The Vestibulo-Ocular Reflex (VOR) stabilizes the images of the world on the retinae when the head is in motion. Basic daily activities such as walking or driving depend on the proper functioning of this reflex. For several decades,... more
The Vestibulo-Ocular Reflex (VOR) stabilizes the images of the world on the retinae when the head is in motion. Basic daily activities such as walking or driving depend on the proper functioning of this reflex. For several decades, scientists have developed methods to model and identify this system mathematically. However, traditional methods cannot analyze VOR data comprehensively because they disregard pieces of data (fast phases) which biases estimated reflex dynamics. Here we propose, for the first time, an automated tool to analyze entire VOR responses (slow and fast phases), without apriori classification of nystagmus segments.
Research Interests: Computer Science, Algorithms, Artificial Intelligence, Biomedical Engineering, Biomechanics, and 15 morePrincipal Component Analysis, Neurophysiology, Medicine, Humans, Automation, Computer Simulation, Nonlinear Systems, Nystagmus, Prediction error, Neurons, Eye, Nonlinear system, Equipment Design, Hybrid System, and a priori and a posteriori
The Vestibulo-Ocular Reflex (VOR) stabilizes the images of the world on the retinae when the head is in motion. Basic daily activities such as walking or driving depend on the proper functioning of this reflex. For several decades,... more
The Vestibulo-Ocular Reflex (VOR) stabilizes the images of the world on the retinae when the head is in motion. Basic daily activities such as walking or driving depend on the proper functioning of this reflex. For several decades, scientists have developed methods to model and identify this system mathematically. However, traditional methods cannot analyze VOR data comprehensively because they disregard pieces of data (fast phases) which biases estimated reflex dynamics. Here we propose, for the first time, an automated tool to analyze entire VOR responses (slow and fast phases), without apriori classification of nystagmus segments.
Research Interests: Computer Science, Algorithms, Artificial Intelligence, Biomedical Engineering, Biomechanics, and 15 morePrincipal Component Analysis, Neurophysiology, Medicine, Humans, Automation, Computer Simulation, Nonlinear Systems, Nystagmus, Prediction error, Neurons, Eye, Nonlinear system, Equipment Design, Hybrid System, and a priori and a posteriori
This paper presents a new method for smoothing and detection of respiratory signals in noise. The output of the smoothing filter is obtained as a linear combination of some Chebyshev polynomials over a moving window of finite duration.... more
This paper presents a new method for smoothing and detection of respiratory signals in noise. The output of the smoothing filter is obtained as a linear combination of some Chebyshev polynomials over a moving window of finite duration. Each coefficient of the Chebyshev polynomials is computed by the least squares method. The procedure is demonstrated using simulated time series and real neonatal respiratory signals measured in post-anaesthesia recovery rooms.
Research Interests:
This paper presents a new method for smoothing and detection of respiratory signals in noise. The output of the smoothing filter is obtained as a linear combination of some Chebyshev polynomials over a moving window of finite duration.... more
This paper presents a new method for smoothing and detection of respiratory signals in noise. The output of the smoothing filter is obtained as a linear combination of some Chebyshev polynomials over a moving window of finite duration. Each coefficient of the Chebyshev polynomials is computed by the least squares method. The procedure is demonstrated using simulated time series and real neonatal respiratory signals measured in post-anaesthesia recovery rooms.
Research Interests:
ABSTRACT
Research Interests:
ABSTRACT
Research Interests:
We present an automated method for the segmentation of ribcage and abdominal signals measured by noninvasive respiratory inductance plethysmography (RIP) into quiet breathing and artifact-corrupted segments. This procedure, which involves... more
We present an automated method for the segmentation of ribcage and abdominal signals measured by noninvasive respiratory inductance plethysmography (RIP) into quiet breathing and artifact-corrupted segments. This procedure, which involves forward-backward filtering, is applicable to the automated off-line analysis of long records of respiratory signals. Examples of applications include home and sleep laboratory studies of cardiorespiratory data. The new procedure was successfully applied to the segmentation of cardiorespiratory signals acquired post-operatively from infants in the recovery room of the Montreal Children's Hospital (MCH).
