Gangadhar Garipelli - Academia.edu (original) (raw)
Papers by Gangadhar Garipelli
Frontiers in Neurology, Jun 15, 2021
Background: Mirror therapy is thought to drive interhemispheric communication, resulting in a bal... more Background: Mirror therapy is thought to drive interhemispheric communication, resulting in a balanced activation. We hypothesized that embodied virtual mirror visual feedback (VR-MVF) presented on a computer screen may produce a similar activation. In this proof-of-concept study, we investigated differences in movement-related cortical potentials (MRCPs) in the electroencephalogram (EEG) from different visual feedback of user movements in 1 stroke patient and 13 age-matched adults. Methods: A 60-year-old right-handed (Edinburgh score >95) male ischemic stroke [left paramedian pontine, National Institutes of Health Stroke Scale (NIHSS) = 6] patient and 13 age-matched right-handed (Edinburgh score >80) healthy adults (58 ± 9 years; six female) participated in the study. We recorded 16-electrode electroencephalogram (EEG), while participants performed planar center-out movements in two embodied visual feedback conditions: (i) direct (movements translated to the avatar's ipsilateral side) and (ii) mirror (movements translated to the avatar's contralateral side) with left (direct left/mirror left) or right (direct right/mirror right) arms.
International Journal of Physical Medicine and Rehabilitation, 2016
I acknowledge Karthikeyan and Arun Kumar for their continuous discussions and encouragement. I th... more I acknowledge Karthikeyan and Arun Kumar for their continuous discussions and encouragement. I thank P.S. Prashanth, Dinesh, Gunjan, Anchal and J. Srinivas for their assistance during the research work. I thank K. Umender, Rajiv Ranjan Sahay and N. Rajeev Lochan who made my stay at IIT-M memorable. My gratitude to my lab members, particularly Krishnan and Ranjan Kumar Pradhan for their valuable assistance during the work. I am grateful to my parents, brother and my sister for their support and encouragement.
Master of Science by Research is a bonafide record of research work carried out by him under my s... more Master of Science by Research is a bonafide record of research work carried out by him under my supervision. The contents in this thesis, in full or in parts, have not been submitted to any other Institute of University for the award of any degree or diploma.
Journal of the Neurological Sciences, Oct 1, 2019
Conclusions During early stages of Bell's palsy patient exerts constant mental efforts of high in... more Conclusions During early stages of Bell's palsy patient exerts constant mental efforts of high intensity, trying to produce facial movements. Due to high intensity, those efforts cannot be finely differentiated between proper facial muscles. This leads to a "mass-contraction" pattern of resulting efferent signals and suppresses natural mechanism of reciprocal inhibition of antagonists. Volitional mimetic center of the brain begins to form new, Pathological Amplification Mimetic Pattern (PAMP). When the regenerating nerve fibers finally reconnect to their facial muscles, PAMP manifests itself in synkinesis, rigidity of facial muscles, and gradually solidifies into a conditioned reflex. As any conditioned reflex, facial synkinesis can therefore be reversed by negative feedback, as demonstrated by results of our patients.
