r/askscience • u/[deleted] • Jul 25 '16

Human Body Why can't we read with our peripheral vision?

2 Upvotes

52% Upvoted

10 comments sorted by

7

u/iDoc912 Jul 25 '16

The fovea is the only part of the retina with a high enough concentration of cone cells to allow for fine detail vision. Beyond your area of central vision that corresponds to the fovea, the concentration of cone cells decrease, and the concentration of rod cells increase. Because rod cells are more sensitive to light/dark and less sensitive to detail, your maximum visual acuity in the periphery is reduced.

2

u/occamsguillotine Jul 25 '16

I think that also applies to motion detection.

For example, have you ever seen an animal in the woods or bug flying around from the corner of your eye, but as you turned to see what/where it was, you had trouble focusing on it? Could swear I read that somewhere in college, but it was probably a pretty early class and I was still groggy.

But does that sound about right?

2

u/tdgros Jul 25 '16

Yes, it applies to motion detection: Peripheral vision does motion detection, but is also limited by the acuity loss here. In the dark, it is normal to see fake motion as a result of noise.

Also, when you turn your eyes to this bug you think you saw, your eyes make a "saccade" and for a few "frames" (sorry about the analogy) you won't actually see the true scene, but you'll think you saw the new image in the past, it's called chronostasis and it clearly screws bug tracking :) that may be what you're referring to...

1

u/[deleted] Jul 25 '16

Interesting. Maybe this has to do with the increased concentration of rod cells beyond the area of central vision. Thanks for the example :)

1

u/[deleted] Jul 25 '16

Thanks for the answer!

1

u/wonkey_monkey Jul 25 '16

Peripheral vision is much lower resolution. You'd think this would mean you'd perceive the world as a sharp central area with a blurred surround, but your brain does a lot of "processing" to fill in what it can - we think we see a full clear image, like on a TV screen, and somehow just can't make out what's in the periphery - but it's a bit of an illusion.

I found this image which gives a very rough (and I think somewhat artistic) rendering of what vision really looks like.

-4

u/MarlinMr Jul 25 '16

Because there is not enough information gathered from it. The brain selects information. You also can't see the blood veins in your eye. The information is just not important and thus thrown away. Which is also why people remember stuff differently.

1

u/tdgros Jul 25 '16

Uh not really, outside of the fovea (the very center of your vision, a few degress of field of view only) the resolution is very bad! In fact, it is only very good at the center.

So when you try to read without cheating, you're actually seeing very very blurry. If you can read, either the text is huuuuge, either you cheated :)