Prospects and Limitations of Spatial Resolution
Our sense of vision permanently captures, transmits and interprets enormous amounts of visual information. The amount of visual information that can be transmitted to the brain by the means of visual prosthesis will be severely limited and thus also limit
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Prospects and Limitations of Spatial Resolution Jörg Sommerhalder and Angélica Pérez Fornos
Abstract Our sense of vision permanently captures, transmits and interprets enormous amounts of visual information. The amount of visual information that can be transmitted to the brain by the means of visual prosthesis will be severely limited and thus also limit the rehabilitation prospects of such devices. While several parameters contribute to the information content of visual stimuli, this chapter concentrates essentially on spatial resolution. The first part of the chapter is dedicated to discuss the results of simulation studies of prosthetic vision on normal subjects. These studies aimed to respond to the question of how much visual information should be transmitted to the brain to rehabilitate patients. The amount of visual information, necessary to accomplish daily living tasks (such as reading, eye-hand coordination or whole body mobility) is task-dependent and not only image resolution itself, but also other parameters such as the size of the effective visual field seem to be important. In the second part of the chapter we tried to discuss to which extent the information made available by the stimulation device is lost or degraded before reaching the brain. The experience with actual retinal implants shows us that only part of the information provided by the device finds its way to the central nervous system and that this information loss can be highly variable from patient to patient: the spatial resolution provided by the devices corresponds rarely to the spatial resolution perceived by the patients. Keywords Visual prosthesis • Artificial vision • Simulation studies • Spatial resolution • Visual psychophysics • Retinal stimulation • Clinical trials
J. Sommerhalder (*) Department of Ophthalmology, Geneva University Hospitals, Geneva, Switzerland e-mail: [email protected] A. Pérez Fornos Western Switzerland Cochlear Implants Center, Geneva University Hospitals, Geneva, Switzerland © Springer International Publishing Switzerland 2017 V.P. Gabel (ed.), Artificial Vision, DOI 10.1007/978-3-319-41876-6_4
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J. Sommerhalder and A. Pérez Fornos
Key Points • Spatial resolution is clearly an important issue in the context of visual prostheses; it describes the amount of information that can be transmitted by the device. • Simulation studies are a useful tool to determine what spatial resolution should be targeted by such devices: about 500 retinotopically distributed phospenes would be enough in many everyday situations. • Only part of the information, made available by the stimulation device, reaches the brain; this information loss at the electrode-nerve interface is highly variable from patient to patient. • At present, commercially available visual prostheses should be considered as vision aids for blind patients, complementary to traditional vision aids.
Visual prostheses are devices that aim to replace a non-functioning part in the visual pathway by directly stimulating the remaining and stil
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