Anticipation is a mental process during which a person actively engages in a phase required for t... more Anticipation is a mental process during which a person actively engages in a phase required for the sensory perception and execution of the optimal actions at the arrival of the relevant future events. Since this process occurs before the execution of an intended action, it may be used as a control signal for Brain Computer Interface (BCI) applications. Recognition of neural correlates of this process can enhance the performance of a BCI and in turn reduce mental workload of its users. To this end, it is vital to understand the neural correlates involved in this process and to design robust methods for its recognition in single trials. The analysis of these correlates may also contribute to the basic knowledge of the mechanisms underlying this behavior. The thesis provides three major contributions: (i) it reports methods for the robust recognition of anticipation related Electroencephalogram (EEG) potentials (ii) it provides insights into the selection of appropriate preprocessing steps required for enhancing the Signal-to-Noise Ratio (SNR) of anticipatory slow cortical potentials (SCPs) and (iii) it identifies scalp area specific oscillatory activity related to different aspects of anticipatory behavior. First, we focus on methods for the single trial recognition of anticipatory SCPs using the widely known classical contingent negative variation (CNV) paradigm. Using this paradigm, we demonstrate the feasibility of recognizing the anticipatory SCPs (CNV potentials) using features thatmodel its temporal pattern. We propose a Bayesian approach that exploits temporal evolution and redundancy to quickly classify (e.g., within half of the anticipatory period), without compromising classification accuracy. We then improve upon these recognition rates by using a source localization technique based on the biophysical model of the human head. We further validate the feasibility of recognizing CNV potentials in an online experiment, and report for the first time that, under controlled conditions, these potentials can be reproduced and recognized in realistic interaction scenarios (assistive technology web-browsing) with high accuracies. Second, the thesis provides insights into the selection of appropriate preprocessing stages required for improving the SNR of SCPs. The CNV potentials are characterized by low frequencies that are usually recorded with full-DC, and hence suffer from task-irrelevant high amplitude fluctuations and spatial noise. To account for this, we identified appropriate spectral and spatial filters to improve the SNR. We demonstrate the potential of these preprocessing stages by using fusing multiple electrode specific linear classifiers, which achieve recognition performances of 90±2% (area under curve of receiver operating characteristic), where the classifiers are trained using recordings from one day and tested on the recordings from several days apart. Finally, the thesis identifies different facets of anticipatory behavior. Apart from the widely known CNV potentials, it is not clear which other spectral bands could be related to anticipatory behavior. Using recordings from an experiment (i.e., the assistive technology web browser) where multiple warning stimuli predicted an imperative stimulus, we explored the phase and amplitude response of various oscillatory sub-bands for the identification of markers that could be associated with different aspects of anticipation. From this study we report that: (i) there are duration (4-10 seconds) specific changes in Electroencephalography (EEG) activity in the range 0-1 Hz in the central electrodes correlate with reaction time, (ii) there exist slow oscillations (0.1-1 Hz) in the central electrodes that exhibit phase tuning up to 4 seconds before the onset of a target cue, (iii) there are delta oscillations (1.5-3 Hz), which are entrained to predictive rhythmic warning cues, (iv) there is a selective modulation (increase or decrease) in the amplitude of occipital alpha band (8-12 Hz) based on the relevance of forthcoming visual cue, and (v) there exist a reduction in the beta band (14-30 Hz) amplitude in the sensory motor and association areas lasting up to 10 seconds. The phase tuning and entrainment resulted in a low variance of phase values at the arrival of the imperative stimulus, which may be required for its optimal processing. The amplitude modulation of alpha band activity is likely to be a resultant of sensory suppression and attention. The reduction of beta-band activity over long periods of time suggests holding of sensory-motor association areas until the execution of a planned action. We believe that these observations are the consequence of the endogenous drive on the ongoing oscillations to enhance the processing of the forthcoming stimuli and preparation for an intended action. In summary, the thesis provides methods for the recognition of anticipatory SCPs by exploiting spectral and spatio-temporal characteristics with high…
International Journal on Document Analysis and Recognition, Jun 22, 2007
A neuromotor model of handwritten stroke generation, in which stroke velocities are expressed as ... more A neuromotor model of handwritten stroke generation, in which stroke velocities are expressed as a Fourier-style decomposition of oscillatory neural activities, is presented. The neural network architecture consists of an input or stroke-selection layer, an oscillatory layer, and the output layer where stroke velocities are estimated. A separate timing network prepares the network's initial state, which is crucial for accurate stroke generation. Neurobiological significance of this preparation, and a possible mapping of our architecture onto human motor system is suggested. Interaction between timing network and oscillatory layer closely resembles interaction between Basal Ganglia and Supplementary Motor Area in the brain.
Journal of Neural Engineering, Apr 23, 2013
Objective. Abundant literature suggests the use of slow cortical potentials (SCPs) in a wide spec... more Objective. Abundant literature suggests the use of slow cortical potentials (SCPs) in a wide spectrum of basic and applied neuroscience areas. Due to their low signal to noise ratio, these potentials are often studied using grand-average analysis, which conceals trial-to-trial information. Moreover, most of the single trial analysis methods in the literature are based on classical electroencephalogram (EEG) features ([1-30] Hz) and are likely to be unsuitable for SCPs that have different signal properties (such as having the signal's spectral content in the range [0.2-0.7] Hz). In this paper we provide insights into the selection of appropriate parameters for spectral and spatial filtering. Approach. We study anticipation related SCPs recorded using a web-browser application protocol and a full-band EEG (FbEEG) setup from 11 subjects on two different days. Main results. We first highlight the role of a bandpass with [0.1-1.0] Hz in comparison with common practices (e.g., either with full dc, just a lowpass, or with a minimal highpass cutoff around 0.05 Hz). Secondly, we suggest that a combination of spatial-smoothing filter and common average reference (CAR) is more suitable than the spatial filters often reported in the literature (e.g., re-referencing to an electrode, Laplacian or CAR alone). Thirdly, with the help of these preprocessing steps, we demonstrate the generalization capabilities of linear classifiers across several days (AUC of 0.88 ± 0.05 on average with a minimum of 0.81 ± 0.03 and a maximum of 0.97 ± 0.01). We also report the possibility of further improvements using a Bayesian fusion technique applied to electrode-specific classifiers. Significance. We believe the suggested spatial and spectral preprocessing methods are advantageous for grand-average and single trial analysis of SCPs obtained from EEG, MEG as well as for electrocorticogram. The use of these methods will impact basic neurophysiological studies as well as the use of SCPs in the design of neuroprosthetics.
