Listeners were asked to perform two tasks: The first was to keep a mouse cursor on a dot that was moving around a computer screen—which requires constant monitoring. The other was to hold four letters in memory and hit a button any time one of the letters popped up on the screen and refrain from hitting that button when another letter popped up. These tasks required monitoring and decision making. “Both demand a great deal of attention, but in very different ways,” says Emberson. “We wanted to know if there was an attentional effect for the different types of speech.”

The distraction of the conversations caused an effect, the researchers reported in the journal Psychological Science.

Would any blast of random noise derail us? To make sure the effect was specifically caused by understandable speech, Emberson filtered the halfalogue so that it was garbled. She says it sounded like someone talking underwater. You could tell it was speech, but you couldn’t make out the content. In that case, the distracting effects went away. When the halfalogue speech was incomprehensible, people didn’t screw up the task.

When people performed the letter-matching task, Emberson found that people did worse when they were hearing a halfalogue compared with a dialogue or a monologue, which may suggest that we’re more distracted by halfalogues generally. Emberson interprets the findings to mean that “there’s a cost when you can’t predict the succession of speech.”

Liberman generally agrees with the theory that halfalogues are more distracting than dialogues or monologues: “It’s extremely well-established, something that Emberson and company have assumed; when you’re getting lower-quality information coming in, you’re having to work harder to understand and reconstruct it.” Liberman is more cautious about whether the increased cognitive load from unpredictable content is solely responsible for the decrease in performance on the attention tasks.