Now hear only this

By D.N.

DINNER parties can be tiresome ordeals, particularly if you find yourself next to an individual keen to show off worldly credentials, such as a journalist. But they can be even more trying for the hard-of-hearing. Modern hearing aids are capable and discreet. Where they are left wanting, however, is in reducing the background hubbub and focusing on the many supposedly interesting stories from your companion. But that could change if results from the University of Texas, described in the journal Applied Physics Letters, can find their way into a commercial product.

The researchers' subject was a tiny species of fly called Ormia ochracea. A native of the south-eastern United States and Central America, this fly is famed for the pinpoint accuracy of its hearing. Mammalian brains such as our own calculate where a sound is coming from based on the tiny difference in its arrival time at each ear. For many insects, however, this approach does not work. Sound waves are longer than the insects' bodies, so the minuscule difference in arrival time cannot be discerned.

Yet O. ochracea can spot the direction of the chirp from a male cricket—its preferred prey—even though its hearing mechanism is a mere 1.5 millimetres across. And what a mechanism it is. A tiny structure similar to a playground see-saw connects the fly's two sound sensors, and vibration on one side drives the other in the opposite direction. The net motion of the see-saw permits the fly to determine what is known as the "phase" of the sound wave—in other words, the extent to which the peaks and troughs of the sound waves detected by its sound sensors line up with each other. This allows for fantastically precise determination of its direction of origin.

Michael Kuntzman and Neal Hall, of the University of Texas at Austin, set out to replicate this ingenious structure in silicon using a flexible beam surrounded by piezoelectric materials. These turn movement into electricity, and vice versa. The East Japan Railway Company, for example, has installed such devices in floor pads at a Tokyo station to generate power from movement of commuters during the rush hour. But this is the first time these materials have been applied to technological mimicry of O. ochracea.

It could result in a new generation of hearing aids that are no bigger, but are much better. Using an artificial version of the fly's direction-finding technique, they could be designed to focus only on those sounds or conversations that are of interest to the wearer. That would make dinner-party conversations less of a chore—though there is, alas, no technological solution to the problem of a tedious dining companion.