Research Interests: Computer Science, Algorithms, Cardiology, Filtration, Medicine, and 15 morePaediatrics, Humans, Automation, Computer Simulation, Segmentation, Infant, Conference Proceedings, Respiration, Respiratory System, Filter Bank, Plethysmography, Sensitivity and Specificity, Equipment Design, Respiratory Mechanics, and Cardiorespiratory Fitness
We present an automated method for the segmentation of ribcage and abdominal signals measured by noninvasive respiratory inductance plethysmography (RIP) into quiet breathing and artifact-corrupted segments. This procedure, which involves... more
We present an automated method for the segmentation of ribcage and abdominal signals measured by noninvasive respiratory inductance plethysmography (RIP) into quiet breathing and artifact-corrupted segments. This procedure, which involves forward-backward filtering, is applicable to the automated off-line analysis of long records of respiratory signals. Examples of applications include home and sleep laboratory studies of cardiorespiratory data. The new procedure was successfully applied to the segmentation of cardiorespiratory signals acquired post-operatively from infants in the recovery room of the Montreal Children's Hospital (MCH).
Research Interests: Computer Science, Algorithms, Cardiology, Filtration, Medicine, and 15 morePaediatrics, Humans, Automation, Computer Simulation, Segmentation, Infant, Conference Proceedings, Respiration, Respiratory System, Filter Bank, Plethysmography, Sensitivity and Specificity, Equipment Design, Respiratory Mechanics, and Cardiorespiratory Fitness
1. Orienting movements, consisting of coordinated eye and head displacements, direct the visual axis to the source of a sensory stimulus. A recent hypothesis suggests that the CNS may control gaze position (gaze = eye-relative-to-space =... more
1. Orienting movements, consisting of coordinated eye and head displacements, direct the visual axis to the source of a sensory stimulus. A recent hypothesis suggests that the CNS may control gaze position (gaze = eye-relative-to-space = eye-relative-to-head + head-relative-to-space) by the use of a feedback circuit wherein an internally derived representation of gaze motor error drives both eye and head premotor circuits. In this paper we examine the effect of behavioral task on the individual and summed trajectories of horizontal eye- and head-orienting movements to gain more insight into how the eyes and head are coupled and controlled in different behavioral situations. 2. Cats whose heads were either restrained (head-fixed) or unrestrained (head-free) were trained to make orienting movements of any desired amplitude in a simple cat-and-mouse game we call the barrier paradigm. A rectangular opaque barrier was placed in front of the hungry animal who either oriented to a food target that was visible to one side of the barrier or oriented to a location on an edge of the barrier where it predicted the target would reappear from behind the barrier. 3. The dynamics (e.g., maximum velocity) and duration of eye- and head-orienting movements were affected by the task. Saccadic eye movements (head-fixed) elicited by the visible target attained greater velocity and had shorter durations than comparable amplitude saccades directed toward the predicted target. A similar observation has been made in human and monkey. In addition, when the head was unrestrained both the eye and head movements (and therefore gaze movements) were faster and shorter in the visible- compared with the predicted-target conditions. Nevertheless, the relative contributions of the eye and head to the overall gaze displacement remained task independent: i.e., the distance traveled by the eye and head movements was determined by the size of the gaze shift only. This relationship was maintained because the velocities of the eye and head movements covaried in the different behavioral situations. Gaze-velocity profiles also had characteristic shapes that were dependent on task. In the predicted-target condition these profiles tended to have flattened peaks, whereas when the target was visible the peaks were sharper. 4. Presentation of a visual cue (e.g., reappearance of food target) immediately before (less than 50 ms) the onset of a gaze shift to a predicted target triggered a midflight increase in first the eye- and, after approximately 20 ms, the head-movement velocity.(ABSTRACT TRUNCATED AT 400 WORDS)
Research Interests:
1. Orienting movements, consisting of coordinated eye and head displacements, direct the visual axis to the source of a sensory stimulus. A recent hypothesis suggests that the CNS may control gaze position (gaze = eye-relative-to-space =... more
