Mustafa Ozden and Irfan Karagoz
Image processing algorithms play a key role in the development of visual prosthesis systems. In this study, a new electrode stimulation method for retinal implant systems, “Spatio-Temporal Electrode Mapping and Local Interleaved Stimulation (STEMLIS),” is proposed. In this method, the most meaningful spikes that preserve the spatial discrimination in a temporal frame are selected as stimulation data, and phase shifts are applied to all sub electrode groups to minimize undesired electrode interactions. By using this method, both spatial and temporal resolution of stimulation data can be enhanced, since spatio-temporal mapping is used while selecting the stimulation data from a large number of spike data for stimulation of the low-numbered electrode matrix placed on retina surface. The phase delays between the neighboring electrodes are used to introduce interleaved pulses, which minimize the electrical interactions. To evaluate the contribution of the STEMLIS method to perceived image quality, computer based quantitative simulation studies and visual evaluation tests with normal seeing people were performed. For quantitative evaluation, the outputs for the classical method and the STEMLIS method were compared based on the mean squared error (MSE), the histogram similarity ratio (HSR), and edge discrimination parameters. In visual tests, performance of the method was evaluated in terms of contrast discrimination, pattern recognition, text reading and object counting tasks. The subjects reached higher test scores with proposed method and better scores obtained in quantitative comparison. It is concluded that spatio-temporal enhancement of stimulation data can help to improve perceived image quality on visual prostheses.
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