Just joined this a bit late.
I tend to think of head movements in the context of cognitive spatial mapping.
That is, head movements are not wholly random, but can be used to build a
fuller, more robust model of the environment through a) disambiguating
unreliable/distorted cues, and b) 'firming up' cues using multiple, related,
perspectives -
so head movements are ways of improving spatial signal-to-noise ratios.
Thus, head movements are part of cognitive representational mechanisms (ironic,
because Gibson really tried to avoid cognitive constructionism)
I quite agree that the perceptual problem is not one of absolute sensory
acuity, but the signal-to-noise problem of picking up the 'right' information
in timely fashion. Given that many perceptual problems are driven by the pace
of external events, this 'timeliness' is crucial. The solutions humans use are
computationally expensive but offer competitive advantage - use 'offline'
processing to build up knowledge (of the environment) outside the urgent,
event-driven interaction-problems.
So, in a moment-by-moment interaction, it's quite likely that we make crucial
decisions using sparse information sets (which I think of as 'cognitive
cartoons') and, given that "...we are always already in a situation..."
(Dreyfus) most of what comprises our knowledge of the environment comes from
prior knowledge ('cognitive causal mapping') and the signal sets received via
sensation are really used to update and correct the on-going cognitive models.
However...
It must vary from situation to situation. In non-urgent situations, we may,
paradoxically, be able to afford to relax with the helter-skelter cognitive
modelling, and simply attend to sensations - the green-ness of a field, the
smell of some roses, the sound of a distant cricket match. There must be many
instances where urgent interaction is not indicated, where we can just enjoy
experiences. Our plethora of artificial experiences - music, art, etc might be
more of this nature, in which case, perception in artificial environments
qualitatively differs from that in real environments, perhaps?
regards
Dr. Peter Lennox
School of Technology,
Faculty of Arts, Design and Technology
University of Derby, UK
e: p.len...@derby.ac.uk
t: 01332 593155
-----Original Message-----
From: sursound-boun...@music.vt.edu [mailto:sursound-boun...@music.vt.edu] On
Behalf Of etienne deleflie
Sent: 02 April 2013 00:29
To: Eric Carmichel; Surround Sound discussion group
Subject: Re: [Sursound] Anthropometrics, Loudspeakers, & Vision
>
> Head width were certainly affect ITDs, but to what extent does this
> alter our sense of sound-source direction? Relatively gross errors
> seem to have minimal affect on lateralization, but this is different
> from localization in 3D. Pinna size and shape alter the spectral
> nature (name phase /
> amplitude) of higher-frequency, broadband sounds, but we can "re-learn"
> localization ability with a new or different set of ears. Head
> movement is certainly a way of resolving ambiguities
I think head movements do much more than just help in the perception of
discrete spatial attributes, such as sound onset direction. I think they also
contribute by helping our perceptual faculties 'accept' that the information
being presented is correct and reliable. I'm not sure what the right
terminology would be to express this ... maybe one could say that head
movements support the suspension of disbelief, or maybe one could say that head
movements help the perceptual faculties choose the *right* information to
perceive.
One of the characteristics in Gibson's ecological approach that has been
adopted by the VR field is the idea that perceptions are confirmed as true
through 'successful action in the environment'. Tilting one's head can be
considered action in the environment, and if the spatiality of the sounds heard
correlate then that action can be considered successful. So head movements help
to confirm that what is being perceived is correct. Perhaps a way to describe
it is to say that head movements don't just support quantitative aspects of
perception (eg. "this sound is 45deg +- 5 deg on the right) but also
qualitative aspects: "it sounds real" which leads to "it must be right".
I read in Handel's text "Listening" (I haven't looked for more substantive
references) that our perceptual systems are more limited by their ability to
*choose* the right information than by their ability to *pick up* information.
I think the tracking of head-movements on headphone listening systems helps
listeners choose the right information, which contributes to but is
significantly different from just helping resolve ambiguities.
> With the eyes closed and subject under constant rotational velocity
> (i.e., vestibular system in equilibrium or, equivalently, turned off),
> stationary sounds sources appear to move and moving sound sources
> appear to be stationary.
this could be understood in similar terms ... perhaps both the visual field and
the balance system help to confirm that certain information perceived is the
*right* information. I guess one question to ask here is: do the visual field
and vestibular system *add* extra information... or do they just help the
auditory system to choose the right information?
Perhaps one indication would be if the listener's perceptions remain correct
after they have re-closed their eyes. (ie. perhaps the 'learning'
actually exists as 'being able to choose the right info to perceive')
Etienne
> I won't say more at this time because I don't want to pass along info
> without having permission to do so. I'll have a chance to visit Bill's
> lab in the very near future, and ask when the results of the study are
> slated for publication.
>
> Best,
> Eric C.
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