1. Orienting movements, consisting of coordinated eye and head displacements, direct the visual axis to the source of a sensory stimulus. A recent hypothesis suggests that the CNS may control gaze position (gaze = eye-relative-to-space = eye-relative-to-head + head-relative-to-space) by the use of a feedback circuit wherein an internally derived representation of gaze motor error drives both eye and head premotor circuits. In this paper we examine the effect of behavioral task on the individual and summed trajectories of horizontal eye- and head-orienting movements to gain more insight into how the eyes and head are coupled and controlled in different behavioral situations. 2. Cats whose heads were either restrained (head-fixed) or unrestrained (head-free) were trained to make orienting movements of any desired amplitude in a simple cat-and-mouse game we call the barrier paradigm. A rectangular opaque barrier was placed in front of the hungry animal who either oriented to a food target that was visible to one side of the barrier or oriented to a location on an edge of the barrier where it predicted the target would reappear from behind the barrier. 3. The dynamics (e.g., maximum velocity) and duration of eye- and head-orienting movements were affected by the task. Saccadic eye movements (head-fixed) elicited by the visible target attained greater velocity and had shorter durations than comparable amplitude saccades directed toward the predicted target. A similar observation has been made in human and monkey. In addition, when the head was unrestrained both the eye and head movements (and therefore gaze movements) were faster and shorter in the visible- compared with the predicted-target conditions. Nevertheless, the relative contributions of the eye and head to the overall gaze displacement remained task independent: i.e., the distance traveled by the eye and head movements was determined by the size of the gaze shift only. This relationship was maintained because the velocities of the eye and head movements covaried in the different behavioral situations. Gaze-velocity profiles also had characteristic shapes that were dependent on task. In the predicted-target condition these profiles tended to have flattened peaks, whereas when the target was visible the peaks were sharper. 4. Presentation of a visual cue (e.g., reappearance of food target) immediately before (less than 50 ms) the onset of a gaze shift to a predicted target triggered a midflight increase in first the eye- and, after approximately 20 ms, the head-movement velocity.(ABSTRACT TRUNCATED AT 400 WORDS)
Research Interests:
We present an anatomically and neurophysiologically relevant mathematical model for visual-vestibular interaction which reproduces the short-term adaptive behavior of the vestibulo-ocular reflex (VOR) with target distance and... more
We present an anatomically and neurophysiologically relevant mathematical model for visual-vestibular interaction which reproduces the short-term adaptive behavior of the vestibulo-ocular reflex (VOR) with target distance and eccentricity. Adaptive changes are shown to anticipate acquisition of a spatial goal, circumventing the delays associated with visual feedback
Research Interests: Psychology, Computer Science, Biomedical Engineering, Irrigation, Adaptive Control, and 15 moreNeurofeedback, Neurophysiology, Adaptive Optics, Vestibular System, Adaptive behavior, Biocontrol, Eccentricity, Eye, Head, Mathematical Model, Visual Feedback, Eyes, Delays, Vestibulo-ocular reflex, and Target Acquisition
We present an anatomically and neurophysiologically relevant mathematical model for visual-vestibular interaction which reproduces the short-term adaptive behavior of the vestibulo-ocular reflex (VOR) with target distance and... more
We present an anatomically and neurophysiologically relevant mathematical model for visual-vestibular interaction which reproduces the short-term adaptive behavior of the vestibulo-ocular reflex (VOR) with target distance and eccentricity. Adaptive changes are shown to anticipate acquisition of a spatial goal, circumventing the delays associated with visual feedback
Research Interests: Psychology, Computer Science, Biomedical Engineering, Irrigation, Adaptive Control, and 15 moreNeurofeedback, Neurophysiology, Adaptive Optics, Vestibular System, Adaptive behavior, Biocontrol, Eccentricity, Eye, Head, Mathematical Model, Visual Feedback, Eyes, Delays, Vestibulo-ocular reflex, and Target Acquisition
Research Interests:
Research Interests:
Research Interests:
Research Interests:
A hybrid nonlinear bilateral model for the horizontal angular vestibulo-ocular reflex (AVOR) is presented in this paper. The model relies on known interconnections between saccadic burst circuits in the brainstem and ocular premotor areas... more
A hybrid nonlinear bilateral model for the horizontal angular vestibulo-ocular reflex (AVOR) is presented in this paper. The model relies on known interconnections between saccadic burst circuits in the brainstem and ocular premotor areas in the vestibular nuclei during slow and fast phase intervals. A viable switching strategy for the timing of nystagmus events is proposed. Simulations show that this hybrid model replicates AVOR nystagmus patterns that are observed in experimentally recorded data.
