Neural interface for a cortical vision prosthesis

Journal ArticleThe development of a cortically based vision prosthesis has been hampered by a lack of basic experiments on phosphene psychophysics. This basic research has been hampered by the lack of a means to safely stimulate large numbers of cortical neurons. Recently, a number of laboratories have developed arrays of silicon microelectrodes that could enable such basic studies on phosphene psychophysics. This paper describes one such array, the Utah electrode array, and summarizes neurosurgical, physiological and histological experiments that suggest that such an array could be implanted safely in visual cortex. We also summarize a series of chronic behavioral experiments that show that modest levels of electrical currents passed into cortex via this array can evoke sensory percepts. Pending the successful outcome of biocompatibility studies using such arrays, high count arrays of penetrating microelectrodes similar to this design could provide a useful tool for studies of the psychophysics of phosphene perception in human volunteers. Such studies could provide a proof-of-concept for cortically based artificial vision

Biomimetic Space-Variant Sampling in a Vision Prosthesis Improves the User's Skill in a Localization Task

In this experiment, we test the hypothesis of whether a 'retina-like' space variant sampling pattern can improve the efficiency of a visual prosthesis. Subjects wearing a visuo-auditory substitution system were tested for their ability to point at visual targets. The test group (space-variant sampling), performed significantly better than the control group (uniform sampling). The pointing accuracy was enhanced, as was the speed to find the target. Surprisingly, the time spanned to complete the training was also reduced, suggesting that this space-variant sampling scheme facilitates the mastering of sensorimotor contingencies

Microcomputer-based artificial vision support system for real-time image processing for camera-driven visual prostheses

It is difficult to predict exactly what blind subjects with camera-driven visual prostheses (e.g., retinal implants) can perceive. Thus, it is prudent to offer them a wide variety of image processing filters and the capability to engage these filters repeatedly in any userdefined order to enhance their visual perception. To attain true portability, we employ a commercial off-the-shelf battery-powered general purpose Linux microprocessor platform to create the microcomputer-based artificial vision support system (µAVS^2) for real-time image processing. Truly standalone, µAVS^2 is smaller than a deck of playing cards, lightweight, fast, and equipped with USB, RS- 232 and Ethernet interfaces. Image processing filters on µAVS^2 operate in a user-defined linear sequential-loop fashion, resulting in vastly reduced memory and CPU requirements during execution. µAVS^2 imports raw video frames from a USB or IP camera, performs image processing, and issues the processed data over an outbound Internet TCP/IP or RS-232 connection to the visual prosthesis system. Hence, µAVS^2 affords users of current and future visual prostheses independent mobility and the capability to customize the visual perception generated. Additionally, µAVS^2 can easily be reconfigured for other prosthetic systems. Testing of µAVS^2 with actual retinal implant carriers is envisioned in the near future

Perceptual Moment

Moving image art can provide unique possibilities for making sense of our surrounding reality. Consisting of a series of artworks produced through a creative research methodology, this thesis project explores wonderment and its role in visual perception. The series, Perceptual Moments, is comprised of short, evocative video works presented in a variety of modes including interactive and sculptural installation. To question the role of vision in mediating reality, the works engage the viewer through an intensive experience of seeing. This accompanying essay explores key visual and editing devices in the series that appear to have a role in shaping the viewer’s perception and interpretation of the visual experience, including “the chasm,” “the blur” and “interactive installation.” The essay also investigates the motivation behind the works through journal entries and offers critical analyses for each production. The visual devices in question are grounded within the context of psychology, neuroscience, phenomenology and film theories. Philosopher Gaston Bachelard provides an anchor for the concept of wonderment, while theorists Jonathan Crary and Gilles Deleuze create dialogical space around the act of viewing filmic images and the affect that it involves. The devices are also observed in other media works, including seminal pieces by Stan Brackhage, Kurt Kren and Jan Svankmajer as well as contemporary figures such as Nathalie Djurbergand Matt Hope.PsychologyVisual perceptionFil

Dual use of image based tracking techniques: Laser eye surgery and low vision prosthesis

With a concentration on Fourier optics pattern recognition, we have developed several methods of tracking objects in dynamic imagery to automate certain space applications such as orbital rendezvous and spacecraft capture, or planetary landing. We are developing two of these techniques for Earth applications in real-time medical image processing. The first is warping of a video image, developed to evoke shift invariance to scale and rotation in correlation pattern recognition. The technology is being applied to compensation for certain field defects in low vision humans. The second is using the optical joint Fourier transform to track the translation of unmodeled scenes. Developed as an image fixation tool to assist in calculating shape from motion, it is being applied to tracking motions of the eyeball quickly enough to keep a laser photocoagulation spot fixed on the retina, thus avoiding collateral damage

