Drivers beware! Research has shown how even legal amounts of alcohol can cause 'inattentional blindness' in drivers.

Research has shown that subjects who are mildly intoxicated (i.e. below the legal limit) are dangerously compromised in their ability to notice an unexpected visual object when they were focused on another simple taskⁱ. This phenomenon is known as 'inattentional blindness’ in which salient objects that appear in the visual field fail to be ‘seen’ when subjects are focused on another task. This has been demonstrated in other studies, but this is the first instance to show that these visual errors become even more likely under the influence of alcohol.

Subjects were given 10 minutes to consume beverages which, unbeknownst to them, either contained alcohol or did not. The subjects then watched a 25 second video clip that showed two teams of three people playing with a ball. They were instructed to count the ball passes. Part way through the video clip, an individual dressed in a gorilla suit appeared on the screen, walked directly through the players, beat its chest and then walked away. Subjects who were mildly intoxicated were twice as likely to miss seeing the gorilla, even though it had screen time of over a third of the video. Just 18 percent of the drinkers said they noticed the gorilla compared to 46 percent of the sober subjects.

Although the research did not directly test driving aptitude, the implications for driving could be serious. "Driving requires our full attentionⁱⁱ…We rely on our ability to perceive a multitude of information when we drive (speed limit, road signs, other cars, etc.) If even a mild dose of alcohol compromises our ability to take in some of this information, in other words, limits our attention span, then it seems likely that our driving ability may also be compromised," says study lead author Dr. Seema Clifasefi of the University of Washington.

"Say you have been at a party and are driving home after having a couple of drinks. You don't want to be stopped for speeding, so you keep eyeing the speedometer. Our research shows that you will miss other things going on around you, perhaps even a pedestrian trying to cross the street."