Research Interests:
A hybrid nonlinear bilateral model for the horizontal angular vestibulo-ocular reflex (AVOR) is presented in this paper. The model relies on known interconnections between saccadic burst circuits in the brainstem and ocular premotor areas... more
A hybrid nonlinear bilateral model for the horizontal angular vestibulo-ocular reflex (AVOR) is presented in this paper. The model relies on known interconnections between saccadic burst circuits in the brainstem and ocular premotor areas in the vestibular nuclei during slow and fast phase intervals. A viable switching strategy for the timing of nystagmus events is proposed. Simulations show that this hybrid model replicates AVOR nystagmus patterns that are observed in experimentally recorded data.
Research Interests:
We present here a bilateral model for the horizontal rotational vestibulo-ocular reflex (VOR) that integrates sigmoidal nonlinearities in the response of VOR interneurons. This model realistically links the systems level approach to the... more
We present here a bilateral model for the horizontal rotational vestibulo-ocular reflex (VOR) that integrates sigmoidal nonlinearities in the response of VOR interneurons. This model realistically links the systems level approach to the underlying neural mechanisms. It is capable of producing VOR modulations with viewing context using only the efference copies of eye position signals to make novel predictions.
Research Interests:
We present here a bilateral model for the horizontal rotational vestibulo-ocular reflex (VOR) that integrates sigmoidal nonlinearities in the response of VOR interneurons. This model realistically links the systems level approach to the... more
We present here a bilateral model for the horizontal rotational vestibulo-ocular reflex (VOR) that integrates sigmoidal nonlinearities in the response of VOR interneurons. This model realistically links the systems level approach to the underlying neural mechanisms. It is capable of producing VOR modulations with viewing context using only the efference copies of eye position signals to make novel predictions.
Research Interests:
Research Interests: Engineering, Computer Science, Algorithms, Principal Component Analysis, Computational Neuroscience, and 10 moreNonlinear dynamics, Medicine, Humans, Computer Simulation, Reflex, Vestibulo-ocular reflex, Nonlinear system, Psychology and Cognitive Sciences, a priori and a posteriori, and Medical and Health Sciences
Research Interests: Engineering, Computer Science, Algorithms, Principal Component Analysis, Computational Neuroscience, and 10 moreNonlinear dynamics, Medicine, Humans, Computer Simulation, Reflex, Vestibulo-ocular reflex, Nonlinear system, Psychology and Cognitive Sciences, a priori and a posteriori, and Medical and Health Sciences
Recent studies identified an adaptive "Podokinetic" (PK) sensory motor system involved in sensing and controlling spatial orientation during locomotion, by referencing body orientation to the space-stable stance foot. This paper... more
Recent studies identified an adaptive "Podokinetic" (PK) sensory motor system involved in sensing and controlling spatial orientation during locomotion, by referencing body orientation to the space-stable stance foot. This paper investigates the interaction of vestibular and PK systems by asking blindfolded subjects to 'step-in-place' (i.e. without turning) after exposing them to a unidirectional post-rotational vestibular stimulus. Six of the nine subjects consistently began by vigorously propelling themselves round in the direction of preceding turntable rotation, but notably without any sensation of turning. In all these subjects the speed of this PK-induced rotation progressively declined to zero over about the next 30 sec and then reversed direction with increasing speed for about 50 sec. Thereafter the speed of rotation declined slowly to zero over the next 4 to 5 minutes. Since the PK-generated body rotation presumably feeds back into the vestibular-PK drive, we formulated a closed loop model of the combined system to investigate the complex nature of the behavioral response. The simulated response of this model closely resembled the experimental data, suggesting that there is indeed a functionally closed loop operating between the vestibular and podokinetic systems in natural life.
Research Interests:
Recent studies identified an adaptive "Podokinetic" (PK) sensory motor system involved in sensing and controlling spatial orientation during locomotion, by referencing body orientation to the space-stable stance foot. This paper... more
Recent studies identified an adaptive "Podokinetic" (PK) sensory motor system involved in sensing and controlling spatial orientation during locomotion, by referencing body orientation to the space-stable stance foot. This paper investigates the interaction of vestibular and PK systems by asking blindfolded subjects to 'step-in-place' (i.e. without turning) after exposing them to a unidirectional post-rotational vestibular stimulus. Six of the nine subjects consistently began by vigorously propelling themselves round in the direction of preceding turntable rotation, but notably without any sensation of turning. In all these subjects the speed of this PK-induced rotation progressively declined to zero over about the next 30 sec and then reversed direction with increasing speed for about 50 sec. Thereafter the speed of rotation declined slowly to zero over the next 4 to 5 minutes. Since the PK-generated body rotation presumably feeds back into the vestibular-PK drive, we formulated a closed loop model of the combined system to investigate the complex nature of the behavioral response. The simulated response of this model closely resembled the experimental data, suggesting that there is indeed a functionally closed loop operating between the vestibular and podokinetic systems in natural life.
