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Re: Upside down noise

Dear Pierre, Dear List,

Pierre Divenyi wrote:

> I have a different question: Von Hornbostel is credited with describing the
> following situation: a bird singing (presumably sinusoidally) on a branch
> is perceived as if it were flying from right to left as the frequency of
> its song varies (presumably not too fast). Provided v. H. is right, how
> could that phenomenon be explained? I presume there were no reflecting
> surfaces near the bird.

As a matter of fact, I was just finishing the reading of the article
by Aitkin et al. 1985 "Representation of Stimulus Azimuth by Low-Frequency
Neurons in Inferior Colliculus of the Cat" when I received your message.
Though more than 10 years old,  this paper seems to enlight some aspects
of your question (as far as I  understood it) from the point of view
of the physiology of the IC.

They write that "azimuth-selective units form a population suited to the
detection of the azimuthal angle of a low-frequency sound, but the sharpness
of their azimuth functions is related to their Best Frequencies (BFs).

>> "were flying from right to left"
This means that one perceives the bird flying in the "horizontal" plane,
i.e. he/she perceives a change in the azimuth.

It turns out that azimuth-selective units (cat's IC) are uncommon below
0.4 kHz buth also above 2 or 3 Khz; while the sharpest functions occur between
0.8 and 1.35 Khz.

The frontier of these two frequency ranges seems to fall in the range of
some birds songs. In other words, the pitch of this bird song might switch
between ranges of sharp azimuth-selective units and unsharp azimuth-selective
(even omnidirectional) ones.
This switch might explain a concurrent change in the location percept.

(I hope my message is not considered as "noise")

Eric Mousset

------------------- mailto:mousset@iam.unibe.ch ------------------
  Eric Mousset (Ph.D.) - Research Associate
  Institute of Informatics and Applied Mathematics (IAM)
  Neural Computing Research Group
  Neubrueckstrasse 10                     phone: +41 31 631 8607
  CH-3012 Bern, Switzerland               fax:   +41 31 631 3965
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P.S. Reference
L.M. Aitkin, J.D. Pettigrew, M.B. Calford, S.C. Phillips, and L.Z. Wise,
"Representation of Stimulus Azimuth by Low-Frequency Neurons in
Inferior Colliculus of the Cat", Journal of Neurophysiology,
Vol. 53, No. 1, January 1985.

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