Can humans functionally move their eyeballs independently of one another?

Question

Recently I see a lot of links to Ed Macy's book "Apache" (related from Google glass articles' comments).

It took me two years to learn how to "see" properly -- how to see in an Apache World. I once filmed my face during a sortie with a video camera as an experiment. My eyes whirled independently of each other throughout, like a man possessed.

I doubt that that is the real case, it sound more logical to me that Apache pilots just learn to switch their concentration easily from one eye to another, but they don't actually move their eyes like a chameleon. Can humans even move their eyeballs independently of each other and if so, are pilots more prone to doing this?

Answer 1

Chameleons are the only vertebrates that can focus monocularly:

However, unlike other vertebrates, chameleons can focus targets monocularly, using lens effort so that, in theory, they can fixate and focus an approaching threat with one eye, while the other scans in the opposite direction. (From Threat perception in the chameleon (Chamaeleo chameleon): evidence for lateralized eye use).

There is some evidence that the above conclusion isn't so absolute:

This paper will present observations from both normal and abnormal eye movement data that suggest a more complex ocular mo­tor control architecture - independent control of each eye. Because of the inherent bilateral nature of brain stem organization, the latter directly implies independent control of each eye muscle. Taken individually, some of the observations are only mildly suggestive of in­ dependent control; others are strongly sugges­tive. None may, by itself, provide conclusive proof of independent control, although some appear to. However, taken together, they sup­port a strong case for the hypothesis that the neuroanatomy of our ocular motor systems is basically configured for independent control of each eye (muscle) and it is binocularity that imposes the yoking normally seen.

[...]

In 2 of the earlier studies of human saccadic metrics, it was found that the saccadic trajec­tories of each eye might independently over­ shoot or undershoot the target during the pulse portion of the response, and the result­ing "glissade" to the target was specific for the metrics of that eye's saccade.

[...]

The occurrence of uni-ocular dynamic over­ shoots (5) in normals is another instance of disconjugacy that suggests independent neu­ral control signals to each eye.

The above is from (Dell'Osso, L. F. (1994). Evidence suggesting individual ocular motor control of each eye (muscle). J Vestib Res, 4(5), 335-45.)

Answer 2

Yes, humans can move their eyes independently... just watch these videos (link 1 and link 2).

But, how much use is that? What can you see if you cross your eyes? I know when I do it that crossing eyes serves very little purpose other than to help with pulling faces :) Everything just goes blurry and my eyes start to hurt.

One reason our eyes have evolved to work in harmony is because of binocular vision, it's why they are on the front of our heads, not the sides. Depth perception is difficult with one eye; put on an eye-patch, go play catch, see how you do compared to normal.

A chameleon has evolved independent movement of their eyes. The eyes are mounted on the sides of their heads, this is because some of the time they need 360 vision to spot danger. However, because they are also predators using a highly precise method of capture (requiring good eye-tongue coordination) the ability to point both in the same direction, giving them binocular vision, is also highly advantageous, thus they can move them independently to face the same direction. For more info see the wiki page or this article.

With regards to the quote above, you might want to read the answer to this Quora post, one guy says:

I flew the AH-64s for over 12 years. There's no single Apache pilot I know who can move his eyeballs independently, nor who is required to do so. Similar to what Steve mentioned, the trick is to learn how to ignore input from one eye and refer only to the input coming from the other eye, then switch between them and do this every few seconds.