The causal mechanisms of spontaneous attentional performance lapses in alert nonclinical individuals during purposeful responses to complex stimuli remain largely unknown. Current evidence suggests that the forced redirection of attention can modulate preattentive stages of auditory processing. We propose a hypothesis that similar mechanisms may be responsible for spontaneous attentional lapses. To address this issue, the auditory condensation task was used. Four target auditory stimuli that differed in 2 independent features were presented randomly with equal probability. Participants were instructed to respond to each stimulus by pressing 1 of 2 buttons according to a rule based on stimulus feature conjunction. Participants made errors in 10.2% Ϯ .7% of the trials and response omissions in 5.4% Ϯ .5% of the trials. The P2 amplitude was greater in trials with errors compared with correct responses, possibly reflecting a reduction of stimulus processing. Spontaneous attentional performance lapses may be tentatively explained by the inadequate distribution of attentional resources caused by competition with other mental processes, such as mind-wandering. This competition is likely to occasionally subdue early preattentional stages of stimulus processing and thus cause behavioral errors.