Songbirds’ singing is a complex behavior that must be learned. It has stimulated rapidly advancing research in various disciplines, notably neurobiology and behavioral ecology. But do not understand in detail how sound is produced by the birds’ vocal organ, the syrinx. The main reason for this is that the syrinx is located at the base of the trachea (windpipe).
To make it relatively inaccessible to direct physiological studies powerful direct methods have been effectively used to study sound production in the human voice box. That cannot easily be adapted to investigate the avian syrinx.
So, the ideas about sound generation in birds are based on indirect approaches. Such as analysis of vocalizations and of the morphology of the syrinx, and theoretical models. The combination of indirect and direct approaches can support overcoming these difficulties. The careful analysis of the zebra finch (Taeniopygia guttata) song revealed linear and nonlinear phenomena.
That is including switches from periodic to periodic or chaotic oscillations and period doubling. Also, transitions from linear to nonlinear dynamics occurred rapidly (within 1 ms), without silent intervals between the two states. The transitions arise from intrinsic properties of the vibrating components of the syrinx rather than from complex neural control.
So far, it was presumed that the central nervous system directly controls the often-intricate temporal pattern of the song. In birds, singing contains the expiatory muscles that line the body wall and generate pulses of increased air pressure by compressing the posterior air sacs. These pulses define the coarse temporal pattern, which can be modified by the activity of the syringa muscles.
These muscles are well attached to the syrinx. Because they turn sound production on and off by opening and closing the airways through the syrinx. Also, the respiratory and syringeal muscles also control the acoustic structure of the song. Such as sound frequency and amplitude, and frequency modulation. An intricate network of brain areas controls the respiratory and syringeal muscles during song production.
But we now learn that intrinsic mechanical properties of the syrinx can contribute to temporal and acoustic song patterns. These patterns are independent of complex central control, needing a minimal contribution (in the form of slowly changing the pressure from the respiratory and vocal muscles.
This is discovered by studying the vibratory behavior of the zebra finch syrinx in an in vitro preparation. Moreover, the sounds induced by drawing air through the excised syrinx in some species of bird. The acoustic versatility of the song is an indicator of male reproductive fitness. So, this may be important for the choice of mate and encounters between members of the same sex.
Also, If the peripherally generated acoustic structure requires a less precise motor control than complex sound modulation controlled by the action of muscles. It is also weighted differently by a listener who is trying to work out the ‘quality’ of the singer. The findings are also of practical importance for researchers trying to quantify the quality of birdsong.
The assessment of songbird complexity is firmly linked to knowledge of sound-producing mechanisms, and now peripheral contributions to song structure must be added. The task has become even more challenging. At last, they remain the question of whether nonlinear dynamics might also be mixed up in singing by other species of bird.
The nonlinear effects contributing to the temporal and acoustic pattern in bird vocalizations will be described. Also, nonlinearity is well known in the physiology of the human vocal organ. But to those who suffer from the roughness of voice, it must be of little comfort to know that nonlinearity can also be a mechanism to enhance vocal properties.
In the well-known debate between Niels Bohr and Albert Einstein on the nature of quantum reality, a well-asked question central to their debate on the nature of quantum interference has resurfaced. Dürr, Nonn, and Rempe have used an atom interferometer to show that Schrödinger’s concept of ‘entanglement’ between the states of particles is the key to wave-particle duality and to understanding much that is weird about quantum mechanics.
This is quite different from the usual textbook explanation of duality in terms of unavoidable measurement disturbances. It confirms that entanglement is essential in establishing quantum weirdness and in the emergence of classical behavior at larger scales. Quantum entities can act like particles or waves, depending on how they are observed.
They can be diffracted and produce interference patterns (wave behavior) when they can take different paths from some source to a detector in the usual example. The electrons or photons go through two slits and form an interference pattern on the screen behind. On the other hand, with an appropriate detector put along one of the paths, the quantum entities can be detected at a specific place and time, as if they are point-like particles.
But any attempt to determine which path is taken by a quantum object destroys the interference pattern. The central mystery of quantum physics, and Bohr called this vague principle ‘complementarily’, and explained it in terms of the uncertainty principle, put forward by Werner Heisenberg, his postbox at the time.
To persuade Einstein that wave-particle duality is a vital part of quantum mechanics. Bohr constructed models of quantum measurements that showed the futility of trying to determine which path was taken by a quantum object in an interference experiment. As soon as enough information is acquired for this determination, the quantum interferences must vanish.
Because any act of observing will impart uncontrollable momentum kicks to the quantum object. This is quantified by Heisenberg’s uncertainty principle, which relates uncertainty in positional information to uncertainty in momentum when the position of an entity is constrained, the momentum must be randomized to a certain degree.
This explanation in terms of the uncertainty principle has become a talisman foursome, but it has left others uneasy, as it views the measurement and momentum kicks as ‘locally realistic’ in other words, as idealized classical measurements, rather than quantum mechanical phenomena themselves.
This is a treacherous position, and it has led to a debate in this journal between a group centered on the Max-Planck Institute for Quantum Optics and one in Auckland, on whether momentum kicks are necessary to explain the two-slit experiment. Apparently, momentum is involved, because a diffraction pattern is a map of the momentum distribution in the experiment.
But how is it involved? Is it everything, as Bohr would have claimed? This is the question addressed by Dürr. Who has studied the interference fringes produced when a beam of cold atoms is diffracted by standing waves of light?
Their interferometer displays fringes of high contrast but when they encode within the atoms information as to which path is taken, the fringes disappear entirely. The internal labeling of paths does not even need to be read out to destroy the interferences: all you need is the option of being able to read it out.
Songbirds’ singing is complex behavior stimulated by rapidly advancing research various disciplines notably neurobiology & behavioral ecology
