170 research outputs found
A neural model of the motor control system
In this thesis I present the Recurrent Error-driven Adaptive Control Hierarchy (REACH);
a large-scale spiking neuron model of the motor cortices and cerebellum of the motor control system. The REACH model consists of anatomically organized spiking neurons that control a nonlinear three-link arm to perform reaching and handwriting, while being able to adapt to unknown changes in arm dynamics and structure. I show that the REACH model accounts for data across 19 clinical and experimental studies of the motor control system. These data includes a mix of behavioural and neural spiking activity, across normal and damaged subjects performing adaptive and static tasks.
The REACH model is a dynamical control system based on modern control theoretic methods, specifically operational space control, dynamic movement primitives, and nonlinear adaptive control. The model is implemented in spiking neurons using the Neural Engineering Framework (NEF).
The model plans trajectories in end-effector space, and transforms these commands into joint torques that can be sent to the arm simulation. Adaptive components of the model are able to compensate for unknown kinematic or dynamic system parameters, such
as arm segment length or mass. Using the NEF the adaptive components of the system
can be seeded with approximations of the system kinematics and dynamics, allowing faster convergence to stability. Stability proofs for nonlinear adaptation methods implemented in distributed systems with scalar output are presented.
By implementing the motor control model in spiking neurons, biological constraints such
as neurotransmitter time-constants and anatomical connectivity can be imposed, allowing
further comparison to experimental data for model validation. The REACH model is compared to clinical data from human patients as well as neural recording from monkeys
performing reaching experiments. The REACH model represents a novel integration of
control theoretic methods and neuroscientific constraints to specify a general, adaptive,
biologically plausible motor control algorithm.4 month
Non-linear adaptive control inspired by neuromuscular systems
Current paradigms for neuromorphic computing focus on internal computing mechanisms, for instance using spiking-neuron models. In this study, we propose to exploit what is known about neuro-mechanical control, exploiting the mechanisms of neural ensembles and recruitment, combined with the use of second-order overdamped impulse responses corresponding to the mechanical twitches of muscle-fiber groups. Such systems may be used for controlling any analog process, by realizing three aspects: Timing, output quantity representation and wave-shape approximation. We present an electronic based model implementing a single motor unit for twitch generation. Such units can be used to construct random ensembles, separately for an agonist and antagonist 'muscle'. Adaptivity is realized by assuming a multi-state memristive system for determining time constants in the circuit. Using (Spice)-based simulations, several control tasks were implemented which involved timing, amplitude and wave shape: The inverted pendulum task, the 'whack-a-mole' task and a handwriting simulation. The proposed model can be used for both electric-to-electronic as well as electric-to-mechanical tasks. In particular, the ensemble-based approach and local adaptivity may be of use in future multi-fiber polymer or multi-actuator pneumatic artificial muscles, allowing for robust control under varying conditions and fatigue, as is the case in biological muscles
Building Machines That Learn and Think Like People
Recent progress in artificial intelligence (AI) has renewed interest in
building systems that learn and think like people. Many advances have come from
using deep neural networks trained end-to-end in tasks such as object
recognition, video games, and board games, achieving performance that equals or
even beats humans in some respects. Despite their biological inspiration and
performance achievements, these systems differ from human intelligence in
crucial ways. We review progress in cognitive science suggesting that truly
human-like learning and thinking machines will have to reach beyond current
engineering trends in both what they learn, and how they learn it.
Specifically, we argue that these machines should (a) build causal models of
the world that support explanation and understanding, rather than merely
solving pattern recognition problems; (b) ground learning in intuitive theories
of physics and psychology, to support and enrich the knowledge that is learned;
and (c) harness compositionality and learning-to-learn to rapidly acquire and
generalize knowledge to new tasks and situations. We suggest concrete
challenges and promising routes towards these goals that can combine the
strengths of recent neural network advances with more structured cognitive
models.Comment: In press at Behavioral and Brain Sciences. Open call for commentary
proposals (until Nov. 22, 2016).
https://www.cambridge.org/core/journals/behavioral-and-brain-sciences/information/calls-for-commentary/open-calls-for-commentar
Emergent Bio-Functional Similarities in a Cortical-Spike-Train-Decoding Spiking Neural Network Facilitate Predictions of Neural Computation
Despite its better bio-plausibility, goal-driven spiking neural network (SNN)
has not achieved applicable performance for classifying biological spike
trains, and showed little bio-functional similarities compared to traditional
artificial neural networks. In this study, we proposed the motorSRNN, a
recurrent SNN topologically inspired by the neural motor circuit of primates.
By employing the motorSRNN in decoding spike trains from the primary motor
cortex of monkeys, we achieved a good balance between classification accuracy
and energy consumption. The motorSRNN communicated with the input by capturing
and cultivating more cosine-tuning, an essential property of neurons in the
motor cortex, and maintained its stability during training. Such
training-induced cultivation and persistency of cosine-tuning was also observed
in our monkeys. Moreover, the motorSRNN produced additional bio-functional
similarities at the single-neuron, population, and circuit levels,
demonstrating biological authenticity. Thereby, ablation studies on motorSRNN
have suggested long-term stable feedback synapses contribute to the
training-induced cultivation in the motor cortex. Besides these novel findings
and predictions, we offer a new framework for building authentic models of
neural computation
From Unimodal to Multimodal: improving the sEMG-Based Pattern Recognition via deep generative models
Multimodal hand gesture recognition (HGR) systems can achieve higher
recognition accuracy. However, acquiring multimodal gesture recognition data
typically requires users to wear additional sensors, thereby increasing
hardware costs. This paper proposes a novel generative approach to improve
Surface Electromyography (sEMG)-based HGR accuracy via virtual Inertial
Measurement Unit (IMU) signals. Specifically, we trained a deep generative
model based on the intrinsic correlation between forearm sEMG signals and
forearm IMU signals to generate virtual forearm IMU signals from the input
forearm sEMG signals at first. Subsequently, the sEMG signals and virtual IMU
signals were fed into a multimodal Convolutional Neural Network (CNN) model for
gesture recognition. To evaluate the performance of the proposed approach, we
conducted experiments on 6 databases, including 5 publicly available databases
and our collected database comprising 28 subjects performing 38 gestures,
containing both sEMG and IMU data. The results show that our proposed approach
outperforms the sEMG-based unimodal HGR method (with increases of
2.15%-13.10%). It demonstrates that incorporating virtual IMU signals,
generated by deep generative models, can significantly enhance the accuracy of
sEMG-based HGR. The proposed approach represents a successful attempt to
transition from unimodal HGR to multimodal HGR without additional sensor
hardware
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