A user input device includes an optical element comprising a finger interface surface, a light source in optical communication with the finger interface surface and configured to provide light from the light source to the finger interface surface, a sensor array configured to detect light reflected from the finger interface surface in response to contact between a finger and the finger interface surface, a navigation engine coupled to the sensor array, the navigation engine configured to generate lateral movement information, which is indicative of lateral movement of the finger relative to the sensor array, in response to the detected light, wherein the lateral movement information comprises first and second orthogonal components, and a quantization engine coupled to the navigation engine, the quantization engine configured to compare the first orthogonal component to the second orthogonal component and to generate first and second quantized orthogonal components in response to the comparison.