Pitfalls of the Human Visual System - UW Radiology of Dr. Martin Crowe, Consultant Radiologist Hospital, Norfolk, UK. Radius Ulna upside down… Ulna Radius AP Forearm Computer bone

©Ken L Schreibman, PhD/MD 1/25/15 www.schreibman.info

page 1 of 7 Pitfalls in the Human Visual System

Introduction Parallel Lines Orientation is

Important Shapes that

aren’t there Motion that’s

not there Smooth

Motion Perspective Colors Length

© 2015 Ken L Schreibman, PhD/MD www.schreibman.info

Pitfalls in the Human Visual System Can we trust our eyes?

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Radiologists are Experts in Perception Eyes are tools we use to see images It’s not sufficient just to see

the image with our eyes… We need our brains to

interpret what our eyes see.

Like any tool, we need to know the limitations of our eyes

What are the “pitfalls” between the way our eyes see and our brain interprets?

Can we trust our eyes?

Is this turning

clockwise or

counter?

3D SPECT




not there Smooth




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Parallel Lines Seeing parallel articular surfaces is an

important concept in joint imaging

A,T 30yoM T,C 35yoM

Parallelism = Anatomic

Parallel Arcs

Glenohumeral Joint

Parallel Lines ACJ

Lack of Parallelism = Dislocation

Posterior Shoulder Dislocation




not there Smooth




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But if we add

diagonal lines, they no longer appear parallel

Parallel Lines It’s easy to see these 2 lines are parallel




not there Smooth




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Café Wall Illusion

Straight rows of black/white bricks that don’t appear straight




not there Smooth




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Café Wall Illusion

Perception, 1979, vol 8, p 365-380 eyetricks.com Café at the bottom of St Michael's Hill, Bristol, England




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Café Wall Illusion

opticalillusioncollection.com Port 1010 building, Docklands region, Melbourne, Australia

http://www.schreibman.info/





http://www.richardgregory.org/papers/cafe_wall/cafe-wall.pdf

http://eyetricks.com/1401.htm


http://www.opticalillusioncollection.com/2012/02/melbourne-australia-cafe-wall-illusion.html






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Café Wall Illusion

youtube.com “10 optical illusions in 2 minutes”




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2007 ARRS, Universal Studios, Orlando…

Café Wall Illusion

…Men In Black bathroom floor




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“Ulnadius”

Courtesy of Dr. Martin Crowe, Consultant Radiologist The Queen Elizabeth Hospital, Norfolk, UK.

Radius Ulna

Ulna

Radius

Lateral Forearm AP Forearm Computer bone detection

Lateral Forearm AP Forearm

Radius Ulna

Ulna

Radius




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Orientation is Important I was taught a

trained observer could read a

chest radiograph upside down…

Perhaps I can convince you otherwise…

Basically normal Situs Inversus

Increased markings both lower lobes

Kartagener Syndrome

Basically normal




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exploratorium.edu

Orientation: Inverted This is Leonardo

da Vinci’s Mona Lisa (1503)

Arguably the most recognized

painting in the world…

even upside down easily recognized

And if all you had to look at was the

inverted B, like the inverted

chest radiograph, it’s hard to see

anything wrong… Orientation is

important!

But oriented correctly, there is something obviously

very wrong with B

B A

When inverted, it’s hard to see a difference between A & B Introduction Parallel Lines Orientation is



not there Smooth




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Dragon Wall: Frontal View

A B

Orientation: Side-by-Side Dragon

Wall:

A) Steep oblique view

B) Another oblique view…

… or is it?

Forbidden City, Beijing, China

To me this means our eyes are

sensitive to how we orient

our images side-by-side.

