That's what researchers from the University of Houston and the Texas A&M Transportation Institute wanted to find out. In a new study (funded in part by the Toyota Class Action Settlement Safety Research and Education program), they observed how drivers coped when distracted by absentminded thoughts, emotions, and text messages.
The authors noted that while many studies have explored the dangers of texting and driving, there's less research on how other kinds of stressors can affect your behavior at the wheel. But their results indicate that the worst kind of distraction may indeed be checking your phone.
The researchers found that people who drove while absentminded or emotional benefitted from a "sixth sense" instinct that helped them navigate safely. Meanwhile those who were texting while driving did not experience the same protection.
For the study, 59 drivers navigated a simulated stretch of highway four times: once under "normal conditions," once while they were asked cognitively challenging questions (think math problems), once while they were asked emotionally charged questions, and once while they were distracted by texts. Each time the researchers measured the sweat under the drivers' noses (an indicator of their stress level), how jittery their steering became, and whether or not they drifted out of their lane.
The three types of distractions all increased the drivers' perinasal perspiration levels, and caused them to be more jittery. But when the drivers were asked cognitively challenging and emotionally stirring questions, they were able to maintain a straight course; while texting led them to veer out of their lane.
Lead researchers Ioannis Pavlidis, PhD, and Robert Wunderlich speculate that the driver's trajectories remained straight under cognitive and emotional stress thanks to the intervention of a part of the brain called the anterior cingulate cortex (ACC), which provides a "fight or flight" reflex. "For sure, there is corrective action precipitated from some brain center, likely the ACC, when we are distracted while performing a routine dexterous task, driving in this case," Pavlidis says. "When this distraction is purely mental, this corrective mechanism works well."
But to do its job, your ACC requires eye-hand coordination: "It appears that an eye-hand feedback loop is needed for the brain to be able to accomplish these corrections," Wunderlich explains. And that feedback loop is disrupted when you look at your phone.
"When there is a physical distraction, either all by itself or in addition to mental distraction, then this corrective mechanism breaks down," Pavlidis explains. "The reason is that the corrective function depends on all the physical resources, eyes and hands in this case, to keep executing its 'auto-pilot' function."
All of this goes to show that reading and responding to messages on the road is every bit as dangerous as you thought -- and maybe more.
This article originally appeared on Health.com