Relevant bibliographies by topics / Phosphenes

Academic literature on the topic 'Phosphenes'

Author: Grafiati
Published: 4 June 2021
Last updated: 11 March 2023

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Journal articles on the topic "Phosphenes"

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Et.al, Manami, K. "Investigation of Electrical Interference towards Phosphene-Based Walking Support System." Turkish Journal of Computer and Mathematics Education (TURCOMAT) 12, no. 3 (April 10, 2021): 2178–83. http://dx.doi.org/10.17762/turcomat.v12i3.1164.

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A walking support system with phosphenes for blind people has been investigated. Phosphene is a phenomenon where a flash of light is recognized in the brain by giving an electrical stimulus to human’s visual pathway. Phosphenes can be perceived even if their eyes are closed or they are blind. It has been clarified that phosphenes can be induced to several directions if electrodes placements are precisely selected. When phosphenes are presented to two directions for recognizing two obstacles, two pairs of electrodes must be applied. In such a case, however, the electrical interference occurs due to the short distance between electrodes. In the practical use of the phosphene-based walking support system, the avoidance of electrical interference is significant in order to present the phosphenes precisely. Therefore, in this paper, we first practically investigate the electrical interference by considering the difference in phosphene induction generated by a single pair of electrodes and by two pairs of electrodes. Then, the solutions to avoid the electrical interference are discussed.
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Kvašňák, E., M. Orendáčová, and J. Vránová. "Phosphene Attributes Depend on Frequency and Intensity of Retinal tACS." Physiological Research 71, no. 4 (August 31, 2022): 561–71. http://dx.doi.org/10.33549/physiolres.934887.

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Phosphene is the experience of light without natural visual stimulation. It can be induced by electrical stimulation of the retina, optic nerve or cortex. Induction of phosphenes can be potentially used in assistive devices for the blind. Analysis of phosphene might be beneficial for practical reasons such as adjustment of transcranial alternating current stimulation (tACS) frequency and intensity to eliminate phosphene perception (e.g., tACS studies using verum tACS group and sham group) or, on the contrary, to maximize perception of phosphenes in order to be more able to study their dynamics. In this study, subjective reports of 50 healthy subjects exposed to different intensities of retinal tACS at 4 different frequencies (6, 10, 20 and 40 Hz) were analyzed. The effectiveness of different tACS frequencies in inducing phosphenes was at least 92 %. Subject reported 41 different phosphene types; the most common were light flashes and light circles. Changing the intensity of stimulation often induced a change in phosphene attributes. Up to nine phosphene attributes changed when the tACS intensity was changed. Significant positive correlation was observed between number of a different phosphene types and tACS frequency. Based on these findings, it can be concluded that tACS is effective in eliciting phosphenes whose type and attributes change depending on the frequency and intensity of tACS. The presented results open new questions for future research.
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Niketeghad, Soroush, Abirami Muralidharan, Uday Patel, Jessy D. Dorn, Laura Bonelli, Robert J. Greenberg, and Nader Pouratian. "Phosphene perceptions and safety of chronic visual cortex stimulation in a blind subject." Journal of Neurosurgery 132, no. 6 (June 2020): 2000–2007. http://dx.doi.org/10.3171/2019.3.jns182774.

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Stimulation of primary visual cortices has the potential to restore some degree of vision to blind individuals. Developing safe and reliable visual cortical prostheses requires assessment of the long-term stability, feasibility, and safety of generating stimulation-evoked perceptions.A NeuroPace responsive neurostimulation system was implanted in a blind individual with an 8-year history of bare light perception, and stimulation-evoked phosphenes were evaluated over 19 months (41 test sessions). Electrical stimulation was delivered via two four-contact subdural electrode strips implanted over the right medial occipital cortex. Current and charge thresholds for eliciting visual perception (phosphenes) were measured, as were the shape, size, location, and intensity of the phosphenes. Adverse events were also assessed.Stimulation of all contacts resulted in phosphene perception. Phosphenes appeared completely or partially in the left hemifield. Stimulation of the electrodes below the calcarine sulcus elicited phosphenes in the superior hemifield and vice versa. Changing the stimulation parameters of frequency, pulse width, and burst duration affected current thresholds for eliciting phosphenes, and increasing the amplitude or frequency of stimulation resulted in brighter perceptions. While stimulation thresholds decreased between an average of 5% and 12% after 19 months, spatial mapping of phosphenes remained consistent over time. Although no serious adverse events were observed, the subject experienced mild headaches and dizziness in three instances, symptoms that did not persist for more than a few hours and for which no clinical intervention was required.Using an off-the-shelf neurostimulator, the authors were able to reliably generate phosphenes in different areas of the visual field over 19 months with no serious adverse events, providing preliminary proof of feasibility and safety to proceed with visual epicortical prosthetic clinical trials. Moreover, they systematically explored the relationship between stimulation parameters and phosphene thresholds and discovered the direct relation of perception thresholds based on primary visual cortex (V1) neuronal population excitation thresholds.
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Indahlastari, Aprinda, Aditya K. Kasinadhuni, Christopher Saar, Kevin Castellano, Bakir Mousa, Munish Chauhan, Thomas H. Mareci, and Rosalind J. Sadleir. "Methods to Compare Predicted and Observed Phosphene Experience in tACS Subjects." Neural Plasticity 2018 (December 6, 2018): 1–10. http://dx.doi.org/10.1155/2018/8525706.