Doctor of Philosophy

dissertationThis dissertation provides an in-depth evaluation of microstimulation of the primary visual cortex (V1) using chronically implanted Utah Electrode Arrays (UEAs) in macaque monkeys for use as a visual prosthesis. Within the scope of this dissertation are several significant contributions. First, a minimally invasive and robust device for head fixation was developed. In comparison to other available designs, this device improved long-term outcomes by providing a stronger, less invasive interface that reduced the risk of infection. This device made it possible to acquire chronic microstimulation data in macaque monkeys. It has been tested on three animals and has provided a stable interface for over two years. Second, this dissertation is the first to describe the factors influencing the performance and safety of microstimulation of V1 with the UEA. Two UEAs were implanted in V1 of two macaque monkeys, and experiments were performed several months following implantation. The electrical and recording properties of the electrodes and the high-resolution visuotopic organization of V1 were measured. In addition, threshold stimulation levels that evoked behavioural responses using single electrodes were determined. Periodic microstimulation at currents up to 96 pA did not impair the ability to record neural signals and did not affect the animal's vision where the UEAs were implanted. It was discovered, however, that microstimulation at these levels evoked behavioural responses on only 8 of 82 systematically stimulated electrodes. It was suggested that the ability to evoke behavioral responses may depend on the location of the electrode tips within the cortical layers of V1, the distance of the electrode tips to neuronal somata, and the inability of nonhuman primates to recognize and respond to a generalized set of evoked percepts. Finally, this dissertation is the first to describe the spatial and temporal characteristics of microstimulation of V1 with the UEA over chronic time periods. Two years after implantation, it was found that consistent behavioural responses could be evoked during simultaneous stimulation of multiple contiguous electrodes. Saccades to electrically-evoked targets using groups of nine electrodes showed that the animal could discriminate spatially distinct percepts with a resolution comparable to the current epiretinal prostheses. These results demonstrate chronic perceptual functionality and provide evidence for the feasibility of a UEA-based visual prosthesis for the blind

A 16 x 16 CMOS amperometric microelectrode array for simultaneous electrochemical measurements

There is a requirement for an electrochemical sensor technology capable of making multivariate measurements in environmental, healthcare, and manufacturing applications. Here, we present a new device that is highly parallelized with an excellent bandwidth. For the first time, electrochemical cross-talk for a chip-based sensor is defined and characterized. The new CMOS electrochemical sensor chip is capable of simultaneously taking multiple, independent electroanalytical measurements. The chip is structured as an electrochemical cell microarray, comprised of a microelectrode array connected to embedded self-contained potentiostats. Speed and sensitivity are essential in dynamic variable electrochemical systems. Owing to the parallel function of the system, rapid data collection is possible while maintaining an appropriately low-scan rate. By performing multiple, simultaneous cyclic voltammetry scans in each of the electrochemical cells on the chip surface, we are able to show (with a cell-to-cell pitch of 456 μm) that the signal cross-talk is only 12% between nearest neighbors in a ferrocene rich solution. The system opens up the possibility to use multiple independently controlled electrochemical sensors on a single chip for applications in DNA sensing, medical diagnostics, environmental sensing, the food industry, neuronal sensing, and drug discovery

A systematic review of the evidence for single stage and two stage revision of infected knee replacement

BACKGROUND: Periprosthetic infection about the knee is a devastating complication that may affect between 1% and 5% of knee replacement. With over 79 000 knee replacements being implanted each year in the UK, periprosthetic infection (PJI) is set to become an important burden of disease and cost to the healthcare economy. One of the important controversies in treatment of PJI is whether a single stage revision operation is superior to a two-stage procedure. This study sought to systematically evaluate the published evidence to determine which technique had lowest reinfection rates. METHODS: A systematic review of the literature was undertaken using the MEDLINE and EMBASE databases with the aim to identify existing studies that present the outcomes of each surgical technique. Reinfection rate was the primary outcome measure. Studies of specific subsets of patients such as resistant organisms were excluded. RESULTS: 63 studies were identified that met the inclusion criteria. The majority of which (58) were reports of two-stage revision. Reinfection rated varied between 0% and 41% in two-stage studies, and 0% and 11% in single stage studies. No clinical trials were identified and the majority of studies were observational studies. CONCLUSIONS: Evidence for both one-stage and two-stage revision is largely of low quality. The evidence basis for two-stage revision is significantly larger, and further work into direct comparison between the two techniques should be undertaken as a priority

Image remapping strategies applied as protheses for the visually impaired

Maculopathy and retinitis pigmentosa (rp) are two vision defects which render the afflicted person with impaired ability to read and recognize visual patterns. For some time there has been interest and work on the use of image remapping techniques to provide a visual aid for individuals with these impairments. The basic concept is to remap an image according to some mathematical transformation such that the image is warped around a maculopathic defect (scotoma) or within the rp foveal region of retinal sensitivity. NASA/JSC has been pursuing this research using angle invariant transformations with testing of the resulting remapping using subjects and facilities of the University of Houston, College of Optometry. Testing is facilitated by use of a hardware device, the Programmable Remapper, to provide the remapping of video images. This report presents the results of studies of alternative remapping transformations with the objective of improving subject reading rates and pattern recognition. In particular a form of conformal transformation was developed which provides for a smooth warping of an image around a scotoma. In such a case it is shown that distortion of characters and lines of characters is minimized which should lead to enhanced character recognition. In addition studies were made of alternative transformations which, although not conformal, provide for similar low character distortion remapping. A second, non-conformal transformation was studied for remapping of images to aid rp impairments. In this case a transformation was investigated which allows remapping of a vision field into a circular area representing the foveal retina region. The size and spatial representation of the image are selectable. It is shown that parametric adjustments allow for a wide variation of how a visual field is presented to the sensitive retina. This study also presents some preliminary considerations of how a prosthetic device could be implemented in a practical sense, vis-a-vis, size, weight and portability