Re: Head movement and ASA

[Ramani Duraiswami <ramani@xxxxxxxxxxxxxx>]

Dear List,

As observed by In our simulation of virtual sound sources, head motion and environmental modeling (modeling reverberation) are seen to be key in ensuring a compelling demonstration.

I would also like to draw attention to a somewhat theoretical paper, that shows that motion generates sufficient cues for localization,  even for a sphere. The implication is that pinna cues are not needed.

 The reference is  
Handzel, A.A.   Krishnaprasad, P.S.   "Biomimetic sound-source localization," IEEE Sensors Journal, Vol. 2(6), pp. 607- 616,  Dec 2002

Those with IEEE Explore access can find the article at 
http://ieeexplore.ieee.org/xpl/abs_free.jsp?arNumber=1178174

Sincerely,

Ramani Duraiswami

-----Original Message-----
From: AUDITORY Research in Auditory Perception [mailto:AUDITORY@xxxxxxxxxxxxxxx] On Behalf Of John Neuhoff
Sent: Monday, December 19, 2005 9:35 AM
To: AUDITORY@xxxxxxxxxxxxxxx
Subject: Re: Head movement and ASA

 
Hi Pierre, 

Check out Bill Chapin's company (Ausim Inc.) for some incredibly compelling simulations of moving sounds.  The strikingly realistic auditory motion simulations that we recently used included absolute delay (to account for the speed of sound and the changing distance between the listener and the source), Doppler shift, atmospheric filtering, gain attenuation due to atmospheric spreading, ground reflection attenuation, and  dynamic HRTFs from the KEMAR data set  We've just completed some work on the perception of looming and receding auditory motion that they simulated for us.  

Dear Jim & Al, 

The physics (and perception) of the Doppler effect depend on the velocity of the source and the distance from the listener to the patch of the source.  A source travelling at a high velocity, but on a collision course with the listener will not have a perceptible Doppler effect.  The observed frequency will be higher than the emitted frequency, but there will be no frequency change on approach.  So, if the listener doesn't know the source frequency, the Doppler shift will go undetected (except for the influence of the intensity change, see Neuhoff & McBeath, 2002).  

The case of an ice skater (or a slower rotating head) is interesting.  As one ear moves toward the source (causing an increase in frequency) the other moves away (causing a corresponding decrease).  But, the pattern is reversed after 1/2 rotation, causing a modulation effect.  This is much like the old rotating Leslie speakers that came with Hammond organs, only a rotating head instead of loudspeaker.  Regular head turns typically do not produce perceptible Doppler shifts, probably for two reasons.  First, the velocity of the head turn is pretty slow relative to the speed of sound.  Second, as mentioned above, frequency  rises in one ear and falls in the other. If you simulated high-velocity head turns, or a source rotating quickly around the head, this actually creates some interesting situations for ASA.  The pitch of a single source sound going in opposite directions based on the direction of the rotation. I wonder if you could manipulate the stimulus in such a way that the differential pitch cues would override the spatial unity of the source and get one source to sound like two based on Doppler cues.  

Christian wrote:

"...head movements for the improvement of SSL are quite a nice example of the role of action in perception, up to the point where some say "Perception is a behavior, a specific kind of action aiming at the driving home of a maximum amount of information on the object of interest." (Is this Gibsonian?)"

Christian,
Yes, this is quite ecological and quite Gibsonian. Although "Neo-Gibsonian"
might be a better term.  It's doubtful that Gibson would be much enamoured with any of the top-down cognitive aspects of ASA, but head movements, absolutely.  It is striking to me that so much work has been done on localization and the role of spatial separation in ASA while restraining head movements. We've evolved in an environment in which head movements toward a source are adaptive.  If we examine the head movements of newborns toward a source (or hemifield) one could even make the argument that they are somewhat innate. This leaves little doubt in my opinion of their importance.  

Best, 

-John 

 ________________________________
John G. Neuhoff
Department of Psychology
The College of Wooster
Wooster, OH 44691
Phone: 330-263-2475 

http://jneuhoff.com
-----Original Message-----
From: AUDITORY Research in Auditory Perception [mailto:AUDITORY@xxxxxxxxxxxxxxx] On Behalf Of Pierre Divenyi
Sent: Sunday, December 18, 2005 7:48 PM
To: AUDITORY@xxxxxxxxxxxxxxx
Subject: Re: Head movement and ASA

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