Have you ever tried to sneak up on a fly?   It’s impossible as they seem to have a sixth sense for knowing when to fly away just before you swat them with a newspaper.  It’s a difficult task to rid yourself of these pests as you wander aimlessly around the room swatting and missing, swatting and missing.  How do they know that you are just ready to spring your trap?  They can’t really be THAT smart!   Dickinson (2009) says of flies, “Our experiments have shown that the fly somehow ‘knows’ whether it needs to make larger or small postural changes to reach the correct pre-flight posture. This means that the fly must integrate visual information from its eyes telling it where the threat is approaching from and then send mechanosensory information from its legs as to how to move for the proper pre-flight pose.”  The fly’s quick reaction beats that of humans, who need at least 250 milliseconds to react to stimulus. The fly, meanwhile, can perceive the threat, determine where the threat is coming from, and adjust its body in less than half the time. “We really see a marvelous machine, arguably the most sophisticated flying device on the planet, and its all controlled by this brain about the size of a poppy seed.”

The Super Hearing of Flies

Click Here, for SUPER FLY by Curtis Mayfield, 1973

It seems that there is also a mechanism that flies use, allowing them to localize sound easily.  According to Bardi (2014), “humans and other mammals have the ability to pinpoint sound sources because of the finite speed of sound combined with the separation between our ears. The spacing of several centimeters or more creates a slight difference in the time it takes sound waves to hit our ears, which the brain processes perceptually so that we can always experience our settings in surround sound. Insects generally lack this ability because their bodies are so small that sound waves essentially hit both sides simultaneously. Many insects do detect sound vibrations, but they may rely instead on visual or chemical sensing to find their way through the fights, flights and forages of daily life.  The fly, O. ochracea, is a notable exception.”   Bardi further tells us that “it can locate the direction of a cricket’s chirp even though its ears are less than 2 mm apart – a separation so slight that the time of arrival difference between its ears is only about four millionths of a second (0.000004 sec).  But the fly has evolved an unusual physiological mechanism to make the most of that tiny difference in time. What happens is in the four millionths of a second between when the sound goes in one ear and when it goes in the other, the sound phase shifts slightly. The fly’s ear has a structure that resembles a tiny teeter-totter seesaw about 1.5 mm long.  Teeter-totters, by their very nature, vibrate such that opposing ends have 180-degree phase difference, so even very small phase differences in incident pressure waves force a mechanical motion that is 180 degrees out of phase with the other end. This effectively amplifies the four-millionths of a second time delay and allows the fly to locate with remarkable accuracy.”  According to Cummings (2009), Michael Dickenson at the California Institute of Technology with high speed cameras found that within 50–100 milliseconds of seeing the swatter, a fly begins to prepare its getaway by adjusting the position of its legs and body.  Sooo….it’s the combination of the vision, coordination with the legs, flying ability as well as the hearing of “SUPER FLY” that causes us difficulty swatting the enemy!

Could the Fly’s Super Hearing Be Harnessed to Help Humans?

