The roles of N100 and the early and late negative difference
(Nd) waveforms in selective attention were investigated with
primary simulated flying and secondary dichotic listening tasks.
Twenty highly trained participants performed the two tasks
together, either while detecting secondary task deviant tones
in one ear and ignoring tones in the other ear (dual condition)
or while ignoring the tones in both ears (ignore condition).
The amplitude of the N100–P200 complex in both the dual-task
and ignore conditions was reduced equally in the attended and
unattended ear by the introduction of the primary task. In the
dual-task condition, the amplitude of the late Nd but not the
early Nd was reduced by a combination of the introduction of
the primary task and an increase in its difficulty. P300 showed
the same amplitude pattern as the late Nd. We propose that the
reduction in N100–P200 amplitude reflects an automatic
gating mechanism. The dissociation of the early and late Nd
suggests that the latter is not modality specific. The question
is raised whether the late Nd is more closely associated with
P300 than with the early Nd.
