SETI update.436


Larry Klaes (lklaes@bbn.com)
Tue, 29 Jun 1999 14:57:17 -0400


>Date: Tue, 29 Jun 1999 08:29:02 -0400 (EDT) >From: AIP listserver <physnews@aip.org> >To: physnews-mailing@aip.org >Subject: update.436 > >PHYSICS NEWS UPDATE >The American Institute of Physics Bulletin of Physics News >Number 436 June 28, 1999 by Phillip F. Schewe and Ben Stein > >PERCEIVING MUSICAL PITCHES may require much less neural >processing and occur at a lower level of the nervous system than >previously thought, according to a new explanation, offering >possible insights into designing better hearing aids. A musical note >is defined mainly by its lowest pitch, known as its "fundamental >frequency," but a note also typically contains higher-pitched >"overtones" with frequencies that are some multiple of the >fundamental. Even when the fundamental frequency is completely >removed from a note, the overtones often allow listeners to >perceive the missing fundamental anyway. Being able to perceive >missing frequencies may explain why hearing a classical symphony >through a tiny radio, which cannot satisfactory reproduce the >lowest-frequency pitches, sounds reasonably faithful to a live >version heard in a concert hall. Recent explanations of how we >perceive "residue tones" require extensive amounts of neural >processing, which can only take place in the cerebral cortex. >However, researchers in Spain and Italy (Julyan Cartwright, Higher >Council for Scientific Research, Spain, 011-34-958-243360, >julyan@galiota.uib.es) propose that residue perception may result >from a "nonlinear" process, involving the generation of frequencies >that are not multiples of the original signal. Much more efficient >than previous linear models, their proposed mechanism can take >place at neural centers much earlier than the cerebral cortex. >Specifically, they propose a "three-frequency resonance" that takes >place in some neural processing center before the cerebral cortex, >in which the electrical signals generated by two overtones stimulate >a population of nerve cells to fire electrical signals at a third >frequency different from those of the two overtones. Better >understanding of pitch perception may lead to applications in >medicine; it is already known, for example, that hearing aids which >concentrate on making the fundamental frequencies more >intelligible produce better results than simple amplification alone. >(Cartwright et al., Physical Review Letters, 28 June; sound samples >at http://www.imedea.uib.es/~piro/PitchPage/ ) > >LONG BASELINE NEUTRINO OSCILLATION >EXPERIMENTS have now gotten underway with the >announcement that the Super-Kamiokande detector (near Tokyo) >has recorded the arrival of a neutrino launched in its direction from >the KEK proton accelerator 250 km away (near Tsukuba). Last >year Super-Kamiokande established the important fact that >neutrinos (made by cosmic rays striking the atmosphere) >transform, or oscillate, from one type to another on their way >through the Earth (see last week's Update 436 for more recent >results). In the new experiment (dubbed "K2K") physicists >attempt to confirm the oscillation phenomenon by allowing >neutrinos made artificially at an accelerator to pass through a >nearby detector and also the much more distant Super-Kamiokande >detector, aligned so as to receive the same neutrino beam. If, for >example, muon neutrinos oscillate into another type of neutrino, >adjusted event rates would be different for the two detectors. (K2K >website: http://neutrino.kek.jp; for background see Physics Today, >February 1996.) > >FIRE OR ICE IN CALIFORNIA. A new study shows that >episodic volcanism and glaciation have alternated in holding sway >over the California-Nevada borderlands during the past 800,000 >years. Scientists at the University of North Carolina and Duke, >who examined 112 different geological ages in documenting their >study, suggest that the anti-correlation comes about because of >climate-related issues, including perhaps the loading effect of lakes >or overlying ice (300 m thick in places) or the stress on the >lithosphere by changes in atmospheric circulation. (Glazner et al., >Geophysical Research Letters, 15 June.) >



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