Intro to Radiology - Department of Radiology, University of ...
Intro to Radiology - Department of Radiology, University of ...
Intro to Radiology - Department of Radiology, University of ...
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Pitfalls in the Human<br />
Visual System<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
Can we trust our eyes?<br />
Radiologists are Experts in Perception<br />
Eyes are <strong>to</strong>ols we use <strong>to</strong> see images<br />
‣It’s not sufficient just <strong>to</strong> see<br />
the image with our eyes…<br />
‣We need our brains <strong>to</strong><br />
interpret what our eyes see.<br />
Like any <strong>to</strong>ol, we need<br />
www.schreibman.info Click here <strong>to</strong> tips on navigating this ePoster<br />
© 2013 Ken L Schreibman, PhD/MD<br />
3D SPECT<br />
Is this<br />
turning<br />
clockwise<br />
or<br />
counter?<br />
<strong>to</strong> know the limitations <strong>of</strong> our eyes<br />
‣What are the “pitfalls” between the way our<br />
eyes see and our brain interprets?<br />
Can we trust our eyes?<br />
Slide 1 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
page 1 <strong>of</strong> 7<br />
Can we trust our eyes?<br />
Parallel Lines<br />
Seeing parallel articular surfaces is an<br />
important concept in joint imaging<br />
Parallelism = Ana<strong>to</strong>mic<br />
Parallel<br />
Lines<br />
ACJ<br />
Parallel<br />
Arcs<br />
Glenohumeral<br />
Joint<br />
www.schreibman.info A,T 30yoM<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Lack <strong>of</strong> Parallelism<br />
= Dislocation<br />
Posterior Shoulder Dislocation<br />
T,C 35yoM<br />
Slide 3 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Parallel Lines<br />
It’s easy <strong>to</strong> see<br />
these 2 lines<br />
are parallel<br />
But if<br />
we add<br />
diagonal lines,<br />
they no longer<br />
appear parallel<br />
Can we trust our eyes?<br />
Slide 4 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Café Wall Illusion<br />
Straight rows <strong>of</strong> black/white bricks<br />
that don’t appear straight<br />
Can we trust our eyes?<br />
Slide 5 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
Café Wall Illusion<br />
Perception, 1979, vol 8, p 365-380 eyetricks.com<br />
© 2013 Ken L Schreibman, PhD/MD Café at the bot<strong>to</strong>m <strong>of</strong> St Michael's Hill, Bris<strong>to</strong>l, England<br />
Can we trust our eyes?<br />
Slide 6 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Café Wall Illusion<br />
opticalillusioncollection.com<br />
Port 1010 building, Docklands region, Melbourne, Australia<br />
Can we trust our eyes?<br />
Slide 7 <strong>of</strong> 41<br />
©Ken L Schreibman, PhD/MD 2/1/13<br />
www.schreibman.info
Pitfalls in the Human<br />
Visual System<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Café Wall Illusion<br />
youtube.com<br />
“10 optical illusions in 2 minutes”<br />
Can we trust our eyes?<br />
Slide 8 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
2007 ARRS, Universal Studios, Orlando…<br />
© 2013 Ken L Schreibman, PhD/MD …Men In Black bathroom floor<br />
page 2 <strong>of</strong> 7<br />
Café Wall Illusion<br />
Can we trust our eyes?<br />
Slide 9 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
Orientation is Important<br />
I was taught a<br />
trained observer<br />
could read a<br />
chest radiograph<br />
upside down…<br />
Perhaps I can<br />
convince you<br />
otherwise…<br />
Kartagener Syndrome<br />
Increased markings<br />
both lower lobes<br />
Situs Basically Inversus<br />
normal<br />
Slide 10 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
explora<strong>to</strong>rium.edu<br />
Can we trust our eyes?<br />
Orientation: Inverted<br />
When And inverted, if all you it’s hard had <strong>to</strong> see This a difference is Leonardo<br />
between A & B<br />
da Vinci’s<br />
Mona Lisa (1503)<br />
Arguably the most<br />
recognized<br />
<strong>to</strong> look at was the<br />
inverted B,<br />
like the inverted<br />
chest radiograph,<br />
it’s hard <strong>to</strong> see<br />
anything wrong…<br />
Orientation is<br />
