

What everyone should know about the human eye - bkrausz
http://www.gazehawk.com/blog/what-everyone-should-know-about-the-human-eye/

======
btilly
The information about faces and direction of gaze leads to an important tip on
presentations. Always choose images that are facing your text. Flip the image
if necessary to make it happen.

See
[http://perl.plover.com/yak/presentation/samples/slide023.htm...](http://perl.plover.com/yak/presentation/samples/slide023.html)
for an example of this advice being given. (And read the rest of that
presentation if you have to give presentations - it is quite good.)

~~~
mgurlitz
And if you read the rest of the presentation, don't forget to read along with
his notes
[http://perl.plover.com/yak/presentation/samples/notes.html#s...](http://perl.plover.com/yak/presentation/samples/notes.html#sl-23)

~~~
ma2rten
Thanks guys I have learned alot from that.

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extension
What I was surprised to learn about the eye is that the area of foveal vision,
the central part of the image that can see fine details, is about the size of
a quarter held at arms length from your face. You can only ever clearly see a
tiny dot, but your eyes dart around and paint a picture for your brain to show
you.

~~~
ristretto
That's why our fonts can be so small! At night, though (or in low light) the
cones in fovea are useless and peripheral vision becomes more important.

~~~
lbarrow
There's a lot of cool chemistry involved in the eye adjusting to darkness and
light. My favorite fun fact is that as you adjust to darkness, the spectrum of
light your eye perceives becomes slightly blueshifted:
<http://en.wikipedia.org/wiki/Purkinje_effect>

------
Tutorialzine
This reminds me of a book I read a few years ago - Mind Hacks [1]. It
discussed all kinds of interesting mechanisms that our brains use to fool us
into thinking that we are always aware of our environment.

In the eye chapter, there was an interesting side-effect of the saccade
movement - the "broken watch". This is when your brain fools you into thinking
that the picture you see after a saccade has been the same during the movement
itself. When you look at your watch and your timing is just right, you will be
left with the impression that the seconds arm stays fixed for longer than it
should.

I highly recommend the book - it really demonstrates our inner-machinery.

[1] <http://mindhacks.com/>

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timmy-turner
The fact that humans like to look at faces and are pretty good at identifying
differences between them has been exploited in
<http://en.wikipedia.org/wiki/Chernoff_face>.

~~~
nitrogen
Similar in concept, the Robot Hash generator:
<http://news.ycombinator.com/item?id=2742367>

------
dhughes
The best one was left out the blind spot everyone has where the optic nerve
connects.

Wikipedia has a simple test:
<http://en.wikipedia.org/wiki/Blind_spot_(vision)>

------
bobmoretti
anyone interested in this topic should check out Visual Intelligence, by Don
Hoffman:

[http://www.amazon.com/Visual-Intelligence-How-Create-
What/dp...](http://www.amazon.com/Visual-Intelligence-How-Create-
What/dp/0393319679)

The book deduces a set of rules that your brain must follow in order to
construct a (mostly) correct interpretation of the limited data that it gets.
It does this with a series of experiments that the reader can test. While
possibly no longer up to date on the latest research, it's simply a delight to
read.

------
malux85
With my conscious perception being on the 'processed' side of my neocortex, I
used to think that the human eye was basically a hi-res camera .. until I read
Jeff Hawkins 'On Intelligence'

In the book he explains how our brain gets a crappy, distorted image from our
eyes, and manages to assemble it using a hierarchy of cells [regions] in the
neocortex. It's really interesting, I would recommend getting this book, it's
only a couple of hundred pages long, and really opened my eyes (ha!) to how
the human brain learns.

~~~
ristretto
the eye gives a crappy image? Odd, i dont know many cameras that can detect
single photons.

~~~
Zaak
The human eye can't detect single photons. However, it can detect a few
simultaneous photons at the retina, which corresponds to a hundred or so
entering the cornea.

~~~
ristretto
Rod cells can detect single photons

<http://en.wikipedia.org/wiki/Rod_cell>

~~~
a-priori
Sort of. This is from memory, but here's how I remember that experiment
working:

In that experiment, they showed that, for some value of _n_ , rod cells
consistently activated in response n photons, and did not activate in response
to _(n-1)_ photons. Thus, they argue, rods are sensitive to single photons.

In some sense, they're right, in a straw that breaks the camel's back sort of
way. However, the common mis-interpretation of these results is that _n=1_ ;
that is, in utter darkness a rod cell would fire in response to a single
photon. But this is not what the experiment showed.

(Note that just because a rod cell activates doesn't mean that the organism
would perceive light. In order for a signal to reach the optic nerve, a
retinal ganglion cell needs to activate. Ganglion cells only activate in
response to the activation of a significant number of photoreceptors. Only in
some part of the fovea, where there are no rods, is there a 1:1 mapping of
photoreceptor to ganglion cell. In most parts of the retina the ratio is
closer to 1 ganglion cell per 100 photoreceptors. Furthermore, even if a
ganglion cell activates and a signal reaches the optic nerve, that _still_
doesn't mean that the organism will perceive light. It's likely that further
levels of processing may filter out transient activations.)

------
devindotcom
This was good. If you're interested in some further tech/visual neuroscience
crossover, the intros to these two posts I made have some relevant
information:

<http://techcrunch.com/2011/04/08/frame-wars/>

[http://techcrunch.com/2010/06/19/a-guide-to-3d-display-
techn...](http://techcrunch.com/2010/06/19/a-guide-to-3d-display-technology-
its-principles-methods-and-dangers/)

------
taeric
See... I have always felt the opposite. The various parts of your eye are much
more like the various parts of a camera than people admit.

Now, your perception of the visual world is a lot more dynamic than a simple
still shot, which seems to be what this is really saying. No argument there.

