Psychological Science has a brilliantly conceived study that explains why overhearing someone talk on a mobile phone is so much more annoying than simply overhearing two people in conversation.
It turns out that a one-sided conversation (brilliantly named a ‘half-a-logue’) draws in more of our mental resources because the information is less predictable – like being fed a series of verbal cliff-hangers.
Overheard Cell-Phone Conversations: When Less Speech Is More Distracting.
Psychol Sci. 2010 Sep 3. [Epub ahead of print]
Emberson LL, Lupyan G, Goldstein MH, Spivey MJ.
Why are people more irritated by nearby cell-phone conversations than by conversations between two people who are physically present? Overhearing someone on a cell phone means hearing only half of a conversation-a “halfalogue.” We show that merely overhearing a halfalogue results in decreased performance on cognitive tasks designed to reflect the attentional demands of daily activities. By contrast, overhearing both sides of a cell-phone conversation or a monologue does not result in decreased performance. This may be because the content of a halfalogue is less predictable than both sides of a conversation. In a second experiment, we controlled for differences in acoustic factors between these types of overheard speech, establishing that it is the unpredictable informational content of halfalogues that results in distraction. Thus, we provide a cognitive explanation for why overheard cell-phone conversations are especially irritating: Less-predictable speech results in more distraction for a listener engaged in other tasks.
Link to PubMed entry for study.
Mind Hacks 
As I read this post, I was immediately reminded of a scene from Curb Your Enthusiasm, where Larry David decides to demonstrate the annoyance of overhearing one side of a conversation by talking to himself in a restaurant. The man on a mobile at the table next to him was not amused: http://www.youtube.com/watch?v=pI3I9NTHtAQ
I wonder if this could have applications for learning foreign languages. Attempting to predict the next utterance could be beneficial in reinforcing learnt material. Also, if a “half-a-logue” is so engaging, it could be useful for maintaining motivation.
So we should put our cell phone conversations on speaker when in public.
It makes sense, but I think people tend to talk louder on the phone, and even louder on cell phones (for some reason, even *louder* in elevators), which contributes.
Natural human curiosity causes me to try to guess what question or comment prompted the statements I overhear. So the thought process moves forward and backward and forward again, from the overheard response back to possible prompts for it, then forward again to the next overheard reply. This adds to the challenge of deciphering the overall topic of conversation. Having ADD and no filter to block unwanted audio distractions like this, these half-conversations are a bigger distraction to me than complete conversations which, depending on the voices and topic of conversation, can often blend into the white noise of everyday life.
If I’m in the company of friends and they speak on the cell phone – it does not bother me that I am listening to a ‘half-a-logue’, nor do I wonder what the unheard half of the conversation is about.
But strangers are another matter. I feel as though they have invaded my space and I just want them to shut-up! I am not interested in their half of the conversation – never mind the unheard half.
I use mine as little as possible, but admit that I am aware my voice is raised on the rare ocassion I do use it! Personally, I think this is because of all the noise around me – I can barely hear who I am speaking to, and I assume they can’t hear me either.
You might want to add the following commentary by LanguageLog to the main post, which points out some interesting methodological issues with this piece of work:
Link
I wonder if there’s not another explanation. When I hear someone talking nearby, but don’t hear someone immediately answer them, I wonder if they are talking to me for a brief second until I realize they’re on the phone. This is in contrast to the conversations I hear because I hear someone else answering, therefore I know it’s not me that they are speaking to. I couldn’t get access to the full article, so I couldn’t tell if they somehow controlled for this explanation.
Nothing new here; Andrew Monk studied and published this phenomenon back in 2004.
Click to access 517MonkCellPhone.pdf
This study is a little different from Monk’s 2004 study. Monk’s study investigated whether the half a logue’s were truly annoying and found they were. this study replicated the annoyance, but went on to hypothesize WHY it’s annoying…
and even if they were the same… it’s always good to replicate.
I’m curious from a cog psy and legal point of view the complexities that could be raised via our notions of confabulation.