|
First Summary: Lateral Inversion in Spatial
Hearing
On September, 2nd, I have put the following query
on this list:
> I wonder if anybody on the Auditory List knows
something about a lateral
> inversion phenomenon I discovered when preparing sounds for a series of > experiments on spatial hearing: certain binaural recordings of > bandpass-filtered clicks with interaural time differences but without > interaural intensity differences seem to be lateralized as predicted by > cross-correlation models in a frequency range below 2 Kilohertz but on the > opposite side than predicted by these models in a frequency range above > 8 Kilohertz. In response to some
of your questions I have put an example sound file for the lateral inversion
phenomenon on http://Heinrich.Zimmermann.com.
Thanks for the following postings:
Joachim Neubaum:
> In dem Buch > * J. Blauert > * Räumliches Hören > * Monographien der Nachrichtentechnik, 1964 > steht was über Lokalisation verschiedener Frequenzbänder. > Das könnte helfen, das von Ihnen beobachtete Phänomen zu verstehen. Harry Erwin:
> I have a bat model that uses IIDs to estimate
azimuth. I did this
> because there's a tradeoff between timing and intensity (1 dB > corresponding to 47 microseconds of advance or delay in the Mexican > free-tailed bat, Pollak 1988), and the bat head is too small for ITDs > to work well at high frequencies (no more than 40-50 microseconds in > E fuscus) while IIDs of 20-30 dB are seen due to head shadowing (see > Moss and Schnitzler in Popper and Fay, ed., 1995, Hearing by Bats, > Springer). At low frequencies (less than about 3 kHz), the signal in > auditory nerve does track the variation, of course, and you can > do cross-correlation. My model works beautifully for a single target. > You may have seeing some sort of phenomenon having to do with the > time/intensity tradeoff. Assuming a head diameter of 15 cm, you're > getting a ITD of about 750 microseconds at most. Richard R Fabbri:
> What does the time domain waveform (the
"click") exiting the
> bandpass look like ? > Could you send a 'scope trace ? Daniel J. Tollin: > Don't know if it is relevant to your work or
not, but you might check out
> the following paper: > Tollin and Henning (1999). Some aspects of the lateralization of echoed > sound in man. II. The role of the stimulus spectrum, J. Acoust. Soc. AM. > 105, 838-849. > In that paper I describe a lateralization illusion in which observers > lateralize a signal opposite that expected based on the ITD in the signal. > I also give reasons for the anomalous lateralization. S. L. J. D. E. van de Par > It is not entirely clear to me what exactly
you observed,
> but I assume that the clicks were lateralized to one > side below 2 kHz and to the other side above 8 kHz > (or was it the case that they were lateralized to > the same side but that the models predicted otherwise?). > One thing came to mind which may be important. > When binaural stimuli are presented through headphones > there may likely exist IIDs which vary as a function > of frequency due to differences in acoustic coupling of > the left and right earphones. These IIDs of course may > influence the perceived laterality. But I assume that you > have checked for that. Ward Drennan
> I'd be suprised anything was lateralized
without ILDs at 8KHz.
> Timing info is lost. > An onset asynchrony might give you a little cue, but I'd think in the > direction would be towards the leading filtered click. I don't know the > bandwidths, the onset characteristics, the > delay times or the precise levels--- a 1 dB difference in level between the > left and right ears could give you a lateralization at 8 KHz-- expecially if > there were no onset asynchronies. |