The ball was floated on a jet of air so that it could easily be turned by a walking fly. Then they placed a tethered fly on the ball, turned on the cricket sounds from the speaker and sat back to see what would happen next. No matter where the sound was directed, to the right or left of center, the fly altered its path to walk directly toward the cricket chirps. Ormia flies, the biologists discovered, can detect changes in sound-source position as small as 2 degrees. Even humans trying to detect who is speaking in a crowded room can't do better than that.
Sound waves cause each fly eardrum to beat out of phase with the other.
Applications of these new principles may improve life for individuals with hearing loss who depend upon hearing aids.