395 research outputs found
Time-Frequency based Feature Selection for Discrimination of non stationary Biosignals.
This research proposes a generic methodology for dimensionality reduction upon time-frequency representations applied to the classification of different types of biosignals. The methodology directly deals with the highly redundant and irrelevant data contained in these representations, combining a first stage of irrelevant data removal by variable selection, with a second stage of redundancy reduction using methods based on linear transformations. The study addresses two techniques that provided a similar performance: the first one is based on the selection of a set of the most relevant time?frequency points, whereas the second one selects the most relevant frequency bands. The first methodology needs a lower quantity of components, leading to a lower feature space; but the second improves the capture of the time-varying dynamics of the signal, and therefore provides a more stable performance. In order to evaluate the generalization capabilities of the methodology proposed it has been applied to two types of biosignals with different kinds of non-stationary behaviors: electroencephalographic and phonocardiographic biosignals. Even when these two databases contain samples with different degrees of complexity and a wide variety of characterizing patterns, the results demonstrate a good accuracy for the detection of pathologies, over 98%.The results open the possibility to extrapolate the methodology to the study of other biosignals
Data-driven multivariate and multiscale methods for brain computer interface
This thesis focuses on the development of data-driven multivariate and multiscale methods
for brain computer interface (BCI) systems. The electroencephalogram (EEG), the
most convenient means to measure neurophysiological activity due to its noninvasive nature,
is mainly considered. The nonlinearity and nonstationarity inherent in EEG and its
multichannel recording nature require a new set of data-driven multivariate techniques to
estimate more accurately features for enhanced BCI operation. Also, a long term goal
is to enable an alternative EEG recording strategy for achieving long-term and portable
monitoring.
Empirical mode decomposition (EMD) and local mean decomposition (LMD), fully
data-driven adaptive tools, are considered to decompose the nonlinear and nonstationary
EEG signal into a set of components which are highly localised in time and frequency. It
is shown that the complex and multivariate extensions of EMD, which can exploit common
oscillatory modes within multivariate (multichannel) data, can be used to accurately
estimate and compare the amplitude and phase information among multiple sources, a
key for the feature extraction of BCI system. A complex extension of local mean decomposition
is also introduced and its operation is illustrated on two channel neuronal
spike streams. Common spatial pattern (CSP), a standard feature extraction technique
for BCI application, is also extended to complex domain using the augmented complex
statistics. Depending on the circularity/noncircularity of a complex signal, one of the
complex CSP algorithms can be chosen to produce the best classification performance
between two different EEG classes.
Using these complex and multivariate algorithms, two cognitive brain studies are
investigated for more natural and intuitive design of advanced BCI systems. Firstly, a Yarbus-style auditory selective attention experiment is introduced to measure the user
attention to a sound source among a mixture of sound stimuli, which is aimed at improving
the usefulness of hearing instruments such as hearing aid. Secondly, emotion experiments
elicited by taste and taste recall are examined to determine the pleasure and displeasure
of a food for the implementation of affective computing. The separation between two
emotional responses is examined using real and complex-valued common spatial pattern
methods.
Finally, we introduce a novel approach to brain monitoring based on EEG recordings
from within the ear canal, embedded on a custom made hearing aid earplug. The new
platform promises the possibility of both short- and long-term continuous use for standard
brain monitoring and interfacing applications
Analogue mouse pointer control via an online steady state visual evoked potential (SSVEP) brain-computer interface
The steady state visual evoked protocol has recently become a popular paradigm in brainâcomputer interface (BCI) applications. Typically (regardless of function) these applications offer the user a binary selection of targets that perform correspondingly discrete actions. Such discrete control systems are appropriate for applications that are inherently isolated in nature, such as selecting numbers from a keypad to be dialled or letters from an alphabet to be spelled. However motivation exists for users to employ proportional control methods in intrinsically analogue tasks such as the movement of a mouse pointer. This paper introduces an online BCI in which control of a mouse pointer is directly proportional to a user's intent. Performance is measured over a series of pointer movement tasks and compared to the traditional discrete output approach. Analogue control allowed subjects to move the pointer faster to the cued target location compared to discrete output but suffers more undesired movements overall. Best performance is achieved when combining the threshold to movement of traditional discrete techniques with the range of movement offered by proportional control
EEG-Based Brain-Computer Interfacing via Motor-Imagery: Practical Implementation and Feature Analysis
The human brain is the most intriguing and complex signal processing unit ever known to us.