The pioneering work in discovering the fly’s unusual hearing mechanism was done by Ronald Miles, Distinguished Professor of Mechanical Engineering at Binghamton University and colleagues Daniel Robert from Bristol College in the UK and Ronald Hoy of Cornell Ronald Hoy and Daniel Robert, who first described the phase amplification mechanism the fly uses to achieve its remarkable directional hearing some 20 years ago. The fly relies upon a sophisticated sound-processing mechanism that resembles a teeter-totter to determine direction of sound within two degrees (See left).  Dr. Miles studies the hearing of Ormia ochracea, a house fly-sized insect that is native to the southeast United States and Central America. Unlike most other flies, the Ormia ochracea has eardrums that sense sound pressure, as do our ears, and, according to Miles, “they can hear quite well. The female flies use their “remarkable” directional hearing to locate singing male crickets, on which they deposit their larvae. In 1994, Miles, Robert and Hoy described the mechanism by which the fly achieves its directional hearing, despite its small size. Miles and his colleagues presented a microphone inspired by the fly’s ears and presented the concept in the Journal of Acoustical Society of America (JASA).  In the event that you missed that issue, Newswise (2013) describes their design as a microelectromechanical microphone with a 1 mm by 3 mm diaphragm that is designed to rotate about a central pivot in response to sound pressure gradients. The motion of the diaphragm is detected using optical sensors. To minimize the adverse effects of resonances on the response, the design used a feedback system to achieve so-called active Q control.  Dr. Miles explains that “Q control basically is an electronic feedback control system to introduce electronic damping so that the microphone diaphragm will not ring like a bell.” He further explains “that in order for the microphone to achieve a very low noise floor (which is the quietest sound that can be detected without the signal being buried in the microphone’s noise ), it is important to minimize any passive damping in these sensors. If you do that, the diaphragm will resonate at its natural frequency. They were the first group to show that you can use this sort of electronic damping in a microphone without adversely affecting the noise floor of the microphone.”  In subsequent research, the team claims that the noise floor of the fly-inspired microphone is about 17 decibels lower than what can be achieved using a pair of low-noise hearing aid microphones to create a directional hearing aid. The new design could be used in applications ranging from hearing aids and cell phones to surveillance and acoustic noise control systems, Miles says, and “could easily be made as small as the fly’s ear.”

Dr. Neal Hall, Click here for an Eagles Song…

  The NEW Kid In Town…….

Now enter the next generation of fly microphone researchers.  Neal Hall, an assistant professor in the Cockrell School’s Department of Electrical and Computer Engineering at the University of Texas at Austin, and his team of graduate students, drew their inspiration from pioneering work by Miles, Robert and Hoy.  According to Paddock (2014), Hall and his UT colleagues have as their goal to build a hearing aid microphone on the principles of how the fly’s ear works. To replicate the fly’s hearing mechanism, the team made a flexible beam incorporating piezoelectric materials that allowed them to use the flexing and rotation of the beam as a way to measure sound pressure and pressure gradient at the same time. While other teams have already tried to build hearing devices that emulate the fly’s super-hearing, Professor Hall and colleagues are the first to use piezoelectric materials, which convert mechanical pressure into electrical signals and allow the device to work with very little power.  In Professor Hall’s words, “Because hearing aids rely on batteries, minimizing power consumption is a critical consideration in moving the hearing aid device technology forward.”

Who knows? We might soon see some new microphones “flying” into the hearing instruments based upon the principles of how Super fly’s ear works! Think about that the next time that pesky  fly takes off before you can get rid of him!

References:

Paddock, C. (2014). Next generation hearing aids emulate fly’s ability to pinpoint sound. MNT.  Retrieved February 16, 2015:  http://www.medicalnewstoday.com/articles/280000.php http://www.aip.org/publishing/journal-highlights/fly-inspired-sound-detector

Cummings, D., (2009).  The science of fly swatting.  Finding Dulcinea.  Retrieved February 17, 2015:  http://www.findingdulcinea.com/news/science/September-October/The-Science-of-Fly-Swatting.html

Newswise (2013).  Researchers design sensitive new microphone modeled on fly ear.  Newswise.  Retrieved February 17, 2015:  http://newswise.com/articles/researchers-design-sensitive-new-microphone-modeled-on-fly-ear

Robert, D., Hoy, R. & Miles, R. (1994).  A novel mechanism for directional hearing in a parasitoid fly.  Journal of Acoustical Society of America.  Retrieved February 17,2015: http://scitation.aip.org/content/asa/journal/jasa/96/5/10.1121/1.410864 

Images:

http://syntheticdaisies.blogspot.com/2013/09/perceptual-time-and-evolution-of.html

http://www.findingdulcinea.com/news/science/September-October/The-Science-of-Fly-Swatting.html http://www.wired.com/2015/01/flies-fly/

Songs:

Mayfield Curtis. (1973) Superfly.  Retrieved February 16, 2015:  https://www.youtube.com/watch?v=-cmo6MRYf5g

Eagles, (1977).  New Kid In Town.  Concert Washington DC.  Retrieved February 18, 2015:  https://www.youtube.com/watch?v=vANZfQ1bTAk