Re: [Ika-auditory] [AUDITORY] ITDs

[Nilesh Madhu <Nilesh.Madhu@xxxxxxxxxxxxxxxxxx>]

Hi Martin,

I wouldn't completely agree with your statement. It is true that doing
narrowband processing at the higher frequencies would lead to the phenomenon
you've described (which, by the way, is referred to as "spatial aliasing" in
the array processing literature). However, this can be avoided by computing
the ITD on the basis of the envelopes of a suitably band-passed region in
these frequencies. This could also be the reason for the increasing bandwidth
of the auditory filters, with increasing center frequency.

regards,

Nilesh


Martin Eklöf schrieb am 2009-09-23:
> 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
> ________________
> MSc
> Karolinska University Hospital, Huddinge
> Cochlear implant clinic, M43
> http://www.karolinska.se/ci
> martin.eklof@xxxxxxxxxxxxx
> 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 :

> > Re: [AUDITORY] ITDs
> > 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.

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-- 
Nilesh Madhu, M.Sc.(TUM),
Institute for Communications Acoustics,
Ruhr University Bochum,
D-44780, Bochum.
Tel.: +49 234 32 5872
Fax: +49 234 32 14165
Email: Nilesh.Madhu@xxxxxxxxxxxxxxxxxx
Web: http://www.ika.ruhr-uni-bochum.de