Attentional dysfunctions are considered to be core schizophrenic sympt
oms. Selective attention to specific attributes of auditory stimuli re
sults in characteristic changes of event-related brain potentials. Dep
ending on stimulation rate, either an N1 enlargement or a more endurin
g ''processing negativity'' (19) is found. Twelve schizophrenics, diag
nosed according to DSM III-R, 12 patients with alcohol dependency, and
12 matched normal controls took part in an auditory selective attenti
on task with fast (2 Hz) or slow (1 Hz) stimulation rate. Schizophreni
cs made more errors and had slower reaction times, as compared with bo
th other groups. This behavioral impairment was paralleled by a signif
icantly smaller early phase (200-400 ms) of the processing negativity
(Nd, fig. 2). Groups did not differ for a later phase of Nd. The small
er N1 amplitude of schizophrenics was probably a concomitant of neurol
eptic medication, because group differences for N1-amplitude disappear
ed when neuroleptic dosage was statistically controlled for. Alcoholic
s, but not schizophrenics did have a smaller P300 amplitude than norma
ls (fig. 3). The results are consistent with the assumption that an im
paired matching process between stored and momentary information under
lies some of the attentional difficulties in schizophrenia.