A unique characteristic of our brain is its plasticity property, i.e., the ability of neurons to modify
their behavior (structure and functionality) in response to environmental diversity. The plasticity
property of brain has motivated design of brain-computer interfaces (BCI) to develop an alternative
form of communication channel between brain signals and the external world. The BCI systems
have several therapeutic applications of significant importance including but not limited to rehabilitation/
assistive systems, rehabilitation robotics, and neuro-prosthesis control. Despite recent
advancements in BCIs, such systems are still far from being reliably incorporated within humanmachine
inference networks. In this regard, the thesis focuses on Motor Imagery (MI)-based BCI
systems with the objective of tackling some key challenges observed in existing solutions. The
MI is defined as a cognitive process in which a person imagines performing a movement without
peripheral (muscle) activation. At one hand, the thesis focuses on feature extraction, which is
one of the most crucial steps for the development of an effective BCI system. In this regard, the
thesis proposes a subject-specific filtering framework, referred to as the regularized double-band
Bayesian (R-B2B) spectral filtering. The proposed R-B2B framework couples three main feature
extraction categories, namely filter-bank solutions, regularized techniques, and optimized Bayesian mechanisms to enhance the overall classification accuracy of the BCI. To further evaluate the effects
of deploying optimized subject-specific spectra-spatial filters, it is vital to examine and investigate
different aspects of data collection and in particular, effects of the stimuli provided to subjects to
trigger MI tasks. The second main initiative of the thesis is to propose an element of experimental design dealing with MI-based BCI systems. In this regard, we have implemented an EEG-based
BCI system and constructed a benchmark dataset associated with 10 healthy subjects performing
actual movement and MI tasks. To investigate effects of stimulus on the overall achievable performance,
four different protocols are designed and implemented via introduction of visual and voice
stimuli. Finally, the work investigates effects of adaptive trimming of EEG epochs resulting in an
adaptive and subject-specific solution
Pattern recognition-based real-time myoelectric control for anthropomorphic robotic systems : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Mechatronics at Massey University, Manawatƫ, New Zealand
All copyrighted Figures have been removed but may be accessed via their source cited in their respective captions.Advanced human-computer interaction (HCI) or human-machine interaction (HMI) aims to help
humans interact with computers smartly. Biosignal-based technology is one of the most promising
approaches in developing intelligent HCI systems. As a means of convenient and non-invasive
biosignal-based intelligent control, myoelectric control identifies human movement intentions from
electromyogram (EMG) signals recorded on muscles to realise intelligent control of robotic systems.
Although the history of myoelectric control research has been more than half a century, commercial
myoelectric-controlled devices are still mostly based on those early threshold-based methods. The
emerging pattern recognition-based myoelectric control has remained an active research topic in
laboratories because of insufficient reliability and robustness. This research focuses on pattern
recognition-based myoelectric control. Up to now, most of effort in pattern recognition-based
myoelectric control research has been invested in improving EMG pattern classification accuracy.
However, high classification accuracy cannot directly lead to high controllability and usability for
EMG-driven systems. This suggests that a complete system that is composed of relevant modules,
including EMG acquisition, pattern recognition-based gesture discrimination, output equipment and its
controller, is desirable and helpful as a developing and validating platform that is able to closely emulate
real-world situations to promote research in myoelectric control.
This research aims at investigating feasible and effective EMG signal processing and pattern
recognition methods to extract useful information contained in EMG signals to establish an intelligent,
compact and economical biosignal-based robotic control system. The research work includes in-depth
study on existing pattern recognition-based methodologies, investigation on effective EMG signal
capturing and data processing, EMG-based control system development, and anthropomorphic robotic
hand design. The contributions of this research are mainly in following three aspects:
Developed precision electronic surface EMG (sEMG) acquisition methods that are able to
collect high quality sEMG signals. The first method was designed in a single-ended signalling
manner by using monolithic instrumentation amplifiers to determine and evaluate the analog
sEMG signal processing chain architecture and circuit parameters. This method was then
evolved into a fully differential analog sEMG detection and collection method that uses
common commercial electronic components to implement all analog sEMG amplification and
filtering stages in a fully differential way. The proposed fully differential sEMG detection and collection method is capable of offering a higher signal-to-noise ratio in noisy environments
than the single-ended method by making full use of inherent common-mode noise rejection
capability of balanced signalling. To the best of my knowledge, the literature study has not
found similar methods that implement the entire analog sEMG amplification and filtering chain
in a fully differential way by using common commercial electronic components.
Investigated and developed a reliable EMG pattern recognition-based real-time gesture
discrimination approach. Necessary functional modules for real-time gesture discrimination
were identified and implemented using appropriate algorithms. Special attention was paid to
the investigation and comparison of representative features and classifiers for improving
accuracy and robustness. A novel EMG feature set was proposed to improve the performance
of EMG pattern recognition.
Designed an anthropomorphic robotic hand construction methodology for myoelectric control
validation on a physical platform similar to in real-world situations. The natural anatomical
structure of the human hand was imitated to kinematically model the robotic hand. The
proposed robotic hand is a highly underactuated mechanism, featuring 14 degrees of freedom
and three degrees of actuation.
This research carried out an in-depth investigation into EMG data acquisition and EMG signal pattern
recognition. A series of experiments were conducted in EMG signal processing and system
development. The final myoelectric-controlled robotic hand system and the system testing confirmed
the effectiveness of the proposed methods for surface EMG acquisition and human hand gesture
discrimination. To verify and demonstrate the proposed myoelectric control system, real-time tests were
conducted onto the anthropomorphic prototype robotic hand. Currently, the system is able to identify
five patterns in real time, including hand open, hand close, wrist flexion, wrist extension and the rest
state. With more motion patterns added in, this system has the potential to identify more hand
movements. The research has generated a few journal and international conference publications
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