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Background Mismatch negativity (MNN) and P3a are event related potential (ERP) measures of early sensory information processing. These components are usually conceptualized as being “pre-attentive” and therefore immune to changes with variations in attentional functioning. This study aimed to determine whether manipulations of attention influence the amplitudes and latencies of MMN and P3a and, if so, the extent to which these early sensory processes govern concurrent behavioral vigilance performance in schizophrenia patients and normal subjects. Methods Schizophrenia patients (SZ; n = 20) and Nonpsychiatric Control Subjects (NCS; n = 20) underwent auditory ERP testing to assess MMN and P3a across 4 EEG recording sessions in which attentional demand (low vs. high) and sensory modality of directed attention (visual vs. auditory) were experimentally varied. Results Across conditions, SZ patients exhibited deficits in MMN and P3a amplitudes. Significant amplitude and latency modulation were observed in both SZ and NCS but there were no group-by-condition interactions. The amount of MMN amplitude attenuation from low- to high-demand tasks was significantly associated with increased vigilance performance in both SZ and NCS groups (r = − 0.67 and r = − 0.60). Several other robust associations were also observed among neurophysiologic, clinical and cognitive variables. Conclusions Attentional demand and modality of directed attention significantly influence the amplitude and latencies of “pre-attentive” ERP components in both SZ and NCS. Deficits in MMN and P3a were not “normalized” when attention was directed to the auditory stimuli in schizophrenia patients. The adaptive modulation of early sensory information processing appears to govern concurrent attentional task performance. The temporal window reflecting automatic sensory discrimination as indexed as MMN and P3a may serve as a gateway to some higher order cognitive operations necessary for psychosocial functioning.