The Experts below are selected from a list of 4218 Experts worldwide ranked by ideXlab platform
Claude Veraart - One of the best experts on this subject based on the ideXlab platform.
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Electrical Stimulation of Anterior Visual Pathways
2015Co-Authors: In Retinitis Pigmentosa, Delphine Pins, Jean Delbeke, Marie-chantal Wanet-defalque, Simone Parrini, Claude VeraartAbstract:PURPOSE. To explore electrically induced phosphenes in blind patients with retinitis pigmentosa (RP) in comparison with healthy subjects and to develop a screening test for candidates for an optic nerve Visual Prosthesis implantation. METHODS. Phosphenes are obtained by charge balanced bipha-sic pulse stimulations through a surface cathode over the closed eyelids and an anode near the opposite ear. The result-ing strength–duration relationship for somatosensory, phos-phene, and pain threshold has been recorded in five RP pa-tients as well as in 10 healthy volunteers. RESULTS. In sighted subjects, the average rheobase and chronaxy for phosphene perception are 0.28 mA and 3.07 msec, respec-tively. For pulse durations longer than 2 msec, phosphenes are usually obtained at current strengths below the level giving rise to any other electrically generated sensation. In RP patients
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object localization discrimination and grasping with the optic nerve Visual Prosthesis
Restorative Neurology and Neuroscience, 2006Co-Authors: Florence Duret, Jean Delbeke, Benoit Gerard, Marten E Brelen, Valerie Lambert, Claude VeraartAbstract:PURPOSE: This study involved a volunteer completely blind from retinis pigmentosa who had previously been implanted with an optic nerve Visual Prosthesis. The aim of this two-year study was to train the volunteer to localize a given object in nine different positions, to discriminate the object within a choice of six, and then to grasp it. METHODS: In a closed-loop protocol including a head worn video camera, the nerve was stimulated whenever a part of the processed image of the object being scrutinized matched the center of an elicitable phosphene. The accessible Visual field included 109 phosphenes in a 14 degrees x 41 degrees area. RESULTS: Results showed that training was required to succeed in the localization and discrimination tasks, but practically no training was required for grasping the object. The volunteer was able to successfully complete all tasks after training. The volunteer systematically performed several left-right and bottom-up scanning movements during the discrimination task. Discrimination strategies included stimulation phases and no-stimulation phases of roughly similar duration. CONCLUSION: This study provides a step towards the practical use of the optic nerve Visual Prosthesis in current daily life.
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creating a meaningful Visual perception in blind volunteers by optic nerve stimulation
Journal of Neural Engineering, 2005Co-Authors: Marten E Brelen, Jean Delbeke, Benoit Gerard, Florence Duret, Claude VeraartAbstract:A blind volunteer, suffering from retinitis pigmentosa, has been chronically implanted with an optic nerve Visual Prosthesis. Vision rehabilitation with this volunteer has concentrated on the development of a stimulation strategy according to which video camera images are converted into stimulation pulses. The aim is to convey as much information as possible about the Visual scene within the limits of the device's capabilities. Pattern recognition tasks were used to assess the effectiveness of the stimulation strategy. The results demonstrate how even a relatively basic algorithm can efficiently convey useful information regarding the Visual scene. By increasing the number of phosphenes used in the algorithm, better performance is observed but a longer training period is required. After a learning period, the volunteer achieved a pattern recognition score of 85% at 54 s on average per pattern. After nine evaluation sessions, when using a stimulation strategy exploiting all available phosphenes, no saturation effect has yet been observed.
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prediction of Visual perceptions with artificial neural networks in a Visual Prosthesis for the blind
Artificial Intelligence in Medicine, 2004Co-Authors: Cedric Archambeau, Jean Delbeke, Claude Veraart, Michel VerleysenAbstract:Within the framework of the OPTIVIP project, an optic nerve based Visual Prosthesis is developed in order to restore partial vision to the blind. One of the main challenges is to understand, decode and model the physiological process linking the stimulating parameters to the Visual sensations produced in the Visual field of a blind volunteer. We propose to use adaptive neural techniques. Two prediction models are investigated. The first one is a grey-box model exploiting the neurophysiological knowledge available up to now. It combines a neurophysiological model with artificial neural networks, such as multi-layer perceptrons and radial basis function networks, in order to predict the features of the Visual perceptions. The second model is entirely of the black-box type. We show that both models provide satisfactory prediction tools and achieve similar prediction accuracies. Moreover, we demonstrate that significant improvement (25%) was gained with respect to linear statistical methods, suggesting that the biological process is strongly non-linear.
