Artificial Intelligence Enabled Neuroprosthetic Hand
20230086004 · 2023-03-23
Inventors
- Zhi Yang (Minneapolis, MN, US)
- Anh Tuan Nguyen (Minneapolis, MN, US)
- Diu Khue Luu (Minneapolis, MN, US)
Cpc classification
A61F2002/6827
HUMAN NECESSITIES
International classification
Abstract
A prosthetic limb in amputation rehabilitation, having a forearm and a hand with four fingers and a thumb, with the wrist and the fingers & thumb thereof being fully independently controlled by nerve signals originating in the amputee's brain and not being controlled by the actions of nearby muscles in the amputee's upper arm or shoulder. Control of the prosthesis is achieved by a fully contained electronic unit in the forearm of the prosthesis that receives neural signals from the brain, converts the analog neural signals to digital signals that are fed into an artificial intelligence engine circuit that utilizes a library of algorithms to learn from the brain what the signals are that will produce a desired hand and finger movement, then convert its computed digital output to analog electrical signals that are fed to the prosthetic hand and finger to produce actual motion as instructed by the brain.
Claims
1. A neuroprosthesis device, comprising: a nerve interface; an artificial intelligence engine an artificial intelligence neural decoder run by said artificial intelligence engine; and an electromechanical prosthetic limb.
2. The device as claimed in claim 1, wherein said nerve interface is comprised of a frequency shaping neural recorder and a redundant crossfire neural stimulator.
3. The device as claimed in claim 1, wherein said nerve interface is configured to establish bidirectional neural recording and neural stimulating communications with one or more selected residual peripheral nerves.
4. The device as claimed in claim 2, wherein said frequency-shaping neural recorder and said redundant crossfire neural stimulator are configured to establish said bidirectional recording and stimulating communications in near-simultaneous time.
5. The device as claimed in claim 4, wherein said frequency-shaping neural recorder and said redundant crossfire neural stimulator are configured to establish said bidirectional recording and stimulating communications simultaneously.
6. The device as claimed in claim 1, wherein said artificial intelligence neural decoder is configured to execute a deep learning architecture.
7. The device as claimed in claim 6, wherein said neural decoder using deep learning architecture gathers inputted nerve data from an amputee's movement intentions or motion intentions.
8. The device as claimed in claim 7, wherein said neural decoder using deep learning architecture gathers said inputted nerve data and translates said data into control of said electromechanical prosthetic limb.
9. The device as claimed in claim 8, wherein said electromechanical prosthetic limb is an electromechanical prosthetic hand.
10. The device as claimed in claim 9, where said artificial intelligence neural decoder is integrated into said electromechanical prosthetic hand.
11. The device as claimed in claim 10, wherein said electromechanical hand is a neuroprosthetic hand.
12. The device as claimed in claim 11, wherein said neuroprosthetic hand is configured to function as a phantom hand.
13. The device as claimed in claim 12, where said neuroprosthetic phantom hand comprises a prosthetic wrist having the ability to move through motions and a set of prosthetic fingers having the ability to move through motions, wherein said motions are directly controlled by said artificial intelligence engine.
14. The device as claimed in claim 13, where said artificial intelligence engine is configured so as to control said prosthetic wrist and said prosthetic fingers through movements and motions characterized as those of a natural wrist and natural fingers.
15. The device as claimed in claim 14, where said movements and motions are under intuitive control by a human wearing said device.
16. The device as claimed in claim 15, wherein said prosthetic fingers additionally comprise touch-sensitive sensors, said sensors configured to generate microstimulation patterns.
17. The device as claimed in claim 16, wherein said artificial intelligence decoder is configured to modulate said microstimulation patterns and provide somatosensory feedback to said prosthetic wrist and said prosthetic fingers.
18. The device as claimed in claim 17 configured so as to sequentially collect training data from said human, use said training data to train said artificial intelligence neural decoder, use said trained artificial intelligence neural decoder to create a trained model of movement through motions of said prosthetic wrist and said prosthetic fingers, and to deploy said trained model to generation of motion through movements of said prosthetic wrist and said prosthetic fingers.
19. The device as claimed in claim 1, where said nerve interface comprises a fully integrated bioelectronics circuit, comprising a plurality of fascicular microelectrodes implanted into selected nerve fibers of a peripheral nervous system, thereby connecting said selected nerve fibers with said artificial intelligence engine.