A<br />
important!<br />
But painting oriented correctly, in the there<br />
is something world… obviously<br />
even very upside wrong with down B<br />
easily recognized B<br />
Slide 11 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
Can we trust our eyes?<br />
Orientation: Side-by-Side<br />
<strong>Intro</strong>duction Dragon To me this<br />
Parallel Lines means our<br />
eyes Wall: are<br />
Orientation is sensitive <strong>to</strong><br />
Important A) how Steep we orient<br />
Shapes that our oblique images<br />
aren’t there side-by-side.<br />
view<br />
Motion that’s On our PACS<br />
not there B) I always Another use<br />
Smooth the same<br />
oblique<br />
Motion<br />
side-by-side<br />
arrangement: view…<br />
Perspective<br />
‣ PA vs Lat Views<br />
Colors … or is it?<br />
‣ T1 vs T2 series<br />
Length<br />
A<br />
www.schreibman.info<br />
Forbidden City, Beijing, China<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Dragon Wall: Frontal View<br />
B<br />
Slide 12 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines ‣Pareidolia: random images perceived as significant*<br />
Orientation is<br />
Important ‣Faces<br />
Shapes that Man in Moon Face in Mars Old Man <strong>of</strong> the Mountain<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
1955<br />
Perspective<br />
White Mountains<br />
Colors<br />
New Hampshire<br />
Length<br />
nasa.gov<br />
Viking1 orbiter 1976 pre 2003<br />
www.schreibman.info<br />
*wikipedia.org<br />
Slide 13 <strong>of</strong> 41<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
Shapes that aren’t there<br />
Human brain is hardwired <strong>to</strong> see shapes<br />
©Ken L Schreibman, PhD/MD 2/1/13<br />
www.schreibman.info
Pitfalls in the Human<br />
Visual System<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
Shapes that aren’t there<br />
Cow in the Milk Bottle<br />
Wisconsin Dells<br />
Slide 14 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
page 3 <strong>of</strong> 7<br />
Can we trust our eyes?<br />
There Do you are see no the white white circles circles? here<br />
Rows <strong>of</strong> black crosses<br />
Slide 15 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction Once we see the<br />
Parallel Lines triangle, it’s<br />
Orientation is hard <strong>to</strong> not see<br />
Important<br />
Shapes that the triangle!<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
Shapes There there is no aren’t triangle there…<br />
We start with 3 circles (pizzas)<br />
Take a slice out <strong>of</strong> each…<br />
Rotate them…<br />
We now see a triangle…<br />
…that’s not really there<br />
Even if we pull the circles<br />
away from each other…<br />
We still see the<br />
triangle that’s<br />
not there!<br />
Slide 16 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
There are no spirals here<br />
What shapes do<br />
we see here…<br />
Spirals, right?<br />
So we should be<br />
able <strong>to</strong> start at<br />
some point and<br />
trace the spiral in<br />
<strong>to</strong> the center…<br />
ritsumei.ac.jp<br />
wikipedia.org<br />
Slide 17 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
There Motion are that’s no spirals not there…<br />
ritsumei.ac.jp<br />
Slide 18 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction “Rotating rays”<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
Motion that’s not there…<br />
ritsumei.ac.jp<br />
Slide 19 <strong>of</strong> 41<br />
©Ken L Schreibman, PhD/MD 2/1/13<br />
www.schreibman.info
Pitfalls in the Human<br />
Visual System<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction “Rotating<br />
Parallel Lines Snakes”<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
Motion that’s not there…<br />
ritsumei.ac.jp<br />
Slide 20 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction “Rollers”<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
page 4 <strong>of</strong> 7<br />
Can we trust our eyes?<br />
Motion that’s not there…<br />
ritsumei.ac.jp<br />
Slide 21 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction “Pouring<br />
Parallel Lines Water”<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
