bit murkier here.
For all normal images this info from ganglion cells is integrated & heavy luminance distortion is removed.
Surprisingly, in current illusion, inverse transformation applied to correct this retinal convolution somehow "breaks down"!
67
30 Saccadic Masking/suppression
Saccades- Rapid eye movements between 2 fixation targets
Now stand close to a mirror(nose nearly touching) & look to n fro between the eyes
Do you see you eyes move?
I bet u not!
So what happened?
Eye movements r there but u can't see ur own
30 Saccadic Masking/suppression
Saccades- Rapid eye movements between 2 fixation targets
Now stand close to a mirror(nose nearly touching) & look to n fro between the eyes
Do you see you eyes move?
I bet u not!
So what happened?
Eye movements r there but u can't see ur own
68
Phenomenon in visual perception where brain selectively blocks visual processing during eye movements so that neither the motion of eye (& subsequent motion blur of the image) nor the gap in visual perception is noticeable to the viewer
Own eyes can NEVER b observed in motion
Phenomenon in visual perception where brain selectively blocks visual processing during eye movements so that neither the motion of eye (& subsequent motion blur of the image) nor the gap in visual perception is noticeable to the viewer
Own eyes can NEVER b observed in motion
69
31 Contour Erasure/Adaptation
Keep your gaze steadily in the center When the flicker stops, the squares on sides r gone – only to reappear after a few seconds
31 Contour Erasure/Adaptation
Keep your gaze steadily in the center When the flicker stops, the squares on sides r gone – only to reappear after a few seconds
70
High contrast during flicker phase shifts the contrast transfer function (locally!) to the right
Thus small luminance step of contour that defines the squares becomes sub-threshold
It’s interesting that loss of step-perception leads to loss of the entire area (eg. squares)
High contrast during flicker phase shifts the contrast transfer function (locally!) to the right
Thus small luminance step of contour that defines the squares becomes sub-threshold
It’s interesting that loss of step-perception leads to loss of the entire area (eg. squares)
71
32 Contrast Gain Control
Set gaze for a few seconds at the fixation cross in the center of the 2 neighboring images
After 10 seconds 2 new halves will appear, and I want u to judge the contrast of these halves
32 Contrast Gain Control
Set gaze for a few seconds at the fixation cross in the center of the 2 neighboring images
After 10 seconds 2 new halves will appear, and I want u to judge the contrast of these halves
72
1st difference between 2 halves was obvious- 1 was blurry, and other sharp
After the change, on LEFT u initially perceived HIGH CONTRAST &on right noticeably less contrast
It persists only for few sec
After a while it becomes apparent that the 2new halves are both identical
1st difference between 2 halves was obvious- 1 was blurry, and other sharp
After the change, on LEFT u initially perceived HIGH CONTRAST &on right noticeably less contrast
It persists only for few sec
After a while it becomes apparent that the 2new halves are both identical
73
Contrast adaptation (slow, seconds) & contrast gain control (fast, ≈100 ms) r at work all over the place
It's just to make up for inhomogeneity of retinal sampling
The basic idea is to have the contrast transfer characteristic adapt optimally to the mean contrast
Contrast adaptation (slow, seconds) & contrast gain control (fast, ≈100 ms) r at work all over the place
It's just to make up for inhomogeneity of retinal sampling
The basic idea is to have the contrast transfer characteristic adapt optimally to the mean contrast
74
33 Visual/Grid Masking
Visibility of 1 image (target) is reduced by presence of another image (mask)
As time difference between target & mask increases, masking effect decreases
This is because the integration time of a target stimulus has an upper limit 200 ms
33 Visual/Grid Masking
Visibility of 1 image (target) is reduced by presence of another image (mask)
As time difference between target & mask increases, masking effect decreases
This is because the integration time of a target stimulus has an upper limit 200 ms
75
Masking can be explained by feed forward lateral inhibition circuits
Edges of mask, if positioned closely to target, may inhibit the responses caused by edges of the target, inhibiting perception of target
This is same illusion as previously discussed https://twitter.com/dr_gsharma/status/1231223978141847553?s=19
Masking can be explained by feed forward lateral inhibition circuits
Edges of mask, if positioned closely to target, may inhibit the responses caused by edges of the target, inhibiting perception of target
This is same illusion as previously discussed https://twitter.com/dr_gsharma/status/1231223978141847553?s=19
76
34 Lilac Chaser
See a circle of magenta blobs, 1 of which briefly disappears, circling around
When u are fixating well, after few cycles u will see a rotating green spot!
If ur gaze is steady, the magenta patches will disappear completely, leaving only a rotating green spot
34 Lilac Chaser
See a circle of magenta blobs, 1 of which briefly disappears, circling around
When u are fixating well, after few cycles u will see a rotating green spot!