20. The device as claimed in claim 19, wherein said nerve interface comprises a plurality of microelectronic microchips configured so as to establish neural recording and neural stimulation simultaneously, said microelectronic microchips comprising at least one frequency-shaping amplifier configured to obtain ultra-low energy noise nerve signals, and to simultaneously suppress undesirable signal artifacts.
21. The device as claimed in claim 19, wherein said nerve interface comprises a high-precision analog to digital converter.
22. The device as claimed in claim 1, wherein said artificial intelligence engine comprises a standalone computer means.
23. The device as claimed in claim 1, wherein said artificial intelligence engine is configured to perform real-time motor decoding of outputs from said artificial intelligence neural decoder.
24. The device as claimed in claim 1, wherein said artificial intelligence engine comprises at least one system-on-chip mini-computer module, said computer module comprising an integrated central processing unit, a graphics processing unit, a random access memory, and a flash storage, and wherein said computer module is configured to deploy artificial intelligence software in an autonomous application.
25. The device as claimed in claim 24, wherein said graphics processing unit comprises a plurality of computer unified device architecture parallel processors, configured to run a deep learning library.
26. The device as claimed in claim 25, wherein said deep learning library is selected from the group consisting of TensorFlow, PyTorch, Caffe, Caffe 2, Chainer, CNTK, DSSTNE, DyNet, Genism, Gluon, Keras, Mxnet, Paddle, or BigDL.
27. The device as claimed in claim 24, where said artificial intelligence engine is optimized to require a minimum of electrical power required to run a selected deep learning library.
28. The device as claimed in claim 1, additionally comprising a rechargeable battery power supply.
29. The device as claimed in claim 9, where said hand comprises a hand controller comprised of a plurality of microcontrollers, a hand controller power supply, and a plurality of direct current motors for each digit of said hand, wherein said direct current motors are operated through said microcontrollers in response to decoded movement signals generated by deep-learning predictions calculated by said artificial intelligence engine.
30. The device as claimed in claim 1, additionally comprising an input/output unit configured to receive and transmit data, and a memory means configured to store data.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
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[0045] Sciences and technologies used in the application of the invention. Deep neural network to process nerve neural signals. The ultimate goal of an upper-limb neuroprosthesis is to achieve dexterous and intuitive control of individual fingers. Previous literature shows that deep learning (DL) is an effective tool to decode the motor intent from neural signals obtained from different parts of the nervous system. However, it still requires complicated deep neural networks that are inefficient and not feasible to work with in real-time. Different approaches were incorporated herein to enhance the efficiency of the DL-based motor decoding paradigm. First, a comprehensive collection of feature extraction techniques was applied to reduce the input data dimensionality. Next, two different strategies were used for deploying DL models: a one-step (1S) approach when big input data were available and a two-step (2S) when input data were limited. With the 1S approach, a single regression stage predicted the trajectories of all fingers. With the 2S approach, a classification stage identified the fingers in motion, followed by a regression stage that predicted those active digits' trajectories. The addition of feature extraction substantially lowered the motor decoder's complexity, making it feasible for translation to a real-time paradigm. The 1S approach using a recurrent neural network (RNN) generally gave better prediction results than all prior art machine learning (ML) algorithms, with mean squared error (MSE) ranges from 10.sup.−3 to 10.sup.−4 for all fingers while variance accounted for (VAP) scores are above 0.8 for the most degree of freedom (DOE). This result reaffirmed that DL is more advantageous than classic ML methods for handling a large dataset. However, when training on a smaller input data set as in the 2S approach, ML techniques offered a simpler implementation while ensuring comparably good decoding outcomes compared to the DL ones. In the classification step, either machine-learning (ML) or DL models achieve accuracy and an F1 score of 0.99. Thanks to the classification step, in the regression step, both types of models resulted in comparable MSE and VAF scores as those of the 1S approach. Recording nerve neural signals with cuff electrodes is an important milestone towards developing a high-performance, minimally invasive neural interface. The thrust of this is to develop tools to analyze and understand the observed neural signal recordings. Differing from a brain single-unit recording which contains activities of a few neurons, a cuff electrode records neural signals from a nerve bundle of thousands of axons, where the recorded signals can vary in shape and in pattern, and are characterized in having poorer signal to noise ratios. Therefore, methods commonly used to process brain signals (for example, spike sorting, firing interval engineering, and rate based codings) will be less effective in processing nerve neural data. The ability to separate weak neural signals from background noise is crucial in nerve signal processing. Signal detection is preferably accomplished in a preferred embodiment of the invention by using a modified deep variational autoencoder (VAE) means for signal detection. An exemplary deep VAE consists of sequentially connected encoder and decoder networks, where the encoder learns a class label y and a probability distribution of the code z with stochastic variables of the input data x, and the decoder aims to reconstruct the input based on the class label and the code. Use of such a deep VAE means may enable the development of a large-scale, well-annotated nerve dataset, as well as a thorough exploration of inputted signals and noise, and the generation of representations of the collected and inputted signals and noise, all through the use of the deep VAE, which in turn enables the enforcement use of a de-noising criterion such that the noise will be maximally removed. After such a training phase, the deep VAE will be able to de-noise the received data in a subject or patient and hence to improve signal detection. The present invention's novel method of use of a conventional VAE is performed in combination with a novel dataset and a novel de-noising algorithm.
