Subject: Re: Head movement and ASA (and spinning) From: Peter Lennox <P.Lennox(at)DERBY.AC.UK> Date: Mon, 19 Dec 2005 15:50:05 +0000Although one can make a plausible argument for movement as part of perception, that doesn't really begin to approach how. I would argue that an intermediate, representational stage that supports non-body-centred cognitive mapping is necessary to postulate that successive - and differing- sound fields can be integrated into a holistic grasp of a sound environment. This was at the heart of why I was asking for opinions on sound fields and sound environments a few years ago - in the archive, I expect.. yes, http://www.auditory.org/mhonarc/2000/msg00505.html . The point was that a given environment contains uncountable different sound fields - each of which may (perhaps) be precisely measurable, but there's no real basis for assuming that this is how peception proceeds; if we were less than accurate at each stage, the accumulated error would be enormous. Therefore, it would be interesting to assume that we perform some 'quick and dirty' representation of an externalised world, and use movement to flesh out as we go along. I remember that Barbara Shinn-Cunningham et al noticed a learning effect in reverberant rooms, where spatial detection continued to improve over some hours' exposure to a room (even for changing listening positions) and the improvement lasted at least overnight. The question then is what is being mapped, in this scheme of things? the background-foreground distinction (crudely: sound of place, sound of things in the place) is a reasonable place to start. Again, if you make both behave exactly the same way, so as to simulate spinning of the perceiver, I think the perceiver will be disorientated. Incidentally, a ballet dancer doesn't spin the head smoothly - usually orientating to an external feature for a limited period, then whipping the head to a new, 'fixed' (with respect to external features) position, and so on. And probably not doing much by way of auditory spatial perception, either. Also, it is quite feasible to spin a whole sound field round, using 1st or 2nd order ambisonics. However, as the speed of rotation goes up the impression gained soon turns into that "Leslie speaker modulation" John describes. Angelo Ferrina noticed this a few years ago, that the spatial modulation soon becomes a timbral modulation. So auditory spatial perception probably becomes indistinct long before Doppler becomes distinct, in the spinning paradigm. regards ppl >>> John Neuhoff <jneuhoff(at)WOOSTER.EDU> 19/12/2005 14:35 >>> 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 ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________