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Background. Phosphene generation is an objective physical measure of potential transcranial alternating current stimulation (tACS) biological side effects. Interpretations from phosphene analysis can serve as a first step in understanding underlying mechanisms of tACS in healthy human subjects and assist validation of computational models. Objective/Hypothesis. This preliminary study introduces and tests methods to analyze predicted phosphene occurrence using computational head models constructed from tACS recipients against verbal testimonies of phosphene sensations. Predicted current densities in the eyes and the occipital lobe were also verified against previously published threshold values for phosphenes. Methods. Six healthy subjects underwent 10 Hz tACS while being imaged in an MRI scanner. Two different electrode montages, T7-T8 and Fpz-Oz, were used. Subject ratings of phosphene experience were collected during tACS and compared against current density distributions predicted in eye and occipital lobe regions of interest (ROIs) determined for each subject. Calculated median current densities in each ROI were compared to minimum thresholds for phosphene generation. Main Results. All subjects reported phosphenes, and predicted median current densities in ROIs exceeded minimum thresholds for phosphenes found in the literature. Higher current densities in the eyes were consistently associated with decreased phosphene generation for the Fpz-Oz montage. There was an overall positive association between phosphene perceptions and current densities in the occipital lobe. Conclusions. These methods may have promise for predicting phosphene generation using data collected during in-scanner tACS sessions and may enable better understanding of phosphene origin. Additional empirical data in a larger cohort is required to fully test the robustness of the proposed methods. Future studies should include additional montages that could dissociate retinal and occipital stimulation.
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Császár, Noémi, Felix Scholkmann, Vahid Salari, Henrik Szőke, and István Bókkon. "Phosphene perception is due to the ultra-weak photon emission produced in various parts of the visual system: glutamate in the focus." Reviews in the Neurosciences 27, no. 3 (April 1, 2016): 291–99. http://dx.doi.org/10.1515/revneuro-2015-0039.

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AbstractPhosphenes are experienced sensations of light, when there is no light causing them. The physiological processes underlying this phenomenon are still not well understood. Previously, we proposed a novel biopsychophysical approach concerning the cause of phosphenes based on the assumption that cellular endogenous ultra-weak photon emission (UPE) is the biophysical cause leading to the sensation of phosphenes. Briefly summarized, the visual sensation of light (phosphenes) is likely to be due to the inherent perception of UPE of cells in the visual system. If the intensity of spontaneous or induced photon emission of cells in the visual system exceeds a distinct threshold, it is hypothesized that it can become a conscious light sensation. Discussing several new and previous experiments, we point out that the UPE theory of phosphenes should be really considered as a scientifically appropriate and provable mechanism to explain the physiological basis of phosphenes. In the present paper, we also present our idea that some experiments may support that the cortical phosphene lights are due to the glutamate-related excess UPE in the occipital cortex.
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Gebrehiwot, Adonay N., Tatsuya Kato, and Kimitaka Nakazawa. "Inducing lateralized phosphenes over the occipital lobe using transcranial magnetic stimulation to navigate a virtual environment." PLOS ONE 16, no. 4 (April 14, 2021): e0249996. http://dx.doi.org/10.1371/journal.pone.0249996.

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Electrical stimulation involving visual areas of the brain produces artificial light percepts called phosphenes. These visual percepts have been extensively investigated in previous studies involving intracortical microsimulation (ICMS) and serve as the basis for developing a visual prosthesis for the blind. Although advances have been achieved, many challenges still remain with implementing a functional ICMS for visual rehabilitation purposes. Transcranial magnetic stimulation (TMS) over the primary occipital lobe offers an alternative method to produce phosphenes non-invasively. A main challenge facing blind individuals involves navigation. Within the scientific community, methods to evaluate the ability of a visual prosthesis to facilitate in navigation has been neglected. In this study, we investigate the effectiveness of evoking lateralized phosphenes to navigate a computer simulated virtual environment. More importantly, we demonstrate how virtual environments along with the development of a visual prosthesis share a mutual relationship benefiting both patients and researchers. Using two TMS devices, a pair of 40mm figure-of-eight coils were placed over each occipital hemisphere resulting in lateralized phosphene perception. Participants were tasked with making a series of left and right turns using peripheral devices depending on the visual hemifield in which a phosphene is present. If a participant was able to accurately perceive all ten phosphenes, the simulated target is able to advance and fully exit the virtual environment. Our findings demonstrate that participants can interpret lateralized phosphenes while highlighting the integration of computer based virtual environments to evaluate the capability of a visual prosthesis during navigation.
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Kanamaru, Manami, Phan Xuan Tan, and Eiji Kamioka. "Simulation-Based Designing of Suitable Stimulation Factors for Presenting Two Phosphenes Simultaneously to Lower Side of Field of View." Bioengineering 9, no. 12 (December 2, 2022): 752. http://dx.doi.org/10.3390/bioengineering9120752.