[0046] Datasets. Deep learning algorithms rely on large-scale, well-annotated datasets to achieve a superior performance. For example, ImageNet, a large-scale visual database designed for use in visual object recognition software research, contains over 14 million hand-annotated images, and is considered by those of ordinary skill in the art as having enabled a revolution in deep learning. The database of annotations of third-party image URLs is freely available directly from ImageNet at https://www.image-net.org. In the present invention, to bridge deep learning and neural signal processing, a dataset similar to the taxonomy and annotation strategy of ImageNet is first constructed, according to procedures and processes well known to those of ordinary skill in the AI arts. The dataset then is used for developing neural signal processing algorithms.
[0047] Dataset generation. Cuff electrode data are a data summation from both filtered intraneural signals (signals within the nerve) and from noise arising out of external sources. Normally, cuff electrode data (both signals and labels) are not available for learning algorithms, especially for supervised learning, to record high quality, multi-site intraneural signals, and must be generated as part of the practice of the invention. We have now built a cuff electrode dataset based on intraneural signals. First, a finite element model of epineurium is developed to simulate cuff electrode neural signals based on multi-site intraneural signals. To this database is added noise that has been segmented from cuff electrode recordings, and the procedure is repeated with data from different electrodes and animal model preparations. This yields a dataset derived from real experiments that can support the development of supervised learning algorithms to process neural signals.
[0048] Deep learning de-noising. Mathematically, the data representation process with the deep VAE can be expressed as:
pθ(x,y,z)=pθ(x|y,z)p(y)p(z)
[0049] where pθ(x|y, z) quantifies how the observed values of x are related to the latent random variables y and z, and p(y), p(z) represent a known prior distribution of the latent variables y and z. Given this representation model, the posterior distribution pθ(y|z, x) can be used to infer y, z and to find parameters θ that maximize the marginal likelihood pθ(x). To approximate the intractable pθ(y|z, x) a decoding distribution qΦ(y|z, x) is modeled by learning the parameters Φ from the data. Next, consider a 1-D time-series input xt={Xt−T1, . . . , Xt+T2}, where X represents a single-electrode recording and [t−T1, t+T2] is a temporal scanning window. The binary classification label (i.e., neural signals or noise) at time t is denoted as a one-hot vector yt, and the corresponding latent variables are represented as zt. The preferred embodiment of the deep VAE models a joint distribution according to pθ(xt|yt, zt) factorized as pθ(xt, yt, zt)=pθ(xt|yt, zt)p(yt)p(zt). For the decoder model, use pθ(xt|zt, yt)=N(μθ(zt, yt), σ2θ(zt, yt)I); for the encoder, relying on the theory of variational inference to approximate the intractable posterior pθ((z|x,yt) with a tractable auxiliary distribution qθ(zt|xt, yt)=N(μΦ(xt, yt), σ2Φ(xt)I). In the supervised case with an annotated dataset, the label yt is observed, allowing the parameters θ and Φ to be optimized by maximizing the extended variational lower bound:
log pθ(xt,yt)≥EqΦ(zt|xt,yt)[log pθ(xt|yt,zt)+log pθ(yt)+log pθ(zt)−log qΦ(zt|xt,yt)]=LL(xt,yt).
[0050] For de-noising a nerve recording, the user injects the cuff electrode noise ε into x.sub.t to synthesize cuff recordings ˜xt=xt+ε, where the noise is picked from the cuff data.
