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Re: ITDs

Dear David,

Maybe this is too basic but for completeness:
One reason that high frequency sinusoids does not provide reliable ITD
clues is the fact the distance between the ears is limited (~23 cm). This
yields a maximum ITD of 690 us. Which in turn corresponds to more than one
period of a 1500Hz sinusoid so a certain ITD can correspond to more than
one angle. The ITD gets more and more ambiguous as the frequency goes
beyond that.

See pages 236-237 in "An introduction to the Psychology of Hearing", Brian
CJ Moore

Best regards,

Martin Eklöf
Karolinska University Hospital, Huddinge
Cochlear implant clinic, M43
Tel: +46(0)8 - 585 89 329
Fax: +46(0)8 - 585 87 960
AUDITORY - Research in Auditory Perception <AUDITORY@xxxxxxxxxxxxxxx> skrev
2009-09-23 10:20:22 :

> John Culling
> 2009-09-23 10:29
> ITD is not an effective cue at high frequencies for pure tones,
> but other waveforms - noise bands, high-pass-filtered clicks
> and particularly "transposed stimuli" (cf. JASA papers by
> Bernstein, van de Par etc.) - it is still effective.
> The reason it is not effective for pure tones is
> presumed to be the fact that there is a loss of phase-locking to
> the fine structure of the stimulating waveform at stages of the
> auditory system that precede binaural interaction. It is known,
> for instance, that the capacitance of inner hair cells prevents
> their intracellular potential from following carrier frequencies
> in excess of 4-5 kHz in mammals. This results in a corresponding
> loss of encoding on the auditory nerve. Carrier ITDs cease to be
> effective above about 1500 Hz, however, so there may be
> further losses upstream. ITDs encoded by the waveform
> envelope (which are present for noises, clicks etc.) are not
> subject to this limitation,
> John.