Hyperacute directional hearing in a microscale auditory system

The physics of sound propagation imposes fundamental constraints on sound l ocalization: for a given frequency, the smaller the receiver, the smaller t he available cues(1). Thus, the creation of nanoscale acoustic microphones with directional sensitivity is very difficult. The fly Ormia ochracea poss esses an unusual 'ear' that largely overcomes these physical constraints(2- 5); attempts to exploit principles derived from O. ochracea for improved he aring aids are now in progress(6). Here we report that O. ochracea can beha viourally localize a salient sound source with a precision equal to that of humans(7). Despite its small size and minuscule interaural cues, the fly l ocalizes sound sources to within 2 degrees azimuth. As the fly's eardrums a re 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 timecoding(8,9). These results demonstrate that nanoscale/microscale directional microphones patterned after O. ochra cea have the potential for highly accurate directional sensitivity, indepen dent of their size. Notably, in the fly itself this performance is dependen t on a newly discovered set of specific coding strategies employed by the n ervous system.