2,472 research outputs found
Phase demodulation system with two phase locked loops Patent
Development of phase demodulation system with two phase locked loop
Auditory neuroscience: Development, transduction and integration
Hearing underlies our ability to locate sound sources in the environment, our appreciation of music, and our ability to communicate. Participants in the National Academy of Sciences colloquium on Auditory Neuroscience: Development, Transduction, and Integration presented research results bearing on four key issues in auditory research. How does the complex inner ear develop? How does the cochlea transduce sounds into electrical signals? How does the brain's ability to compute the location of a sound source develop? How does the forebrain analyze complex sounds, particularly species-specific communications? This article provides an introduction to the papers stemming from the meeting
Volterra-series approach to stochastic nonlinear dynamics: linear response of the Van der Pol oscillator driven by white noise
The Van der Pol equation is a paradigmatic model of relaxation oscillations.
This remarkable nonlinear phenomenon of self-sustained oscillatory motion
underlies important rhythmic processes in nature and electrical engineering.
Relaxation oscillations in a real system are usually coupled to environmental
noise, which further enriches their dynamics, but makes theoretical analysis of
such systems and determination of the equation's parameter values a difficult
task. In a companion paper we have proposed an analytic approach to a similar
problem for another classical nonlinear model, the bistable Duffing oscillator.
Here we extend our techniques to the case of the Van der Pol equation driven by
white noise. We analyze the statistics of solutions and propose a method to
estimate parameter values from the oscillator's time series. We use
experimental data of active oscillations in a biological system to demonstrate
how our method applies to real observations and how it can be generalized for
more complex models.Comment: 12 pages, 6 figures, 1 tabl
Discrimination of low-frequency tones employs temporal fine structure
An auditory neuron can preserve the temporal fine structure of a
low-frequency tone by phase-locking its response to the stimulus. Apart from
sound localization, however, little is known about the role of this temporal
information for signal processing in the brain. Through psychoacoustic studies
we provide direct evidence that humans employ temporal fine structure to
discriminate between frequencies. To this end we construct tones that are based
on a single frequency but in which, through the concatenation of wavelets, the
phase changes randomly every few cycles. We then test the frequency
discrimination of these phase-changing tones, of control tones without phase
changes, and of short tones that consist of a single wavelets. For carrier
frequencies below a few kilohertz we find that phase changes systematically
worsen frequency discrimination. No such effect appears for higher carrier
frequencies at which temporal information is not available in the central
auditory system.Comment: 12 pages, 3 figure
Two adaptation processes in auditory hair cells together can provide an active amplifier
The hair cells of the vertebrate inner ear convert mechanical stimuli to
electrical signals. Two adaptation mechanisms are known to modify the ionic
current flowing through the transduction channels of the hair bundles: a rapid
process involves calcium ions binding to the channels; and a slower adaptation
is associated with the movement of myosin motors. We present a mathematical
model of the hair cell which demonstrates that the combination of these two
mechanisms can produce `self-tuned critical oscillations', i.e. maintain the
hair bundle at the threshold of an oscillatory instability. The characteristic
frequency depends on the geometry of the bundle and on the calcium dynamics,
but is independent of channel kinetics. Poised on the verge of vibrating, the
hair bundle acts as an active amplifier. However, if the hair cell is
sufficiently perturbed, other dynamical regimes can occur. These include slow
relaxation oscillations which resemble the hair bundle motion observed in some
experimental preparations.Comment: 13 pages, 6 figures,REVTeX 4, To appear in Biophysical Journa
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