Re: Upside down noise (Eric Mousset )

Subject: Re: Upside down noise
From:    Eric Mousset  <mousset(at)IAM.UNIBE.CH>
Date:    Thu, 6 Aug 1998 21:46:35 +0200

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(at) ------------------ 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 ----------------- ---------------- 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. McGill is running a new version of LISTSERV (1.8c on Windows NT). Information is available on the WEB at

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