A visual image processing method is based on received spatial field information (302) from a spatial field sensor (116). A data store (804) is accessed, which contains a sensor map data structure (206) comprising a set of predefined regions (208) within a spatial field corresponding with the information received via the sensor input. Each predefined region is associated in the data structure with one or more of a set of stimuli (204) applicable to a biological visual system, and each stimulus corresponds with a visual percept (210). The spatial field information associated with each region is processed to generate stimulus control information which is applied to select, from within the sensor map data structure, stimuli from the set of stimuli for application to the biological visual system. Output stimulus signals (310) are generated, which are suitable for application to the biological visual system based upon the selected stimuli. Flexible mappings are thus provided between visual percepts, stimuli which may be applied (e.g. via a prosthetic implant) in order to generate the percepts, and associations between those stimuli and regions of the spatial field corresponding with the visual percepts.