Watch that hybrid! Can sound help us spot objects?

ResearchBlogging.orgRecently we took our hybrid car into the shop for its annual emissions test. In our state, the test is conducted while the car is idling. A hybrid doesn't actually idle -- it shuts the engine off completely. So our car's emissions were tested at 0 RPM. It may be time to rethink our state's emissions laws.

There's another law that might need rethinking in the age of hybrids. Our car's internal combustion engine often doesn't start up even when the car is moving at low speeds -- it uses electric motors, running nearly silently. This can potentially be dangerous for pedestrians in parking lots and crosswalks: if they can't hear us, they might not notice us at all, and if we don't see them, someone could get hurt. Now some states are actually considering legislation requiring cars to make noise even while idling or moving at low speeds.

But how much does noise help us spot objects? Aren't pedestrians supposed to look for cars, not just listen for them? Aren't drivers supposed to look for hazards, not hear them? Indeed, there has been some research suggesting that sounds do help us locate objects. However, most of this research has been on directional sounds -- a sound from the right helps us spot an object on the right side of the computer screen (for an exception, see this post). Does a sound that's not from a particular direction still help us notice a change?

A team led by Toemme Noesselt flashed images using an extra fast-response computer display to flash images at 16 volunteers. The displays looked something like
this movie (click on the image to play):


For each trial, viewers had to say whether the top or the bottom ring of dots disappeared. It's easy in this version because your computer display is probably not fast enough to show the actual flashes. In the actual experiment, viewers were first tested to determine how quick a flash they could spot. Usually this was around 15 milliseconds (the flash in my movie, for comparison, was 100 milliseconds). Then they were shown movies like mine, where either the central cross changed to a circle to cue viewers that one of the rings of dots were disappearing, or a tone was played while the ring disappeared, or nothing cued them.

The length of the flash was gradually decreased until viewers could no longer detect it. Then it was increased, so that for the duration of the experiment, participants were between 55 percent and 80 percent accurate. So, did the tone improve viewer accuracy? Here are the results:


The graph shows the difference in reaction times compared to when no cue was given. As you can see, when there was a visual cue, respondents were significantly less accurate than with no cue. With an audio cue, they were significantly more accurate. And when both audio and visual cues were given, the difference from the no-cue condition wasn't significant (although it was significantly different from both the other conditions). So the audio cue, especially when not paired with a visual cue, made respondents more accurate than a visual cue. If anything, the visual cue seemed to make it more difficult for respondents to identify which circle was disappearing.

In two additional experiments, the researchers varied the timing of the audio cues, finding that an early audio cue didn't help accuracy, but extending the length of the audio cue helped about as much as an audio cue that matched the length of time the ring of dots disappeared.

Remember, regardless of which ring disappeared, the sound always came from the same spot, so it seems that just the fact of a sound accompanying the blink somehow helps focus attention on the change. Since the early cue doesn't help, it doesn't appear that the sound is somehow "warning" observers to look for a change. It's more like the audio simply helps focus attention. And that can be a good thing when a killer hybrid is bearing down on you in a parking lot!

NOESSELT, T., BERGMANN, D., HAKE, M., HEINZE, H., & FENDRICH, R. (2008). Sound increases the saliency of visual events Brain Research, 1220, 157-163 DOI: 10.1016/j.brainres.2007.12.060

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Sounds like the same concept behind clicker training. The sound is saying, "Right now something significant is happening." In training you can use that information to repeat the behavior. In this instance it lets you notice a visual change.

Of course it's easier to "spot" approaching traffic if there's sound as well as something to see, but that doesn't change the fact that there are already silent vehicles on the road.

In my experience as a cyclist, whatever the fractional differences in reaction times may be for visual vs auditory cues, that doesn't matter a monkey's toss because pedestrians often simply don't even look before they walk into the road.

I say roll on the silent, electric car, because it may just mean that idiotic pedestrians start to actually look before they walk out into the street instead of assuming there's nothing coming because they can't hear anything.

By Dave Richards (not verified) on 20 Oct 2009 #permalink

Dave, there have been silent or very quiet cars for ages too, just not in such large numbers I suspect. My dad always told me I should look for cars no matter what, because he inadvertantly snuck up on many people in the past in his race car (driving at legal road speeds of course, probably the reason it was so quiet). Doesn't mean I always do it though :$

Not to take a pot shot at cyclists, but shouldn't you have some sort of bell or something, to serve the same function as a horn on a car (that is, to show your indignation towards pedestrians that stepped out without looking, of course it isn't preventative, nothing is.) I guess I made my own question moot.

By Katherine (not verified) on 20 Oct 2009 #permalink

On the open road is when this seems to become an issue. Driving normally, drivers build up more inertia than they can reasonably control in a surprise situation, so everyone else needs to be aware of that danger. Fortunately, tires make a lot of noise at speed, and a car tearing a hole through the air makes a lot of wind noise; enough to drown out the engine noise of most cars.

At very low speeds is when the lack of noise is an issue. Backing out of a parking space or accelerating through a light, it's not inertia but immediate driver input that is the danger. And that driver honestly needs to be aware of what or who they're backing over when they reverse through a sidewalk, or to look to the right before making a right on red to check for pedestrians legally crossing with the light in the crosswalk.

But if electric vehicles must sound like something, there should be a steam engine option. Or Jetsons car.

Bicycles have been travelling silently or quietly for over a hundred years, horse-drawn vehicles for quite a lot longer, and many internal combustion cars are hard to hear when travelling slowly or with other background noise.