~~~
a-priori
Optically, they're kind of like cameras. I wouldn't be surprised if early
camera designers looked to mammalian eyes for inspiration.

But once you get to the retina all bets are off. That's the point of this
article.

~~~
taeric
Right. I just think it would be better said as "people are not cameras." Seems
many people think your eyes are somehow immune to the optical qualities that
cameras have to deal with.

~~~
lbarrow
Good point. But I would argue that, fundamentally, the interaction between the
eyes and the brain is much different than the interaction we have with
cameras. The optic system is deeply, deeply meshed with the brain's perception
of reality.

------
eof
Somewhat related:

<http://www.visionsofjoy.org/pdfs/BatesPerfectSightWG.pdf>
<http://www.i-see.org/perfect_sight/>

William Horatio Bates (1860-1931) first published his treatise, The Cure of
Imperfect Sight by Treatment Without Glasses (title page), also known as
Perfect Sight Without Glasses (cover), in 1920.

This guy has some kind of crazy ideas; but the general thing I learned from
him is that the shape of the lens of the eye is a function of three sets of
muscles that can be trained/relaxed to help vision come back to 'normal'.

A great read. The HN worthy title would be "hacking your crappy vision"

~~~
sevenproxies
>shape of the lens of the eye is a function of three sets of muscles that can
be trained/relaxed to help vision come back to 'normal'.

Didn't read your link but could this explain why programmers get poor eyesite
as they frequently focus on close objects (monitors) and thus the three sets
of muscles become accustom to focusing on close objects?

~~~
cydonian_monk
My eye doctor certainly thinks that's a contributing factor. His
recommendation (for me) was that after every hour (or 55 minutes) of PC work,
I should spend five minutes looking at things at distance (buildings, trees,
etc). It's probably frowned upon by my employers (as I don't have a window
office), but it's helped reduce my eye strain quite a bit.

~~~
endgame
> It's probably frowned upon by my employers

Too bad for them. Your eyes are more important.

~~~
cydonian_monk
I agree. Which is why I'm not overly concerned with what they think about the
subject. ;) My supervisor seemed content with "doctor's recommendation" once
when I mentioned it to him.

------
ristretto
There is also another kind of movements, smooth pursuit movements where the
eyes move smoothly following a target. While we use saccades when reading
text, an smooth page animation would trigger them. That's why i find jerky
animations annoying and disorienting

~~~
lbarrow
Right. I thought about including a description of pursuit movement, but
omitted it because I didn't think it came up frequently when viewing web
pages. Humans actually have a whole bunch of special-case eye movement
patterns, like the "catch-something heuristic"
(<http://en.wikipedia.org/wiki/Gaze_heuristic>), which we share with dogs!
([http://www.mansfield.osu.edu/faculty/dshaffer/Shaffer%20Publ...](http://www.mansfield.osu.edu/faculty/dshaffer/Shaffer%20Publication%20pdfs/Publications/Dogs%20Catching%20Frisbees.pdf))

~~~
fferen
That is awesome; thanks for the link! I always expected that we used a more
complex algorithm, but this extremely simple one probably works just as well.

------
AltIvan
I do that all the time when people look at me. Look away like you are staring
at something important; they very quickly try to see what you are interested
in.

------
shawndumas
"[P]eople love to look at faces, but we often use them as clues as to where
else to look. Following a person’s gaze is almost a reflex. James Breeze
demonstrated this really well in a blog post called “You look where they
look.” His experiment was simple: about 100 people were shown a picture of an
advertisement with a baby and some text. Half the time, the baby was facing
the reader, while the other time, the baby was looking at the text. Breeze
found that not only did the people shown the baby looking at the text pay more
attention to the text, but they actually stopped looking at the baby faster in
order to follow its gaze."

~~~
sukuriant
Instead of downvoting, I'm going to ask why you're quoting this. So, why are
you quoting this?

~~~
shawndumas
lol; It was the most useful part of a good article and I thought it would
entice more people to read the whole article.

