The endogenous components of auditory evoked potentials were studied in the human brain, arising in conditions of voluntary and involuntary attention. Variation of the duration of acoustic stimuli led to a situation in which the generation of mismatch negativity was blocked. The recognition of acoustic stimuli was compared in conditions in which passive perception of the deviant signal in some cases evoked mismatch negativity and in others did not. This demonstrated the following: 1) stimuli not evoking mismatch negativity in the classical "oddball" paradigm can be recognized efficiently; 2) recognition of stimuli evoking mismatch negativity (in conditions of passive perception) occurs with a significantly shorter response time. The difference in the present experiments was 49-51 msec. There was also an increase in the proportion of correct responses to the deviant stimulus (to 92%). Thus, if the experimental conditions allow the mechanism generating mismatch negativity to trigger, then the response time to the actively perceived stimulus decreases. These results are evidence that the mechanisms of involuntary attention contribute to the active perception of acoustic stimuli.