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pattern recognition with the optic nerve Visual Prosthesis
Artificial Organs, 2003Co-Authors: Claude Veraart, Annick Vanlierde, Mc Wanetdefalque, Benoit Gerard, Jean DelbekeAbstract:A volunteer with retinitis pigmentosa and no residual vision was chronically implanted with an optic nerve electrode connected to an implanted neurostimulator and antenna. An external controller with telemetry was used for electrical activation of the nerve which resulted in phosphene perception. Open-loop stimulation allowed the collection of phosphene attributes and the ability to elicit perception of simple geometrical patterns. Low perception thresholds allowed for large current intensity range within safety limits. In a closed-loop paradigm, the volunteer was using a head-worn video camera to explore a projection screen. The volunteer underwent performance evaluation during the course of a training program with 45 simple patterns. After learning, the volunteer reached a recognition score of 63% with a processing time of 60 s. Mean performance in orientation discrimination reached 100% with a processing time of 8 s.
Qiushi Ren - One of the best experts on this subject based on the ideXlab platform.
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penetrative optic nerve based Visual Prosthesis research
2017Co-Authors: Yan Yan, Xinyu Chai, Pengjia Cao, Jingjing Sun, Yao Chen, Steven E Katz, Pengcheng Sun, Qiushi RenAbstract:A number of research groups around the world have been dedicated to restoring some functional vision for blind patients through Visual prostheses. The C-sight project (Chinese Project for Sight) proposed a Visual Prosthesis with penetrative stimulating electrode array implanted into the ON as a neural interface to couple the encoded electrical stimuli for vision recovery, since then a decade of effort has been devoted to the development of the first-generation prototype. In this article, the outcomes of this approach and its status quo were briefly summarized and introduced from different perspectives. Besides hardware system and surgical methods description, the cortical response characteristics in response to penetrating ON stimulation in in vivo animal experiments were extensively introduced. Firstly, as a widely used methodology of evaluating the effect of a certain electrical stimulus, the basic spatiotemporal properties of the electrically evoked cortical potentials (EEPs) elicited by penetrating ON stimulation were investigated. Secondly, the exact implantation sites of ON electrode array were considered and evaluated taking account of realizing fine visuotopic correspondence between ON electrical stimulation sites and the Visual field. Thirdly, the optimal stimulus parameters were explored, as well as the relationship between response properties of electrical vs. Visual stimulation. Furthermore, several potential future directions of this approach were also briefly discussed.
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penetrating electrode stimulation of the rabbit optic nerve parameters and effects on evoked cortical potentials
Graefes Archive for Clinical and Experimental Ophthalmology, 2013Co-Authors: Jingjing Sun, Xinyu Chai, Yao Chen, Qiushi RenAbstract:Background Stimulus parameters, in particular pulse shape, are an important consideration in the application of electrical stimulation when experimentally testing a Visual Prosthesis. We changed the biphasic pulse shape of several asymmetric charge-balanced pulses to investigate their effect on optic nerve (ON) stimulation and the recorded cortical response.
