Re: Head movement and ASA (John Neuhoff )


Subject: Re: Head movement and ASA
From:    John Neuhoff  <jneuhoff(at)WOOSTER.EDU>
Date:    Mon, 19 Dec 2005 09:35:01 -0500
         http://www.intellireach.com

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(at)LISTS.MCGILL.CA] On Behalf Of Pierre Divenyi Sent: Sunday, December 18, 2005 7:48 PM To: AUDITORY(at)LISTS.MCGILL.CA 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


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