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Re: Integration of ITD information

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!)



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