Re: Integration of ITD information

[Jan Schnupp <jan.schnupp@xxxxxxxxxxxxxxxx>]

I must admit that I don't know the psychophysics literature on that, but 
from the Physiology point-of-view I would be surprised if there was much 
across-frequency-band integration in ITD processing. The reason for this 
is that ITDs must be inferred from inter-aural-phase differences as they 
are encoded in spike intervals in the auditory nerve, and these are 
different in different frequency bands and depend on the cochlear 
filtering as much as on the stimulus. Imagine you play a loud click into 
the ears. The 100 Hz place of the cochleas might ring in response to 
that stimulus at 100Hz, producing short trains of action potentials at 
10 ms intervals, while the 250 Hz location might ring at 250 Hz, 
producing 4 ms spike interval trains. Except for the first spike, these 
spike trains won't "line up", and comparing the 250 Hz band in the left 
ear with the 100 Hz band in the right ear cannot give you an unambiguous 
answer about the ITD. That's at least how I think about these things 
when I ask myself why the medial superior olive, where ITD extraction is 
thought to take place, is said to exhibit a very tight tonotopic 
organisation. If there was much to be gained by cross-frequency channel 
integration, one might expect the MSO not to exhibit such clearly 
defined and separated frequency channels. (However, I might be wrong 
about all this, so if some other list members do quote some good 
psychophysical evidence for cross-frequency integration, then listen to 
them and not to me!)

Regards,

Jan



Bernhard Laback wrote:

> Dear list,
>
> Is there any evidence for integration of interaural time difference 
> (ITD) information across frequency channels in ITD detection / 
> discrimination tasks? More specifically, are ITD JNDs lower for a 
> broadband stimulus compared to any narrowband stimulus within the 
> spectral range covered by the broadband stimulus?
>
> Of course, I assume that the overall intensity is held constant.
>
> I would appreciate any hint,
>
> With best regards,
>
> Bernhard Laback

--
Dr Jan Schnupp
University Laboratory of Physiology 
Parks Road - Oxford OX1 3PT
Tel +44-1865-272513
email: jan@xxxxxxxxxxxxxxxx
http://www.physiol.ox.ac.uk/~jan/