Perception isn't as straightforward as it seems

This morning's newscasts have been highlighting the third serious vehicle-pedestrian accident in East Vancouver in the past five days.

It reminded me of how difficult it can be to see something when we least expect it to enter our field of vision.

Last year, I had the privilege of interviewing UBC psychology and computing science professor Ron Rensink, who is an expert in "change blindness".

He told me tales of people who were completely sober driving straight into a train because they didn't see it.

“Even if you know there is going to be a change at some point, you still can’t see it unless you’re attending to it at the time it changes,” Rensink said at the time.

The most famous demonstration of change blindness occurred in a study by U.S. cognitive psychologists Christopher Chabris and Daniel Simons.

Watch this video and count how many times the basketball passes between the players.


Count how many times the ball passes between players.

In their remarkable 2010 book, The Invisible Gorilla: And Other Ways Our Intitutions Deceive Us, Chabris and Simons reported that about half the people who've watched the video do not see a person in a gorilla suit walking through the basketball players. That's because these viewers were so focused on counting the number of passes.

Chabris and Simons won the Ig Nobel Prize for psychology in 2004 for "demonstrating that when people pay close attention to something, it's all too easy to overlook anything else—even a woman in a gorilla suit".

The lesson for drivers is to expect the unexpected. Watch for it. And even if it appears, you still might not see it if you're focusing your attention somewhere else.

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