Pedestrians who talk on a mobile phone are slower, change direction more, have difficulty navigating -- and are less likely to notice obvious distractions like a unicycling clown, a study showed Tuesday.

Researchers observed 317 pedestrians as they crossed the main square of the campus of Western Washington University using the 375-foot-long (114-meter-long) main diagonal pathway.

The people observed were either talking on a mobile phone, listening to a personal music player, in conversation with another pedestrian, or walking alone, without any electronic devices.

The researchers noted the time it took them to cross the square, whether they stopped, zig-zagged or stumbled; how many times they changed direction, and whether they collided with another person, or nearly did.

The pedestrians were also monitored to see if they noticed the "unusual stimulus" the researchers had placed just off the walking path: a brightly-colored unicycling clown.

"Unicyclists are very rare on campus pathways," the authors of the study, which will be published in the December issue of Applied Cognitive Psychology, wrote.

Only 25 percent of people using their mobile phones noticed the clown, while more than half of people in the other groups noticed him.

Failure to see the clown could not be blamed on the use of an electronic device per se, because 61 percent of people using a music player saw the unicyclist, or on having a conversation, because chatting couples were the most likely -- 71 percent -- to see the clown, the study said.

Instead, the study suggested that mobile phone users fail to notice what is going on around them, a phenomenon called "inattentional blindness."

"This means that they may miss more than the unicycling clown and experience difficulty recognizing and using information needed to navigate through a complex and changing environment," which might not be overly dangerous when walking in a pedestrian zone but can be when bikes or cars are introduced into the equation, or the mobile phone user is driving.