SAGE Publications India Pvt Ltd eBooks, Oct 6, 2014
Human Movement Science, Oct 1, 2009
Journal of Advanced Computational Intelligence and Intelligent Informatics, 2005
It is argued that weight adaptations even during retrieval phase can greatly enhance the performa... more It is argued that weight adaptations even during retrieval phase can greatly enhance the performance of a neurodynamic associative memory. Our simulations with an electronic implementation of an associative memory showed that extending the Hopfield dynamics with an appropriate adaptive law in retrieval phase could give rise to significant improvements in storage capacity and computational reliability. Weights, which are supposed to encode the information stored in the Hopfield neural network, are usually held constant once training/storage is complete. In our case, weights also change during retrieval, hence losing information in the process, but resulting in much better retrieval of stored patterns. We describe and characterize the functional elements comprising the network, the learning system, and include the experimental results obtained from applying the network for character recognition in various noisy conditions. Stability issues emerging as a consequence of retrieval phase ...
2009 4th International IEEE/EMBS Conference on Neural Engineering, NER '09, 2009
Anticipation increases the efficiency of daily tasks by partial advance activation of neural subs... more Anticipation increases the efficiency of daily tasks by partial advance activation of neural substrates involved in it. Previous off-line studies have shown the possibility of exploiting this activation for a Brain-Computer Interface (BCI) using electroencephalogram (EEG). In the current paper we report real-time and single trial recognition of this activation using a prototype of anticipation based BCI (aBCI). We report on-line classification accuracies with peak values of 85% and 80%, and with average values of 69.0 ± 7.9% and 58.5 ± 14.1% for subjects 1 and 2, respectively. Posterior off-line analysis showed improved accuracies for both subjects, with an average of 80.5±10.1% and 69.0 ± 10.5% with peak values of 95% and 85% respectively.
Neural Computation, 2008
Handwriting in Parkinson's disease (PD) is typically characterized by micrographia, jagged li... more Handwriting in Parkinson's disease (PD) is typically characterized by micrographia, jagged line contour, and unusual fluctuations in pen tip velocity. Although PD handwriting features have been used for diagnostics, they are not based on a signaling model of basal ganglia (BG). In this letter, we present a computational model of handwriting generation that highlights the role of BG. When PD conditions like reduced dopamine and altered dynamics of the subthalamic nucleus and globus pallidus externa subsystems are simulated, the handwriting produced by the model manifested characteristic PD handwriting distortions like micrographia and velocity fluctuations. Our approach to PD modeling is in tune with the perspective that PD is a dynamic disease.
IEEE Transactions on Biomedical Engineering, 2009
Anticipation increases the efficiency of daily tasks by partial advance activation of neural subs... more Anticipation increases the efficiency of daily tasks by partial advance activation of neural substrates involved in it. Here we develop a method for the recognition of electroencephalogram (EEG) correlates of this activation as early as possible on single trials which is essential for Brain-Computer Interaction (BCI). We explore various features from the EEG recorded in a Contingent Negative Variation (CNV) paradigm. We also develop a novel technique called Time Aggregation of Classification (TAC) for fast and reliable decisions that combines the posterior probabilities of several classifiers trained with features computed from temporal blocks of EEG until a certainty threshold is reached. Experiments with 9 naive subjects performing the CNV experiment with GO and NOGO conditions with an inter-stimulus interval of 4 s show that the performance of the TAC method is above 70% for four subjects, around 60% for two other subjects, and random for the remaining subjects. On average over all subjects, more than 50% of the correct decisions are made at 2 s, without needing to wait until 4 s.
