isak gath - Academia.edu (original) (raw)
Papers by isak gath
Physiological Measurement, May 1, 1998
The SA node response to modulations in canine vagal tone was investigated by means of the heart r... more The SA node response to modulations in canine vagal tone was investigated by means of the heart rate variability power spectrum. A new algorithm that was developed for accurate power spectrum estimation of short R-R segments is described. The performance of the algorithm was assessed for ECG recordings obtained from a controlled experiment, in which a frequency modulated pulse train was applied to the vagal nerve after vagal transaction and blockade of the sympathetic system. The power spectrum calculated for 20-25 heartbeats showed conspicuous spectral peaks in accordance with the different modulating frequencies between 0.1 and 0.3 Hz. The presence of spurious peaks was negligible even when the analysed signal segment consisted of only 20-25 beats. These results imply that for a certain range of modulating frequencies the sinoatrial node responds linearly to fluctuations in the parasympathetic tone. System identification methods that include fitting a linear model to the heart rate variability signal and analysis of the residuals were used for confirming the hypothesis of linearity. For higher frequencies of the modulating signal, usually above 0.3 Hz, the system was found to deviate from linearity.
Journal of Voice, Sep 1, 2019
Dual-channel adaptive segmentation of the electroencephalogram (EEG) signal is proposed. The purp... more Dual-channel adaptive segmentation of the electroencephalogram (EEG) signal is proposed. The purpose is to divide the signals into quasi-stationary segments, on the basis of information common for the two channels. The segment boundary is determined by changes in the cross spectrum of the two signals. It has been shown theoretically, as well as by simulation studies, that this method is sensitive to changes common to both channels, whereas segmentation does not occur as a result of changes in each channel separately.<<ETX>>
ABSTRACT The influence of the autonomic nervous system on the heart rate signal is interpreted as... more ABSTRACT The influence of the autonomic nervous system on the heart rate signal is interpreted as a frequency modulating signal which is composed of two opposing sources: the sympathetic and the parasympathetic systems. A derivation of a theoretical method for extracting the power spectrum of this compound modulator is presented together with experimental results. The estimation method is generally developed, providing an alternative formulation for power spectrum estimation of modulated random processes which follow certain limitations
Long segments of heart rate variability signals are usually nonstationary and dynamic, thus limit... more Long segments of heart rate variability signals are usually nonstationary and dynamic, thus limiting the length of the signal available for spectral analysis. An algorithm was developed for accurate power spectrum estimation of short R-R segments not exceeding 15-20 beats. The algorithm was tested during an experiment in two dogs, where frequency modulated pulse train was applied to the vagal nerve after vagal transaction and blockade of the sympathetic system by propranolol. The calculated power spectra presented conspicuous spectral peaks in accordance with the different modulating frequencies between 0.1 Hz and 0.3 Hz. The presence of spurious peaks was negligible even when the analyzed signal segments consisted of 15-20 beats only. These results imply that for a certain range of modulating frequencies the sinoatrial node responds linearly to fluctuations in the parasympathetic tone. System identification methods were used for confirming this hypothesis. For higher frequencies of the modulating signal usually above 0.3 Hz the system tends to deviate from linearity.
Pattern Recognition Letters, Oct 1, 1989
Abstract Syntactic pattern recognition approach was applied to classification of EEG segments bel... more Abstract Syntactic pattern recognition approach was applied to classification of EEG segments belonging to sleep stage I and stage REM. Feature extraction was carried out using adaptive segmentation of the EEG signal, and the process of primitive recognition was implemented through unsupervised fuzzy clustering. Grammatical inference was done automatically constructing canonical derivative finite-state grammers for the two training sets. For the classification, a minimum-distance error-correcting parser was used, to account for substitution errors in the process of primitive recognition.