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electrical stimulation with a penetrating optic nerve electrode array elicits visuotopic cortical responses in cats
Journal of Neural Engineering, 2013Co-Authors: Yan Yan, Xinyu Chai, Qiushi Ren, Yao ChenAbstract:Objective. A Visual Prosthesis based on penetrating electrode stimulation within the optic nerve (ON) is a potential way to restore partial functional vision for blind patients. We investigated the retinotopic organization of ON stimulation and its spatial resolution. Approach. A five-electrode array was inserted perpendicularly into the ON or a single electrode was advanced to different depths within the ON (~1–2 mm behind the eyeball, 13 cats). A sparse noise method was used to map ON electrode position and the Visual cortex. Cortical responses were recorded by a 5 × 6 array. The visuotopic correspondence between the retinotopic position of the ON electrode was compared with the Visual evoked cortical map and the electrical evoked potentials elicited in response to ON stimulation. Main results. Electrical stimulation with penetrating ON electrodes elicited cortical responses in visuotopographically corresponding areas of the cortex. Stimulation of the temporal side of the ON elicited cortical responses corresponding to the central Visual field. The Visual field position shifted from the lower to central Visual field as the electrode penetrated through the depth of the ON. A spatial resolution of ~ 2° to 3° within a limited cortical visuotopic representation could be obtained by this approach. Significance. Visuotopic electrical stimulation with a relatively fine spatial resolution can be accomplished using penetrating electrodes implanted at multiple sites and at different depths within the ON just behind the globe. This study also provides useful experimental data for the design of electrode density and the distribution of penetrating ON electrodes for a Visual Prosthesis.
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simulated phosphene model for Visual Prosthesis
BioMedical Engineering and Informatics, 2012Co-Authors: Ying Zhao, Kun Yang, Bo Pang, Yongji Wang, Qiushi RenAbstract:Two simulated phosphene models were proposed in this paper. Model I was based on uniform or Gaussian round or square spots which arranged in rectangle or hexagonal arrays. Model II was based on partial clinical experiment data of one optic nerve Prosthesis research. Numbers, letters and Chinese characters were pixelated by these models. The feasibility of using Model II to perform simulation experiments was discussed and confirmed.
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Estimation of simulated phosphene size based on tactile perception.
Artificial organs, 2011Co-Authors: Panpan Chen, Ying Zhao, Jingru Shi, Qiushi Ren, Xinyu ChaiAbstract:Clinical trials have successfully shown that a Visual Prosthesis can elicit Visual perception (phosphenes) in the Visual field. Psychophysical studies based on simulated prosthetic vision offer an effective means to evaluate and refine prosthetic vision. We designed three experiments to examine the effect of phosphene luminance, flicker rate, and eccentricity on the ability to estimate simulated phosphene sizes using tactile perception. Thirty subjects participated in the three experiments. There was a linear increase in reported size as Visual stimulus size increased. Judgment was significantly affected by stimulus luminance and eccentricity (P < 0.05) but not by flicker rates. Brighter stimuli were perceived as being larger, and the more eccentric the position, the larger the estimated size. These simulation studies, although idealized, suggested that tactile perception is a potential way to estimate phosphene sizes.
Jean Delbeke - One of the best experts on this subject based on the ideXlab platform.
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Electrical Stimulation of Anterior Visual Pathways
2015Co-Authors: In Retinitis Pigmentosa, Delphine Pins, Jean Delbeke, Marie-chantal Wanet-defalque, Simone Parrini, Claude VeraartAbstract:PURPOSE. To explore electrically induced phosphenes in blind patients with retinitis pigmentosa (RP) in comparison with healthy subjects and to develop a screening test for candidates for an optic nerve Visual Prosthesis implantation. METHODS. Phosphenes are obtained by charge balanced bipha-sic pulse stimulations through a surface cathode over the closed eyelids and an anode near the opposite ear. The result-ing strength–duration relationship for somatosensory, phos-phene, and pain threshold has been recorded in five RP pa-tients as well as in 10 healthy volunteers. RESULTS. In sighted subjects, the average rheobase and chronaxy for phosphene perception are 0.28 mA and 3.07 msec, respec-tively. For pulse durations longer than 2 msec, phosphenes are usually obtained at current strengths below the level giving rise to any other electrically generated sensation. In RP patients
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object localization discrimination and grasping with the optic nerve Visual Prosthesis
Restorative Neurology and Neuroscience, 2006Co-Authors: Florence Duret, Jean Delbeke, Benoit Gerard, Marten E Brelen, Valerie Lambert, Claude VeraartAbstract:PURPOSE: This study involved a volunteer completely blind from retinis pigmentosa who had previously been implanted with an optic nerve Visual Prosthesis. The aim of this two-year study was to train the volunteer to localize a given object in nine different positions, to discriminate the object within a choice of six, and then to grasp it. METHODS: In a closed-loop protocol including a head worn video camera, the nerve was stimulated whenever a part of the processed image of the object being scrutinized matched the center of an elicitable phosphene. The accessible Visual field included 109 phosphenes in a 14 degrees x 41 degrees area. RESULTS: Results showed that training was required to succeed in the localization and discrimination tasks, but practically no training was required for grasping the object. The volunteer was able to successfully complete all tasks after training. The volunteer systematically performed several left-right and bottom-up scanning movements during the discrimination task. Discrimination strategies included stimulation phases and no-stimulation phases of roughly similar duration. CONCLUSION: This study provides a step towards the practical use of the optic nerve Visual Prosthesis in current daily life.