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Using a phosphene has been discussed as a means of informing the visually impaired of the position of an obstacle. Obstacles underfoot have a risk, so it is necessary to inform the visually impaired. A previous study clarified a method of presenting phosphene in three directions in the lower vision; however, the simultaneous presentation of these phosphenes has not been discussed. Another study discussing the effect of electrical interference when stimulating the eyeball with multiple electrodes indicated that it is important to select appropriate stimulation factors to avoid this effect. However, when the stimulation electrodes are arranged remarkably close, there is a high possibility that the stimulus factor presented in the previous study will not apply. In this study, a method for simultaneously presenting phosphenes in the lower vision is presented. The electrode arrangements reported in the previous study to present phosphene in the lower field of vision are used, and the difficulty in the simultaneous presentation of multiple phosphenes in the lower vision is the focus. In this paper, the method of designing the stimulation factors is discussed numerically when the electrodes are arranged remarkably close. As a result, it is shown that stimulation factors different from the previous research were appropriate depending on the distance between the electrodes.
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Niketeghad, Soroush, Abirami Muralidharan, Uday Patel, Jessy Dorn, Robert Greenberg, and Nader Pouratian. "150 Effect of Stimulation Parameters on Visual Percepts Elicited by Stimulation of a Visual Cortical Prosthesis for the Blind." Neurosurgery 64, CN_suppl_1 (August 24, 2017): 236. http://dx.doi.org/10.1093/neuros/nyx417.150.

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Abstract INTRODUCTION Stimulation of human visual cortex is known to elicit visual percepts (phosphenes) which makes it a suitable candidate for generating artificial vision for blind. Although there have been a few attempts to build visual cortical prostheses, a greater understanding of the physiology of stimulation is required to generate useful perceptions. This study aims to characterize the phosphenes elicited by a neurostimulation device and explore the effects of stimulation parameters (amplitude, frequency, pulse-width and burst duration) on the quality of these percepts. METHODS A 30-year-old volunteer with an 8-year history of bare light perception secondary to Voght-Koaynagi-Harada Syndrome participated in this study. Two parallel cortical strip leads (each with four contacts) were implanted over the right medial occipital lobe. Phosphene characteristics were assessed postoperatively using subject's drawings of on a touch screen as well as subjective description of the percepts intensity and color. The stimulus parameters for eliciting a well-defined phosphene were obtained by varying the stimulus parameters for each contact at the beginning of each session during the eight months' period of the study. RESULTS >Stimulation of each of the eight contacts elicited phosphenes with a consistent shape and location in the visual field. The stimulus parameters for generating a well-defined phosphene were stable for six contacts and had to be adjusted for two over the period of the study. Increasing the amplitude and frequency resulted in more intense perceptions and the subject indicated seeing colored phosphenes for certain amplitudes. Simultaneous stimulation of multiple contacts was perceived as a summation of percepts elicited by stimulating the contacts individually. Sequential stimulation of two contacts generated two phosphenes and the subject was able to identify them in order. CONCLUSION Visual cortical prostheses are feasible candidates for creating artificial sight due to reproducibility of the perceptions and consistency of the stimulation parameters required to generate basic visual perceptions.
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Kanamaru, Manami, Phan Xuan Tan, and Eiji Kamioka. "Design of Electrode Placement for Presenting Phosphenes in the Lower Visual Field Based on Electric Field Simulation." Applied Sciences 11, no. 22 (November 19, 2021): 10972. http://dx.doi.org/10.3390/app112210972.

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Presenting visual information, called phosphenes, is a critical method for providing information on the position of obstacles for users of walking support tools for the visually impaired. A previous study has established a method for presenting phosphenes to the right, center, and left of the visual field. However, a method for presenting information on the position of obstacles around the feet using phosphenes, which is essential for the visually impaired, has not been clarified. Therefore, in this study, a method for presenting phosphenes in the lower visual field is presented, towards the aim of realizing a safe walking support tool. Electrode placement is proposed in this paper for the presentation of phosphenes to the right, center, and left of the lower visual field based on the electrode placement method used in the previous study, which presents the phosphene in three locations of the visual field. In addition, electric field simulation is performed, focusing on the electric field value on the eyeball surface, in order to observe whether the proposed electrode placement is able to stimulate the intended region. As a result, it is shown that the intended region on the eyeball surface can be stimulated locally with each of the proposed electrode placements.
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Chen, Xing, Feng Wang, Eduardo Fernandez, and Pieter R. Roelfsema. "Shape perception via a high-channel-count neuroprosthesis in monkey visual cortex." Science 370, no. 6521 (December 3, 2020): 1191–96. http://dx.doi.org/10.1126/science.abd7435.

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Blindness affects 40 million people across the world. A neuroprosthesis could one day restore functional vision in the blind. We implanted a 1024-channel prosthesis in areas V1 and V4 of the visual cortex of monkeys and used electrical stimulation to elicit percepts of dots of light (called phosphenes) on hundreds of electrodes, the locations of which matched the receptive fields of the stimulated neurons. Activity in area V4 predicted phosphene percepts that were elicited in V1. We simultaneously stimulated multiple electrodes to impose visible patterns composed of a number of phosphenes. The monkeys immediately recognized them as simple shapes, motions, or letters. These results demonstrate the potential of electrical stimulation to restore functional, life-enhancing vision in the blind.
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Dissertations / Theses on the topic "Phosphenes"

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RINALDI, ADELE. "Phosphenes in space: a study on the interaction between carbon ions and rod photoreceptor." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2009. http://hdl.handle.net/2108/995.

