The mismatch negativity (MMN) component of the auditory event-related
potential (ERP) is elicited by infrequent, physically deviant stimuli
in a sequence of frequent homogeneous stimuli (standards). It has been
suggested that the MMN is generated by an automatic (attention-indepe
ndent) neural mismatch process with a memory trace that encodes the ph
ysical features of the standard stimulus. The proposed MMN independenc
e of attention was addressed in the present study. Standard stimuli an
d two types of deviant stimuli, differing from standards either in fre
quency or intensity, were dichotically presented in random order and a
t a very rapid rate. The subject attended either to left- or right-ear
stimuli, counting the number of a designated type of deviants in that
ear. In the present conditions of very strongly focused attention, th
e MMN was elicited even by frequency change in the ignored input strea
m, and its amplitude was very similar to that of the MMN elicited by e
quivalent deviant stimuli (targets) in the attended input stream. In c
ontrast, the MMN to intensity deviation was clearly attenuated in the
absence of attention. This effect is, however, probably due to the att
ention effect on the MMN generator itself rather than the antecedent s
ensory-analysis and -storing functions.