Research Interests:
The identification of potential sites for plasticity in the VOR has thus far been limited mainly to the investigation of very specific signal components that are modified following a particular reflex-training paradigm (i.e., broadband... more
The identification of potential sites for plasticity in the VOR has thus far been limited mainly to the investigation of very specific signal components that are modified following a particular reflex-training paradigm (i.e., broadband reflex training). Yet, the richness of different behavioral observations associated with different training paradigms points to the existence of multiple potential adaptation sites within the VOR
Research Interests:
We have developed a monitor that acquires, classifies, annotates and displays patient cardiorespiratory data in an on-line and fully automated manner. The monitor is compact, portable and battery-operated; it applies automated methods... more
We have developed a monitor that acquires, classifies, annotates and displays patient cardiorespiratory data in an on-line and fully automated manner. The monitor is compact, portable and battery-operated; it applies automated methods that detect apnea and classify cardiorespiratory state on-line from non-invasive measurements of patient respiratory movements, blood oxygen saturation and heart rate, logging the raw and processed data. The monitor provides continuous, on-line, objective, standardized cardiorespiratory classification and has a graphical display and interface for patient monitoring by a clinician; it has immediate application in the clinical setting.
Research Interests:
In [3] we developed a method for the automated estimation of the phase relation between thoracic and abdominal signals measured by noninvasive respiratory inductance plethysmography (RIP). In the present paper, we improve on the phase... more
In [3] we developed a method for the automated estimation of the phase relation between thoracic and abdominal signals measured by noninvasive respiratory inductance plethysmography (RIP). In the present paper, we improve on the phase estimator by including an automated procedure for the detection of periods of gross body movements. We assume that the number of sleep obstructive events during periods of gross body movements is zero in probability. We hope that combining the phase estimator with the gross body movement detector should yield improved diagnostic tools for the automated classification of obstructive hypopnea events.
Research Interests:
The vestibulo-ocular reflex (VOR) plays an important role in our daily activities by enabling us to fixate on objects during head movements. Modeling and identification of the VOR improves our insight into the system behavior and improves... more
The vestibulo-ocular reflex (VOR) plays an important role in our daily activities by enabling us to fixate on objects during head movements. Modeling and identification of the VOR improves our insight into the system behavior and improves diagnosis of various disorders. However, the switching nature of eye movements (nystagmus), including the VOR, makes dynamic analysis challenging. The first step in such analysis is to segment data into its subsystem responses (here slow and fast segment intervals). Misclassification of segments results in biased analysis of the system of interest. Here we develop a novel 3-step algorithm to classify the VOR data into slow and fast intervals automatically. The proposed algorithm is initialized using a Kmeans clustering method. The initial classification is then refined using system identification approaches and prediction error statistics. The performance of the algorithm is evaluated on simulated and experimental data. It is shown that the new algorithm performance is much improved over the previous methods, in terms of higher specificity.
Research Interests:
It is commonly believed that during the compensatory slow-phases of the vestibulo-ocular reflex (VOR), eyes move in a perfectly conjugate fashion (i.e. the vergence component is zero). Consequently, VOR measurements are often restricted... more
It is commonly believed that during the compensatory slow-phases of the vestibulo-ocular reflex (VOR), eyes move in a perfectly conjugate fashion (i.e. the vergence component is zero). Consequently, VOR measurements are often restricted to either conjugate recordings or to single eye recordings. During binocular recordings of the angular VOR in the dark, we observed a significant vergence component even in normal subjects. More interestingly, the measured vergence component modulated with head velocity. The modulation of vergence during the VOR in the dark could imply a vestibular contribution to vergence. These observations suggest a shared central controller for both version and vergence.