IEEE Transactions on Biomedical Engineering, 1991
High resolution analysis of voiced speech signals in Parkinsonian patients using a pitch synchron... more High resolution analysis of voiced speech signals in Parkinsonian patients using a pitch synchronous pole-zero model is introduced. A modified estimation error is defined leading to an accurate and consistent determination of the excitation instants of the model. An infinite resolution in determining these instants, despite the finite sampling interval, is achieved by mapping the discrete (digitized) problem into a continuous one. The proposed analysis was found to be useful in analyzing Parkinsonian speech where the goal was to detect and quantify the Parkinsonian tremor and rigidity from sustained voiced sounds.
Experimental Brain Research, Aug 1, 1981
In Situ Measurement of the Innervation Ratio of Motor Units in Human Muscles
IEEE Transactions on Biomedical Engineering, Jun 1, 1979
ACKNOWLEDGMENT The authors wish to thank Ms. S. Wendling for typing the manuscript and R. Berrett... more ACKNOWLEDGMENT The authors wish to thank Ms. S. Wendling for typing the manuscript and R. Berretta for preparation of the figures and P. Gochin for his many helpful suggestions. Thanks are also due to D. A. Robinson for his critical comments on the manuscript.
Neurology, Apr 1, 1969
Either your web browser doesn't support Javascript or it is currently turned off. In the lat... more Either your web browser doesn't support Javascript or it is currently turned off. In the latter case, please turn on Javascript support in your web browser and reload this page. ... Or filteryour current search. Gath I, Find all citations by this author (default). ...
Electroencephalography and Clinical Neurophysiology, Oct 1, 1975
Biological Cybernetics, Nov 1, 1981
In 12 epileptic patients suffering from "absences" 8-channel EEG was recorded by telemetry. The a... more In 12 epileptic patients suffering from "absences" 8-channel EEG was recorded by telemetry. The autoregressive model was applied to the signal and the prediction coefficients being the basis for calculation of the poles of the predictor. The location of the poles in the z-and s-planes was described as a function of time for 0.1 s steps along the pre-seizure EEG. In 10 of the 12 patients, and in 25 of the 28 recorded seizures this presentation of the poles of the predictor showed specific pattern linked with the occurrence of the seizure. The trajectory of the "most mobile pole" during the pre-seizure period could aid in the prediction of the seizure by several seconds.
IEEE Transactions on Pattern Analysis and Machine Intelligence, 1994
TRANSACTIONS ON PATERN ANALYSIS AND MACHINE INTELLIGENCE, VOL. 16, NO. 8. AUGUST 1994 ... LA Flet... more TRANSACTIONS ON PATERN ANALYSIS AND MACHINE INTELLIGENCE, VOL. 16, NO. 8. AUGUST 1994 ... LA Fletcher and R. Kasturi, A robust algorithm for text string separation from mixed texvgraphics images, IEEE Trans. Pattern Anal. Machine Intell., vol. IO, pp. ...
Proceedings of the IEEE, 1988
A point process model of the speech excitation wave for sustained vowels has been formulated, whe... more A point process model of the speech excitation wave for sustained vowels has been formulated, where the pitch is modulated by a physiological disturbance (vocal tremor). It has been demonstrated that the power spectrum of an impulse train, representing the glottal pulses, is composed of a periodic replication of the spectrum of the modulating signal, accompanied by an impulse train at the carrier frequency. Hence, the power spectrum of the vocal tremor can be estimated from the pitch. A trend location algorithm has been developed, in order to locate and remove local trends from the signal, prior to the evaluation of the pitch power spectrum. Thus, spectral representation of the speech excitation enables estimation of vocal tremor.
