In order to generate the smallest phosphenes possible, it is advantageous to selectively stimulate smaller cells. By hyperpolarizing the somas of the large cells selectively with sub-threshold anodic pre-pulse stimuli (making them more difficult to stimulate) and then selectively depolarize the smaller cells one can selectively stimulate smaller cells. Alternatively, one can hyperpolarize the dendrites of the cells with larger dendritic fields by applying sub-threshold anodic currents on surrounding electrodes and then depolarizing the smaller cells in the center. Further, one can manipulate the phases of an individual biphasic wave to affect selective stimulation resulting in more focal responses. It is possible to increase resolution with the pre-pulse described above. One can also effect resolution by modifying the pulse order of the cathodic and anodic phases. Further, one can isolate the effect of the phases by separating them in time (long inter-phase interval) or by making one of the phases long and low amplitude - always keeping equal total charge for the two phases. As an example, one can preferentially stimulate smaller ganglion cells by providing a longer sub-threshold anodic pulse balanced with a shorter supra-threshold cathodic pulse. Preferentially stimulating the smaller ganglion cells will allow stimulation of different brightness levels while maintaining high spatial resolution.Le procédé selon linvention consiste à stimuler sélectivement des cellules plus petites afin de générer les phosphènes les plus petits possibles. En hyperpolarisant sélectivement les somas des grandes cellules au moyen de stimuli de « pré-impulsion » anodiques infra-liminaires (ce qui les rend plus difficiles à stimuler) puis en dépolarisant sélectivement les cellules plus petites, on peut stimuler sélectivement les cellules plus petites. Dans une variante, on peut hyperpolariser les dendrites des cellules possédant des champs dendritiques plus grands en appliquant des couran
