There is provided a temporal processor node for use as an input node in the input layer of a class network in an artificial neural network, the class network being operable to generate an output signal based on a network input vector component received by the input layer, the temporal processor node being operable to receive observation data representing the observed state of a monitored entity as a component of the network input vector. The temporal processor node comprises a memory module operable to store a most recently observed state of the monitored entity in the memory module as a current state, a modification module having a timer, the timer being operable to output a value representing time elapsed since observation of the current state, the modification module being operable to modify the current state with a modification factor dependent on the value output by the timer, wherein when triggered, the temporal processor node is operable to output the modified current state as a representation of the current state.