You don't need science to tell you overhearing a cellphone conversation can be annoying and distracting, but a new study may explain why.

Overhearing only half of the conversation — such as eavesdropping on a phone conversation — grabs more attention from bystanders than listening to an exchange between two people, researchers at the University of San Diego found.

COMING UP Veronica Galvan talks to Quirks & Quarks on March 16 at noon on CBC Radio One.

The study, published in the science journal PLoS ONE this month, found bystanders can better recall the content of cellphone conversations that they overhear than that of live conversations where they can hear both sides. They are also better at remembering words used in overheard cellphone conversations.

"There is a period of silence in the cellphone conversation … and the brain wants to understand, 'Why is that person saying that and what context is there for this conversation?'" Veronica Galvan, assistant professor of psychology at the University of San Diego, told CBC Radio's Quirks and Quarks in an interview that airs Saturday.

She also said the study is the first to show that cellphone conversations have an effect on bystanders' memory and attention.

Galvan said the findings are consistent with previous research, which suggest 82 per cent of people are annoyed by others' cellphone use in public.

To test cellphone conversations' effect on bystanders' memory and attention, researchers recruited 164 undergraduate students to complete a series of word scramble games while being subjected to one of two conditions. During the task, half of the students listened to a scripted exchange between two people planted by the researchers in the same room. The other half overheard cellphone conversations, which meant they could only hear one side of the chat.

Despite reports of annoyance with the latter situation, Galvan said that she was surprised that both groups had similar scores on the word scramble test.

"What we think is going on is that cellphone conversations might not interrupt all kinds of tasks. It probably interferes with particular kinds of tasks," she said.

"What we are trying to do now is try to understand the nature of what particular kinds of tasks would be susceptible."