Research Interests:
Research Interests:
Ocular tracking of targets in biological systems involves switching between two strategies: slow pursuit and fast corrective saccades producing pursuit nystagmus. Here, a symmetric (bilateral) controller is used as a model for the... more
Ocular tracking of targets in biological systems involves switching between two strategies: slow pursuit and fast corrective saccades producing pursuit nystagmus. Here, a symmetric (bilateral) controller is used as a model for the oculomotor control system (OCS) to drive two cameras on a robotic head. It relies, as in biology, on internal switching in shared premotor circuits to alternate automatically between the two types of movements comprising nystagmus. The symmetric structural concept is gaining acceptance as evidence points to sharing of both fast phase and slow phase control in brainstem structures previously thought to be solely involved in one mode alone. This bilateral OCS model is a parsimonious design that is at once biomimetic and analytically simple. We extend prior results by incorporating more biological clues from floccular projections to establish rudimentary prediction mechanisms for both slow and fast phases; prediction is achieved by using retinal slip, which contains target velocity information. This provides a more accurate replication of the difference between fast phase and slow phase dynamics, and considers neural activity profiles in the superior colliculus to refine the controller performance. The resulting controller eliminates the need for saccades in steady state for low frequency inputs, and each saccade now has better accuracy, despite visual delays.
Research Interests: Engineering, Robotics, Computer Science, Biomedical Engineering, Biomechanics, and 15 moreBiomimetics, Automatic Control, Motion perception, Neurophysiology, Medicine, Low Frequency, Control system, Humans, Computer Simulation, Animals, Motor Cortex, Predictive models, Eye, Biological systems, and Electrical And Electronic Engineering
Research Interests:
Research Interests:
It is argued that vestibular internuclear commissural pathways are functionally important in the vestibuloocular reflex (VOR), particularly since they appear to be modulated during nystagmus. A bilateral approach to VOR modeling is... more
It is argued that vestibular internuclear commissural pathways are functionally important in the vestibuloocular reflex (VOR), particularly since they appear to be modulated during nystagmus. A bilateral approach to VOR modeling is essential to an effective study of the effects of commissural connections on response dynamics. A bilateral model of the VOR central pathways is proposed, with three main postulates: neural filters (NF) on each side of the brain stem, each linked to tonic cells in the ipsilateral vestibular nuclei in negative feedback loops; strong coupling between these bilateral loops by reciprocal commissural connections that significantly affect response dynamics; and modulation of this coupling by inhibitory burst neurons during fast phases. Mathematical analysis of this model shows that the NF need not be good integrators. During slow-phase operation, commissural pathways provide a positive-feedback effect that improves the effective integration function of the bilateral system beyond that of the NF in each side. Analysis suggests that the time constant of the NF might even be as small as that of the eye plant (approximately 0.24 s), so that the NF might be considered to be internal models of the eye plant rather than pseudointegrators. In the model, modulation of commissural gains by burst cells is shown to be sufficient to cause the system to switch between a compensatory position-tracking mode (slow phases) and an anticompensatory velocity-tracking mode (fast phases) during nystagmus. The model simulates a number of behavioral and neurophysiological findings, such as a) tonic vestibular nuclei (VN) cells have sensitivities and decay times larger than primary vestibular fibers, and their response polarity may reverse after section of superficial commissural fibers; b) effective VOR integration deteriorates after cerebellectomy or commissurectomy; c) peak fast-phase eye velocity is modulated by the vestibular signal as well as by fast-phase amplitude. The model accounts for the modulation of central VN responses during nystagmus and, as a result, simulations strongly imply that envelopes of slow-phase eye velocity or smoothed central firing rates will depend on fast-phase strategy and, hence, may not always yield accurate estimates of VOR dynamics. Similarly, the model predicts that "apparent" disassociation between central and ocular responses may occur because of interactions during nystagmus, despite appropriate behavior within slow-phase segments (since VN responses are not simple estimates of eye velocity).(ABSTRACT TRUNCATED AT 400 WORDS)
Research Interests:
Research Interests:
Research Interests: Psychology and Gaze
Research Interests:
Research Interests:
Experimental and theoretical methods can be two complementary arms in clinical research. Mathematical or geometrical models implemented on computers provide the means of testing new medical procedures, or evaluating the effects of surgery... more
Experimental and theoretical methods can be two complementary arms in clinical research. Mathematical or geometrical models implemented on computers provide the means of testing new medical procedures, or evaluating the effects of surgery and drugs on patient recovery and functional limits. When sufficiently accurate physiological or structural models are available, it is preferable to perform ‘bloodless’ experiments on the computer models before attempting actual treatment. In clinical applications, predictions from model simulations can be used to explore new protocols for the evaluation of patients; if the models relate well with known anatomy and physiology, they can even be used to evaluate the function of selected central nervous system pathways, noninvasively. Examples of the potential role of computer models in medical research and practice are presented below, followed by an application in the study of the human vestibulo-ocular system.
