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:
> 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.
> 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.
> 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.