One of the core principles of scientific skepticism is that human perception, information processing, and memory, while powerful, are deeply flawed. We need rigorous controls in observation and analysis in order to compensate for these flaws and arrive at reliable conclusions. Otherwise we are slaves to the vagaries of our own neurological function.

One of the coolest and most dramatic examples of our flawed perception is the phenomenon known as inattentional blindness. Before I go any further, for any of you who have not seen the basketball demonstration, take a look at it now before you continue reading. See if you can count how many times the players in the white shirt pass the ball around. This is more tricky than it seems.

Cool, eh. Most people do not see the gorilla. I have shown this video several times at lectures, and only about 20-30% of people typically see the gorilla. Those who did not see it often insist that it was not there the first time – it is simply difficult to believe that they could have missed something so blatant. But they did. I missed it the first time I viewed the video.

The concept is actually quite simple – in order to focus our attention on one thing we filter out distracting information. We are therefore blind to the distracting information, blind due entirely to lack of attention to it, hence inattentional blindness. The more we focus on one thing, the greater this effect is.

A recent study by Ira Hyman et al asked whether or not the increased risk of accidents from talking on cell phones while driving is due to inattentional blindness. It has been well established that talking on a cell phone while driving is distracting and comes with an increased risk of accidents. This has led to hands-free laws in some states, but the evidence also suggests that this does not help. The problem does not derive from using a hand to hold the phone, but the diversion of attention to the conversation. Meanwhile, the same risk is not present from talking to a passenger in the car.

Hyman designed a pair of studies where he had subjects walk across a certain path without distraction, while listening to an iPod, while talking on a cell phone, and while walking and talking with another person. He found in the first study that people talking on a cell phone walked more slowly, and had to make more course corrections than the other groups.

In the second study he place a unicycling clown (yes – the one in the picture above) along the path, in a location that should have been clearly visible. He found:

Only 25% of the cell phone users had noticed the clown and many turned around at that point to see what they had missed. In essence, 75% of the cell phone users experienced inattentional blindness to the unicycling clown. In contrast, over half of the people in the other conditions reported seeing the clown (51% of single individuals, 61% of music player users, and 71% of people in pairs).

So talking on a cell phone cut in half the probability of seeing the clown. Listening on a music player had a slightly increased chance of seeing the clown. Either this is statistical noise, and there was no real effect, or alternatively listening to music may make us slightly more attentive. (Sounds like a question for further research.) Walking with a buddy resulted in almost exactly what we would predict from adding the individual chances of seeing the clown independently.

What this all might mean is that there is something about talking on a cell phone that is particularly demanding of our attention – more so than listening to music or talking with someone who is physically present. These results also support the hypothesis that talking with a passenger is not as dangerous because the extra pair of eyes increases the chance that someone will notice a sudden obstacle or unexpected traffic pattern.

To be clear, while this study supports prior research showing that talking on a cell phone while driving is dangerous, the study was not designed to measure the danger of talking on a cell phone, but rather why is talking on a cell phone dangerous. Their answer is that it is probably due, at least in part, to inattentional blindness.

But I do think this study reinforces the other lines of evidence showing that this behavior is risky. I would also like to see that same kind of research but looking at texting, which I suspect will be far worse than talking on a cell phone. But texting might involve more of diverting your gaze to the keyboard rather than consuming attention, but it may also involve both.

And the take home message should be crystal clear – don’t text, talk on cell phones, or engage in otherwise demanding or diverting activities while driving. But listening to music is OK, maybe even slightly helpful.

These studies and studies like them also demonstrate for me a broad principle – the more we understand how our own brains work, given that they are the most important tool we have, the better we will be able to use them.