Differential processing of duration changes within short and long sounds in humans.

It has been postulated that there exist two different mechanisms of duration processing. Brief durations, shorter than 500 ms, are processed sensorially, whereas longer durations are processed via a cognitive mechanism. We investigated whether electrophysiological evidence for this distinction can be found. In particular, we measured the mismatch negativity (MMN) to auditory duration deviants (40% decrements) in blocks of short (200 ms) and long sounds (1000 ms) in Ignore and in Attend conditions. Our results show a typical MMN for long and short durations in the Attend condition, whereas no MMN was obtained for long durations in the Ignore condition. This interaction between duration and attention seems to reflect a breakdown of the sensorial mechanism of temporal processing at some critical duration of about 1 s when sounds are ignored.