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I fosfeni, o light flash, sono stati percepiti per la prima volta durante il volo verso la luna della navicella Apollo. In genere sono avvertiti al buio, prima di addormentarsi. In questa tesi si studia l'ipotesi di una eccitazione dei fotorecettori della retina da parte di ioni pesanti (carbonio). Campioni di recettori dei bastoncelli vengono irradiati, e viene studiato l'effetto degli ioni carbonio su topo, attraverso la registrazione della risposta elettrofisiologica (segnale retinico e corticale). La tesi si e' sviluppata nell'ambito del progetto ALTEA (Anomaluos Long Term Effect on Astronauts) e tutti gli esperimenti relativi a questo lavoro sono stati svolti a terra. L’obiettivo di ALTEA e’ piu’ generale e riguarda lo studio del rischio funzionale sul sistema nervoso centrale degli astronauti dovuto alla particelle ionizzanti presenti in condizioni di microgravita’ durante le missioni spaziali a lungo termine; ALTEA include sia esperimenti a terra che in orbita, a bordo della Sazione Spaziale Internazionale. La tesi inizia con una introduzione al progetto ALTEA; nel secondo capitolo e’ descritto lo studio chiamato ALTEA-MICE (Mice intermittent Irradiation with Concurrent Electrophysiological monitoring). Nel terzo capitolo sono descritto il sistema costituito dai segmenti esterni dei bastoncelli bovini in sospensione e il meccanismo di attivazione dei fotorecettori. Nel quarto capitolo e quinto capitolo mi sono occupata della interazione radiazione – materia nei tessuti e del caso specifico dell’irradiazione dei campioni dei segmenti esterni contenenti la rodopsina. Nel quinto e ultimo capitolo viene presentato un modello che spiega l’isomerizzazione (attivazione) del retinale della rodopsina come prodotto dell’azione dei radicali liberi provenienti dalla radiolisi dell’acqua.
Phosphenes, or light flashes, have been reported by astronauts since the first Apollo flights to the Moon. They are usually described as occurring in the dark and typically before falling asleep. The light flashes are thought to originate as an effect of high- energy particles interacting with the visual system. The study presented in this thesis investigates the hypothesis of a direct excitation of the rod photoreceptors inside the retina and in particular the interaction between carbon ions and rods. Also the retinal and cortical electrophysiological response of mice submitted to carbon ions irradiation have been studied. This thesis has been developed as a section of the ’Anomalous Long Term Effects on Astronauts’ (ALTEA) program, and all the experiments concerning this thesis took place on ground. The objective of the ALTEA project is more general, and is aimed to assess the functional risks on the central nervous system due to particle flux in microgravity conditions during long term space mission. ALTEA includes a series of experiments both in orbit and on ground. The experiments on board International Space Station will contribute to define the causes of the anomalous phosphene perception of the astronauts by detecting the incident particles through the head of the astronauts and concurrently monitoring the central nervous system functionality. The experiments on ground include the direct irradiation with carbon ions of the outer segments of the rods, and an animal model to investigate the retina/cortex responses of mice irradiated in controlled laboratory experiments. In these experiments on ground I directly contributed in the preparation, the test and the optimization of the experiments and in the following analysis of the data. The whole project has been supported by the Italian Space Agency. The outline of this thesis includes an introduction to the interdisciplinary ALTEA program in the first chapter. In the second chapter ALTEA-MICE (Mice intermittent Irradiation with Concur- rent Electrophysiological monitoring) study is described: the experimental sessions as well as the evidences in the electrophysiological responses of the mouse retina have been described in detail. My role has been chiefly the experimental set up, and I also collaborated on the data analysis. The main results of this investigations have been published. In the third chapter the system of the rod outer segments in suspension and the mechanism of the activation of the photoreceptors are described. The fourth chapter deals with the radiation effects in the biological tissue, and in the fifth chapter there is particular regard to the effects of radiation on samples containing a suspension of rods extracted from bovine retinae. The effects on the rod photoreceptor rhodopsin has been studied: measurements have been performed irradiating with carbon ions the outer segments of the rods in suspension. The amount of the isomeric transformations (bleaching) of the molecules of chromophore into the photoreceptor gives the extent of the effects of radiation. I collaborated to the experiment and carried out the following data analysis. Finally, in the sixth chapter the process of the photo-isomerization of rhodopsin is explained by a model: the process starts with the water radiolysis and the formation of hydroxyl radicals OH in order to achieve the lipid peroxidation, then there is the subsequent emission of visible photons which are responsible for the photoreceptor bleaching. Since rhodopsin is surrounded by phospholipids, present in high concentration in the disc membranes, the effect of chemiluminescence is proposed to be the cause of the photo-transduction cascade and the light flash perception as a consequence. In order to test this hypothesis, a series of experiments was aimed at studying the effects of the hydroxyl radicals produced in an enzymatic way. The main results of this work are illustrated in chapter six, and have been published.
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Ledger, Araminta. "Chelating phosphine complexes of ruthenium for the co-ordination and activation of small molecules." Thesis, University of Bath, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545330.

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Chen, Spencer Chin-Yu Graduate School of Biomedical Engineering Faculty of Engineering UNSW. "The perception and comprehension of prosthetic vison: patient rehabilitation and image processing considerations from simulated prosthetic vision psychophysics." Publisher:University of New South Wales. Graduate School of Biomedical Engineering, 2009. http://handle.unsw.edu.au/1959.4/44414.

