Yet you do not see?

Inattentional blindness at

How much do we truly see?

“You see, her eyes are open.”
Ay, but their sense is shut,”  William Shakespeare, Macbeth

In 1999 Daniel Simons shot a video clip in which the viewer became part of a psychological experiment. The video went on to be a hit and the experiment became one of the most famous psychological experiments ever. As such there is a good chance that you have already seen it. Below is an updated video that caters for those who saw and did not see the original, please watch it before continuing with the article. You have a 50/50 chance of your mind being blown!

Did it work for you? What is going on?

We tend to think of our mind passively watching what our eyes show us, but there is growing evidence that the brain constantly interprets and changes what we see. The Invisible Gorilla experiment in the video is an example of Inattentional  Blindness. Just like we can focus on one conversation in a loud room and blot out the competing noises, so too can we fail to see something as seemingly obvious as a man in a gorilla costume when we’re concentrating. Subsequent studies have tracked the eye movements of the viewers and found that some people failed to see the gorilla even when they were staring straight at it! When the brain is under a higher cognitive load caused by concentration, it can block out extraneous information, like the “invisible” gorilla.

Inattentional Blindness is not the only way our mind can be tricked, however. Below is another video by Daniel Simons that illustrates the concept of Change Blindness.

You may have seen this on hidden camera shows, where sometimes even the gender of the person can change without the subject noticing! The brain takes shortcuts with vision and concentrates on what it views as important information about the scene you are viewing. If the scene makes sense then “minor” details like the person you are talking to changing into someone else may go unnoticed.

Brain scans suggest that the brain may go even further. There is evidence to suggest that the brain actually constructs the scene it expects you to see before you even see it! When you enter your home for example, your brain saves energy by predicting what you’ll see rather than processing the scene entirely anew. If something is out of place or somehow does not fit the mental image you subconsciously have then your visual cortex becomes more active to process what you are seeing. When you are in a familiar place you have no way of knowing how much you see is what you actually see and how much is filled in by your mind!

“[This] might explain why sometimes you don’t notice something different in a familiar environment because your brain is seeing what it expects to see, rather than what is actually there.” Dr. Lars Muckli, University of Glasgow

Although unsettling, these instances of Mental Blindness should not come as a surprise. We have long know that the brain fills in the blanks for our vision when it comes to our blind spot, for example. Rather having a scary dark blob we seem to have uninterrupted vision that has the added benefit of amusing visual tricks like making a sausage from our fingers!

How much of what you see is real?Click To Tweet

However, did you know that you also spend a proportion of your time physically blind? Although the human eye can smoothly track a moving object, most of the time we move our eyes in a series of small jumps known as saccades. These saccades can last up to one tenth of a second so to avoid becoming dizzy our minds turn off the visual input until the movement is complete. As our eyes move a lot we can imagine our vision as a series of snapshots stitched together to make for a video representation of what we see. Again, the brain fills in the scene for the parts when we are blind to avoid a flickering sensation.

In general our vision works perfectly well or at least well enough for us to function in the world. The brain can only process so much information at a time and when it struggles the consequences are generally no worse than a minor nuisance or maybe it can be highly entertaining. Magicians exploit this failing for their stupefying illusions, for example.  Also, Optical Illusions have long played tricks at the limits of our vision. However there can be disastrous consequences to our imperfect visual processing as well. We can literally not see something right in front of us when we are concentrating on something else, so never use a phone while driving!

Have you ever experienced not seeing something that’s right in front of you? Let us know about it in the comments below!

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Image by Lucie Kout

  1. Jenny 19th October 2015
    • Dermot Barry 20th October 2015

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