Neurology, Oct 1, 1968
HUNTINGTON’S CHOREA is a degenerative disease of the central nervous system, characterized mainly... more HUNTINGTON’S CHOREA is a degenerative disease of the central nervous system, characterized mainly by three features: dominant heredity, extrapyramidal involuntary movements, and mental changes. The pathological changes are confined to the basal ganglia, especially to the caudate nucleus,’ and to the cerebral cortex. The clinical symptoms, as well, seem to be causally related to the above-mentioned pathological findings. The mental changes are probably due to the cortical affection, and the involuntary movements to the striatal involvement.2 The localization of the pathological changes may explain the unusual type of the cerebral atrophy found by pneumoencephalographic studies in cases of Huntington’s chorea.3-5 There are, however, only a few reports dealing with air encephalographic studies in relation to Huntington’s chorea, and all of them present a limited number of cases.3-5 Likewise, modern textbooks in neuroradiology have not dealt thoroughly with this subject.6.7 The purpose of the present work was, therefore, to reexamine the pneumoencephalographic features of Huntington’s chorea in a fairly large series of cases, the relation of these features to the clinical symptoms, and the value of pneumoencephalography as a diagnostic tool in case of Huntington’s chorea.
Electroencephalography and Clinical Neurophysiology, May 1, 1978
Action potentials from 16 single muscle fibres were recorded with a multi-electrode from the huma... more Action potentials from 16 single muscle fibres were recorded with a multi-electrode from the human brachial biceps. Propagation velocity was calculated for 10 of the fibres, and the volume conduction at distances of 79, 152 and 251 micrometer, was measured for 6 of these fibres. The radial decline of the action potentials was calculated from the Fourier transform of the action potential at the origin, simulating the low-pass filter characteristics of the muscle tissue by sections of RC elements. A good agreement was found between the calculated data and the experimental data on the radial decline of the action potentials. The 90% attenuation radius of the action potential recorded with a 25 micrometer electrode, calculated for 16 action potentials, was derived from the volume conduction calculations. The average value found was 191 +/- 20 micrometer. A linear correlation was found between this radius and the peak spectral amplitude of the action potentials. Likewise, a linear correlation between the 90% attenuation radius and the propagation velocity of the fibres was confirmed.
IEEE Transactions on Pattern Analysis and Machine Intelligence, Jul 1, 1989
Physiological Measurement, May 1, 1998
The SA node response to modulations in canine vagal tone was investigated by means of the heart r... more The SA node response to modulations in canine vagal tone was investigated by means of the heart rate variability power spectrum. A new algorithm that was developed for accurate power spectrum estimation of short R-R segments is described. The performance of the algorithm was assessed for ECG recordings obtained from a controlled experiment, in which a frequency modulated pulse train was applied to the vagal nerve after vagal transaction and blockade of the sympathetic system. The power spectrum calculated for 20-25 heartbeats showed conspicuous spectral peaks in accordance with the different modulating frequencies between 0.1 and 0.3 Hz. The presence of spurious peaks was negligible even when the analysed signal segment consisted of only 20-25 beats. These results imply that for a certain range of modulating frequencies the sinoatrial node responds linearly to fluctuations in the parasympathetic tone. System identification methods that include fitting a linear model to the heart rate variability signal and analysis of the residuals were used for confirming the hypothesis of linearity. For higher frequencies of the modulating signal, usually above 0.3 Hz, the system was found to deviate from linearity.
