Very interesting. I believe there is a greater need for hearing on a bike than in a car and often do not see people using their other senses (sight) when they give up hearing. Other cyclists and runners who are listening to music consistently do not hear any warnings given, those who are not will hear me for the most part.
cool story. i sometimes put earbuds in to reduce the wind chatter off my lobes. counterintuitive.
I'll listen to an iPod, with both earbuds, while road running, and during the rare times when I do rail-trail riding by myself, but never while road cycling. Having cars passing from behind and not being able to hear them coming would scare the crap out of me. It seems like if you wanted to listen to an iPod while road riding, you'd have to have the music cranked in order to drown out the wind blasting. It just seems unsafe, even if you ride with mirrors.
I don't use buds, I like the sound of the wind in my ears... but after 8 hrs that can get annoying. I've also read that reducing the sound of the wind in your ears can improve your power output. (It was in Bicycling mag about a year or so ago, not sure if I buy it though...)
Anyway, a while back there was a company called OneEarBud that was following me on twitter. They made single bud headphones (as if you couldn't guess that from the name) that were supposedly high quality and designed for cycling.
That always seemed like a good compromise to me. Although I'm not sure if they are still around.
The fact that cars are essentially sound-proof...well, that doesn't surprise me. That's why car horns are designed to be loud. I remember seeing an ad for Acura or some other luxury brand boasting that their vehicles are the most sound-proof on the market. I guess some drivers want to be disconnected from what's going on in the road around them, and I guess that's why they make air horns for bikes.
I've never tried the one ear bud thing before, but it seems like it would be really annoying only having one channel. I remember at CtC a few years ago I rode with someone who had a small set of speakers taped to their handlebars, which where connected to an iPod. Something like that seems like a good compromise.
This reminds me of those high-end car commercials that actually make a big deal about how much road and traffic noise their cars eliminate. They're eliminating information.
Due to being fed up with the free noise provided by local stations (for the car), and ill-fitting earbuds that fall out of my ears (for road running), I spend all of my time on the roads in relative silence. I can't imagine riding with music in my ears, I definitely use my ears for information more than when I drive.
I def. agree with Orionz, listening is wicked important for cyclists, and less so for motor vehicles - but is that just because drivers are used to not being able to or can't hear? Would the ability to hear what's going on make people better drivers?
It'd be a neat problem to eliminate road noise that held no useful traffic or vehicular information from the cab of a motor vehicle, but leave in all the information. Dude, that would be an awesome filtering project. Hmm...
Having driven a convertible, no, extra noise does not help. Having 3 mirrors properly adjusted to see everything around you is where the advantage lies, for those who choose to use them. On a bike there are no mirrors, enter hearing.
The whole experiment is flawed. Bikers were completely expected noise while in real life your brain is tuned to music and it filters out other noises. It's the same phenomenon as drivers don't see cyclists.
I had a lot bad experience with runners and bikers on trails with ear buds. And I conducted experiments of my own. Bells, "on your left" pretty much useless. But if you record sound of car accident and play it at 85-90dB (at my bike, I don't know what level was at a person location) then people just jump. It worked but it could give a heart attack so I don't do it anymore.
edit: errors
Yeah, I was going to say what Mikhail said - anyone who has ever ridden on a trail has seen empirical evidence that this "research" is pretty suspect.
Vindication!
I've posted before and I know I'm in the minority, but for those who "don't get it" about being able to hear what's going on around you while also listening to music...I feel vindicated. Key to note is "played at a reasonable volume". Also, you can zone out while running/biking with or without music. Particularly on trails I think there is just a zoning out factor. When riding in traffic with music I'm perfectly able to hear the same noises around/behind me as I would otherwise plus I use my eyes *gasp* to help too. Believe it or not, just because I'm listening to music my other senses are not numbed.
that listening to headphones removes less sound than being inside a car does is not terribly surprising, i guess. doesn't meant it's safe to do it, though.
personally, i just sing to myself while riding. i know an awful lot of songs, so why not? today's commute featured "good times roll" from the cars, and a few selected songs from sonic youth's album "dirty" (because i saw a girl wearing a shirt with that album cover on it).
...I just don't ride with ear phones and won't...unless new research comes out that says that it improves my awareness on a bike! 
When I'm in a car, I use the mirrors to detect what is coming up behind me. On my bike, I use my ears - so I need to hear way better than a cager in a metal cage.
I have a cell phone holster on the strap of my messenger bag. I play music over my phone's speaker so I can hear it, but it doesn't really block out much in the way of other road sounds. Sometimes I'll put it on my camelback for road rides.
Aside from safety, I love the combination of disconnection from everything and immersion in the moment and my own thoughts that I get when riding, it's one of the aspects I enjoy the most. Why would I F that up with earbuds?
When I learned to drive a car, I learned with a 3 speed manual on the steering wheel and no tachometer. It didn't even occur to me to turn on the radio for 6 months. Many hours and years of motorcycle riding, same thing, matching the revs to the gears and the road by ear, that's music, never even missed a radio. Just me.
I'm a musician (crappy and amateurish, sure). I love the sounds I hear on the street!
(With the the possible exception of the jail trail.)
I've become a much better listener and musician (but still crappy and amateurish, of course) just by considering the phrase "music as wallpaper."
edmonds59 & I are cut from the same cloth: 3-on-the-tree, no radio, much time spent on a motorcycle and in cars with no (working) radio.
At home, my record collection is enormous, and almost daily I'm putting something on the turntable. Once in my head, I no longer need to have it piped into my ear, thus freeing my ears -- both of them -- for listening to what's going on around me when on the bike. The sound in my head automatically cuts off when something more pressing requires my attention. No fumbling for rheostats necessary.
oh, Stu and edmonds - you guys reminded me of the year dad, little bro, and I drove from Montreal to Vancouver in his mother's 72(ish) Ford (Something very green) eating nothing but poutine, twizzlers, and pepsi. No radio. No tape deck. No AC. I was 8, my little brother was 4.
We sang exactly 4 songs, non-stop:
1. Great Green Gobs of Ooey Gooey Gopher Guts (with numerous improvised disgusting verses added)
2. Theme song to Fist Full of Dollars
3. Theme song to For A Few Dollars More
4. Theme song to The Good, The Bad, and The Ugly. (the last three were really just me and bro wailing, whistling, grunting, and air-guitaring in a synchronized yet incoherent mess)
To this day I'm amazed my dad survived.
If grandma had ridden a bicycle instead, he would have just given it to the neighbor kid and we would have flown home.
Wow, that's painful just reading. Was dad just clueless to the existence of the very nice thing known as Via Rail?
Earbuds are like bathsalts and turn people into zombies!
The goal was to move the car and the people. I guess it seemed simplest to him to do it all together (he taught us song #1, perhaps in feeble self defense). As 8 and 4 year old, it was fun. Like I said, though, I'm not sure how he survived. It might have been the shock of his parents' passing that helped numb him to our incessant and noisy shenanigans.
Maybe your dad was wearing earbuds^H^H^H^Hplugs...
I just ride with earplugs. It takes the edge off of wind/road/traffic noise, but otherwise I can hear just fine.