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creating a meaningful Visual perception in blind volunteers by optic nerve stimulation
Journal of Neural Engineering, 2005Co-Authors: Marten E Brelen, Jean Delbeke, Benoit Gerard, Florence Duret, Claude VeraartAbstract:A blind volunteer, suffering from retinitis pigmentosa, has been chronically implanted with an optic nerve Visual Prosthesis. Vision rehabilitation with this volunteer has concentrated on the development of a stimulation strategy according to which video camera images are converted into stimulation pulses. The aim is to convey as much information as possible about the Visual scene within the limits of the device's capabilities. Pattern recognition tasks were used to assess the effectiveness of the stimulation strategy. The results demonstrate how even a relatively basic algorithm can efficiently convey useful information regarding the Visual scene. By increasing the number of phosphenes used in the algorithm, better performance is observed but a longer training period is required. After a learning period, the volunteer achieved a pattern recognition score of 85% at 54 s on average per pattern. After nine evaluation sessions, when using a stimulation strategy exploiting all available phosphenes, no saturation effect has yet been observed.
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prediction of Visual perceptions with artificial neural networks in a Visual Prosthesis for the blind
Artificial Intelligence in Medicine, 2004Co-Authors: Cedric Archambeau, Jean Delbeke, Claude Veraart, Michel VerleysenAbstract:Within the framework of the OPTIVIP project, an optic nerve based Visual Prosthesis is developed in order to restore partial vision to the blind. One of the main challenges is to understand, decode and model the physiological process linking the stimulating parameters to the Visual sensations produced in the Visual field of a blind volunteer. We propose to use adaptive neural techniques. Two prediction models are investigated. The first one is a grey-box model exploiting the neurophysiological knowledge available up to now. It combines a neurophysiological model with artificial neural networks, such as multi-layer perceptrons and radial basis function networks, in order to predict the features of the Visual perceptions. The second model is entirely of the black-box type. We show that both models provide satisfactory prediction tools and achieve similar prediction accuracies. Moreover, we demonstrate that significant improvement (25%) was gained with respect to linear statistical methods, suggesting that the biological process is strongly non-linear.
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pattern recognition with the optic nerve Visual Prosthesis
Artificial Organs, 2003Co-Authors: Claude Veraart, Annick Vanlierde, Mc Wanetdefalque, Benoit Gerard, Jean DelbekeAbstract:A volunteer with retinitis pigmentosa and no residual vision was chronically implanted with an optic nerve electrode connected to an implanted neurostimulator and antenna. An external controller with telemetry was used for electrical activation of the nerve which resulted in phosphene perception. Open-loop stimulation allowed the collection of phosphene attributes and the ability to elicit perception of simple geometrical patterns. Low perception thresholds allowed for large current intensity range within safety limits. In a closed-loop paradigm, the volunteer was using a head-worn video camera to explore a projection screen. The volunteer underwent performance evaluation during the course of a training program with 45 simple patterns. After learning, the volunteer reached a recognition score of 63% with a processing time of 60 s. Mean performance in orientation discrimination reached 100% with a processing time of 8 s.
Gregg J Suaning - One of the best experts on this subject based on the ideXlab platform.