If ur gaze is steady, the magenta patches will disappear completely, leaving only a rotating green spot
77
35 Color contrast
We've seen this effect in greyscale
But it's astounding in color
This pic is made by mirroring 1 half of face
U can appreciate that eye color looks different in each
But this is just an illusion
Bluish hue APPEARS coz of pink mask
It's not actually there
35 Color contrast
We've seen this effect in greyscale
But it's astounding in color
This pic is made by mirroring 1 half of face
U can appreciate that eye color looks different in each
But this is just an illusion
Bluish hue APPEARS coz of pink mask
It's not actually there
78
It's a case of simultaneous colour contrast & probably also of colour adaptation
Redish tint next to eye shifts neutral gray of eye to opponent colour, which for red is blue-green
Also, when ur gaze travels around red part of face, central part of retina adapts to red
It's a case of simultaneous colour contrast & probably also of colour adaptation
Redish tint next to eye shifts neutral gray of eye to opponent colour, which for red is blue-green
Also, when ur gaze travels around red part of face, central part of retina adapts to red
79
36 Afterimage illusion
If u stare for 1 mnt on this image (dots on nose) & then look at any white paper.
U will find negative of negative is positive...image of actress in full color!
Well u can guess the actress
36 Afterimage illusion
If u stare for 1 mnt on this image (dots on nose) & then look at any white paper.
U will find negative of negative is positive...image of actress in full color!
Well u can guess the actress
80
37 Munker Illusion
Notice swift change in color of 3 circles moving behinds color stripes!
Since now u must have guessed...These 3 circles are all a constant shade of grey!
This illusion shows how much perception of color is influenced by its neighborhood.
37 Munker Illusion
Notice swift change in color of 3 circles moving behinds color stripes!
Since now u must have guessed...These 3 circles are all a constant shade of grey!
This illusion shows how much perception of color is influenced by its neighborhood.
81
38 Munker-White Illusion
Similar to above but in B&W...
The hair and clothes in the left image appear to be whitish whereas those in the right one appear to be blackish,
Though they are the same luminance!
38 Munker-White Illusion
Similar to above but in B&W...
The hair and clothes in the left image appear to be whitish whereas those in the right one appear to be blackish,
Though they are the same luminance!
82
39 Equiluminance/ Richard Anuszkiewicz's Plus Reversed
When viewed at larger size and true colour, this picture appears highly unstable with the image seeming to float around in an uncomfortable, jittery way.
39 Equiluminance/ Richard Anuszkiewicz's Plus Reversed
When viewed at larger size and true colour, this picture appears highly unstable with the image seeming to float around in an uncomfortable, jittery way.
83
Light hitting retina generates separate signals 4colour &luminance
Former for recognition &latter for spatial location
At equiluminance, whilst objects are clearly visible by their colour, difficulties occur in locating them precisely coz luminance related spatial data is lost
Light hitting retina generates separate signals 4colour &luminance
Former for recognition &latter for spatial location
At equiluminance, whilst objects are clearly visible by their colour, difficulties occur in locating them precisely coz luminance related spatial data is lost
84
40 Gender Illusion
Look at the twin picture below.
Can u guess which 1 is male & which is female?
Disclaimer-
1. It's a subtle illusion (not appreciable to all)
2. This is scientific study & NOT racist NOR anti-feminist
40 Gender Illusion
Look at the twin picture below.
Can u guess which 1 is male & which is female?
Disclaimer-
1. It's a subtle illusion (not appreciable to all)
2. This is scientific study & NOT racist NOR anti-feminist
85
Both pics r same except for change in contrast at some places in face
But our brain can sense greater luminance contrast surrounding eyes & lips & label it as feminine
Means-To us, perceptibly, female skin is lighter than male but female eyes & lips r not lighter than male
Both pics r same except for change in contrast at some places in face
But our brain can sense greater luminance contrast surrounding eyes & lips & label it as feminine
Means-To us, perceptibly, female skin is lighter than male but female eyes & lips r not lighter than male
86
41 #thedress
Viral sensation on net on 26 feb 2015
With 10 million views, viewers disagreed over whether dress was colored black & royal blue or white & gold
Dress confirmed as royal blue "Lace Bodycon Dress" from the retailer Roman Originals, which was actually black & blue
41 #thedress
Viral sensation on net on 26 feb 2015
With 10 million views, viewers disagreed over whether dress was colored black & royal blue or white & gold
Dress confirmed as royal blue "Lace Bodycon Dress" from the retailer Roman Originals, which was actually black & blue
87
Explanation-
Visual system is looking at this thing, and u r trying to discount the chromatic bias of the daylight axis
People either discount the blue side, in which case they end up seeing white & gold, or discount the gold side, in which case they end up with blue & black!
Explanation-
Visual system is looking at this thing, and u r trying to discount the chromatic bias of the daylight axis
People either discount the blue side, in which case they end up seeing white & gold, or discount the gold side, in which case they end up with blue & black!