On our PACS I always use

the same side-by-side arrangement:

PA vs Lat Views

T1 vs T2 series


http://www.youtube.com/watch?v=URLRdcnU6Hk





http://www.exploratorium.edu/exhibits/mona/mona.html







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Shapes that aren’t there Human brain is hardwired to see shapes Pareidolia: random images perceived as significant* Faces

*wikipedia.org nasa.gov

Man in Moon Face in Mars

Viking1 orbiter 1976

Old Man of the Mountain

1955

White Mountains New Hampshire

pre 2003




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Shapes that aren’t there

Wisconsin Dells

Cow in the Milk Bottle




not there Smooth




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Do you see the white circles?

Rows of black crosses

There are no white circles here Introduction Parallel Lines Orientation is



not there Smooth




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Shapes there aren’t there… There is no triangle here Once we see the triangle, it’s hard to not see the triangle!

We start with 3 circles (pizzas) Take a slice out of each… Rotate them… We now see a triangle… …that’s not really there

Even if we pull the circles away from each other…

We still see the triangle that’s not there!




not there Smooth




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There are no spirals here What shapes do we see here…

Spirals, right?

So we should be able to start at

some point and trace the spiral in

to the center…

wikipedia.org ritsumei.ac.jp




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There are no spirals here Motion that’s not there…

ritsumei.ac.jp


http://en.wikipedia.org/wiki/Pareidolia

http://www.nasa.gov/centers/langley/news/researchernews/supermoon.html





http://en.wikipedia.org/wiki/Fraser_spiral_illusion

http://www.ritsumei.ac.jp/~akitaoka/uzu-e.html


http://www.ritsumei.ac.jp/~akitaoka/uzu-e.html






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Motion that’s not there…

ritsumei.ac.jp

“Rotating rays” Introduction Parallel Lines Orientation is



not there Smooth




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ritsumei.ac.jp

“Rotating Snakes”




not there Smooth




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ritsumei.ac.jp

“Rollers” Introduction Parallel Lines Orientation is



not there Smooth




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moillusions.com

“Pouring Water”




not there Smooth




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Smooth Motion Traditionally, radiologists looked at static pictures Ultrasound allows for dynamic examinations US is being used increasingly in MSK “Snapping” Ilio-psoas tendon (source of hip pain)

Static US

IP Tendon

Dynamic US




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Smooth Motion: Linear

Black & White squares moving same speed in smooth linear motion back & forth


http://www.ritsumei.ac.jp/~akitaoka/index-e.html






http://www.moillusions.com/2011/07/pouring-water-optical-illusion.html/blue-lines-optical-illusions








not there Smooth




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Smooth Motion: Rotational Purple star… surrounded by a blue star… surrounded by a purple star

Rotate the blue star…

The blue star is rotating

smoothly…

But it appears to rotate in

a cog-wheel fashion!




not there Smooth




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Focus your attention on the blinking green dot

We add in 3 yellow

dots in the periphery

Even when we add in many blue crosses, you can still

easily see all 3 yellow dots

while focusing on the green dot

But if we make the crosses

move…

Soon, 1, 2 ,or even all 3

yellow dots will briefly

disappear!

and you stay focused on the

green dot…

Motion Induced Blindness




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Importance of Multiple Views We all know whenever we

deal with radiographs we need to

have multiple views.

Here’s an example…

Here I am stabbing a steak knife

through my skull…

Not really…

But with only one view you can’t tell

what’s in front and what’s behind

The lateral view shows I’m just holding the

knife in front of my skull

We need to put the two views together in our own brains to understand what’s in front and what’s behind.

This is a made up example…




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This is a real example

PA view thumb

…negative

Oblique view

…negative

Lateral view

DISLOCATED!

For joints need three views




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Forced Perspective

Marty age 8

Marty is not taller than

the Sears Tower




not there Smooth




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Forced Perspective: Deception

Picture on real estate site

HUGE pool!

epicfail.com







http://www.funnyism.com/i/epicfail/33229






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Forced Perspective: Static

games.yahoo.com




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Forced Perspective: Dynamic

illusioncontest.neuralcorrelate.com 2010 Best Illusion of the Year Winner




not there Smooth




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Focus your attention of the

I’ll add in some pink circles…

but keep focus on the

See what happens when we take away circles…

It looks like the pink circles get replaced

by green circles! or

it looks like there is a green circle

moving around a clock face

But there is NO green circle!