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long term anesthetic protocol in rats feasibility in electrophysiology studies in Visual Prosthesis
Veterinary Ophthalmology, 2018Co-Authors: Nigel H Lovell, John W. Morley, Alejandro Barrigarivera, Veronica Tatarinoff, Gregg J SuaningAbstract:Electrical stimulation of excitable cells provides therapeutic benefits for a variety of medical conditions, including restoration of partial vision to those blinded via some types of retinal degeneration. To improve Visual percepts elicited by the current technology, researchers are conducting acute electrophysiology experiments, mainly in cats. However, the rat can provide a model of a range of retinal diseases and possesses a sufficiently large eye to be used in this field. This article presents a long-term anesthetic protocol to enable electrophysiology experiments to further the development of Visual prostheses. Six Long-Evans rats (aged between 14 and 16 weeks) were included in this study. Surgical anesthesia was maintained for more than 15 h by combining constant intravenous infusion of ketamine (24.0-34.5 mg/kg/h), xylazine (0.9-1.2 mg/kg/h), and inhaled isoflurane in oxygen (<0.5%). Overall heart rate, respiratory rate, and body temperature remained between 187-233 beats/min, 45-58 breaths/min, and 36-38 °C, respectively. Neural responses to 200-ms light pulses were recorded from the superior colliculus using a 32-channel neural probe at the beginning and before termination of the experiment. Robust responses were recorded from distinct functional types of retinal pathways. In addition, a platinum electrode was implanted in the retrobulbar space. The retina was electrically stimulated, and the activation threshold was determined to be 5.24 ± 0.24 μC/cm2 . This protocol may be used not only in the field of Visual Prosthesis research, but in other research areas requiring longer term acute experiments.
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Visual Prosthesis interfacing stimulating electrodes with retinal neurons to restore vision
Frontiers in Neuroscience, 2017Co-Authors: Alejandro Barrigarivera, Lilach Bareket, Josef Goding, Ulises A Areguetarobles, Gregg J SuaningAbstract:The bypassing of degenerated photoreceptors using retinal neurostimulators is helping the blind to recover functional vision. Researchers are investigating new ways to improve Visual percepts elicited by these means as the vision produced by these early devices remain rudimentary. However, several factors are hampering the progression of bionic technologies: the charge injection limits of metallic electrodes, the mechanical mismatch between excitable tissue and the stimulating elements, neural and electric crosstalk, the physical size of the implanted devices, and the inability to selectively activate different types of retinal neurons. Electrochemical and mechanical limitations are being addressed by the application of electromaterials such as conducting polymers, carbon nanotubes and nanocrystalline diamonds, among other biomaterials, to electrical neuromodulation. In addition, the use of synthetic hydrogels and cell-laden biomaterials is promising better interfaces, as it opens a door to establishing synaptic connections between the electrode material and the excitable cells. Finally, new electrostimulation approaches relying on the use of high-frequency stimulation and field overlapping techniques are being developed to better replicate the neural code of the retina. All these elements combined will bring bionic vision beyond its present state and into the realm of a viable, mainstream therapy for vision loss.
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high amplitude electrical stimulation can reduce elicited neuronal activity in Visual Prosthesis
Scientific Reports, 2017Co-Authors: Alejandro Barrigarivera, Nigel H Lovell, Gregg J Suaning, Chih Yu Yang, Tianruo Guo, Socrates Dokos, John W. Morley, Amr Al AbedAbstract:Retinal electrostimulation is promising a successful therapy to restore functional vision. However, a narrow stimulating current range exists between retinal neuron excitation and inhibition which may lead to misperformance of Visual prostheses. As the conveyance of representation of complex Visual scenes may require neighbouring electrodes to be activated simultaneously, electric field summation may contribute to reach this inhibitory threshold. This study used three approaches to assess the implications of relatively high stimulating conditions in Visual prostheses: (1) in vivo, using a suprachoroidal Prosthesis implanted in a feline model, (2) in vitro through electrostimulation of murine retinal preparations, and (3) in silico by computing the response of a population of retinal ganglion cells. Inhibitory stimulating conditions led to diminished cortical activity in the cat. Stimulus-response relationships showed non-monotonic profiles to increasing stimulating current. This was observed in vitro and in silico as the combined response of groups of neurons (close to the stimulating electrode) being inhibited at certain stimulating amplitudes, whilst other groups (far from the stimulating electrode) being recruited. These findings may explain the halo-like phosphene shapes reported in clinical trials and suggest that simultaneous stimulation in retinal prostheses is limited by the inhibitory threshold of the retinal ganglion cells.