Research Interests:
We develop an adaptive controller for multi-joint, multi-muscle arm movements based on simplified spinal-like circuits found in the periphery, muscle synergies, and interpretations of gain-field projections from reach related neurons in... more
We develop an adaptive controller for multi-joint, multi-muscle arm movements based on simplified spinal-like circuits found in the periphery, muscle synergies, and interpretations of gain-field projections from reach related neurons in the Superior Colliculus. The resulting innovation provides a highly robust sensory based controller that can be adapted to systems which require multi-muscle co-ordination. It provides human-like responses during perturbations elicited either internally or by the environment and for simple point-topoint reaching. We simulate limb motion and EMGs in Simulink using Virtual Muscle models and a variety of paradigms, including motion with external perturbations, and varying levels of antagonist muscle co-contractions. The results show that the system can exhibit smooth coordinated motions, without explicit kinematic or dynamic planning even in the presence of perturbations. In addition, we show by varying the level of muscle co-contractions from 0% to 40%, that the effects of external perturbations on joint trajectories can be reduced by up to 42%. The improved controller design is novel providing robust behavior during dynamic events and an automatic adaptive response from sensory-integration.
Research Interests: Engineering, Computer Science, Biomedical Engineering, Biomechanics, Skeletal muscle biology, and 13 moreBiomimetics, Adaptive Control, Medicine, Humans, Computer Simulation, Movement, Kinematics, Spinal Cord, Arm, Muscle contraction, Postural Balance, Task Performance and Analysis, and Electrical And Electronic Engineering
Research Interests: Computer Science, Algorithms, Biomedical Engineering, Computational Complexity, Computational Modeling, and 15 moreMedicine, Estimation Theory, Nonlinear filters, Humans, Correlation, Movement, Infant, Filtering, Linear Filtering, Biological clocks, Breathing, Electrical And Electronic Engineering, Linear Filters, Abdomen, and Nonconvex optimization
The vestibulo-ocular reflex (VOR) is traditionally evaluated by the gain (sensitivity) and offset (bias) of nystagmus slow phases during sinusoidal, passive, head rotation in the dark. The analysis methods used are typically only truly... more
The vestibulo-ocular reflex (VOR) is traditionally evaluated by the gain (sensitivity) and offset (bias) of nystagmus slow phases during sinusoidal, passive, head rotation in the dark. The analysis methods used are typically only truly applicable to linear systems, but are widely used despite the fact that the VOR has been known to be non-linear since the 19th century. We show here that the parameters obtained by linear methods, with data derived from a non-linear system, can be very noisy and unreliable. The questions are: under what conditions can linear approximations be tolerated, or justified, and can an analysis approach be devised which inherently tolerates non-linearities? Using both simulated and experimental data, it is found that assuming linear analysis methods can produce variable VOR gains and erroneous estimates of the VOR bias. changing with the selected oscillation protocol. Examples of' parameter distortions in bias and VOR gain are first given using simulated data relating slow phase eye velocity to head velocity, at different peak velocities. The relevance of these distortions is then illustrated with selected examples from a database of recordings on normals and unilateral vestibular patients, during rotations in the dark 1/6 Hz and maximum speeds of 90 to 180 degrees/s. More consistent estimates of the gain and bias can be found by properly correcting for phase differences between head and eve velocity, and allowing for non-linear reflex properties. Special indices are suggested to decide whether a particular subject's VOR should be considered non-linear, in order to select the appropriate representation in each case, before estimating VOR characteristics. Selecting the appropriate model (linear or non-linear) will contribute to a better unmasking of parametric trends in the VOR, when comparing normal vs. acute-lesioned subjects, or acute vs, compensated patients. These results have many implications for the design of clinical vestibular protocols and in the evaluation of patient functional deficits.