Neurocomputing, 2010
We present a comprehensive model of basal ganglia in which the three important reinforcement lear... more We present a comprehensive model of basal ganglia in which the three important reinforcement learning components—Actor, Critic and Explorer (ACE),—are represented and their anatomical substrates are identified. Particularly, we identify the subthalamic-...
Brain-Computer Interfaces (BCIs) are no longer only used by healthy volunteers (mostly students) ... more Brain-Computer Interfaces (BCIs) are no longer only used by healthy volunteers (mostly students) under artificially controlled conditions in laboratory environments, but by patients controlling real applications at their homes, or by healthy users as an alternative input device for playing computer games, but definitely without any BCI experts around. But, are the BCI technologies and the field mature enough for addressing these requirements? In other words, is BCI technology still depending on expert knowledge and monitoring? In this work, we summarize the experiences gained and the lessons learned while transferring our BCI technology from the lab to the user’s home. In our case we started with naive patients (not healthy users) who first performed BCI training and then used their BCI to evaluate several BCI controlled prototypes (either a writing application for communication or a robotic tele-presence platform). Rather than presenting the technical description about these setups...
L'invention concerne un systeme de mesure de parametres physiologiques et de suivi des mouvem... more L'invention concerne un systeme de mesure de parametres physiologiques et de suivi des mouvements comprenant un systeme de commande (12), un systeme de detection (13) et un systeme de stimulation (17). Le systeme de detection comprend un ou plusieurs capteurs physiologiques comportant au moins des capteurs d'activite electrique cerebrale (22). Le systeme de stimulation (17) comprend un ou plusieurs dispositifs de stimulation comportant au moins un systeme de stimulation visuelle (32). Le systeme de commande comprend un module d'acquisition (53) configure pour recevoir des signaux de detection emis par le systeme de detection, et un module de commande (51) configure pour traiter les signaux provenant du module d'acquisition et pour controler la generation de signaux de stimulation vers un ou plusieurs dispositifs du systeme de stimulation. Le systeme de commande comprend par ailleurs un module horloge (106) et est configure pour recevoir des signaux de code de contenu...
Frontiers in Neurology, Jun 15, 2021
Background: Mirror therapy is thought to drive interhemispheric communication, resulting in a bal... more Background: Mirror therapy is thought to drive interhemispheric communication, resulting in a balanced activation. We hypothesized that embodied virtual mirror visual feedback (VR-MVF) presented on a computer screen may produce a similar activation. In this proof-of-concept study, we investigated differences in movement-related cortical potentials (MRCPs) in the electroencephalogram (EEG) from different visual feedback of user movements in 1 stroke patient and 13 age-matched adults. Methods: A 60-year-old right-handed (Edinburgh score >95) male ischemic stroke [left paramedian pontine, National Institutes of Health Stroke Scale (NIHSS) = 6] patient and 13 age-matched right-handed (Edinburgh score >80) healthy adults (58 ± 9 years; six female) participated in the study. We recorded 16-electrode electroencephalogram (EEG), while participants performed planar center-out movements in two embodied visual feedback conditions: (i) direct (movements translated to the avatar's ipsilateral side) and (ii) mirror (movements translated to the avatar's contralateral side) with left (direct left/mirror left) or right (direct right/mirror right) arms.
International Journal of Physical Medicine and Rehabilitation, 2016
I acknowledge Karthikeyan and Arun Kumar for their continuous discussions and encouragement. I th... more I acknowledge Karthikeyan and Arun Kumar for their continuous discussions and encouragement. I thank P.S. Prashanth, Dinesh, Gunjan, Anchal and J. Srinivas for their assistance during the research work. I thank K. Umender, Rajiv Ranjan Sahay and N. Rajeev Lochan who made my stay at IIT-M memorable. My gratitude to my lab members, particularly Krishnan and Ranjan Kumar Pradhan for their valuable assistance during the work. I am grateful to my parents, brother and my sister for their support and encouragement.
Master of Science by Research is a bonafide record of research work carried out by him under my s... more Master of Science by Research is a bonafide record of research work carried out by him under my supervision. The contents in this thesis, in full or in parts, have not been submitted to any other Institute of University for the award of any degree or diploma.
