scholarly journals Applications of Phenomenological Loudness Models to Cochlear Implants

2021 ◽  
Vol 11 ◽  
Author(s):  
Colette M. McKay
Keyword(s):  
Cochlear Implants ◽  
Temporal Integration ◽  
Practical Method ◽  
Electrical Stimulus ◽  
Model Parameters ◽  
Specific Information ◽  
Detailed Model ◽  
Processing Strategies ◽  
Stimulus Parameters ◽  
Neural Excitation

Cochlear implants electrically stimulate surviving auditory neurons in the cochlea to provide severely or profoundly deaf people with access to hearing. Signal processing strategies derive frequency-specific information from the acoustic signal and code amplitude changes in frequency bands onto amplitude changes of current pulses emitted by the tonotopically arranged intracochlear electrodes. This article first describes how parameters of the electrical stimulation influence the loudness evoked and then summarizes two different phenomenological models developed by McKay and colleagues that have been used to explain psychophysical effects of stimulus parameters on loudness, detection, and modulation detection. The Temporal Model is applied to single-electrode stimuli and integrates cochlear neural excitation using a central temporal integration window analogous to that used in models of normal hearing. Perceptual decisions are made using decision criteria applied to the output of the integrator. By fitting the model parameters to a variety of psychophysical data, inferences can be made about how electrical stimulus parameters influence neural excitation in the cochlea. The Detailed Model is applied to multi-electrode stimuli, and includes effects of electrode interaction at a cochlear level and a transform between integrated excitation and specific loudness. The Practical Method of loudness estimation is a simplification of the Detailed Model and can be used to estimate the relative loudness of any multi-electrode pulsatile stimuli without the need to model excitation at the cochlear level. Clinical applications of these models to novel sound processing strategies are described.

scholarly journals Generalized Integrate-and-Fire Models of Neuronal Activity Approximate Spike Trains of a Detailed Model to a High Degree of Accuracy

2004 ◽  
Vol 92 (2) ◽  
pp. 959-976 ◽  
Author(s):  
Renaud Jolivet ◽  
Timothy J. Lewis ◽  
Wulfram Gerstner
Keyword(s):  
Cortical Neurons ◽  
Direct Reduction ◽  
Spike Trains ◽  
Model Parameters ◽  
Detailed Model ◽  
Fire Model ◽  
Integrate And Fire ◽  
Fire Models ◽  
Wide Range ◽  
Simple Models

We demonstrate that single-variable integrate-and-fire models can quantitatively capture the dynamics of a physiologically detailed model for fast-spiking cortical neurons. Through a systematic set of approximations, we reduce the conductance-based model to 2 variants of integrate-and-fire models. In the first variant (nonlinear integrate-and-fire model), parameters depend on the instantaneous membrane potential, whereas in the second variant, they depend on the time elapsed since the last spike [Spike Response Model (SRM)]. The direct reduction links features of the simple models to biophysical features of the full conductance-based model. To quantitatively test the predictive power of the SRM and of the nonlinear integrate-and-fire model, we compare spike trains in the simple models to those in the full conductance-based model when the models are subjected to identical randomly fluctuating input. For random current input, the simple models reproduce 70–80 percent of the spikes in the full model (with temporal precision of ±2 ms) over a wide range of firing frequencies. For random conductance injection, up to 73 percent of spikes are coincident. We also present a technique for numerically optimizing parameters in the SRM and the nonlinear integrate-and-fire model based on spike trains in the full conductance-based model. This technique can be used to tune simple models to reproduce spike trains of real neurons.

scholarly journals Inferring black hole spins and probing accretion/ejection flows in AGNs with the Athena X-ray Integral Field Unit

2019 ◽  
Vol 628 ◽  
pp. A5 ◽  
Author(s):  
Didier Barret ◽  
Massimo Cappi
Keyword(s):  
Black Hole ◽  
Extreme Values ◽  
Model Parameters ◽  
Gravitational Radius ◽  
Detailed Model ◽  
Spin Geometry ◽  
X Ray ◽  
Field Unit ◽  
Reflection Component ◽  
Integral Field

