The processing of time has been a subject of research since centuries. It is controversial whether the psychological time is mapped by means of a unique mechanism or whether separate mechanisms are relevant for time processing. A few findings assume brief durations, shorter than 500 ms, to be processed sensorially, whereas long durations are processed via cognitive operations. In an electrophysiological experiment we tested the assumption of different modes of processing of short and long durations. For this purpose the Mismatch Negativity to duration deviants was measured in a 2x2 factorial design in blocks of short and long duration sounds in ignore and attend conditions. Our results show comparable MMNs evoked by deviants in the attend condition in both short and long duration blocks. However, in ignore condition no MMN was measured in the long duration blocks. In short ignore condition a distinct MMN was obtained, albeit not as high in amplitude compared to the short attend condition. These results possibly suggest that directing attention to the auditory stimuli has, in some way, an influence on the duration MMN. Furthermore, the pattern of results in ignore condition could be explained by the breakdown of the sensorial mechanism regarding duration processing for long sounds when they are not attended. This seems to be in line with the assumption of different mechanisms for duration processing.