Journal of the Neurological Sciences, Oct 1, 2019
Conclusions During early stages of Bell's palsy patient exerts constant mental efforts of high in... more Conclusions During early stages of Bell's palsy patient exerts constant mental efforts of high intensity, trying to produce facial movements. Due to high intensity, those efforts cannot be finely differentiated between proper facial muscles. This leads to a "mass-contraction" pattern of resulting efferent signals and suppresses natural mechanism of reciprocal inhibition of antagonists. Volitional mimetic center of the brain begins to form new, Pathological Amplification Mimetic Pattern (PAMP). When the regenerating nerve fibers finally reconnect to their facial muscles, PAMP manifests itself in synkinesis, rigidity of facial muscles, and gradually solidifies into a conditioned reflex. As any conditioned reflex, facial synkinesis can therefore be reversed by negative feedback, as demonstrated by results of our patients.
Anticipation is a mental process during which a person actively engages in a phase required for t... more Anticipation is a mental process during which a person actively engages in a phase required for the sensory perception and execution of the optimal actions at the arrival of the relevant future events. Since this process occurs before the execution of an intended action, it may be used as a control signal for Brain Computer Interface (BCI) applications. Recognition of neural correlates of this process can enhance the performance of a BCI and in turn reduce mental workload of its users. To this end, it is vital to understand the neural correlates involved in this process and to design robust methods for its recognition in single trials. The analysis of these correlates may also contribute to the basic knowledge of the mechanisms underlying this behavior. The thesis provides three major contributions: (i) it reports methods for the robust recognition of anticipation related Electroencephalogram (EEG) potentials (ii) it provides insights into the selection of appropriate preprocessing steps required for enhancing the Signal-to-Noise Ratio (SNR) of anticipatory slow cortical potentials (SCPs) and (iii) it identifies scalp area specific oscillatory activity related to different aspects of anticipatory behavior. First, we focus on methods for the single trial recognition of anticipatory SCPs using the widely known classical contingent negative variation (CNV) paradigm. Using this paradigm, we demonstrate the feasibility of recognizing the anticipatory SCPs (CNV potentials) using features thatmodel its temporal pattern. We propose a Bayesian approach that exploits temporal evolution and redundancy to quickly classify (e.g., within half of the anticipatory period), without compromising classification accuracy. We then improve upon these recognition rates by using a source localization technique based on the biophysical model of the human head. We further validate the feasibility of recognizing CNV potentials in an online experiment, and report for the first time that, under controlled conditions, these potentials can be reproduced and recognized in realistic interaction scenarios (assistive technology web-browsing) with high accuracies. Second, the thesis provides insights into the selection of appropriate preprocessing stages required for improving the SNR of SCPs. The CNV potentials are characterized by low frequencies that are usually recorded with full-DC, and hence suffer from task-irrelevant high amplitude fluctuations and spatial noise. To account for this, we identified appropriate spectral and spatial filters to improve the SNR. We demonstrate the potential of these preprocessing stages by using fusing multiple electrode specific linear classifiers, which achieve recognition performances of 90±2% (area under curve of receiver operating characteristic), where the classifiers are trained using recordings from one day and tested on the recordings from several days apart. Finally, the thesis identifies different facets of anticipatory behavior. Apart from the widely known CNV potentials, it is not clear which other spectral bands could be related to anticipatory behavior. Using recordings from an experiment (i.e., the assistive technology web browser) where multiple warning stimuli predicted an imperative stimulus, we explored the phase and amplitude response of various oscillatory sub-bands for the identification of markers that could be associated with different aspects of anticipation. From this study we report that: (i) there are duration (4-10 seconds) specific changes in Electroencephalography (EEG) activity in the range 0-1 Hz in the central electrodes correlate with reaction time, (ii) there exist slow oscillations (0.1-1 Hz) in the central electrodes that exhibit phase tuning up to 4 seconds before the onset of a target cue, (iii) there are delta oscillations (1.5-3 Hz), which are entrained to predictive rhythmic warning cues, (iv) there is a selective modulation (increase or decrease) in the amplitude of occipital alpha band (8-12 Hz) based on the relevance of forthcoming visual cue, and (v) there exist a reduction in the beta band (14-30 Hz) amplitude in the sensory motor and association areas lasting up to 10 seconds. The phase tuning and entrainment resulted in a low variance of phase values at the arrival of the imperative stimulus, which may be required for its optimal processing. The amplitude modulation of alpha band activity is likely to be a resultant of sensory suppression and attention. The reduction of beta-band activity over long periods of time suggests holding of sensory-motor association areas until the execution of a planned action. We believe that these observations are the consequence of the endogenous drive on the ongoing oscillations to enhance the processing of the forthcoming stimuli and preparation for an intended action. In summary, the thesis provides methods for the recognition of anticipatory SCPs by exploiting spectral and spatio-temporal characteristics with high…
International Journal on Document Analysis and Recognition, Jun 22, 2007
A neuromotor model of handwritten stroke generation, in which stroke velocities are expressed as ... more A neuromotor model of handwritten stroke generation, in which stroke velocities are expressed as a Fourier-style decomposition of oscillatory neural activities, is presented. The neural network architecture consists of an input or stroke-selection layer, an oscillatory layer, and the output layer where stroke velocities are estimated. A separate timing network prepares the network's initial state, which is crucial for accurate stroke generation. Neurobiological significance of this preparation, and a possible mapping of our architecture onto human motor system is suggested. Interaction between timing network and oscillatory layer closely resembles interaction between Basal Ganglia and Supplementary Motor Area in the brain.
