Richard F. Lyon wrote, On 6/25/2013 1:43 PM:
Jennifer, I believe the answer is primarily in the transducer: to make the beeper cheep, they use a resonant transducer, which has a slow buildup at the onset and makes the resulting signal not very broadband at all, depriving you of all ITD cues. And they make the beeps so brief that you don't have much chance to turn your head and vary the ILD cue;
It also turns out that front/back location is much more readily disambiguated by head turning in stimuli that carry low-frequency ITD than in those carrying only high-frequency ILD (such as the ~3-kHz, more-or-less pure tones from smoke detectors). The dynamic ILD cue does not seem to be able to beat the phantom spectral cue due to the narrow high-frequency peak in the spectrum. This is true under anechoic conditions, and presumably would be even worse in reverberation.
http://asadl.org/poma/resource/1/pmarcw/v19/i1/p050131_s1 EAM