[0051] Simultaneous recording and stimulation on a peripheral nerve. Proof of concept of electroceuticals requires integrating the stimulation function and performing personalized adaptive neural modulation therapies based on neural feedback. Another challenge that the invention had to overcome is that nerve neural signals are very weak, and thus they are vulnerable to the stimulation noise artifacts. To reduce such noise artifacts, a key feature of the novel invention is that of redundant crossfire (RXF) stimulator design based upon redundant sensing theory.
[0052] Redundant sensing. Redundancy is a fundamental characteristic of many biological processes such as those in the genetic, visual, muscular, and nervous systems; yet its underlying causative driving mechanism is not well understood. A complete discussion of the phenomenon of redundancy is set forth at A Bio-inspired Redundant Sensing Architecture, accessible at http://papers.nips.cc/paper/6564-a-bio-inspires-redundant-sensing-architecture.pdf, the entire disclosure of which is incorporated herein by reference. The present invention utilizes the redundancy from materials engineering to enhance the accuracy and precision aspects of the system, by focusing on the application of the phenomenon of redundancy to reduce stimulation signal residual charge, and thus reduce the effects of stimulation noise artifacts. In the invention's use of redundant sensing, each entry of information can be represented by a plurality of distinct configurations or microstates, and there is a distinct subset of such microstates that will allow linear representation of the entries of information, and such a set or subset will not be bounded by the classic Shannon limit (see C. E. Shannon, The Mathematical Theory of Communication, by Claude E. Shannon and Warren Weaver. University of Illinois Press, 1964) when processed according to the practice of one preferred embodiment of the present invention. The invention's identification of an optimized subset is an NP-incomplete problem, but it is possible to find a sub-optimal solution with sufficient efficiency to obtain a well-operating final complete embodiment of the invention. For example, in the case where a target stimulus signal is a 100 μA biphasic current, with a 6-bit resolution in amplitude, the anodic and cathodic branches will have up to a 3% mismatch depending on electrode conditions and clock jitter. Thus, the mismatch current is 100 μA×(3%+{right arrow over (1/2)}.sup.6)=4.5 μA, which represents the cause of the resulting residual charge and stimulation noise artifacts. It can be seen from this example that a given amount of mismatch is stimulus dependent, time variant, and sensitive to electrode-electrolyte offset, thus posing a significant challenge to effective reduction of residual charge and stimulation noise artifacts, without having to resort to the prior art strategies of increasing the amount of power consumed or increasing the size of the neurostimulation device, both of which are product design strategies that ultimately produce a finished device of poor ergonomics and disappointing user satisfaction.
[0053] RXR stimulator. Based on the redundant sensing strategy, the present invention comprises as one element a reverse crossfire (RXF) stimulator, wherein the outputs of two or more independent stimulation channels with a current-digital-to-analog converter (IDAC) output driver will effectively form a redundant sensing structure. See United States patent application U.S. Ser. No. 15/876,030, U.S. Ser. No. 15/864,668, U.S. Ser. No. 17/066,456, and U.S. Ser. No. 17/849,534, the entire disclosure and teachings of which are respectively incorporated herein by reference. The sensed redundancy is exploited to fine tune and achieve precise matching between the anodic and cathodic stimulation currents, thus suppressing the residual charge and stimulation noise artifacts.
[0054] Inherent challenges. The prior art suffers from multiple challenges: an inability to harness the full range of movements potentially possible from currently available dexterous prosthetic systems, for example the DEKA Arm, the APL Arm, and the DLR Hand/Arm systems; the efficacy of deep learning comes at the cost of computational complexity; the inefficiency of conventional central processing units (CPU) that are found on most low-power platforms; and that prior art deep learning models must be trained and deployed using graphics processing units (GPU), which have hundreds to thousands of multi-threaded computing units specialized for parallelized floating-point matrix multiplication. As for the necessary supporting software, prior art edge computing devices are compact hardware and therefore attractive for use in prostheses, and are suitable for deep learning uses, but current software is limited to highly customized neural networks, which hinders full potential of, for example, a preferred embodiment of the invention as claimed, namely a neural decoder implementation based on recurrent neural network (RNN) architecture.
[0055] Prior art approaches do not adequately address the challenge of efficiently deploying deep learning neural decoders on a portable, edge computing platform, and translating existing benchtop motor decoding experiments into real-life applications toward long-term clinical uses. Many studies have demonstrated the superior efficacy of deep learning approaches compared to conventional algorithms for decoding human motor intent from neural data. However, the application of deep learning on portable devices for long-term clinical uses has remained challenged due to the high cost of computational complexity. It is well-known that running deep learning models on conventional the type of CPUs found on most low-power platforms is hugely inefficient. The vast majority of deep learning models in the prior art must be trained and deployed using GPU, which has hundreds to thousands of multi-threaded computing units specialized for parallelized floating-point matrix multiplication.