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A successful restoration of vision should allow the blind to look, to see and to understand. The engineering of a microelectronic vision prosthesis has come a long way over the last forty years, but the understanding of how the restored form of vision would be interpreted and functionally applied to everyday living has made little progress until recent times. Prosthetic vision is not what most people think it would be; it is a visual scene composed of relatively large, isolated, spots of light so-called "phosphenes", very much like a magnified pictorial print. This thesis dissertation seeks to obtain a complete survey of the visual description of phosphenes from the human trial reports in the literature, simulate it, obtain a measure of the functional capacity of such visual perception, and explain the measured performance against design aspects of phosphene presentation, human perception, cognition and behaviour. Specifically, "visual acuity" (VA) was assessed on normally sighted subjects (N=15) administered with "simulated prosthetic vision". VA is a functional measure of vision highly correlated to many daily activities. Aggregating the results from the study with the other VA studies in prosthetic vision, it is shown that in general, the density of the phosphene field determines the affordable VA; however, design aspects relating to the phosphene field lattice (0.03 10gMAR with the hexagonal lattice as opposed to a square lattice) and image processing routines (0.15 10gMAR at optimised settings) can be further fine-tuned to improve VA performance. Significant performance improvement also arose from learning (0.13 10gMAR over ten visitations) and visual scanning adaptation (0.20 10gMAR with a circular scanning strategy). Performance improvements are likely related to various preferences and perceptual preferences of the human visual system. A rehabilitation program targeting the appropriate behavioural adaptation coupled with image processing routine optimised for image comprehension should provide a vision prosthesis recipient with the best functional experience to restored vision.
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CONVENTO, SILVIA. "The “multisensory” visual cortex: crossmodal shaping of visual cortical ​responses and ​​perception​." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2015. http://hdl.handle.net/10281/68621.

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The convergence and integration of information from the different sensory channels represents a fundamental ability of the human brain: in our daily life, multisensory cues impact our sensory system, shaping our perception of sensory events. Classical models of multisensory perception defer integration until sensory-specific information has been extensively processed. Strikingly, several anatomical studies now suggest that this view may be over-simplistic and that the substrate for multisensory integration is not constrained to the classical area of multisensory convergence; rather, it also occurs in the early stages of sensory processing, rising the intriguing hypothesis that most of the brain, including the primary sensory cortices, is essentially multisensory. The present dissertation inquires the causal involvement of classical ‘sensory-specific’ visual areas in multisensory processing. Using a combination of behavioral, neuromodulatory, and neuropsychological evidence, I seek the behavioral and brain signatures of a causal link between visual cortical excitability and multisensory perception. In parallel, I provide a characterization of the impact of distinct crossmodal stimuli on subjective visual experience. By directly measuring visual cortical excitability via Transcranial Magnetic Stimulation (TMS), the first study shows facilitatory effects by spatially-specific bimodal and trimodal stimuli on visual cortical responses, which, in turn, improve visual perception. Moreover, by using Transcranial Direct Current Stimulation (tDCS), I demonstrate the role played by higher order multisensory cortices in mediating such spatially-specific crossmodal influences on visual perception, reporting the presence of regional preferences for auditory or somatosensory influences on visual responses. In the second experiment, I further extend these findings by showing that multisensory influences on vision not only express themselves through an enhancement of visual perception, but they can also provoke phenomenological changes in conscious visual perception, namely a crossmodal illusion, when incongruent auditory cues are provided. Crossmodal illusory effects show a specific time-course, compatible with the occurrence of early visual-auditory interaction in the primary visual cortex. At complement with evidence in the healthy brain, in the third study I investigate how a well-known crossmodal illusion, the Sound-Induced Flash Illusion (SIFI), is processed by brain-damaged patients with visual field defect (with damage to the primary visual cortex, the sensory visual pathways, or both), and unilateral spatial neglect (with damage to the posterior parietal and fronto-temporal regions). Perception of the SIFI is defective in patients with visual field defects, but not in those with unilateral spatial neglect, further supporting the role of low-level visual areas in integrating multisensory cues. Overall, this set of experiments shows a causal link between the crossmodal modulation of visual perception and the activity of the primary visual areas, which represents a key site for multisensory integration.
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Hallum, Luke Edward Graduate School of Biomedical Engineering Faculty of Engineering UNSW. "Prosthetic vision : Visual modelling, information theory and neural correlates." Publisher:University of New South Wales. Graduate School of Biomedical Engineering, 2008. http://handle.unsw.edu.au/1959.4/41450.

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Electrical stimulation of the retina affected by photoreceptor loss (e.g., cases of retinitis pigmentosa) elicits the perception of luminous spots (so-called phosphenes) in the visual field. This phenomenon, attributed to the relatively high survival rates of neurons comprising the retina's inner layer, serves as the cornerstone of efforts to provide a microelectronic retinal prosthesis -- a device analogous to the cochlear implant. This thesis concerns phosphenes -- their elicitation and modulation, and, in turn, image analysis for use in a prosthesis. This thesis begins with a comparative review of visual modelling of electrical epiretinal stimulation and analogous acoustic modelling of electrical cochlear stimulation. The latter models involve coloured noise played to normal listeners so as to investigate speech processing and electrode design for use in cochlear implants. Subsequently, four experiments (three psychophysical and one numerical), and two statistical analyses, are presented. Intrinsic signal optical imaging in cerebral cortex is canvassed appendically. The first experiment describes a visual tracking task administered to 20 normal observers afforded simulated prosthetic vision. Fixation, saccade, and smooth pursuit, and the effect of practice, were assessed. Further, an image analysis scheme is demonstrated that, compared to existing approaches, assisted fixation and pursuit (but not saccade) accuracy (35.8% and 6.8%, respectively), and required less phosphene array scanning. Subsequently, (numerical) information-theoretic reasoning is provided for the scheme's superiority. This reasoning was then employed to further optimise the scheme (resulting in a filter comprising overlapping Gaussian kernels), and may be readily extended to arbitrary arrangements of many phosphenes. A face recognition study, wherein stimuli comprised either size- or intensity-modulated phosphenes, is then presented. The study involved unpracticed observers (n=85), and showed no 'size' --versus--'intensity' effect. Overall, a 400-phosphene (100-phosphene) image afforded subjects 89.0% (64.0%) correct recognition (two-interval forced-choice paradigm) when five seconds' scanning was allowed. Performance fell (64.5%) when the 400-phosphene image was stabilised on the retina and presented briefly. Scanning was similar in 400- and 100-phosphene tasks. The final chapter presents the statistical effects of sampling and rendering jitter on the phosphene image. These results may generalise to low-resolution imaging systems involving loosely packed pixels.
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KRUGER, VIRGINIE. "Synthese de nouveaux phosphetanes chiraux et applications en catalyse." Paris 6, 1997. http://www.theses.fr/1997PA066405.

