Hyperacute directional hearing in a microscale auditory system

The physics of sound propagation imposes fundamental constraints on sound localization: for a given frequency, the smaller the receiver, the smaller the available cues1. Thus, the creation of nanoscale acoustic microphones with directional sensitivity is very difficult. The fly Ormia ochracea possesses an unusual ‘ear’ that largely overcomes these physical constraints2,3,4,5; attempts to exploit principles derived from O. ochracea for improved hearing aids are now in progress6. Here we report that O. ochracea can behaviourally localize a salient sound source with a precision equal to that of humans7. Despite its small size and minuscule interaural cues, the fly localizes sound sources to within 2° azimuth. As the fly's eardrums are less than 0.5 mm apart, localization cues are around 50 ns. Directional information is represented in the auditory system by the relative timing of receptor responses in the two ears. Low-jitter, phasic receptor responses are pooled to achieve hyperacute timecoding8,9. These results demonstrate that nanoscale/microscale directional microphones patterned after O. ochracea have the potential for highly accurate directional sensitivity, independent of their size. Notably, in the fly itself this performance is dependent on a newly discovered set of specific coding strategies employed by the nervous system.