Context. Active galactic nuclei (AGNs) display complex X-ray spectra that exhibit a variety of emission and absorption features. These are commonly interpreted as a combination of (i) a relativistically smeared reflection component, resulting from the irradiation of an accretion disk by a compact hard X-ray source; (ii) one or several warm or ionized absorption components produced by AGN-driven outflows crossing our line of sight; and (iii) a nonrelativistic reflection component produced by more distant material. Disentangling these components via detailed model fitting could be used to constrain the black hole spin, geometry, and characteristics of the accretion flow, as well as of the outflows and surroundings of the black hole. Aims. We investigate how a high-throughput high-resolution X-ray spectrometer such as the Athena X-ray Integral Field Unit (X-IFU) can be used to this aim, using the state-of-the-art reflection model relxill in a lamp-post geometrical configuration. Methods. We simulated a representative sample of AGN spectra, including all necessary model complexities, as well as a range of model parameters going from standard to more extreme values, and considered X-ray fluxes that are representative of known AGN and quasar populations. We also present a method to estimate the systematic errors related to the uncertainties in the calibration of the X-IFU. Results. In a conservative setting, in which the reflection component is computed self consistently by the relxill model from the pre-set geometry and no iron overabundance, the mean errors on the spin and height of the irradiating source are < 0.05 and ∼0.2 Rg (in units of gravitational radius). Similarly, the absorber parameters (column density, ionization parameter, covering factor, and velocity) are measured to an accuracy typically less than ∼5% over their allowed range of variations. Extending the simulations to include blueshifted ultra-fast outflows, we show that X-IFU could measure their velocity with statistical errors < 1%, even for high-redshift objects (e.g., at redshifts ∼2.5). Conclusion. The simulations presented here demonstrate the potential of the X-IFU to understand how black holes are powered and how they shape their host galaxies. The accuracy in recovering the physical model parameters encoded in their X-ray emission is reached thanks to the unique capability of X-IFU to separate and constrain narrow and broad emission and absorption components.

An Introduction to Cochlear Implant Technology, Activation, and Programming

2002 ◽  
Vol 33 (3) ◽  
pp. 153-161 ◽  
Author(s):  
Jan A. Moore ◽  
Holly F. B. Teagle
Keyword(s):  
Hearing Loss ◽  
Cochlear Implant ◽  
Cochlear Implants ◽  
Speech Processing ◽  
Academic Development ◽  
School Age Children ◽  
School Age ◽  
Technology In The Classroom ◽  
Processing Strategies ◽  
Cochlear Implant Surgery

Over the last decade, cochlear implantation has become an increasingly viable alternative for the treatment of profound sensorineural hearing loss in children. Although speech and hearing professionals play an important role in the communicative, social, and academic development of children with cochlear implants, many may be unfamiliar with recent advances in implant technology. This article provides an overview of the components of cochlear implant systems and the speech processing strategies that are currently being used by toddlers, preschoolers, and school-age children. A brief description of cochlear implant surgery and the procedures for programming these devices are also included. Finally, information regarding the use of assistive listening technology in the classroom is presented.

The Duncan-Chang Model Parameters for Municipal Solid Waste

2011 ◽  
Vol 48-49 ◽  
pp. 1235-1240
Author(s):  
Zhen Ying Zhang ◽  
Da Zhi Wu
Keyword(s):  
Theoretical Analysis ◽  
Municipal Solid Waste ◽  
Solid Waste ◽  
Void Ratio ◽  
Practical Method ◽  
Model Parameters ◽  
Mechanical Parameters ◽  
Initial Void Ratio ◽  
The Relationship ◽  
Chang Model

By theoretical analysis and laboratory test, the model parameters of Duncan-Chang for municipal solid waste have been studied. To obtain the mechanical parameters, a new simple and practical method has been established. Research results show that the damage ratio is 0.6, parameter n is about 1.05, parameter F varies between 0 and 0.1, and parameter G varies between 0.3 and 0.4. Besides, the relationship between parameter k and the initial void ratio is linear, and the slope of the line is 5.0.

scholarly journals Inferring Biological Mechanisms by Data-Based Mathematical Modelling: Compartment-Specific Gene Activation during Sporulation in Bacillus subtilis as a Test Case

2011 ◽  
Vol 2011 ◽  
pp. 1-12 ◽  
Author(s):  
Dagmar Iber
Keyword(s):  
Bacillus Subtilis ◽  
Gene Activation ◽  
Experimental Information ◽  
Specific Gene ◽  
Model Parameters ◽  
Test Case ◽  
Detailed Model ◽  
Wide Range ◽  
Technical Advances ◽  
Biological Functionality

Biological functionality arises from the complex interactions of simple components. Emerging behaviour is difficult to recognize with verbal models alone, and mathematical approaches are important. Even few interacting components can give rise to a wide range of different responses, that is, sustained, transient, oscillatory, switch-like responses, depending on the values of the model parameters. A quantitative comparison of model predictions and experiments is therefore important to distinguish between competing hypotheses and to judge whether a certain regulatory behaviour is at all possible and plausible given the observed type and strengths of interactions and the speed of reactions. Here I will review a detailed model for the transcription factor , a regulator of cell differentiation during sporulation in Bacillus subtilis. I will focus in particular on the type of conclusions that can be drawn from detailed, carefully validated models of biological signaling networks. For most systems, such detailed experimental information is currently not available, but accumulating biochemical data through technical advances are likely to enable the detailed modelling of an increasing number of pathways. A major challenge will be the linking of such detailed models and their integration into a multiscale framework to enable their analysis in a larger biological context.