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Cette these illustre la synthese de nouveaux phosphetanes chiraux et leur utilisation comme ligands pour la catalyse enantioselective par les complexes du palladium et du rhodium. Apres une etude bibliographique des voies de synthese du cycle phosphetane, la preparation de l'oxyde de 1-menthyl-2, 2, 3, 3-tetramethylphosphetane est decrite. Ce compose est utilise comme produit de depart pour la synthese des differents ligands fonctionnalises en du phosphore. Divers electrophiles sont en effet introduits sur le cycle phosphore par une reaction de metallation-alkylation, conduisant a des phosphetanes monodentes ou potentiellement bidentes. Ces ligands sont ensuite testes dans les reactions d'hydrosilylation des olefines et de substitution nucleophile allylique catalysees par les complexes du palladium. L'hydrogenation de l'acide -acetamidocinnamique par les complexes du rhodium est egalement abordee.
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Jus, Sébastien. "Synthese de nouveaux phosphetanes chiraux - applications en hydrogenation catalytique enantioselectivite." Paris 6, 2000. http://www.theses.fr/2000PA066238.

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Au cours de ce travail, nous avons developpe la synthese des 1,2-bis(2,4-dialkylphosphetano)benzenes et 1,2-bis(2,4-dialkylphosphetano)ethanes chiraux. L'hydrogenation catalytique enantioselective de dicetones 1,3 nous a permis un acces aise et efficace aux diols 1,3 anti symetriques optiquement purs. Ces diols ont servi a la synthese d'une serie de bisphosphetanes portant sur les cycles phosphores des substituants alkyles d'encombrements varies. Nous avons montre l'efficacite des bisphosphetanes en tant que ligands dans l'hydrogenation catalytique enantioselective. Des exces enantiomeriques proches de 90% sont obtenus dans l'hydrogenation de cetones fonctionnalisees catalysee par le ruthenium. Les complexes de ruthenium utilises jusqu'ici comme precurseurs ne generent pas une espece catalytique unique et bien definie, laissant esperer une optimisation des resultats par un choix plus approprie du systeme catalytique. Dans l'hydrogenation de dehydroaminoesters par des complexes rhodium-bisphosphetane, l'enantioselectivite varie fortement selon les ligands et les substrats. Cependant, on observe des effets tres significatifs de la pression, de la temperature et de la nature du solvant sur les exces enantiomeriques, effets qui permettent d'optimiser ces hydrogenations et d'atteindre des enantioselectivites elevees. De plus, ces effets etonnants ont porte notre attention sur le mecanisme de l'hydrogenation asymetrique catalysee par les phosphines riches en electrons. Des hypotheses mecanistiques ont ete formulees sur la base d'observations experimentales. Enfin, la synthese du (r,r)-1-2-(r,r)-2,4-dimethylazetidinophenyl-2,4-dimethylphosphetane et du (r,r)-1-2-(r,r)-2,4-dimethylazetidinoethyl-2,4-dimethylphosphetane, ligands mixtes p-n analogues des bisphosphetanes, a ete mise au point. Leur etude donnera des indications sur l'influence de la difference d'electronegativite entre phosphore et azote sur l'activite et/ou la selectivite des reactions catalytiques.
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Gün, Hülya [Verfasser], Walter [Gutachter] Frank, and Christian [Gutachter] Ganter. "Untersuchungen zur Reaktivität von ausgewählten Phosphanen und Phospheten gegenüber Lewis-Säuren / Hülya Gün ; Gutachter: Walter Frank, Christian Ganter." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2017. http://d-nb.info/1143899083/34.

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Mocanu, Olivia. "Phosphole and phosphepine-based π-systems : synthesis, reactivity and physical properties." Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S166.

