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Re: Head movement and ASA

We actually implemented (and published, Jacobson et al. J. Neurosci. Methods 2001) an exact algorithm for simulating motion, and verified it by reconstructing signals measured during real motion (admittedly, of an artificial system, not real HRTFs). In that paper, we also reported the results of behavioral experiments in barn owls (conducted by Iris Poganiatz in the lab of Hermann Wagner). The experiments used pre-synthesized stimuli, and therefore they moved the wrong way when the owls moved their heads. The owls initially followed the trajectory of the sound, and then 'saccaded', presumably trying to catch up with the perceived location of the sound. Eventually they stopped responding to these sounds, again presumably because they realized they were being fooled. We also used stimuli that were synthesized with this algorithm in a set of (as yet unpublished) electrophysiological experiments in auditory cortex.
As Pierre correctly says, this required huge amount of computer time six years ago, when we conducted this study. We implemented synthesis in the time domain, following the time course of the source and using at each sample the appropriate impulse response at that time. Interpolating the impulse responses turned out to be the main computational load. These days, computers are so much more powerful that it would be possible to synthesize accurate stimuli, at least for fixed-head experiments, in a reasonable amount of time.

Dear Al,

The major problem with the complex (=multi-source) moving source experiments you are talking about is procedural: as far as I know, there is no algorithm that would generate good dynamically changing HRTF's and generating even a single moving source in free field requires quite an undertaking.


Israel Nelken
Dept. of Neurobiology The Alexander Silberman Institute of Life Sciences
Edmond Safra Campus, Givat Ram | Tel: Int-972-2-6584229
Hebrew University | Fax: Int-972-2-6586077 Jerusalem 91904, ISRAEL | Email: israel@xxxxxxxxxxxxx