Guide for the Practical Application of the ICRP Human Respiratory Tract Model

2002 ◽  
Vol 32 (1-2) ◽  
pp. 13-14 ◽  
Author(s):  
J. Valentin
Keyword(s):  
Respiratory Tract ◽  
Reference Values ◽  
Model Parameters ◽  
Specific Information ◽  
Guidance Document ◽  
Human Respiratory Tract ◽  
Additional Information ◽  
Dose Coefficients ◽  
Bioassay Data ◽  
Parameter Values

The ICRP Publication 66 Human Respiratory Tract Model for Radiological Protection (HRTM) has been applied to calculate dose coefficients (doses per unit intake) and bioassay functions in ICRP Publications 68, 71, 72 and 78. For these purposes, ICRP assigned numerical values to a range of model parameters, such as the size of the inhaled particles and the breathing rate of the subjects. These are known as ‘default’ or ‘reference’ values, and were chosen to be typical, representative values. In any particular situation the actual values of many parameters can be considerably different from the reference values. Usually, doses from intakes of radionuclides are low compared with the relevant limit or constraint, and the resulting difference is unimportant. There are, however, circumstances where more reliable assessments of intake and dose are desirable. This Guidance Document therefore gives advice on applying specific information within the framework of the HRTM for assessing occupational and environmental exposures and for interpreting bioassay data. Chapters on each aspect of the model (morphometry, physiology, deposition, clearance, gases and vapours, dosimetry) provide: A summary of how the HRTM treats that topic; Information on the reference values of relevant parameters; Guidance on choosing between default values; Information on how doses and bioassay quantities (lung retention, urine, and faecal excretion) vary with the values of selected parameters, giving guidance on the importance of obtaining specific information; Simple examples of the use of specific information relating to the topic. Annexes give additional information for those directly involved in applying the HRTM to specific situations, including guidance on obtaining parameter values. A brief overview is given of the deposition, characterisation, and sampling of aerosols, with references to further information, as there are relevant text books already available. Issues specific to radioactive aerosols, such as low particle number concentrations for high specific activity materials are, however, addressed. Guidance on obtaining information about absorption of inhaled radionuclides into blood is given in greater detail, because this is a topic on which ICRP has traditionally given guidance, and because a compilation of such information is not readily available elsewhere. Several detailed examples are also provided. One involves assessment of an individual's intake and committed dose from comprehensive bioassay monitoring data. The others deal with the derivation of HRTM absorption parameter values from experimental data, and their application, with additional information on e.g. size distribution, to calculate dose coefficients and interpret bioassay data.

Making the Most of What We Have: A Practical Application of Multidimensional Item Response Theory in Test Scoring

2005 ◽  
Vol 30 (3) ◽  
pp. 295-311 ◽  
Author(s):  
Jimmy de la Torre ◽  
Richard J. Patz
Keyword(s):  
Item Response ◽  
Practical Method ◽  
Multidimensional Item Response Theory ◽  
Model Parameters ◽  
Practical Application ◽  
Multidimensional Item Response ◽  
Multiple Tests ◽  
Monte Carlo Techniques ◽  
Estimation Of Model Parameters ◽  
Highly Correlated

This article proposes a practical method that capitalizes on the availability of information from multiple tests measuring correlated abilities given in a single test administration. By simultaneously estimating different abilities with the use of a hierarchical Bayesian framework, more precise estimates for each ability dimension are obtained. The efficiency of the proposed method is most pronounced when highly correlated abilities are estimated from multiple short tests. Employing Markov chain Monte Carlo techniques allows for straightforward estimation of model parameters.

A Comparison of the Speech Understanding Provided by Acoustic Models of Fixed-Channel and Channel-Picking Signal Processors for Cochlear Implants

2002 ◽  
Vol 45 (4) ◽  
pp. 783-788 ◽  
Author(s):  
Michael F. Dorman ◽  
Philipos C. Loizou ◽  
Anthony J. Spahr ◽  
Erin Maloff
Keyword(s):  
Speech Recognition ◽  
Cochlear Implants ◽  
Stimulus Material ◽  
Channel Strategy ◽  
Processing Strategies ◽  
High Level ◽  
Signal Processors ◽  
Very High ◽  
Device Programming ◽  
A Performance

Vowels, consonants, and sentences were processed by two cochlear-implant signal-processing strategies—a fixed-channel strategy and a channel-picking strategy—and the resulting signals were presented to listeners with normal hearing for identification. At issue was the number of channels of stimulation needed in each strategy to achieve an equivalent level of speech recognition in quiet and in noise. In quiet, 8 fixed channels allowed a performance maximum for the most difficult stimulus material. A similar level of performance was reached with a 6-of-20 channel-picking strategy. In noise, 10 fixed channels allowed a performance maximum for the most difficult stimulus material. A similar level of performance was reached with a 9-of-20 strategy. Both strategies are capable of providing a very high level of speech recognition. Choosing between the two strategies may, ultimately, depend on issues that are independent of speech recognition—such as ease of device programming.

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