A very large format neural stimulator device, to be used in future retinal prosthesis experiments, has been designed, fabricated, and tested. The device was designed to be positioned against a human retina for short periods in an operating room environment. Demonstrating a very large format, parallel interface between a 2-D microelectronic stimulator array and neural tissue would be an important step in proving the feasibility of high resolution retinal prosthesis for the blind. The architecture of the test device combines several novel components, including microwire glass, a microelectronic multiplexer, and a microcable connector. The array format is 80 times 40 array pixels with approximately 20 microwire electrodes per pixel. The custom assembly techniques involve indium bump bonding, ribbon bonding, and encapsulation. The design, fabrication, and testing of the device has resolved several important issues regarding the feasibility of high-resolution retinal prosthesis, namely, that the combination of conventional CMOS electronics and microwire glass provides a viable approach for a high resolution retinal prosthesis device. Temperature change from power dissipation within the device and maximum electrical output current levels suggest that the device is acceptable for acute human tests.
Current target acquisition models are for monochrome imagery systems (single detector). The increasing interest in multispectral infrared systems and color daylight imagers highlights the need for models that describe the target acquisition process for color systems (2 or more detectors).This study investigates the detection of simple color targets in a noisy color background. Color targets are varied separately either in hue or saturation. Noise is created with a mixture ofrandom hue and saturation combinations. Our preliminary result showed a simple two-color (yellow-blue) representation did not improve the standard black-and-white Minimum Resolvable Temperature Difference sensitivity. Subsequent psychophysical experiments reveal that human hue and saturation discriminations interact (the Abney effect) and need to be separated in color target detection modeling. Research is continuing to better define the mathematical relationship between the target acquisition parameters (e.g., temperature difference or intensity contrast) and the color space of hue and saturation.
A general method is described to improve the operational resolution of an Electro-Optic (EO) imaging sensor using multiple frames of an image sequence. This method only assumes the constituent video has some ambient motion between the sensor and stationary background, and the optical image is electronically captured and digitally recorded by a staring focal plane detector array. Compared to alternative techniques that may require externally controlled or measured dither motion, this approach offers significantly enhanced operational resolution with substantially relaxed constraints on sensor stabilization, optics, and exposure time.
-There is a growing interest in the development of a retinal prosthesis device based on a number of recent experiments demonstrating electrical stimulation of retinal tissue with single electrodes. An intraocular retinal prosthesis test device is currently under development at NRL/JHU. The microelectronic device has an image format of 80 X 40 unit cells interfaced to the retinal surface via an array of microwires in a glass matrix. The system architecture and technology development issues are discussed as well as the topic of biocompatibility. This test device will enable acute human experiments in an operating room environment to demonstrate a massively parallel interface between retinal tissue and a microelectronic array. Keywords -Retina, prosthesis, channel glass, multiplexer 1. INTRODUCTION Recent advances in the fields of microelectronics, neurophysiology, and retinal surgery have progressed to the point where an implantable visual prosthesis system, based on electrical stimulation, is now considered feasible. Currently a number of research projects around the world are aimed at developing prosthetic vision systems. The device discussed in this paper addresses the technical problem of positioning a high-density electrode array against the retina to achieve high-resolution retinal stimulation and perception of image sequences in the patient.The outermost layer of the sensory retina consists of photoreceptors; in the macular region, the photoreceptors are mostly cones (color-sensitive). The next layers of the sensory retina are the bipolar, amacrine, horizontal, and the ganglion cells. The axons of the ganglion cells form the optic nerve.Photoreceptor loss from diseases such as retinitis pigmentosa and age-related macular degeneration are the leading causes of legal blindness. Despite near-total loss of photoreceptors, there is relative preservation of the other retinal neurons. By stimulating the remaining functional retinal layers, it may be possible to restore visual perception.Initial experiments with intraocular stimulation, were performed by de Juan and Humayun several years ago [I]. Since that time, a number of research groups have begun the development of retinal prostheses [2,3,4,5,6,7,8]. Some groups are working toward a device that will be implanted on the epiretinal retinal surface while others are developing a subretinal implant.Epiretinal implantation has the advantage of leaving the retina intact by placing the implant in the vitreous cavity, a naturally existing and fluid-filled space. Studies at John Hopkins University Hospital have demonstrated that this array position is biocompatible [9]. Subretinal implantation of a retinal prosthesis essentially replaces the diseased photoreceptors with a microelectronic stimulator device. However, the surgical implantation requires detaching the retina, and the location of the device may be disruptive to the health of the retina.Section 2 gives an overview of the intraocular retinal prosthesis (IRP) concept and associated electrical stimul...
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