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Ce manuscrit décrit la synthèse et les caractérisations physico-chimiques de nouveaux systèmes hétérocycliques π-conjugués contenant un atome de phosphore. Le chapitre d'introduction présente les différentes voies de synthèse du cycle phospholes pouvant être incorporé dans des systèmes π-conjugués. Le chapitre I décrit la synthèse et les propriétés physico-chimiques de dérivés du pyrène contenant soit un phosphole, soit un silole. La synthèse de ces nouvelles structures a été réalisée à l'aide de réactions métallo-catalysées. Deux types de régioisomères ont ainsi été synthétisés afin de déterminer l'impact de la nature de l'hétéroatome (P ou Si) sur leurs propriétés optiques et électrochimiques et sur l'organisation des molécules à l'état solide. Le chapitre II décrit la synthèse et les propriétés physico-chimiques de nouveaux complexes d'Ir(III) ortho-métallés contenant un ligand phosphole. La présence de deux centres stéréogènes induit la formation de diastéréoisomères, dont la formation peut être contrôlée par les conditions réactionnelles. De plus, les propriétés électroniques du ligand phosphole permettent de moduler à façon les propriétés redox et optiques du complexe. Le chapitre III se focalise sur l'utilisation de la phosphépine comme sous-unité pour la construction de nouveaux systèmes π-conjugués. Deux systèmes π-conjugués ont été synthétisés : un squelette de PAH contenant la phosphépine et les dithieno-phosphépines. Les propriétés optiques et redox de ces dérivés ont été étudiées et discutées dans le manuscrit
This manuscript describes the synthesis and characterisation of new heterocyclic π-conjugated systems built around the phosphorus atom. Firstly, an introduction to the phosphole chemistry (synthesis methods and integration into π-conjugated systems) is presented. The chapter I describes the synthesis and physico-chemical properties of pyrene functionalised either by a phosphole or silole ring. The synthesis of these new structures was achieved by using a transition-metal catalysis. Two types of regioisomers were synthesised in order to study the effect of the heteroatom (P or Si) on the optical and electrochemical properties together with the impact on the solid-state organisation. The chapter II describes the synthesis and the physical properties of the first phosphole-based Ir(III) ortho-metallated complexes. The presence of two stereogenic centres in the complex induced diastereoselectivity issues that could be solved by carefully choosing the reaction conditions. Furthermore, it was demonstrated that the nature of the ligands can tune the optical and the redox properties. The chapter III describes the use of P-containing seven-membered rings (phosphepines) for the development of new π-conjugated systems. Two original π-systems have been synthesised and studied: (i) phosphepine based PAH and (ii) dithieno-phosphepines. The optical and redox properties have been investigated and discussed in the manuscript
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Fjellander, Ester. "Self-adaptable catalysts : Importance of flexibility and applications in asymmetric catalysis." Doctoral thesis, KTH, Organisk kemi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12852.

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The topic of this thesis is the design and synthesis of biaryl-based self adaptableligands for asymmetric metal catalysis. The results discussed in papers I-III are covered, together with some unpublished results concerning substrate-adaptable catalysts. A general survey of self-adaptable catalysts is presented first. The second chapter of this thesis starts with a survey of inversion barriers in biphenyl-based ligands and catalysts. Thereafter, the determination of barriers to conformational adaptation in dibenzoazepines and dibenzophosphepines is described. Palladium complexes with a diphosphine ligand or a diamine ligand, as well as the free diamine ligand, were studied. Entropies and enthalpies of activation were determined with variable temperature NMR spectroscopy. The mechanism of conformational change in the metal complexes was elucidated. The third chapter describes the synthesis of semiflexible and rigid phosphinite ligands, as well as their application in rhodium-catalysed asymmetric hydrogenation. Modest enantioselectivities (up to 63% ee) were obtained. The semiflexible ligand was found to behave like the most active rigid diastereomer. The fourth chapter describes the behaviour of amine and phosphoramidite ligands in model complexes relevant to the palladium-catalysed asymmetricallylic alkylation of benchmark substrates. Diphosphoramidite and aminephosphoramiditeligands were designed and synthesised. Pd(olefin) complexesof diamine and diphosphoramidite ligands were studied, and their symmetry determined. It was found that both types of ligands are able to adapt their conformation to the substrate.
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Books on the topic "Phosphenes"

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Todorova, Denitsa. Denitsa Todorova: Phosphenes (seeing stars). Duffel: Stockmans NV, 2021.

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Lefébure, Francis. Phosphenism: The art of visualisation developing memory and intelligence. Church Crookham, U.K: Psychotechnic Publications, 1990.

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Brogaard, Berit. Arguments Against the Representational View. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780190495251.003.0005.

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This chapter defends the representational view of visual experience against objections by Brewer, Siegel, Johnston, and Travis. Four problems are discussed: (1) the generality problem, or how to account for the specificity of visual experience; (2) how to explain illusions; (3) how the representational view can be true of all the visual experiences that we have, including brain grey, pink glow, after-images and phosphenes; and (4) how the phenomenology of visual experience can determine a unique representational content, given that there are indefinitely many different environments that could give rise to any particular look. The author takes on each of these objections and shows why they fail.
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Montgomery, Erwin B. Approach to DBS in the Vicinity of the Globus Pallidus Interna. Oxford University Press, 2016. http://dx.doi.org/10.1093/med/9780190259600.003.0012.

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The regional anatomy around the DBS lead in the globus pallidus interna (GPi) determines efficacy and adverse effects. Understanding the regional anatomy allows the programmer to adjust the stimulation to provide optimal benefit and the absence of adverse effects. Just ventral to the sensorimotor region of the GPi is the optic tract. Spread of stimulation to the optic tract can produce phosphenes (the experience of seeing light without light actually entering the eye). The internal capsule lies just posterior to the globus pallidus, and stimulation there can cause tonic muscle contractions. Anteriorly lies the non-motor region, and stimulation of this region could cause changes in cognition and personality, although the incidences of these problems is much less that with STN DBS. This chapter discusses the regional anatomy of the GPi segment, adverse effects from malpositioning of DBS leads, approaches to GPi DBS for Parkinson’s, treating dystonia with DBS of the GPi, and treating hyperkinetic disorders.
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Book chapters on the topic "Phosphenes"

1

Ermentrout, G. Bard, and Vincent A. Billock. "Flicker-Induced Phosphenes." In Encyclopedia of Computational Neuroscience, 1212–16. New York, NY: Springer New York, 2015. http://dx.doi.org/10.1007/978-1-4614-6675-8_511.