Then main problem now seems to be the absolute refusal of the majority of people to take any sort of responsibility for their own actions; they'll happily walk straight into your path with their eyes on the cell phone, iPod in the ears, then blame the vehicle driver for not being loud enough.

Then main problem now seems to be the absolute refusal of the majority of people to take any sort of responsibility for their own actions; they'll happily walk straight into your path with their eyes on the cell phone, iPod in the ears, then blame the vehicle driver

Agreed. What the hell ever happened to "look both ways before crossing the street"? That wasn't just an old saying passed down from parent to child; it's advice for staying alive. On that same note, what ever happened to drivers being aware of their surroundings? Just because we have more tech toys and gadgets to play with doesn't mean we have to pay less attention to what's around us (although often that is what ends up happening anyway).

Bring on the silent cars. Noise pollution sucks. As much as I don't want roaring internal combustion engines disrupting quiet neighborhoods, a city or suburban area emitting sounds of artificial beeps or futuristic whooshes (Fisker Karma, anyone?) from so-called "silent" cars doesn't at all sound appealing, either.

A lot of this work is done because incidents involving blind pedestrians have increased since the implementation of hybrid cars and it appears that the removal of the sound cue is at least one contributing factor. Sometimes "looking both ways" is not an option. Most large enough cities have crosswalks with an aural signal as well as a visual one, but in areas that have not implemented this cue for the blind, the car noise is a big factor in understanding when it is safe to cross.

Hey, Scott... source please? There have been no instances of blind pedestrians being hit by hybrids any more than other cars. (I could give you a source... but you first, k)

Re: idling during emissions tests... hybrids have an inspection mode that will put the engine on at idle... inspectors just have to learn how to do it. Or the inspectors can just download the codes from the OBDII port to find out if anything is wrong, since these cars have more sensors on them and know when something is screwing up before a sniffer on the exhaust could find it.

I could put a bell on my hybrid, but I wouldn't want it ringing when not needed... I don't ring the bell on my bike continually either.

The problem is how to deal with blind pedestrians. They have a right to be on the street too. There's no easy answer for this. I believe they should be accompanied by a guide dog or another human if they are legally blind.

As for those of us who have all the usual senses intact and functioning normally, there is simply no excuse for not using them. This goes for drivers, pedestrians, and bicyclists.

Bicyclists need to follow the rules of the road. As an urban driver, the chances of me not seeing a bicyclist are far greater than having a blind person not see me.

If bicyclicts do not have to follow a set of traffic rules, then we're just out there in a big shooting gallery with bike-projectiles able to be shot into the system at any time. I don't think that's the way it's supposed to work.

I'm not saying bicyclists necessarily have to follow all the traffic rules made for cars, but there should be some standardized rules for bikes, and they should be enforced by tickets or fines for safety violations, just as is true for motorists.

Having sounds is good. As a bicyclist, sound is the primary way you know a car is BEHIND you. Having bells and horns on bicycles is a good idea for pedestrians, but rather useless when competing with drivers who have newer cars that block out road sounds for the drivers while they blast their favorite music or talk radio to themselves in the car, thus blocking out all outside environmental sounds.

The crux here is that the single most important safety practice - being aware, and concentrating undistractedly on your driving, is also one of the hardest to enforce.

It is possible to change the laws so that all vehicles have to have advanced computerized sensing systems that unfailingly detect all objects in a given radius, determine their motion, and assign a threat level.

In other words, a car where you climb in, take nap and are awakened when you safely arrive at your destination.

A problem arises because drivers try to behave as if that's what their car already is.

It's not. We don't have those kinds of cars yet. For now, we are saddled with the demands of actually staying awake and aware while driving. One day, maybe science will be so advanced we can snooze through life and be totally protected. Not exactly my idea of a fulfilling existence, to be sure, but that seems to be what some drivers want.

Another inconvenient truth, I suppose.

I work for the DOT. I am not directly working on the project involving Hybrid cars and blind pedestrians (specifically looking at noise), but I know that it is a project that is ongoing right now.

I certainly don't have any specific knowledge that there have been any more collisions. I didn't mean to indicate that. However, incidents of some sort have been elevated to the point where it seemed like something needed to be looked at. I wish I had more to share, but I don't.

Obviously the life of a careless pedestrian (adult or child) is as nothing compared the inconveniencing, and possible bruising and scraping of a cyclist, but how many of those bastards do you think it will be necessary to kill before they learn to keep off the sidewalks too?

I'm for manaufactures installing a bullhorn or PA system. The driver simply would grab the microphone, press the button, yell "Hey dip shit! Watch out, I'm in a hybrid!" and the clueless person strolling the parking lot with the iPod on would have ample warning. :) Wonder if that would violate a noise ordinance? Some laws are SO STUPID.

I agree, pedestrians and drivers alike should be looking AND listening to their surroundings. The two go together when driving. Interesting article, thanks for sharing.

This is actually one of the (myriad) reasons I won't wear a cycle-helmet - it cuts down on ambient noise, and especially on my ability to know where sound is coming from, to the point that it has a noticeable impact on my knowledge of what else is on the road. Of course, you can turn to look, and I do before committing to a manoeuvre, but while you're looking you've shifted your blindspot forward and thrown yourself off balance. When tenths of a second matter, it is a significant impairment. I've not yet had trouble with hybrids, possibly because to a cyclist the noise of the tyres on the road is still audible.

By stripey_cat (not verified) on 23 Oct 2009 #permalink