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Re: Head movement and ASA

Dear Jim,

Thanks for pointing out the importance of the Doppler effect.  However what
I had in mind was not the general case of moving sources, but an
experimental setup in which a number of actual speakers (or their HRTF
equivalents), each with its own signal (a complex sound, or sequence of
complex sounds) were mounted on a circular wheel around the head.  One
would compare the ASA effects of rotations of the speaker array as a whole
(i.e., the wheel) with voluntary rotations of the head in the opposite
direction.  As a control, one would have to match the rotary acceleration
of the wheel to  previously recorded voluntary rotations of the head, to
get the accelerations right.  In this case, any Doppler effects or lack
thereof should be identical in the two cases. That being said, the
importance of the Doppler effect in the general case of object motion
should be investigated for its effects on ASA.

Dear Christian,

I agree with you that a study of the role of head movements in ASA would be
important.  However I have a different intuition than yours about how
listeners would orient their heads.  Although logic would dictate that they
should orient them to maximize the signal-to-noise ratio of the target
sound to the background in one ear, I have a feeling that they would try to
directly face the target location, especially if discovering the target's
location was part of the motivation for the head rotation.  I have no idea
about why; it's just an intuition. (maybe it has something to do with one's
history of facing talkers in order to read their facial movements).  It
should be easy enough to find out the answer.  Unfortunately I don't have
the experimental resources or graduate students to address the general
question (e.g., tracking and recording head movements), but would be
delighted to know the results if somebody else did it.

Best to both of you,


----- Original Message ----- 
From: "beaucham" <beaucham@xxxxxxxxxxxxxxxxxxxxxx>
To: <AUDITORY@xxxxxxxxxxxxxxx>
Sent: Sunday, December 18, 2005 3:47 PM
Subject: Re: Head movement

> Al, Pierre, and all,
> One thought that comes to mind is a substantial difference between
> rotating the head and a moving sound source: Doppler effect.
> Moving sound sources, like flies, exhibit a great deal of Doppler,
> but I've never perceived it when moving my head. Maybe skaters who
> rotate fast on the ice would, but it's not normal experience.
> Another thought is that a virtual reality system implements an
> HRTF in real time. If a sound source is simulated as stationary
> and you move your head, the system is supposed to monitor a head
> position detector and keep the illusion of the source stationary.
> Jim Beauchamp
> UIUC, Urbana, IL
> Al Bregman wrote:
> >From: Al Bregman <bregman@xxxxxxxxxxxxxxxxxxxx>
> >Date: Sun, 18 Dec 2005 00:58:36 -0500
> >To: AUDITORY@xxxxxxxxxxxxxxx
> >Subject: Head movement
> >Comments: To: Pierre Divenyi <pdivenyi@xxxxxxxxx>
> >
> >Hi Pierre and List,
> >
> >In addition, as you move your head, the change in amplitude in the high
> >frequencies, -- resulting from different positions of the ear relative
> >the head's shadowing of the sound source -- will be different for sound
> >sources that are at different angles from the head.
> >
> >Physically, the rotation of the head affects the sound in a similar way
> >rotating the set of sound sources around the head.  However, we don't
> >whether the efferent motor signal plays a role, in the case of voluntary
> >head movement.
> >
> >Best wishes,
> >
> >Al