[0056] Innovative Elements. The invention herein disclosed and claimed efficiently implements deep learning neural decoders in a sufficiently portable platform for clinical neuroprosthetic applications, made feasible by combining and integrating multiple innovative elements that we have chosen to combine and apply across various of the system's components. A first innovative element lies in using the development of an intrafascicular microelectrode array that connects nerve fibers and bioelectronics, as presented in Overstreet et al. Fascicle Specific Targeting For Selective Peripheral Nerve Stimulation. Journal of Neural Engineering, 16(6), 066040. (2019), the disclosure of which is incorporated herein by reference. The second innovation lies in the novel incorporation of a design of Neuronix® neural interface microchips, that allow simultaneous neural recording and stimulation, as presented in Nguyen & Xu et al. A Bioelectric Neural Interface Towards Intuitive Prosthetic Control For Amputees. Journal of Neural Engineering, 17(6), 066001, describing our Scorpius device therein, and which is further described below, and Nguyen et al. Redundant Crossfire: A Technique to Achieve Super-Resolution in Neurostimulator Design by Exploiting Transistor Mismatch. IEEE Journal of Solid-State Circuits. (2021), the two disclosures of which are incorporated herein, describing redundant crossfire neural stimulator and somatosensory experiments. The third innovation lies in incorporating optimization of the deep learning motor decoding paradigm that results in significantly reducing the decoder's computational complexity, as described in Luu et al Achieving Super-Resolution with Redundant Sensing. IEEE Transactions on Biomedical Engineering, 66(8), 2200-2209. (2019), the disclosure of which is incorporated herein by reference. There, the aim was to achieve engineering information redundancy, built into the system's architecture, in order to exploit the phenomenon of random transistor mismatch, and to thereby enhance the overall effective resolution capability of the device. The application of RXF in the present invention involves combining the RXF (i.e., crossfiring) outputs of two or more current drivers in order to form a redundant structure. When properly configured, this novel redundant structure may produce accurate current pulses with an effective super-resolution that is beyond the limitation commonly permitted by the physical constraints. The fourth innovation lies in the implementation of software and hardware based on a state-of-the-art edge computing platform that could support real-time motor decoding, as is further described below.
[0057] Accordingly, a need exists for a solution to address the multiple challenges and shortcomings currently existing in the prosthesis industry. The present invention addresses the challenges of the shortcomings of the prior art in addressing the problems described above, in an integrated multi-prong approach by the features of: having a nerve interface comprising a frequency shaping (FS) neural recorder and a redundant crossfire (RXF) neural stimulator on a chip to establish near-simultaneous bidirectional recording and stimulating communications with residual peripheral nerves of interest; using an artificial intelligence (AI) neural decoder, based on a deep learning architecture, to translate, in real time, an amputee's movement or motion intentions, as gathered from the amputee's nerve data; having a portable, self-contained, battery-powered AI engine to run the AI neural decoder, where the decoder is integrated into an electromechanical prosthetic hand; having the capacity to be able to intuitively control individual finger and/or wrist movements just like a natural hand, manifested as the ability to control the electromechanical prosthesis by directly moving the prosthetic fingers and/or wrist so that the prosthetic hand effectively becomes a phantom hand, thereby elevating the electromechanical prosthesis to the status of a neuroprosthesis; being able to provide somatosensory feedback in real-time by modulating a microstimulation pattern generated by the neuroprosthetic hand having touch-sensitive sensors; and by applying a procedure to collect training data, train the AI neural decoder, and deploy the trained model on the prosthetic hand.
DETAILED DESCRIPTION OF THE DRAWINGS AND OF THE INVENTION
[0058] Turning first to
[0059] The neural recorders and stimulators of the invention interface with an amputee's peripheral nerve through multiple microelectrode arrays 140 that are surgically implanted into the individual's nerve fascicles in the forearm. Most preferably, the ulnar 132 and median 134 nerves are used, since they control the movements of the fingers and wrist, and since they carry the hand's somatosensory perception neurosignals (e.g., touch and proprioception). Other preferred embodiments may also include the radial nerve, which controls certain wrist movements and which carries additional somatosensory perception. Raw nerve data acquired by the neural recorders 110 are directly streamed to the AI engine nerve data processing circuit module 114 for further processing via a wired or a wireless connection 106.