Journal of Voice, Sep 1, 2019
Dual-channel adaptive segmentation of the electroencephalogram (EEG) signal is proposed. The purp... more Dual-channel adaptive segmentation of the electroencephalogram (EEG) signal is proposed. The purpose is to divide the signals into quasi-stationary segments, on the basis of information common for the two channels. The segment boundary is determined by changes in the cross spectrum of the two signals. It has been shown theoretically, as well as by simulation studies, that this method is sensitive to changes common to both channels, whereas segmentation does not occur as a result of changes in each channel separately.<<ETX>>
ABSTRACT The influence of the autonomic nervous system on the heart rate signal is interpreted as... more ABSTRACT The influence of the autonomic nervous system on the heart rate signal is interpreted as a frequency modulating signal which is composed of two opposing sources: the sympathetic and the parasympathetic systems. A derivation of a theoretical method for extracting the power spectrum of this compound modulator is presented together with experimental results. The estimation method is generally developed, providing an alternative formulation for power spectrum estimation of modulated random processes which follow certain limitations
Long segments of heart rate variability signals are usually nonstationary and dynamic, thus limit... more Long segments of heart rate variability signals are usually nonstationary and dynamic, thus limiting the length of the signal available for spectral analysis. An algorithm was developed for accurate power spectrum estimation of short R-R segments not exceeding 15-20 beats. The algorithm was tested during an experiment in two dogs, where frequency modulated pulse train was applied to the vagal nerve after vagal transaction and blockade of the sympathetic system by propranolol. The calculated power spectra presented conspicuous spectral peaks in accordance with the different modulating frequencies between 0.1 Hz and 0.3 Hz. The presence of spurious peaks was negligible even when the analyzed signal segments consisted of 15-20 beats only. These results imply that for a certain range of modulating frequencies the sinoatrial node responds linearly to fluctuations in the parasympathetic tone. System identification methods were used for confirming this hypothesis. For higher frequencies of the modulating signal usually above 0.3 Hz the system tends to deviate from linearity.
Pattern Recognition Letters, Oct 1, 1989
Abstract Syntactic pattern recognition approach was applied to classification of EEG segments bel... more Abstract Syntactic pattern recognition approach was applied to classification of EEG segments belonging to sleep stage I and stage REM. Feature extraction was carried out using adaptive segmentation of the EEG signal, and the process of primitive recognition was implemented through unsupervised fuzzy clustering. Grammatical inference was done automatically constructing canonical derivative finite-state grammers for the two training sets. For the classification, a minimum-distance error-correcting parser was used, to account for substitution errors in the process of primitive recognition.
IEEE Transactions on Biomedical Engineering, 1991
High resolution analysis of voiced speech signals in Parkinsonian patients using a pitch synchron... more High resolution analysis of voiced speech signals in Parkinsonian patients using a pitch synchronous pole-zero model is introduced. A modified estimation error is defined leading to an accurate and consistent determination of the excitation instants of the model. An infinite resolution in determining these instants, despite the finite sampling interval, is achieved by mapping the discrete (digitized) problem into a continuous one. The proposed analysis was found to be useful in analyzing Parkinsonian speech where the goal was to detect and quantify the Parkinsonian tremor and rigidity from sustained voiced sounds.
Experimental Brain Research, Aug 1, 1981
In Situ Measurement of the Innervation Ratio of Motor Units in Human Muscles
IEEE Transactions on Biomedical Engineering, Jun 1, 1979
ACKNOWLEDGMENT The authors wish to thank Ms. S. Wendling for typing the manuscript and R. Berrett... more ACKNOWLEDGMENT The authors wish to thank Ms. S. Wendling for typing the manuscript and R. Berretta for preparation of the figures and P. Gochin for his many helpful suggestions. Thanks are also due to D. A. Robinson for his critical comments on the manuscript.
Neurology, Apr 1, 1969
Either your web browser doesn't support Javascript or it is currently turned off. In the lat... more Either your web browser doesn't support Javascript or it is currently turned off. In the latter case, please turn on Javascript support in your web browser and reload this page. ... Or filteryour current search. Gath I, Find all citations by this author (default). ...
Electroencephalography and Clinical Neurophysiology, Oct 1, 1975
Biological Cybernetics, Nov 1, 1981
In 12 epileptic patients suffering from "absences" 8-channel EEG was recorded by telemetry. The a... more In 12 epileptic patients suffering from "absences" 8-channel EEG was recorded by telemetry. The autoregressive model was applied to the signal and the prediction coefficients being the basis for calculation of the poles of the predictor. The location of the poles in the z-and s-planes was described as a function of time for 0.1 s steps along the pre-seizure EEG. In 10 of the 12 patients, and in 25 of the 28 recorded seizures this presentation of the poles of the predictor showed specific pattern linked with the occurrence of the seizure. The trajectory of the "most mobile pole" during the pre-seizure period could aid in the prediction of the seizure by several seconds.
