My last blog was about other drivers not seeing bikers. While that is definitely an issue, there is also something to be said about what we, the bikers, don’t see. Most people are surprised at what they don’t see. Our visual field is not created or maintained in our eyeballs. It’s actually in our brains. Our eyes are the major contributing organ to the information in the visual field, but they are not the only source, and they don’t record images unfailingly like a camera. A lot of image processing is done at the retina.
One would intuitively suppose that if there were a blind spot on the back of your eye, you would see a blank spot when you looked out at the world. In truth there is a blind spot where the optic nerve attaches. Yet we are unaware of the blank spot in our visual field unless we make a specific effort to recognize it. For a quick test, find a spot on the wall. Close one eye and focus on the spot with the open eye. Now hold your extended arm with thumb up and covering the spot you selected. Now, keeping your eye fixed on the spot on the wall, slowly move your arm to the side at the same level. Somewhere around 20° you’ll notice that you can no longer see your thumb. You’re not overtly aware of the blind spot in your field of view, but you won’t see anything that’s in it.
A lot of what we “see” is built upon our experience and expectation. Most people have had the experience of looking at something, but being unable to figure out what it is. Suddenly you recognize it and it becomes clear. I’ve had this happen to me while deer hunting. A place I’ve been watching will catch my attention. I’ll stare, but not see anything for a minute. Then the deer moves and suddenly I see it plainly. Even after it stops moving I can still see it, because I know it’s there. My eyes are not collecting any additional information. Everything I’m seeing now was there a second ago, but now that I know what I’m looking at I can see it.
One way this plays into operation of a motorcycle is in the head check. All good riders know that mirrors can’t tell you yes, only no. Before you change lanes you must do a head check, or turn your head and look to see that the lane is clear. Unfortunately human physiology often shows us what we expect, so if we’re looking to see an empty lane that may be exactly what we see whether it’s really empty or not. It may sound like semantics, but it’s a good habit to start looking to see where the car is. It’s the same physical movement, but a different mindset that may well have a different result.
Also move your eyes around as you look. Remember the disappearing thumb? As you look back over your right shoulder that thing in the middle of your face that the sunglasses sit on is probably blocking your left eye. That means you’re only looking with your right eye. A car coming up fast from 30 or 40 yards back doesn’t take up much more room on your retina than your thumb did at arm’s length. If it happens to be about 20° off the vertical on the horizontal plane in your visual field, you’re going to see exactly what you saw with the thumb experiment. The cage operator will be telling the police. “He just pulled right in front of me like he didn’t even see me.” And your biking friends will probably be sitting around convinced that a careless cager just wasn’t paying attention and ran over you.
— Guy Wheatley