Journal of Neural Engineering, Apr 23, 2013
Objective. Abundant literature suggests the use of slow cortical potentials (SCPs) in a wide spec... more Objective. Abundant literature suggests the use of slow cortical potentials (SCPs) in a wide spectrum of basic and applied neuroscience areas. Due to their low signal to noise ratio, these potentials are often studied using grand-average analysis, which conceals trial-to-trial information. Moreover, most of the single trial analysis methods in the literature are based on classical electroencephalogram (EEG) features ([1-30] Hz) and are likely to be unsuitable for SCPs that have different signal properties (such as having the signal's spectral content in the range [0.2-0.7] Hz). In this paper we provide insights into the selection of appropriate parameters for spectral and spatial filtering. Approach. We study anticipation related SCPs recorded using a web-browser application protocol and a full-band EEG (FbEEG) setup from 11 subjects on two different days. Main results. We first highlight the role of a bandpass with [0.1-1.0] Hz in comparison with common practices (e.g., either with full dc, just a lowpass, or with a minimal highpass cutoff around 0.05 Hz). Secondly, we suggest that a combination of spatial-smoothing filter and common average reference (CAR) is more suitable than the spatial filters often reported in the literature (e.g., re-referencing to an electrode, Laplacian or CAR alone). Thirdly, with the help of these preprocessing steps, we demonstrate the generalization capabilities of linear classifiers across several days (AUC of 0.88 ± 0.05 on average with a minimum of 0.81 ± 0.03 and a maximum of 0.97 ± 0.01). We also report the possibility of further improvements using a Bayesian fusion technique applied to electrode-specific classifiers. Significance. We believe the suggested spatial and spectral preprocessing methods are advantageous for grand-average and single trial analysis of SCPs obtained from EEG, MEG as well as for electrocorticogram. The use of these methods will impact basic neurophysiological studies as well as the use of SCPs in the design of neuroprosthetics.
SAGE Publications India Pvt Ltd eBooks, Oct 6, 2014
Human Movement Science, Oct 1, 2009
Journal of Advanced Computational Intelligence and Intelligent Informatics, 2005
It is argued that weight adaptations even during retrieval phase can greatly enhance the performa... more It is argued that weight adaptations even during retrieval phase can greatly enhance the performance of a neurodynamic associative memory. Our simulations with an electronic implementation of an associative memory showed that extending the Hopfield dynamics with an appropriate adaptive law in retrieval phase could give rise to significant improvements in storage capacity and computational reliability. Weights, which are supposed to encode the information stored in the Hopfield neural network, are usually held constant once training/storage is complete. In our case, weights also change during retrieval, hence losing information in the process, but resulting in much better retrieval of stored patterns. We describe and characterize the functional elements comprising the network, the learning system, and include the experimental results obtained from applying the network for character recognition in various noisy conditions. Stability issues emerging as a consequence of retrieval phase ...