Research Interests:
Research Interests:
The Vestibulo-Ocular Reflex (VOR) plays an essential role in the majority of daily activities by keeping the images of the world steady on the retina when either the environment or the body is moving. The modeling and identification of... more
The Vestibulo-Ocular Reflex (VOR) plays an essential role in the majority of daily activities by keeping the images of the world steady on the retina when either the environment or the body is moving. The modeling and identification of this system plays a key role in the diagnosis and treatment of various diseases and lesions, and their associated syndromes. Today, clinical protocols incorporate mathematical techniques for testing the functionality of patients' VORs through the analysis of the patients' responses to various stimuli. We have developed a new tool for simultaneous identification of the two modes of the horizontal VOR, using a novel algorithm. This algorithm, HybELS (Hybrid Extended Least Squares), is a regression-based identification method tailored for hybrid ARMAX (AutoRegressive Moving Average with eXogenous inputs) models, which can also be used for the identification of other neural systems. In the context of the VOR, MELS (Modified Extended Least Squares) has been proposed previously for the identification of vestibular nystagmus dynamics, one mode at a time. It also involved searching for segment initial conditions to avoid biased results. Our hybrid approach identifies the two modes simultaneously, and does not require estimation of initial conditions, since it takes advantage of state continuity in the transitions between fast and slow phases. The results on experimental VOR in the dark show that HybELS outperforms MELS in several aspects: It proves to be more robust than MELS with respect to the system order used for identification, while resulting in more accurate estimates in almost all contexts as well. Furthermore, due to the hybrid nature of the method, its calculations are algebraically more compact, and HybELS turns out to be much less computationally expensive than MELS.
Research Interests:
The study of binocular control systems has unmasked several advantages linked to the topology of premotor neural networks. In the angular vestibulo-ocular reflex (VOR), there is a need to tune the gain of the reflex separately for each... more
The study of binocular control systems has unmasked several advantages linked to the topology of premotor neural networks. In the angular vestibulo-ocular reflex (VOR), there is a need to tune the gain of the reflex separately for each eye with head perturbations, depending on the distance and eccentricity of a visual target from the midsaggital plane of the head. The natural structural symmetry of the ocular premotor circuits can imbed the required changes in simultaneous vergence and conjugate components of the binocular VOR system. Here we demonstrate that including simple nonlinearities on the function of premotor cells in this symmetric circuit achieves the desired context-dependence for the binocular VOR. This approach allows very complex behaviors in response to sensory patterns without resorting to currently assumed complex cortical computations. The local premotor topology with its nonlinear properties can be sufficient for on-line reflex adaptation to behavioral context in the ocular system and has implications for other motor systems (such as stretch reflex modulation during rhythmic walking).
Research Interests: Psychology and Reflex
Research Interests: Neuroscience, Psychology, Nonlinear dynamics, Neurophysiology, Medicine, and 15 moreCats, Humans, Cerebellum, Gaze, Animals, Eye Movements, Neurons, Head Movements, Eye Movement, Neural pathways, Action Potentials, Brain stem, Haplorhini, Psychology and Cognitive Sciences, and Medical and Health Sciences
Research Interests:
Research Interests: Psychology, Computer Science, Biomedical Engineering, Nonlinear dynamics, Medicine, and 13 moreVestibular System, Linear Model, Humans, Computer Simulation, Eye Movements, Reflex, Vestibulo-ocular reflex, Nonlinear system, Nonlinear Model, Electrical And Electronic Engineering, Vestibular Diseases, Model fitting, and Semicircular Canals
The properties of the vestibulo-ocular reflex (VOR) were examined during sinusoidal passive head rotation in the dark at 1/6 Hz, in 9 normal subjects and 14 unilateral vestibular patients. Rotation speeds ranged from 90 to 180 degrees/s.... more
The properties of the vestibulo-ocular reflex (VOR) were examined during sinusoidal passive head rotation in the dark at 1/6 Hz, in 9 normal subjects and 14 unilateral vestibular patients. Rotation speeds ranged from 90 to 180 degrees/s. The bias (offset of slow-phase velocity from zero) and gain in the VOR were estimated by using a polynomial (cubic) fit between head and slow-phase eye velocity, thereby allowing for possible non-linearities in the reflex. The gain in the VOR in this context refers to the linear components of the fit, and so predicts sensitivity only at low head velocities. The aim of the study was to verify previous theoretical predictions that VOR bias could vary with the rotation parameters, that this bias could be used to detect the side of a vestibular lesion even at low frequency rotation, and make non-linearities more obvious. Confirming these predictions, the VOR bias in a given test is never equal to any spontaneous nystagmus, even if present before rotation. The range of values for the gain in the VOR (as defined above) in normals and compensated unilateral vestibular patients overlap, so that they cannot be statistically separated into two response sets.(ABSTRACT TRUNCATED AT 250 WORDS)