1. A method of tracking movement of one or more objects on a touch surface of a touch-sensitive apparatus, the touch-sensitive apparatus being operable to propagate light from a plurality of incoupling points to a plurality of outcoupling points, wherein at least one light detector is optically coupled to the plurality of outcoupling points to generate an output signal representing received light at the plurality of outcoupling points, said method comprising: processing the output signal to generate an interaction map indicative of local changes in interaction on the touch surface; processing the interaction map to identify positive and negative apparent peaks, each positive apparent peak representing a locally increased interaction in the interaction map, and each negative apparent peak representing a locally decreased interaction in the interaction map; processing the positive and negative apparent peaks to identify potentially false peaks among the positive and negative apparent peaks; and updating, based on the potentially false peaks, movement trajectories of all objects deemed to exist on the touch surface at a preceding time point, wherein the processing the positive and negative apparent peaks applies at least a first heuristic to identify the potentially false peaks, said first heuristic designating a positive apparent peak as a potentially false peak when the positive apparent peak is deemed to be associated with one or more of the negative apparent peaks.