2009 4th International IEEE/EMBS Conference on Neural Engineering, NER '09, 2009
Anticipation increases the efficiency of daily tasks by partial advance activation of neural subs... more Anticipation increases the efficiency of daily tasks by partial advance activation of neural substrates involved in it. Previous off-line studies have shown the possibility of exploiting this activation for a Brain-Computer Interface (BCI) using electroencephalogram (EEG). In the current paper we report real-time and single trial recognition of this activation using a prototype of anticipation based BCI (aBCI). We report on-line classification accuracies with peak values of 85% and 80%, and with average values of 69.0 ± 7.9% and 58.5 ± 14.1% for subjects 1 and 2, respectively. Posterior off-line analysis showed improved accuracies for both subjects, with an average of 80.5±10.1% and 69.0 ± 10.5% with peak values of 95% and 85% respectively.
Neural Computation, 2008
Handwriting in Parkinson's disease (PD) is typically characterized by micrographia, jagged li... more Handwriting in Parkinson's disease (PD) is typically characterized by micrographia, jagged line contour, and unusual fluctuations in pen tip velocity. Although PD handwriting features have been used for diagnostics, they are not based on a signaling model of basal ganglia (BG). In this letter, we present a computational model of handwriting generation that highlights the role of BG. When PD conditions like reduced dopamine and altered dynamics of the subthalamic nucleus and globus pallidus externa subsystems are simulated, the handwriting produced by the model manifested characteristic PD handwriting distortions like micrographia and velocity fluctuations. Our approach to PD modeling is in tune with the perspective that PD is a dynamic disease.
IEEE Transactions on Biomedical Engineering, 2009
Anticipation increases the efficiency of daily tasks by partial advance activation of neural subs... more Anticipation increases the efficiency of daily tasks by partial advance activation of neural substrates involved in it. Here we develop a method for the recognition of electroencephalogram (EEG) correlates of this activation as early as possible on single trials which is essential for Brain-Computer Interaction (BCI). We explore various features from the EEG recorded in a Contingent Negative Variation (CNV) paradigm. We also develop a novel technique called Time Aggregation of Classification (TAC) for fast and reliable decisions that combines the posterior probabilities of several classifiers trained with features computed from temporal blocks of EEG until a certainty threshold is reached. Experiments with 9 naive subjects performing the CNV experiment with GO and NOGO conditions with an inter-stimulus interval of 4 s show that the performance of the TAC method is above 70% for four subjects, around 60% for two other subjects, and random for the remaining subjects. On average over all subjects, more than 50% of the correct decisions are made at 2 s, without needing to wait until 4 s.
Neurocomputing, 2010
We present a comprehensive model of basal ganglia in which the three important reinforcement lear... more We present a comprehensive model of basal ganglia in which the three important reinforcement learning components—Actor, Critic and Explorer (ACE),—are represented and their anatomical substrates are identified. Particularly, we identify the subthalamic-...
Brain-Computer Interfaces (BCIs) are no longer only used by healthy volunteers (mostly students) ... more Brain-Computer Interfaces (BCIs) are no longer only used by healthy volunteers (mostly students) under artificially controlled conditions in laboratory environments, but by patients controlling real applications at their homes, or by healthy users as an alternative input device for playing computer games, but definitely without any BCI experts around. But, are the BCI technologies and the field mature enough for addressing these requirements? In other words, is BCI technology still depending on expert knowledge and monitoring? In this work, we summarize the experiences gained and the lessons learned while transferring our BCI technology from the lab to the user’s home. In our case we started with naive patients (not healthy users) who first performed BCI training and then used their BCI to evaluate several BCI controlled prototypes (either a writing application for communication or a robotic tele-presence platform). Rather than presenting the technical description about these setups...
L'invention concerne un systeme de mesure de parametres physiologiques et de suivi des mouvem... more L'invention concerne un systeme de mesure de parametres physiologiques et de suivi des mouvements comprenant un systeme de commande (12), un systeme de detection (13) et un systeme de stimulation (17). Le systeme de detection comprend un ou plusieurs capteurs physiologiques comportant au moins des capteurs d'activite electrique cerebrale (22). Le systeme de stimulation (17) comprend un ou plusieurs dispositifs de stimulation comportant au moins un systeme de stimulation visuelle (32). Le systeme de commande comprend un module d'acquisition (53) configure pour recevoir des signaux de detection emis par le systeme de detection, et un module de commande (51) configure pour traiter les signaux provenant du module d'acquisition et pour controler la generation de signaux de stimulation vers un ou plusieurs dispositifs du systeme de stimulation. Le systeme de commande comprend par ailleurs un module horloge (106) et est configure pour recevoir des signaux de code de contenu...