Schizophrenics were compared to schizoaffective, bipolar, and nonpsychotic depressed patients in a visual masking paradigm in which an informational target stimulus was followed at varying intervals by a noninformational masking stimulus. In limiting the availability of the sensory signal provided by the target stimulus, the mask was used to probe how information from the environment enters and is processed by the central nervous system. The use of the masking paradigm was originally based on the hypothesis that thought disorder is a result of a more primary dysfunction in the processes that precede and result in thought. Results confirmed previous findings of a performance deficit in the schizophrenics when compared to nonpsychotic controls. Schizoaffective and bipolar patients also showed evidence of impaired processing, however. Results were interpreted in terms of a trait/state formulation in which impaired information processing is seen as a fundamental trait of schizophrenia spectrum disorders and as a state that can covary with psychotic illness in general. A unifying concept centers on the effects of psychopathological conditions on an individual's processing resources that results in either underprovision or overprovision of information from sensory input to complex cognitive operations dependent on the cerebral cortex. Findings from a variety of paradigms are consistent with those of the masking paradigm in revealing that the processing deficits of schizophrenics are time dependent and occur in the 500 ms following stimulus input.