[0060] The AI engine 108 is powered by a miniaturized, low-power edge computing device. The edge computing device is essentially a mini-computer equipped with dedicated hardware such as a central processing unit (CPU) and graphical processing unit (GPU) to perform data processing and deep learning inference. Here, fully-trained AI neural decoders 110 based on deep learning architecture are deployed to translate nerve signals of the amputee's true intentions to individual finger movements in real-time in the form of predictions made by the AI architecture, based on the input of the amputee's true intention neurological signals. The final predictions are sent over to the hand controller 122 to actuate the prosthetic hand 144. The AI engine also uses data from the neuroprosthetic hand's fingertips touch sensors 148 as additional data from the touch data acquisition circuit 128 to modulate stimulation patterns to create somatosensory feedback.
[0061] The mechanical hand can be modified from any existing commercial system with individually motorized fingers and/or wrist. Off-the-shelf touch sensors 148 are attached to the fingertips and palm to sense the force generated when the hand grasps an object. Another component of the invention is a customized microcontroller(s) 124 that receives decoded movement intents/intentions 118 from the AI engine and independently drives the finger and thumb motors accordingly. This controller also acquires touch sensor data 120 and relays such data to the AI engine 108. A rechargeable Li-ion battery 116 powers the entire system. Additional voltage regulator circuits are included to generate the proper power supply for each component.
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[0063] The AI engine module 108 in this example of a preferred embodiment of the invention is powered by the NVIDIA® Jetson Nano® computer module 202 (NVIDIA, California, USA). This AI engine module 108 is preferably equipped with the Tegra X1® system-on-chip (SoC) that has a Quad-Core ARM Cortex-A57® CPU and a 128-core NVIDIA® Maxwell-type microarchitecture GPU. This exemplary GPU has 472 gigaflops (GFLOP)s of computational power available for deep learning inference. The module can operate in a preferred 10 W power mode (4-core CPU 1900 MHz, GPU 1000 GHz) or a preferred 5 W power mode (2-core CPU 918 MHz, GPU 640 MHz). The prosthetic motorized hand 144, drawing its power from the rechargeable battery means 116, is based on the i-Limb® platform (TouchBionics®, Ossur, Iceland) which features five individually actuated motorized fingers 147. In a preferred embodiment of the invention, the i-Limb default driver is replaced, by procedures well known to those of ordinary skill in the art, with the inventor's customized hand controller 204, described below, which directly operates the DC motors 146 hidden and not here visible, in each finger. The controller 122 is designed around the ESP32 module (Espressif Systems, Shanghai, China) with control signals being distributed to one or more low-power microcontroller(s) 124. The touch sensors 148 fixably mounted at each fingertip and the prosthetic hand's palm may be resistive force sensors (FSR Series, Interlink Electronics, CA, USA) and/or capacitive force sensors (SingleTact®, Medical Tactile Inc., CA, USA).
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[0068] Turning now to
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[0072] The data acquisition thread 1000 polls data from the incoming data streams 1002 of two or more Scorpius devices and aligns them 1004 into appropriate channels. The data streams, one for every Scorpius device, continuously fill up the USB buffers at a bitrate of 1.28 Mbps per device. Each of the data streams 1002 contains data from eight channels, at a sampling rate of 10 kHz. Headers were also added to properly separate and align the data bytes into individual channels, and the data bytes were then placed into first-in-first-out (FIFO) queues 1006 and discarded excess data 1008 in preparation the data pre-processing thread 1010.