IEEE Transactions on Pattern Analysis and Machine Intelligence, 1994
TRANSACTIONS ON PATERN ANALYSIS AND MACHINE INTELLIGENCE, VOL. 16, NO. 8. AUGUST 1994 ... LA Flet... more TRANSACTIONS ON PATERN ANALYSIS AND MACHINE INTELLIGENCE, VOL. 16, NO. 8. AUGUST 1994 ... LA Fletcher and R. Kasturi, A robust algorithm for text string separation from mixed texvgraphics images, IEEE Trans. Pattern Anal. Machine Intell., vol. IO, pp. ...
Proceedings of the IEEE, 1988
A point process model of the speech excitation wave for sustained vowels has been formulated, whe... more A point process model of the speech excitation wave for sustained vowels has been formulated, where the pitch is modulated by a physiological disturbance (vocal tremor). It has been demonstrated that the power spectrum of an impulse train, representing the glottal pulses, is composed of a periodic replication of the spectrum of the modulating signal, accompanied by an impulse train at the carrier frequency. Hence, the power spectrum of the vocal tremor can be estimated from the pitch. A trend location algorithm has been developed, in order to locate and remove local trends from the signal, prior to the evaluation of the pitch power spectrum. Thus, spectral representation of the speech excitation enables estimation of vocal tremor.
Neurology, Oct 1, 1968
HUNTINGTON’S CHOREA is a degenerative disease of the central nervous system, characterized mainly... more HUNTINGTON’S CHOREA is a degenerative disease of the central nervous system, characterized mainly by three features: dominant heredity, extrapyramidal involuntary movements, and mental changes. The pathological changes are confined to the basal ganglia, especially to the caudate nucleus,’ and to the cerebral cortex. The clinical symptoms, as well, seem to be causally related to the above-mentioned pathological findings. The mental changes are probably due to the cortical affection, and the involuntary movements to the striatal involvement.2 The localization of the pathological changes may explain the unusual type of the cerebral atrophy found by pneumoencephalographic studies in cases of Huntington’s chorea.3-5 There are, however, only a few reports dealing with air encephalographic studies in relation to Huntington’s chorea, and all of them present a limited number of cases.3-5 Likewise, modern textbooks in neuroradiology have not dealt thoroughly with this subject.6.7 The purpose of the present work was, therefore, to reexamine the pneumoencephalographic features of Huntington’s chorea in a fairly large series of cases, the relation of these features to the clinical symptoms, and the value of pneumoencephalography as a diagnostic tool in case of Huntington’s chorea.
Electroencephalography and Clinical Neurophysiology, May 1, 1978
Action potentials from 16 single muscle fibres were recorded with a multi-electrode from the huma... more Action potentials from 16 single muscle fibres were recorded with a multi-electrode from the human brachial biceps. Propagation velocity was calculated for 10 of the fibres, and the volume conduction at distances of 79, 152 and 251 micrometer, was measured for 6 of these fibres. The radial decline of the action potentials was calculated from the Fourier transform of the action potential at the origin, simulating the low-pass filter characteristics of the muscle tissue by sections of RC elements. A good agreement was found between the calculated data and the experimental data on the radial decline of the action potentials. The 90% attenuation radius of the action potential recorded with a 25 micrometer electrode, calculated for 16 action potentials, was derived from the volume conduction calculations. The average value found was 191 +/- 20 micrometer. A linear correlation was found between this radius and the peak spectral amplitude of the action potentials. Likewise, a linear correlation between the 90% attenuation radius and the propagation velocity of the fibres was confirmed.
IEEE Transactions on Pattern Analysis and Machine Intelligence, Jul 1, 1989