One Eye at a Time


Even as we look at the world through both eyes, our brains can tell which eye is taking in what information – and can direct each eye separately to focus on certain details, says a new study.

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The more one of our eyes is focused on details in its visual field, the more sensitive it is to changes in the area it sees, and the faster it is to detect changes in that area. These abilities can allow both eyes to work together, or the brain can focus just one eye’s energy on detecting details and changes – even if both eyes are open.

The human visual pathway can perform some pretty incredible tricks – after all, its role is to convert energy waves from the external world into multicolored, moving three-dimensional images. Scientists have been studying binocular vision for decades, and have learned that the visual cortex integrates information from both eyes, and makes selections as to eye dominance – which eye’s viewpoint we see – for various spots in our visual field.

But now, as the journal Psychological Science reports, a team led by the University of Minnesota’s Peng Zhang have found that each eye’s visual pathway seems to have its own somewhat discrete regulatory system. The team selected six volunteers, and had them look into a special stereoscope-like device that shows separate images to each eye.

For the first experiment, the researchers showed their volunteers a “cue” – an small shape that changed color, form, or size – in one of their eyes, and a “noise” pattern in the other. They then had a “target” – a small spot of color – gradually appear to one eye:

Participants had to press a button when [the cue] turned, say, red or fat and gray. At the same time, they had to press as soon as they saw any part of the target appear. The viewers took less time to notice the emerging target when it was in the same eye as the cue.

In other words, people are able to “tune in” to small changes from just one eye’s visual field – even when they’re simultaneously being distracted by stimuli in the other eye’s field.

A second experiment tested this ability in a different way:

Two cues were displayed at once and participants had to attend to both or to two “features” at once—indicating for instance when both were red or both red and thick. … Again, the target appeared even faster when the cues were in the target eye and even slower when they were in the noise eye.

In short, whichever eye is tuned in to the cue stimulus is more likely to perceive changes – and to perceive them more quickly than an eye that wasn’t watching a cue.

This suggests that, although our brains are adept at integrating information from both our eyes into a single image, each of our eyes may also be involved in its own individual feedback loop with the visual cortex. It just goes to show that our brains are constantly up to all kinds of tricks that never even enter our conscious awareness.

It’s enough to make you want to sleep with one eye open.

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