American Scientist

There’s something about overhearing someone talk on a cell phone in public that’s profoundly annoying. But what?

Lauren L. Emberson, a Ph.D. candidate at Cornell University, and her colleagues formed a hypothesis based on the known effects of predictability on human behavior. Human speech is relatively predictable when listening to dialogue or monologue, but when we can hear only half a dialogue, what the investigators call a “halfalogue,” we have much less information about what may be coming. How might this distraction affect the ability to perform tasks of different types?

The team assembled 24 volunteer undergraduates, a cadre almost certain to be comfortable with cell phones, and tested their performance on two tasks while they were exposed to silence and recorded monologues, dialogues and halfalogues.

The first task was mainly visual: The subjects attempted to track a moving dot on a computer screen using a mouse. Emberson and colleagues consider this to be analogous to the vigilance required to stay within a traffic lane. While listening to halfalogue, the tracking error exhibited by the students increased by a mean of 2.74 pixels (about six times) over what it had been during the silence prior to halfalogue. Dialogue or monologue had no such effect.

The second test recorded the recall of four target letters from short term memory—an activity with a linguistic element. “Interestingly, accuracy was reduced about 10 percent by halfalogue, but it did not affect reaction time,” says Emberson. Nor did adding the linguistic element change the outcome.

Finally, to help confirm that the information content of halfalogue was the culprit, they readministered the same tests to 17 additional participants but rendered the words unintelligible while preserving the acoustics of the speech. The negative effects disappeared.

It is well established that driving while talking on a cell phone impairs performance, but this is the first time that listening to passengers talk has been implicated. “The effect turns out to be broad, rather than specific,” Emberson says, making the results all the more compelling.