Event-related potentials (ERPs) and reaction times
(RTs) were used to study how the processing of sentences
with morphosyntactic violations is constrained by working
memory (WM) capacity. The available WM capacity was varied
by three orthogonal manipulations: (1) syntactic complexity;
(2) additional WM load; and (3) verbal WM span. The processing
of the morphosyntactic violations was reflected in longer
RTs in ungrammatical compared with grammatical sentences,
and in an anterior negativity and a centroparietal positivity
in the ERPs. While the behavioral grammaticality effect
was not influenced by the WM manipulations, the ERP effects
were. The amplitude of the anterior negativity was modulated
by the combination of complexity and load, and by WM span.
The onset of the centroparietal positivity was delayed
in the high-load condition, and for the low-span group.
ERPs over the course of the sentences showed a frontal
negative slow wave under high WM load, largest for the
low-span group. The finding that online syntactic processing
is related to WM span and to additional WM load does not
support the theory that there is a WM capacity specific
for syntactic processing.