[0073] The data pre-processing thread 1010 filters and downsamples raw nerve data 1012, and subsequently performs feature extraction 1014 according to the procedures outlined in Luu & Nguyen et al., “Deep Learning-Based Approaches for Decoding Motor Intent from Peripheral Nerve Signals”, https://www.biorxiv.org/content/10.1101/2021.02.18.431483v1 (2021) the entire disclosure and teaching of which is incorporated herein by reference. This preferred embodiment data stream utilized nerve data in the 25-600 Hz band, which are known in the art to contain the majority of a neurosignals' power. We applied an anti-aliasing filter at 80% of the Nyquist frequency, downsampling by 2-times, and then applied the main 4th-order bandpass filter with 25-600 Hz cut-offs. In the feature extraction task 1014, each feature data point was computed over a sliding window of 100 msec with 20 msec increments, resulting in an effective feature data rate of 50 Hz. Feature is used here in the machine learning and statistics sense, meaning variable or predictor, so that a subset of the most relevant of such features can be assembled via various feature selection techniques to construct a behavior or activity model. Redundant or irrelevant features are removed by such techniques without much loss of information in order to shorten training times, simplify models, avoid dimensionality, and other uses. Here, the feature data were placed into last-in-first-out LIFO queues 1016 (rolling matrices) for the motor decoding thread 1018. Unlike prior art approaches, no data were stored for offline analysis. Nerve data were processed and fed to the motor decoder thread 1018 as soon as they were acquired or discarded if the thread cannot keep up. This LIFO setup ensures that the motor decoder thread 1018 always receives the latest, or most recently generated, data. In practice, the buffer to Python queue time is negligible, and the pre-processing time is the bulk of the non-motor decoding latency. Excess data could also be caused by small mismatches in clock frequency between different Scorpius® devices (a problem inherent in the device manufacturing process-see the discussion of transistor mismatch, above-, which creates data streams with a higher bitrate than others. As a result, up to 60 msec of raw data is occasionally discarded.
[0074] Deep learning inference is the use of a fully trained deep neural network to make inferences or predictions on of from new or novel data that the model has never seen before. Here, the motor decoding thread 1018 ran deep learning inference by using deep learning models 1020 processing the most up-to-date feature data from the LIFO queues corresponding to the past 1 sec of nerve signals. For the neuroprosthetic hand, there were one to five deep learning models 1020; so that each model decoded the movements of one or more fingers. All deep learning models 1020 have the same architecture but may be trained on different datasets to optimize the performance of a specific finger. The reason for this is that while an individual deep learning model can produce a [5×1] prediction matrix, it is often difficult to train a single deep learning model that is optimized for all five fingers. For example, the first model in
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[0077] The input 1200 is fed into the initial convolutional layer 1201, which performs the convolution function 1203, and identifies different representations of data input. The subsequent encoder-decoder 1204 utilizes first 1026 and second 1208 gated recurrent units (GRU) to represent the time-dependent aspect of motor decoding. The two linear layers perform analysis on the decoder's output and produce the final output matrix 1210, which are the probabilities that an individual finger is active. 50% dropout layers are added to avoid over-fitting and improve the network's efficiency. Overall, each model consists of 1.6 million parameters in total.
[0078] The models were trained on a desktop PC with an Intel® Core i7-8086K, and an NVIDIA® RTX 2080 Super graphics card. We used the Adam optimizer method with the default parameters being β.sub.!=0.99, β.sub.″=0.999, and weight decay regularization L.sub.″=10.sup.#$. The mini-batch size was set to 64. The number of epoch (2-10) and initial learning rate (10.sup.#%-10.sup.#&) were adjusted for each model to optimize the performance while preventing over-fitting. The learning rate was reduced by a factor of 10 when the training loss stopped improving for two consecutive epochs. The training time for each epoch depended on the dataset's size and typically took about 10-15 msec.
[0079] In
[0080] There were collected at least four or more mirrored bilateral training sessions for each hand gesture. Within a session, the patient performed a given gesture at different shoulder, arm, and body postures, recreating real-life conditions. Additional sessions may alternatively be required for gestures that are difficult to predict. The last data session, which contained the most up-to-date nerve data, was strongly preferred to be used for validation while the remaining were used for training. This configuration translates to a training-to-validation ratio two ranges of approximately 75:25 for able participants to 85:15 for an amputee.
[0081] In the flow chart of
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[0083] Performance results are shown at
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[0091]
[0092] While the above description contains much specificity, these should not be construed as limitations on the scope of any embodiment, but as exemplifications of the presented embodiments thereof. Many other alternative embodiments and variations are possible within the teachings of the various embodiments. While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made, and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention will not be limited to the particular embodiment disclosed as the best or only mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are, unless otherwise stated, used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or hierarchy of importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items.
[0093] While the invention has been described, exemplified, and illustrated in reference to certain preferred embodiments thereof, those skilled in the art will appreciate that various changes, modifications, and substitutions can be made therein without departing from the spirit and scope of the invention. It is intended, therefore that the invention be limited only by the scope of the claims which follow, and that such claims be interpreted as broadly as is reasonable.