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Multipolar Field Shaping in a Suprachoroidal Visual Prosthesis
IEEE Transactions on Neural Systems and Rehabilitation Engineering, 2017Co-Authors: Calvin D. Eiber, Nigel H Lovell, Socrates Dokos, Gregg J SuaningAbstract:Visual prostheses are now an available mobility aid for patients blinded by degenerative retinal diseases. However, the spatial resolution of existing devices is still insufficient to deliver normal levels of mobility vision without stimulation strategies, which enable existing devices to deliver several different percepts per stimulation site. A stimulation strategy, in which field shaping is achieved by incorporating multipolar (bipolar and tripolar) stimulation could convey additional information to a user of a Visual Prosthesis, as compared with monopolar stimulation, is investigated. Electrical stimulus response thresholds were simulated using morphologically and physiologically accurate cable models of human retinal ganglion cell (RGC) axons. From the population response patterns which could be evoked in simulation, multipolar field-shaping stimulation from one location could convey as much information as monopolar array stimulation. This result is confirmed in vitro by applying a Bayesian classification analysis to multielectrode array recordings of RGC population responses to extracellular stimulation. In vitro recorded population responses to individual stimuli in vitro could be used to train a Baysian classifier, which could correctly identify individual stimuli as predicted by the simulated population responses. In both simulation and in vitro experiments, monopolar thresholds were not significantly different to multipolar thresholds.
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a 4 1 architecture for in vivo electrophysiology Visual Prosthesis
JACCES: Journal of accessibility and design for all, 2016Co-Authors: Alejandro Barrigarivera, Nigel H Lovell, John W. Morley, Spencer C Chen, Calvin D. Eiber, Paul B Matteucci, Gregg J SuaningAbstract:Researchers around the globe are working towards restoring vision to the blind through the development of a Visual neuroProsthesis. Overcoming physical, technical and biological limitations represents one of the main challenges for the scientific community and will eventually benefit the wellbeing of the recipients of these devices. Thus, understanding the physiological mechanisms of prosthetic vision plays a key role. In this context, in vivo electrophysiological studies are aiming to shed light on new stimulation paradigms that can potentially lead to improved Visual perception. This paper describes a multi-viewpoint architecture of an experimental setup for the investigation of electrically evoked potentials in a retinal neuroProsthesis.
Xinyu Chai - One of the best experts on this subject based on the ideXlab platform.
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penetrative optic nerve based Visual Prosthesis research
2017Co-Authors: Yan Yan, Xinyu Chai, Pengjia Cao, Jingjing Sun, Yao Chen, Steven E Katz, Pengcheng Sun, Qiushi RenAbstract:A number of research groups around the world have been dedicated to restoring some functional vision for blind patients through Visual prostheses. The C-sight project (Chinese Project for Sight) proposed a Visual Prosthesis with penetrative stimulating electrode array implanted into the ON as a neural interface to couple the encoded electrical stimuli for vision recovery, since then a decade of effort has been devoted to the development of the first-generation prototype. In this article, the outcomes of this approach and its status quo were briefly summarized and introduced from different perspectives. Besides hardware system and surgical methods description, the cortical response characteristics in response to penetrating ON stimulation in in vivo animal experiments were extensively introduced. Firstly, as a widely used methodology of evaluating the effect of a certain electrical stimulus, the basic spatiotemporal properties of the electrically evoked cortical potentials (EEPs) elicited by penetrating ON stimulation were investigated. Secondly, the exact implantation sites of ON electrode array were considered and evaluated taking account of realizing fine visuotopic correspondence between ON electrical stimulation sites and the Visual field. Thirdly, the optimal stimulus parameters were explored, as well as the relationship between response properties of electrical vs. Visual stimulation. Furthermore, several potential future directions of this approach were also briefly discussed.
