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We propose a stimulation strategy for retinal prostheses that makes use of irregular shapes of elicited phosphenes. It is patient specific and thus relies on prior psychophysical measurements. Visual perceptions are stored in a phosphene map that relates stimulation parameters to the visual stimulus elicited. Based on this map, stimulation parameters are chosen in such a way that the edges of the...
We present and evaluate different approaches to feature accentuation in phosphenated images for different image resolutions. The goal of this study is to find methods to attract an implantee's visual attention to important image content like faces, obstacles or road signs. We do this by defining an important region in the image and accentuating it by either increasing the brightness of outlining phosphenes...
We consider a form of current steering to elicit desired perceptions in users of a retinal prosthesis. While it is common to use a single, remote return electrode to balance electrical stimulation, advances in chip design and electrical switching have enabled more flexibility in stimulation paradigms. We have created a finite-element model of a retina and a ten electrode prosthesis in COMSOL. Different...
Retinal implants restore limited visual perception to blind implantees by electrical stimulation of surviving neurons. We consider the efficacy of two electrical stimulation parameters, frequency of stimulation and interphase gap between cathodic and anodic phases, on the required charge to reach a desired neuronal spike rate. Using a Hodgkin-Huxley model of a neuron, we find the most efficient means...
In this paper, we use a state of the art saliency model to compare salient locations for unprocessed colour images with those of phosphenated images. The motivation for doing so is to estimate the impact of phosphenisation of input streams as it may occur when someone is equipped with a retinal implant. We aim to determine if there is any need to preprocess images for an implant user to help them...
Implants provide a means to electronically stimulate biological systems. Such stimulation may be designed to be driven by current or voltage. Although the methods are theoretically equivalent, the selection of which to employ has implications as to hardware design, stimulation strategies, and other practical impacts. We model the impact of voltage-driven stimulation, utilising models for producing...
Nystagmus is a condition in which the eyes move in an uncontrolled fashion. These eye movements confound attempts to identify patient fixation, as desired eye positions cannot be maintained. We aim to estimate the eye positions in the case of refixations and superimposed uncontrolled motion. By incorporating saccade detection and resetting our estimation algorithms, we are able to track the nystagmus...
Single pulse waveforms were considered in a recent model for phosphene elicitation in patients with a retinal prosthesis. Waveforms are constrained to charge-balanced stimuli consisting of a single cathodic and anodic pulse pair. Mathematical models of such stimuli have been constructed and presented based upon patient testimonials. In this work, we derive analytic expressions that may be employed...
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