The Blind Spot

The Blind Spot

Written by  R. Bruce Thomas on Sunday, 22 March 2020 13:40

While doing research before a 2016 trip to Australia I discovered the wonderful writing style of Bill Bryson. Bryson's In a Sunburned Country was a terrific primer for touring Down Under (which was also the title the book had in the UK) and provided plenty of laughs throughout. I have since read a number of Bryson's other books and so was quite thrilled when I found his most recent tome, The Body - A Guide for Occupants, on the shelf at my local library. During my years in school I was more interested in physics and chemistry and never took any courses in biology. This head-to-toe tour of where I live was quite eye-opening.

And the chapter on the eye really struck a note with me.

Everyone knows that other motorists often have problems seeing motorcycles or judging their distance or approaching speed. For this reason alone it is imperative to do all you can to be visible by adding extra lights to your bike, wearing bright colored gear, and constantly adjusting your lane position to avoid blending in to the traffic behind you.

We also should all know to avoid riding in the blind spot of other traffic. This takes an awareness of the other vehicles around you and the inherent differences between a sedan and a semi-truck with regards to what they can see.

Did you know you also have a blind spot?

As a matter of fact, all humans have a blind spot

The makeup of the human eye means that it can only focus on the central two to three degrees of your field of vision. This is about equivalent to the size of your thumbnail at arms length. The rest of your vision is peripheral vision - there, but not in focus. The blind spot comes into play due to the optic nerve going out the back of your eye. Your brain will fill in this spot with other information to prevent you from having a hole in your vision.

Bryson detailed a method to find this built-in blind spot. Close your left eye and focus on a spot in front of you with your right eye. Hold your right arm out in front of you, palm up, with one finger pointing upright. Now, while staring at the spot in front of you, slowly move your arm outwards. At a point about 10-15 degrees from straight forward your finger will disappear. I can still see the tip of my finger but, if I put my thumb up and do this, my entire thumb disappears.

What I see is whatever is in the area close to my finger. My brain fills in the optic nerve location with background info.

There are various web sites with versions of this test. One (Google "Lasik Nevada blind spot" to find their "3 fun tests") even demonstrates how the eye substitutes nearby info to turn a yellow dot into a red dot (test 3). Cool and slightly scary at the same time.

A motorcycle, at distance, isn't much different in size than your thumbnail on your outstretched arm. Remember the built-in blind spot and be prepared the next time you're out riding for people to not see you. And maybe know why they don't.

Ride responsibly and be wary of the blind spot.

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