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image processor for Visual Prosthesis based on arm
BioMedical Engineering and Informatics, 2014Co-Authors: Lei Zhao, Xinyu ChaiAbstract:Visual Prosthesis is designed and developed to help the blind people to restore vision [1]. Image processor is an essential part of Visual Prosthesis. It receives image data from a camera, and fulfills specific image processing strategy to transfer image information to data forms that can be recognized by implanted stimulator. To extract useful information from original image and provide satisfying image processing ability are the basic requirements for the image processor. In this article, an image processor based on ARM Cortex-A9 processor running mobile operating system Android is introduced. Image processing algorithms such as edge detection are applied to provide vital information of the scene to the following components. Software optimizations like using native code and hardware acceleration are made to reduce the processing time. After optimization, this image processor can process a 640∗480 image within 50ms. This work could become the foundation of future researches to build Visual Prosthesis with impressive processing ability and flexibility.
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moving object recognition under simulated prosthetic vision using background subtraction based image processing strategies
Information Sciences, 2014Co-Authors: Jing Wang, Chuanqing Zhou, Xinyu ChaiAbstract:Abstract A Visual Prosthesis that applies electrical stimulation to different parts of the Visual pathway has been proposed as a viable approach to restore functional vision. However, the created percept is currently limited due to the low-resolution images elicited from a limited number of stimulating electrodes. Thus, methods to optimize the Visual percepts providing useful Visual information are being considered. We used two image-processing strategies based on a novel background subtraction technique to optimize the content of dynamic scenes of daily life. Psychophysical results showed that background reduction, or background reduction with foreground enhancement, increased response accuracy compared with methods that directly merged pixels to lower resolution. By adding more gray scale information, a background reduction/foreground enhancement strategy resulted in the best performance and highest recognition accuracy. Further development of image-processing modules for a Visual Prosthesis based on these results will assist implant recipients to avoid dangerous situations and attain independent mobility in daily life.
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penetrating electrode stimulation of the rabbit optic nerve parameters and effects on evoked cortical potentials
Graefes Archive for Clinical and Experimental Ophthalmology, 2013Co-Authors: Jingjing Sun, Xinyu Chai, Yao Chen, Qiushi RenAbstract:Background Stimulus parameters, in particular pulse shape, are an important consideration in the application of electrical stimulation when experimentally testing a Visual Prosthesis. We changed the biphasic pulse shape of several asymmetric charge-balanced pulses to investigate their effect on optic nerve (ON) stimulation and the recorded cortical response.
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electrical stimulation with a penetrating optic nerve electrode array elicits visuotopic cortical responses in cats
Journal of Neural Engineering, 2013Co-Authors: Yan Yan, Xinyu Chai, Qiushi Ren, Yao ChenAbstract:Objective. A Visual Prosthesis based on penetrating electrode stimulation within the optic nerve (ON) is a potential way to restore partial functional vision for blind patients. We investigated the retinotopic organization of ON stimulation and its spatial resolution. Approach. A five-electrode array was inserted perpendicularly into the ON or a single electrode was advanced to different depths within the ON (~1–2 mm behind the eyeball, 13 cats). A sparse noise method was used to map ON electrode position and the Visual cortex. Cortical responses were recorded by a 5 × 6 array. The visuotopic correspondence between the retinotopic position of the ON electrode was compared with the Visual evoked cortical map and the electrical evoked potentials elicited in response to ON stimulation. Main results. Electrical stimulation with penetrating ON electrodes elicited cortical responses in visuotopographically corresponding areas of the cortex. Stimulation of the temporal side of the ON elicited cortical responses corresponding to the central Visual field. The Visual field position shifted from the lower to central Visual field as the electrode penetrated through the depth of the ON. A spatial resolution of ~ 2° to 3° within a limited cortical visuotopic representation could be obtained by this approach. Significance. Visuotopic electrical stimulation with a relatively fine spatial resolution can be accomplished using penetrating electrodes implanted at multiple sites and at different depths within the ON just behind the globe. This study also provides useful experimental data for the design of electrode density and the distribution of penetrating ON electrodes for a Visual Prosthesis.
