A computer readable medium storing instructions which cause a processor to generate data structures for an object moving along the perimeter of a curved touch-sensitive user input device, each data structure corresponding to a gesture and including a time stamp, polar angles at which the object starts and ends, a middle polar angle of the object, and an assigned state being one of the group RECOGNIZED, UPDATED and ENDED, wherein the instructions cause the processor to assign the RECOGNIZED state to the data structure when the moving object is initially detected on the perimeter of the device, to assign the UPDATED state to the data structure when the moving object is further detected on the perimeter of the device after the initial detection, and to assign the ENDED state to the data structure when the moving object ceases to be detected on the perimeter of the device.