Re: Head movement and ASA

[Israel Nelken <israel@xxxxxxxxxxxxx>]

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in a set of (as yet unpublished) electrophysiological experiments in 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.
   Eli

> 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.
>
> Pierre

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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
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