People hear in stereo. Thats why we have two ears. The ability to hear sound through two ears enables humans to pinpoint the source of a sound with incredible precision. Human hearing better be precise or our ancestors would have been breakfast for some saber-toothed tiger. Hearing in stereo isnt some kind of luxury. Its an essential defense in nature.
When you cant quite place a sound, you cock your head one way or the other to clarify the sound information youre receiving - same with antelope and gazelle. These animals have two ears and can use their stereo hearing to pinpoint the source of potential danger to decide on a safe time to take that trip to the watering hole.
It Helps to Have a Fat Head
To hear stereoscopically, the two receivers your ears must be separated by some distance. In this case, the degree of separation is the width of your head. Those five or six inches of space between Ear A and Ear B mean that sound reaches A and B at slightly different times.
From this slight difference in hearing between Ears A and B, the brain can instantly calculate the approximate location of a sound source. Sometimes, the brain receives enough sound information from two ears, separated by a head, to pinpoint the source of sound with remarkable specificity, enabling us to excel at the game, Marco Polo and to locate that wandering toddler before she gets too far away.
We use stereoscopic sound every day to locate the source of the sounds around us from a high profile business meeting in Manhattan to a Big Five African photo safari in Kruger National Park. The ability to hear sound through two receivers provides the brain the data it needs to calculate the sounds location all in far less than a second. Whats more, we dont even have to think about it. It happens reflexively, that is, without cognitive thought, aka, thinking. Its a reflex response like blinking.
The Goals of Hearing Aid Technology
In a few words, the fundamental goal of hearing aid technology is to provide wearers with the most natural listening experience possible.
First and foremost that means wearing comfort. You want a device that is physically comfortable enough to have in or on your ears all day long.
Another goal is hearing comfort sounds perceived to be too loud, too many pops and clicks, squealing or whistling, and the unnatural experience of your own voice resonating all issues to be addressed.
In addition to wearing and hearing comfort, the ability to locate the source of a sound even at a loud party is what hearing aid wearers miss most. Manufacturers have addressed the problem through the use of highly directional microphones and open ear hearing technology, which enable the wearer to use whatever natural hearing capacity is available. Highly directional microphones have definitely helped and more sophisticated developments are in the pipeline.
But heres the thing. Researchers have discovered some unique characteristics of the physiology of hearing in the capabilities of Ormia ochracea a parasitic fly. Thats right, its a fly you might swat if you had the chance, but Ormia is a worthy opponent against your measly fly swatter. This bug can hear with an incredible ability to accurately pinpoint sound. Thats all the more amazing when you consider that most flies dont have any sense of hearing at all.
Big Head, Little Head
The ability to pinpoint sound sources has always been the domain of humans and animals of prey. In an interview at www.ScientificAmerican.com researcher Ron Hoy, a Cornell University neurobiologist stated, Ormias ears are a miniscule half millimeter apart, but it has evolved a system of localizing sounds very different from any animal. Hmmm. Smart bug.
The puzzle has been to determine how Ormia pinpoints sound, specifically, the sound of a certain kind of cricket used by Ormia to deposit larvae so those little baby Ormia can feed off the live cricket as they mature. (Isnt nature grand? Icky to the extreme but thats the way things are in the Ormia-cricket match up.)
The Research Was Actually Pretty Simple
Hoy, and his Cornell research team, tethered an Ormia to a specially dotted ping-pong ball that could be tracked with incredible precision by a computer. This research showed that this flying parasite could track sound location within two degrees off axis. Even humans trying to detect who is speaking in a crowded, noisy room cant do that, explained researcher and team member, Andrew Mason from the University of Toronto.
So did scientists discover Ormias secret to improved hearing? Well, sort of. The ability of the fly to localize a sound source is due, in part, to the fact that the tympanic membranes (the ear drums) of Ormia beat out of phase. Hoy explained. The near ear, the one closest to the sound source, responds more vigorously, compared to the far ear. That makes sense. Sound waves have to travel a bit farther to reach the far ear. Okay, no problem.
Based on sound pressure levels picked up by the ears of Ormia, the fly can hear and locate that particular species of unfortunate cricket from a great distance, despite the fact that the bugs hearing apparatus is only a half millimeter apart, limiting the function of stereo sound as part of localization. These flies employ out-of-phase tympanic membranes to locate the sound source they need to keep their species alive. Humans cant do that.
So How Does This Affect Me Since I Dont Lay Eggs on Crickets?
Because Ormia has evolved a new way of hearing that doesnt rely solely on the human, stereoscopic hearing model, researchers have hopes of developing hearing aids that use the same technology that these parasitic flies employ. (Sounds suspiciously like a B grade sci-fi flick, but thats the way researchers are going.)
These researchers have already developed a prototype of a microphone eardrum. However, it can only pick up sounds in the ultrasonic hearing range, making it the ideal hearing aid for bats that have experienced hearing loss. (Just kidding.)
But the research into sound pressure levels as a means of improving the mechanically processed hearing experience in humans continues, and researchers are confident that these studies on little Ormia ochracea will ultimately lead to improved microphone directionality in hearing devices, using a fly to lead the way.
Thats good buzz from the labs at hearing centers, though even professionals have to admit it is somewhat unconventional research. Even so, its paying off with a better understanding of the ability to localize sounds in both bugs and humans.