A concept of human perception called Perceptual Load Theory says that we only have so much attention to give. Once the world gets too complex, our brains start to switch off. And unfortunately for commuters everywhere, something as simple as driving with the radio on is enough to make your brain switch off to the point where you're driving dangerously.
A 2015 study from the University College Cork’s Gillian Murphy, presented last week in Nottingham, England, tested whether traffic reports could distract drivers from driving. Murphy put 36 participants in a full-sized driving simulator, and gave them a task to concentrate on while driving. Half were given a simple task—to listen for when the voice on the radio changed gender. The other half were given a complex task—to listen out for a mention of a specific road.
During one test test, a "large, unexpected visual stimulus" passed by at the side of the road. While 71% of those performing a simple task noticed this stimulus, only 23% of the drivers concentrating on a complex task saw it. And this wasn’t some easy-to-miss object. The "large, unexpected visual stimulus" was a gorilla, or an elephant.
"Road safety campaigns are so focused on telling us to keep our eyes on the road, and this is certainly important," says Murphy, in a press release about the findings. "But this research tells us that it’s simply not enough. We should focus on keeping our brains on the road."
By using a traffic report in the tests, the study shows how even everyday "background" noise can be a distraction. You might note at this point that wearing headphones while riding a bike is illegal in many places, and considered dangerous by pretty much everyone except the cyclists doing it, and yet listening to the radio in the car is considered safe. And we can switch our attention away from the radio if we really need to (if we actually managed to notice that gorilla on the sidewalk, for instance). Hands-free phone conversations are a lot harder to ignore, and yet the law doesn't consider them dangerous.
And it’s not just gorillas and elephants. The study says that "the results showed that perceptual load dramatically affected driver awareness for visual and auditory stimuli, even those that were driving-relevant and safety critical (e.g., pedestrians or the sound of a car horn)."
If listening to drive-time can make drivers miss car horns, and even pedestrians, then it might be as dangerous as driving home after a few beers.
"Anything that draws our attention away from driving can be problematic," says Murphy. "That doesn’t mean that we should ban radios in cars, but that we should all be aware of the limits of our attention."