Motion that’s not there…<br />
moillusions.com<br />
Slide 22 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Ultrasound allows for dynamic examinations<br />
Important ‣US is being used increasingly in MSK<br />
Shapes that “Snapping” Ilio-psoas tendon (source <strong>of</strong> hip pain)<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Static US<br />
Dynamic US<br />
Perspective<br />
IP Tendon<br />
Colors<br />
Length<br />
www.schreibman.info<br />
Slide 23 <strong>of</strong> 41<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
Smooth Motion<br />
Traditionally, radiologists looked at static pictures<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
Smooth Motion: Linear<br />
Black & White squares moving same speed<br />
in smooth linear motion back & forth<br />
Slide 24 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction Purple star…<br />
Parallel Lines<br />
Orientation is surrounded by<br />
Important a blue star…<br />
Shapes that surrounded by<br />
aren’t there a purple star<br />
Motion that’s<br />
not there<br />
Smooth Rotate the<br />
Motion blue star…<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
Smooth Motion: Rotational<br />
The blue star<br />
is rotating<br />
smoothly…<br />
But it appears<br />
<strong>to</strong> rotate in<br />
a cog-wheel<br />
fashion!<br />
Slide 25 <strong>of</strong> 41<br />
©Ken L Schreibman, PhD/MD 2/1/13<br />
www.schreibman.info
Pitfalls in the Human<br />
Visual System<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction Focus your<br />
attention on<br />
Parallel Lines the blinking<br />
Orientation is green dot<br />
Important We add in<br />
Shapes that 3 yellow<br />
aren’t there dots in the<br />
periphery<br />
Motion that’s<br />
not there Even when we<br />
add in many<br />
Smooth blue crosses,<br />
Motion you can still<br />
Perspective easily see all 3<br />
yellow dots<br />
Colors while focusing<br />
Length on the green dot<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
Motion Induced Blindness<br />
But if we make<br />
the crosses<br />
move…<br />
and you stay<br />
focused on the<br />
green dot…<br />
Soon, 1, 2 ,or<br />
even all 3<br />
yellow dots will<br />
briefly<br />
disappear!<br />
Slide 26 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
page 5 <strong>of</strong> 7<br />
Can we trust our eyes?<br />
Importance <strong>of</strong> Multiple Views<br />
We all know<br />
whenever we<br />
Here The I am lateral stabbing view shows<br />
deal with<br />
a I’m steak just knife holding the<br />
through<br />
radiographs<br />
knife in<br />
my<br />
front<br />
skull…<br />
<strong>of</strong> my skull<br />
we need <strong>to</strong><br />
have multiple<br />
views.<br />
Here’s an<br />
example…<br />
We need <strong>to</strong> put the two views <strong>to</strong>gether in our own<br />
brains <strong>to</strong> understand what’s in front and what’s behind.<br />
Not really…<br />
But with only one<br />
view you can’t tell<br />
what’s in front and what’s behind<br />
This is a made up example… Slide 27 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
PA view thumb<br />
Oblique view<br />
…negative …negative<br />
This is a real example<br />
Can we trust our eyes?<br />
For joints need three views<br />
Lateral view<br />
DISLOCATED!<br />
Slide 28 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Forced Perspective<br />
Marty age 8<br />
Can we trust our eyes?<br />
Marty is not taller than<br />
the Sears Tower<br />
Slide 29 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
Forced Perspective: Deception<br />
Picture on real<br />
estate site<br />
‣HUGE pool!<br />
epicfail.com<br />
Slide 30 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
Forced Perspective: Static<br />
games.yahoo.com<br />
Slide 31 <strong>of</strong> 41<br />
©Ken L Schreibman, PhD/MD 2/1/13<br />
www.schreibman.info
Pitfalls in the Human<br />
Visual System<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
Forced Perspective: Dynamic<br />
illusioncontest.neuralcorrelate.com<br />
2010 Best Illusion <strong>of</strong> the Year Winner<br />
