Sunday 20 October 2019

The bizarre way your brain works to compensate for your glitchy eyes

Twitter thread from a software engineer explains how this vital organ helps us see the world.

The brain regards having a silent dialogue with ourselves as similar to talking to other people (Baramee2554/Getty Images)
The brain regards having a silent dialogue with ourselves as similar to talking to other people (Baramee2554/Getty Images)

By Nilima Marshall, Press Association

Our brains play tricks on us all the time – from creating false memories to filling in missing pieces of information – but there is also something else that they are good at.

And it involves solving a messy problem created by our eyes.

As software engineer @foone points in an illuminating Twitter thread, our eyes continuously make small rapid jerky movements as the brain jumps from fixation on one point to another. The phenomena is known as saccades.

There are instances where saccades become more noticeable, for example, when you observe someone reading or looking out of the window of a moving train.


In theory, these jerky eye movements should make our surroundings look blurred and unfocused, but luckily the brain comes to our rescue.

As foone explains, our brain puts visual input on “a pause” as it processes the information.

He writes: “You’re not seeing blackness or even nothing, you’re just not seeing period.


“Then when you finish your saccade, it shows you what you now see at the new position and then it pretends it can time travel.”

As the eyes move around, they locate interesting parts of the scene to build up a mental, three-dimensional “map” corresponding to the scene.

To reconstruct the scene in a way that makes logical sense, the brain “time-shifts it [the scene] backwards so that it seems like you were seeing it the whole time your eyes were moving”, according to foone, making the visual look completely seamless.

A commonly-used example where effect is observed as the stopped-clock illusion, where for a moment, the second hand of an analog clock appears to stay still for longer than normal when looking at it for the first time.

However, the saccadic movement isn’t the only eye-related complication the brain has to solve.

We also have blind spots, ie, areas where we have no vision at all.

Anatomically, it is the point of entry of the optic nerve on the retina that is insensitive to light because the nerve fibres are in front it.

In humans, the blind spot is located about 12–15 degrees temporally and 1.5 degrees below the horizontal.

The area covered is roughly 7.5 degrees high and 5.5 degrees wide.

Foone’s screenshot from Wikipedia is one of the popular blind-spot tests.


However, there are organisms that defy the evolutionary trend.

Octopuses, for example, have their nerve fibres behind the retina instead of the front, which do not block light or disrupt the retina.


And even if their eyes get damaged, these cephalopods can grow them back – because they have the ability to turn their “regeneration genes” back on.

While we may never have octopus-like eyes, we certainly have an incredible brain to compensate for it.

However, foone adds that if you want an accurate representation of what the what things look like, using your camera might be a better way to do it.


For those looking for a more detailed explanation, here’s a handy TED-Ed video that might help.

PA Media

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