(There’s nothing green on this slide)

Colors that aren’t there Introduction Parallel Lines Orientation is



not there Smooth




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Light vs Dark: Blue

We start with black & white bars

We add in some light blue bars...

and some dark blue bars...

Light blue &

Dark blue right?

No, they are the same

exact shade of blue!




not there Smooth




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Light vs Dark: Gray This is a gradient.

It contains all shades of gray.

Human eye cannot assess absolute values of gray, only lighter or darker than background

White

Black

So if we change the background…

It looks like the gradient changes!

If we change only ½ the background It looks like ½ the gradient changes!




not there Smooth




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persci.mit.edu

Shadows: Gray Can you believe squares A & B are the same color?


http://games.yahoo.com/photos/chair-illusion-1311764524-slideshow/brain-chair-illusion-photo.html


http://illusioncontest.neuralcorrelate.com/2010/impossible-motion-magnet-like-slopes/





http://persci.mit.edu/gallery/checkershadow






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Shadows: Color

www.spiegel.de R. Beau Lotto

What color is this tile?

What color is this tile?




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Colors: #TheDress

tumblr(2/25/15) buzzfeed(2/26 5pm) twitter(2/26 6pm)

NYTimes(2/27) WSJ(2/27) NPR(2/27)

If you see GOLD & WHITE

Wave Right Hand

If you see BLACK & BLUE Wave Left Hand

Kim Kardashian West @KimKardashian

“What color is that dress? I see

white & gold. Kanye sees

black & blue, who is color

blind?”

Brightness: -40% Contrast: +40%

Brightness: +40% Contrast: +40% Original JPEG

SNL x3(2/28)




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Our Eyes are Poor at Judging Length We’ve all seen questions like this:

Which horizontal line is longer?

Same length




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Our Eyes are Poor at Judging Length

Two tables of very different shape Green: Rectangular Red: Square

Length

Width

Length

Width

Length

Width

Len

gth

Wid

th

www.spiegel.de R. Beau Lotto




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What have we learned? We are not good at judging length Need to make actual measurements

We are not good at judging gray levels Need to measure Hounsfield Units

How we orient images matters Need to hang things the same way every time

Complex backgrounds can fool you All radiology images have complex

backgrounds…




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Thank you!

media.photobucket.com


http://www.spiegel.de/international/world/starfish-daisies-and-raying-purple-forms-oliver-sacks-on-the-wonder-of-sight-a-739184.html


http://swiked.tumblr.com/post/112073818575/guys-please-help-me-is-this-dress-white-and

http://www.buzzfeed.com/catesish/help-am-i-going-insane-its-definitely-blue.sok90B7mz

https://twitter.com/TheEllenShow/status/571128725112094720/photo/1

http://www.nytimes.com/2015/02/28/business/a-simple-question-about-a-dress-and-the-world-weighs-in.html?_r=0

http://www.wsj.com/articles/the-dress-a-black-and-blue-debate-over-the-color-of-a-dress-stirs-social-media-1425063162

http://www.npr.org/2015/02/27/389585326/a-neuroscientist-weighs-in-why-do-we-disagree-on-the-color-of-the-dress

https://twitter.com/KimKardashian/status/571168149871177730

http://www.nbc.com/saturday-night-live



http://www.spiegel.de/international/world/starfish-daisies-and-raying-purple-forms-oliver-sacks-on-the-wonder-of-sight-a-739184.html



http://media.photobucket.com/image/thank you upside down/helenahjay/ambigram.jpg

Documents

Pitfalls of the Human Visual System - UW Radiology of Dr. Martin Crowe, Consultant Radiologist Hospital, Norfolk, UK. Radius Ulna upside down… Ulna Radius AP Forearm Computer bone