Using the cell-phone while on the move is riskier than most people realise.

Distracted driving has gained much attention because of the inflated crash risk posed by drivers using cell-phones to talk and text. But there are other kinds of problems caused by lower-stakes multitasking like distracted walking, which combines a pedestrian, an electronic device and an unseen step, the pole of a stop sign, a toy left on the living room floor or a parked (or moving) car.

The era of the mobile gadget is making mobility that much more perilous, particularly on crowded streets where too many multi-taskers jostle for road surface on foot or wheels while immersed in the beat of their own devices like cell-phones and MP3/video players. But cell-phone is by far the most dangerous because it requires active participation from its users. Texting (and Twittering) is increasingly popular and newer devices like the iPhone have thousands of new, engaging applications to preoccupy phone users.

Most times, the mishaps for a distracted walker are minor, like the lightly dinged head or a jammed digit or a sprained ankle, and a nasty case of hurt pride. Of course, the injuries can sometimes be serious — and these are on the rise. According to a study conducted by Ohio State University (the first study to tabulate such accidents), slightly more than 1,000 pedestrians visited emergency rooms in 2008 because they got distracted and tripped, fell or ran into something while using a cell-phone to talk or text. That was twice the number from 2007, which had nearly doubled from 2006.

The actual number of mishaps is probably much, much higher considering that most of the injuries are not severe enough to require a hospital visit, thus going unreported. Examples of those that are reported include a 16-year-old boy who walked into a telephone pole while texting and suffered a concussion; a 28-year-old man who tripped and fractured a finger on the hand gripping his cell-phone; and a 68-year-old man who fell off the porch while talking on a cell-phone, spraining a thumb and an ankle and causing dizziness. About half were by people under 30, and a quarter were 16 to 20 years old. But more than a quarter of those injured were 41 to 60 years old.

Pedestrians, like drivers, have long been distracted by myriad tasks, like snacking or reading on the go. But the constant interaction with electronic devices has made single-tasking seem boring or even unproductive. Cognitive psychologists, neurologists and other researchers are beginning to study the impact of constant multitasking, whether behind a desk or the wheel or on foot. It might stand to reason that someone looking at a phone to read a message would misstep, but the researchers are finding that just talking on a phone takes its own considerable toll on cognition and awareness.

Walking and chewing are repetitive, well-practiced tasks that become automatic. They don’t compete for resources like texting and walking. …  the cell-phone gives people a constant opportunity to pursue goals that feel more important than walking down the street. … An animal would never walk into a pole, survival instincts would trump other priorities.

Sometimes, pedestrians using their phones do not notice objects or people that are right in front of them — even a clown riding a unicycle. That was the finding of a recent study published in the journal Applied Cognitive Psychology [abstract and full text PDF]. One of the researchers dressed as a clown and unicycled around a central square on campus. About half the people walking past by themselves said they had seen the clown, and the number was slightly higher for people walking in pairs. But only 25 percent of people talking on a cell-phone said they had.

The term commonly applied to such preoccupation is “inattention blindness,” meaning a person can be looking at an object but fail to register it or process what it is. As people walking in pairs were more than twice as likely to see the clown as were people talking on a cell-phone, it suggests that the act of simply having a conversation is not the cause of inattention blindness.

It’s possible that a cell-phone conversation taxes not just auditory resources in the brain but also visual functions, causing the listener to create visual imagery related to the conversation in a way that overrides or obscures the processing of real images. By comparison, walking and chewing gum (that age-old measure of pedestrian skill at multitasking) is a snap.