An apparatus includes: an input configured to receive information indicative of sensed light locations memory coupled to the input and storing indicia of receptive fields forming a mosaic, each of the receptive fields corresponding to an electrode, the mosaic including first and receptive fields having first and second shapes that are different, the memory further storing instructions a processor coupled to the input and the memory and configured to read and execute the instructions to: analyze the information indicative of sensed light locations determine, for each of respective ones of the sensed light locations, one or more receptive fields that include the corresponding sensed light location and produce excitation indicia the apparatus further including an output coupled to the processor and configured to be coupled to a retinal implant and to convey the excitation indicia toward the retinal implant.