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Ermentrout, G. Bard, and Vincent A. Billock. "Flicker-Induced Phosphenes." In Encyclopedia of Computational Neuroscience, 1–6. New York, NY: Springer New York, 2013. http://dx.doi.org/10.1007/978-1-4614-7320-6_511-3.

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Bard Ermentrout, G., and Vincent A. Billock. "Flicker-Induced Phosphenes." In Encyclopedia of Computational Neuroscience, 1–6. New York, NY: Springer New York, 2018. http://dx.doi.org/10.1007/978-1-4614-7320-6_511-4.

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Soto-Sanchez, C., Andrés Olmedo-Payá, D. de Santos-Sierra, C. Agullo, and Eduardo Fernández. "A Novel Approach for Quantitative Analysis of 3D Phosphenes." In Natural and Artificial Models in Computation and Biology, 342–49. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-38637-4_35.

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Grüsser, Otto-Joachim, and Michael Hagner. "On the history of deformation phosphenes and the idea of internal light generated in the eye for the purpose of vision." In History of Ophthalmology, 57–85. Dordrecht: Springer Netherlands, 1990. http://dx.doi.org/10.1007/978-94-009-0641-9_7.

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Vogt, J. "773 ClOP Phosphenous chloride." In Asymmetric Top Molecules. Part 3, 341–42. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-14145-4_195.

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Vogt, J. "774 ClO2P Phosphenic chloride." In Asymmetric Top Molecules. Part 3, 343–44. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-14145-4_196.

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Vogt, J. "781 FOP Phosphenous fluoride." In Asymmetric Top Molecules. Part 3, 359–61. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-14145-4_203.

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Stronks, H. Christiaan, and Gislin Dagnelie. "Phosphene Mapping Techniques for Visual Prostheses." In Visual Prosthetics, 367–83. Boston, MA: Springer US, 2011. http://dx.doi.org/10.1007/978-1-4419-0754-7_19.

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Evreinova, Tatiana G., Grigori Evreinov, and Roope Raisamo. "Camera Based Target Acquisition Augmented with Phosphene Sensations." In Lecture Notes in Computer Science, 282–89. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-14100-3_42.

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Conference papers on the topic "Phosphenes"

1

Torres, Cesar, Jessica Chang, Advaita Patel, and Eric Paulos. "Phosphenes." In DIS '19: Designing Interactive Systems Conference 2019. New York, NY, USA: ACM, 2019. http://dx.doi.org/10.1145/3322276.3322375.

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Kanamaru, Manami, Phan Xuan Tan, and Eiji Kamioka. "Clarification of Perceived Phosphenes Positions by tACS considering Electrical Current flow and Exposed Visual Retinae." In 2020 IEEE 8th R10 Humanitarian Technology Conference (R10-HTC). IEEE, 2020. http://dx.doi.org/10.1109/r10-htc49770.2020.9356977.

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Lyu, Qing, Wankun Zhu, Pengcheng Sun, Heng Li, Tingting Han, and Xinyu Chai. "Modelling research on different types of retinal ganglion cells for the formation of irregular phosphenes." In 2015 International Symposium on Bioelectronics and Bioinformatics (ISBB). IEEE, 2015. http://dx.doi.org/10.1109/isbb.2015.7344950.

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Cooray, Vernon, Gerald Cooray, and Marley Becerra. "Corona currents generated from a person's head in the vicinity of lightning strikes — Stimulation of phosphenes." In 2011 7th Asia-Pacific International Conference on Lightning (APL). IEEE, 2011. http://dx.doi.org/10.1109/apl.2011.6110241.

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Feely, Grace, and Young-A. Lee. "Phosphene." In Pivoting for the Pandemic. Iowa State University Digital Press, 2020. http://dx.doi.org/10.31274/itaa.11778.

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Nanduri, D., M. S. Humayun, R. J. Greenberg, M. J. McMahon, and J. D. Weiland. "Retinal prosthesis phosphene shape analysis." In 2008 30th Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE, 2008. http://dx.doi.org/10.1109/iembs.2008.4649524.

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Zhao, Ying, Kun Yang, Bo Pang, Yongji Wang, and Qiushi Ren. "Simulated phosphene model for visual prosthesis." In 2012 5th International Conference on Biomedical Engineering and Informatics (BMEI). IEEE, 2012. http://dx.doi.org/10.1109/bmei.2012.6512915.

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Dagnelie, Gislin, and Jacob V. Vogelstein. "Phosphene Mapping Procedures for Prosthetic Vision." In Vision Science and its Applications. Washington, D.C.: OSA, 1999. http://dx.doi.org/10.1364/vsia.1999.mb3.

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Bollen, Caroline J. M., Richard J. A. van Wezel, Marcel A. J. van Gerven, and Yağmur Güçlütürk. "Emotion Recognition with Simulated Phosphene Vision." In the 2nd Workshop. New York, New York, USA: ACM Press, 2019. http://dx.doi.org/10.1145/3347319.3356836.

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Savage, Craig O., and Mark E. Halpern. "Phosphene brightness modelling for voltage driven waveforms." In 2011 Seventh International Conference on Intelligent Sensors, Sensor Networks and Information Processing (ISSNIP). IEEE, 2011. http://dx.doi.org/10.1109/issnip.2011.6146575.

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