Slide 32 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction I’ll add in<br />
Parallel Lines some pink<br />
Orientation is circles…<br />
Important but keep<br />
Shapes that focus on<br />
aren’t there the <br />
Motion that’s<br />
not there<br />
Smooth See what<br />
Motion happens<br />
Perspective when we<br />
Colors take away<br />
Length<br />
circles…<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
page 6 <strong>of</strong> 7<br />
<br />
Can we trust our eyes?<br />
Colors that aren’t there<br />
Focus your attention <strong>of</strong> the <br />
It looks like the pink<br />
circles get replaced<br />
by green circles!<br />
or<br />
it looks like there is<br />
a green circle<br />
moving around a<br />
clock face<br />
But there is NO<br />
green circle!<br />
(There’s nothing<br />
green on this slide)<br />
Slide 33 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
We add in<br />
some light<br />
blue bars...<br />
Light blue<br />
&<br />
Dark blue<br />
right?<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Light vs Dark: Blue<br />
We start with black & white bars<br />
Can we trust our eyes?<br />
and<br />
some dark<br />
blue bars...<br />
No, they are<br />
the same<br />
exact shade<br />
<strong>of</strong> blue!<br />
Slide 34 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
This is a gradient.<br />
It contains all<br />
shades <strong>of</strong> gray.<br />
Human eye cannot<br />
assess absolute<br />
values <strong>of</strong> gray,<br />
only lighter or<br />
darker than<br />
background<br />
Can we trust our eyes?<br />
Light vs Dark: Gray<br />
White<br />
Black<br />
So if we change<br />
the background…<br />
It looks like the<br />
gradient changes!<br />
If we change only<br />
½ the background<br />
It looks like ½ the<br />
gradient changes!<br />
Slide 35 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Shadows: Gray<br />
Can you believe<br />
squares A & B<br />
are the same<br />
color?<br />
persci.mit.edu<br />
Can we trust our eyes?<br />
Slide 36 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
What color is<br />
this tile?<br />
What color is<br />
this tile?<br />
Shadows: Color<br />
Can we trust our eyes?<br />
R. Beau Lot<strong>to</strong><br />
www.spiegel.de<br />
Slide 37 <strong>of</strong> 41<br />
©Ken L Schreibman, PhD/MD 2/1/13<br />
www.schreibman.info
Pitfalls in the Human<br />
Visual System<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
Our Eyes are Poor at Judging Length<br />
We’ve all seen questions like this:<br />
Which horizontal line is longer?<br />
Same length<br />
Slide 38 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
page 7 <strong>of</strong> 7<br />
Can we trust our eyes?<br />
Our Eyes are Poor at Judging Length<br />
Width<br />
Width<br />
Length<br />
Length<br />
Two tables <strong>of</strong> very different shape<br />
Green: Rectangular Red: Square<br />
Width<br />
Length<br />
R. Beau Lot<strong>to</strong><br />
www.spiegel.de<br />
Slide 39 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is ‣Need <strong>to</strong> make actual measurements<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Can we trust our eyes?<br />
What have we learned?<br />
We are not good at judging length<br />
We are not good at judging gray levels<br />
‣Need <strong>to</strong> measure Hounsfield Units<br />
How we orient images matters<br />
‣Need <strong>to</strong> hang things the same way every time<br />
Complex backgrounds can fool you<br />
‣All radiology images have complex<br />
backgrounds…<br />
Slide 40 <strong>of</strong> 41<br />
Pitfalls in the Human Visual System<br />
<strong>Intro</strong>duction<br />
Parallel Lines<br />
Orientation is<br />
Important<br />
Shapes that<br />
aren’t there<br />
Motion that’s<br />
not there<br />
Smooth<br />
Motion<br />
Perspective<br />
Colors<br />
Length<br />
www.schreibman.info<br />
© 2013 Ken L Schreibman, PhD/MD<br />
Thank you!<br />
media.pho<strong>to</strong>bucket.com<br />
Can we trust our eyes?<br />
Slide 41 <strong>of</strong> 41<br />
©Ken L Schreibman, PhD/MD 2/1/13<br />
www.schreibman.info
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